Note: Descriptions are shown in the official language in which they were submitted.
CA 03023981 2018-11-09
FLOW-THROUGH FISH STUNNER AND METHOD OF STUNNING FISH
Field of the Invention
The invention relates to fish stunning and, in particular, fish stunner
apparatus e.g. (referred to as fish
stunner(s)) for flow-through fish stunning and methods for use in same. In a
further aspect the
invention relates to power supplies, apparatus for stunning and methods of
stunning for use in fish or
other animal stunning, particularly e.g. in saltwater fish stunning. Flow-
through fish stunning may also
be referred to as pipeline fish stunning as the fish and transport water
typically travel through a pipe.
Background to the Invention
Humane slaughter techniques on land based farms have outpaced developments in
aquaculture
processing. While some common inhumane practices have been banned by EU
legislation, for
example the use of CO2, many farms in Europe still drop live fish (principally
seabass, bream, tilapia
and salmon smolts) into tubs of ice where it can take an unacceptable duration
for the fish to be killed.
Mechanised percussive machines have been used to kill larger fish, such as
salmon and seatrout,
however they do not cater for portion sized fish. Many animal welfare
organisations do not explicitly
endorse the use of electrical stunning because in the past it has been done
very poorly and systems
capable of humane stunning are relatively new.
The present applicant, Ace Aquatec Ltd, has previously made and sold a flow-
through fish stunner
(HS1) designed for low power fresh water use with a first stage (stun station)
in which lm long
electrodes on opposing sides of the tube were provided with 1000HZ AC voltage
to deliver around 3-
11V/cm transversely across the tube (depending on the current measured) and a
second stun
maintenance stage of around 16-18m comprising seven or more pairs of
electrodes 2m long on
opposing sides of the tube powered with a 50 Hz AC voltage to provide the
required electric field. The
area of these electrodes in this arrangement meant that it could not be used
with saltwater which has
a significantly higher conductivity and so current demand than fresh water. In
a flow-through fish
stunner, the water is not re-circulated and the speed of the flow of water is
preferably sufficient to
overcome motion of the fish against the flow of the water so that fish are
swept along in the direction
of flow of the water.
1
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
A later recirculating fish stunner (HS2) reduced the power demands by reducing
the volume of water
to be electrified and by using recirculating water and controlling the
salinity, and hence conductivity, to
be close to that of fresh water. Fish, including saltwater fish species, could
then be stunned humanely
within one second but in a fixed slow moving volume of low conductivity water.
This system works well
but required regular cleaning of the system, regular water exchange, and
additional fish handling to
deliver these into the recirculating water supply. Nevertheless, the power
requirements of this system
were not too onerous because of the limited (low) volume and controlled
salinity.
However, the recirculated fresh water supply pipeline fish stunner has several
drawbacks: it increases
the fail rate of stunning due to the detritus that builds up in the water, it
limits the quantity of fish that
can be stunned per hour (around 10 tonnes per hour), and it stuns at the end
of the fish transportation
process leading to greater stress in the fish and therefore only modest
quality improvements over
existing methods. Alternative electric stunners have been built in Norway for
salmon which remove
the fish from the water but this method increases stress and introduces damage
to the fish at the point
of contact with the electrodes. At present therefore saltwater species
including seabass and
seabream remain outside the scope of humane slaughter.
There is, therefore, a need to provide apparatus, systems and methods capable
of stunning saltwater
species in saltwater in a flow-through system.
There is also a need to provide improved apparatus, systems and methods
capable of stunning
species in fresh water, or water of any type, in a flow-through system.
GB879314 KREUTZER describes an electrical device which provides a series of
short duration
electrical pulses in water which stun fish in water. Use in saltwater is not
described.
US5327854 SMITH describes electric fish shocking devices for use as fish
barriers and fish collectors
using programmable output waveforms and, in particular, a power inverter to
deliver a variety of
voltage levels and supply enough current at each voltage level to electrify
sufficient volume of water.
A voltage selector provides a means of changing the output voltage to
accommodate a wide range of
water conductivity. A wide variety of pulse derived waveforms can be produced.
The difficulties of
providing a power supply for use in saltwater are not mentioned or addressed.
GB2417408 ACE-HOPKINS describes a device for electronically slaughtering fish
comprising a
stunning station for stunning fish using an electric current in water and a
stun maintenance station to
maintain the fish in an unconscious state in air after stunning until they
leave the stun maintenance
station.
GB2502816 MCKIMM describes a method and apparatus for slaughtering fish
providing an elongate
passage and generating a linear electric field in a first region of the
passage to stun fish and applying
a further electric field downstream to kill fish. No details of the power
supply used are provided. The
difficulties of providing power supplies for use in saltwater are not
mentioned or addressed.
2
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
W02001/95732 ROBB describes a method and device for stunning and killing
aquatic animals so that
during a first period an electric current with a first current intensity is
generated in the animal such that
it is stunned and conditioning the water such that the animal remains stunned
during a second period.
CA2637860 MOHR describes apparatus for applying electro narcosis to fish in
which a transportation
means, such as an endless belt, moves fish through a guide means exposing the
fish or fishes into
contact with current application means such as a plurality of current
transmission elements pivotally
mounted and freely movable. During fish transport the fish touch the current
plates and are exposed
to the voltage of each plate. Fish exposure to the voltage intensity required
for fish sedation is directly
related to fish exposure time to the voltage. This arrangement has the
disadvantage that the fish are
in physical contact with the belt and/or the current plates potentially
risking damage.
LAMBOOIJ et at describe "Evaluation of electrical stunning of sea bass
(Dicentrachus labrax) in sea
water and killing by chilling: welfare aspects, product quality and
possibilities for implementation" in
Aquaculture Research, 2008 39, 50-58.
KNOVVLES et al describe "Effect of electrical stunning at slaughter on the
carcass, flesh and eating
quality of formed sea bass (Dicentrachus labrax)" in Aquaculture Research,
2007 38, 1732-1741.
LINES et al describe "Safeguarding the welfare of formed fish at harvest" in
Fish Physiol. Biochem
DOI 10.1007/s10695-011-9561-5.
The European Food Safety Authority has issued "Species-specific welfare
aspects of the main
systems of stunning and killing formed Atlantic salmon" in The EFSA Journal
(2009) 2012, 1-77, and
has "Species-specific welfare aspects of the main systems of stunning and
killing of formed seabass
and seabream" in The EFSA Journal (2009) 1010, 1-52.
ROBB et al describe "Brain Activity of Atlantic Salmon (Salmo salar) following
electrical stunning
using various field strengths and pulse durations" in Aquaculture 2051 (2003),
pp 363-369.
LINES et al describes "Electrical Stunning of Fish: The relationship between
the electric field strength
and water conductivity" in Aquaculture 241 (2004) 219-234.
U55551377 SHARBER describes an apparatus and method for electro-anesthetising
fish, in which an
electronically insulated water containable member has a first electrode and a
pair of second
electrodes bracketing the first electrode.
KESTIN describes "Welfare of fish at harvest" in Trout News, No 17, December
1993, Ministry of
Agriculture, Fisheries and Food, UK.
COWX et at: Fishing with Electricity, published 1990 by Fishing News Books (a
division of Blackwell
Scientific Publications Ltd)
BIRD et al describe "The selection of suitable pulsed current for electric
fishing in fresh waters" in
Fisheries Research 18 (1993) 363-376.
3
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
HUDY describes "Rainbow Trout and Brook Trout Mortality from High Voltage AC
Electrofishing "
in the North American Journal of Fisheries Management 5:475-479, 1985.
HOLLENDER et al describe "Injury to Wild Brook Trout by Backpack
Electrofishing" in the North
American Journal of Fisheries Management 14: 643-649, 1994
W02006130017 KJOLAAS describes a method and arrangement for applying
electronarcosis to fish
in which two electrodes are arranged in a channel, which come into contact
with fish that move
through the channel.
W00038530 MOLLER describes an apparatus and process for slaughtering fish
wherein electro-
narcosis is induced by exposing the fish to an alternating electrical field
having a frequency of greater
than 20Hz for a predetermined duration wherein if the frequency is less than
200Hz, the duration is
less than 2 seconds and wherein the fish are subsequently killed while
unconscious.
JOHN ACE HOPKINS describes "Humane Slaughter of Fish" in Finfish News 7,
Winter/Spring 2009.
Previous sources have often relied on low voltage battery or generator power
or mains power at its
nominal frequency and voltage, which is not optimal, limiting applicability to
more general use.
Indeed, the need for commercial electric stunning of saltwater species is well
recognised (see
recommendations 8 and10 of the EFSA Report (2009) 1010, 1-52: recommendation 8
-"The
opportunity to develop new methods for slaughtering fish is considerable and
should be encouraged"
and recommendation 10 - "Development of commercial stunning methods to induce
immediate (or
rapid) stunning methods unconsciousness in sea bass and sea bream is urgently
required".
There is therefore a need to develop a saltwater electrical stunner for
rendering fish, e.g. salmon,
seabream and seabass, unconscious prior to slaughter, preferably for rendering
fish unconscious
prior to slaughter consistently, swiftly and humanely.
Further, there is, therefore, a need to develop a high power electric
saltwater stunner in line with the
fish transport pipe in a flow-through arrangement.
Further there is a need to develop apparatus and methods for producing better
quality fish carcasses
from harvesting processes.
Statement of Invention
In one aspect the invention provides a fish stunner comprising a high power
alternating voltage power
supply, stunning electrodes and transportation means configured to create
electric fields in
transported water, preferably saltwater for the purpose of stunning fish,
preferably saltwater, fish
unconscious. Preferably the fish stunner comprises: a high power alternating
voltage power supply; a
plurality of stunning electrodes; and a stunner tube; and means for
transporting fish through the
stunner preferably comprising at least saltwater; whereby the fish stunner is
configured to create
electric fields in transported (salt)water for the purpose of stunning
(salt)water fish unconscious.
4
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
Preferably the fish stunner comprises: an elongate stunner tube; a plurality
of stunning electrodes
along the tube; a high power alternating voltage power supply configured to
supply OV (e.g. with
respect to ground potential) to at least one stunning electrode and at least
one high power alternating
voltage to at least one stunning electrode; means for transporting fish
through the stunner tube
preferably comprising at least (salt)water; whereby the fish stunner is
configured to create alternating
electric fields in transported (salt)water within the stunner tube for the
purpose of stunning (salt)water
fish unconscious.
In a first aspect of the invention there is provided a flow-through fish
stunner for use in saltwater flow-
through fish stunning comprising: an elongate stunner tube configured so that
water can flow, e.g. by
pumping, through the tube in a flow-through manner; at least three stunning
electrodes spaced along
the stunner tube configured to provide, when powered, an electric field
(preferably substantially
longitudinally along the stunner tube); a high power alternating voltage power
supply configured to
supply Ov to at least one stunning electrode and further configured to supply
at least one high power
alternating voltage to at least one remaining stunning electrode; whereby high
power alternating
voltage electric fields are provided along part or substantially all of the
stunner tube (e.g. between the
first stunning electrode and the last stunning electrode).
In one embodiment there is provided a flow-through fish stunner in which the
elongate stunner tube is
configured so that (salt)water and fish, preferably a predetermined species of
fish, can flow through
the tube in a flow-through manner at sufficient speed to overcome any motion
of the fish against the
flow of water; and comprising at least four stunning electrodes spaced along
the stunner tube
configured to provide, when powered, an electric field substantially
longitudinally along the stunner
tube; and, a high power alternating voltage power supply configured to supply
OV to at least two
stunning electrodes and further configured to supply at least one high power
alternating voltage to the
remaining stunning electrodes; and in which at least the first and the last
electrode in the direction of
flow being at OV. This facilitates provision of high power alternating voltage
electric field along part or
substantially all of the stunner of sufficiently high field strength to stun a
predetermined species of
fish, preferably saltwater fish, transported in the water, preferably
saltwater, unconscious.
Preferably, the high power alternating voltage power supply is configured to
supply at least one high
power alternating voltage to all the remaining stunning electrodes.
Preferably, the high power alternating voltage power supply, is configured to
supply Ov to at least two
stunning electrodes.
Preferably, the at least two electrodes at Ov comprise at least one upstream
(e.g. the first) stunning
electrode and/or at least one downstream (e.g. the last) stunning electrode in
the direction of flow.
Preferably, high power alternating voltage electric fields are provided
between each neighbouring pair
of stunning electrodes along part or substantially all of the stunner tube
(e.g. between the first
stunning electrode and the last stunning electrode).
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
Preferably the upstream and downstream stunning electrodes held at OV by the
power supply are
preferably also the first and last stunning electrodes in the direction of
flow. Preferably the upstream
and downstream stunning electrodes held at OV by the power supply are also the
first and last
electrodes in the elongate tube.
Preferably the electric field is substantially symmetrical about a central
longitudinal axis of the tube.
The electric field(s) are preferably substantially longitudinal along the
stunner tube but may be
transverse and/or diagonal. Preferably the electric field is substantially
uniformly distributed across the
cross-section of the stunner tube.
It will be understood by those skilled in the art that one or more further
(non-stunning) electrodes, e.g.
connected to ground, may be provided upstream of the first stunning electrode,
and/or one or more
further (non-stunning) electrodes e.g. connected to ground may be provided
downstream of the last
stunning electrode.
In a further aspect of the invention there is provided a method of stunning
fish comprising: providing
an elongate stunner tube configured so that water preferably saltwater can
flow-through the tube in a
flow-through manner; providing at least three stunning electrodes spaced along
the stunner tube
configured to provide, when powered, an electric field substantially
longitudinally along the stunner
tube; providing a high power alternating voltage power supply, configured to
supply Ov to at least one
stunning electrode and, further configured to supply at least one high power
alternating voltage to at
least one remaining stunning electrode; providing high power alternating
voltage electric fields along
part or substantially all of the stunner tube; flowing water bearing fish
through the stunner tube
preferably in a flow-through manner; stunning fish in the high power
alternating electric field.
Preferably the speed of the flow of water through the apparatus is sufficient
to overcome any motion
of that species of fish in a direction against the flow, so the net direction
of motion of the fish, is in the
same direction as the flow of water.
Optionally, the method comprises flowing (e.g. pumping) water bearing fish
through a stunner tube in
a flow-through manner; stunning the fish in a stun station using a first high
power alternating electric
field; maintaining the stun in a stun maintenance station using a second high
power alternating
electric field, preferably from the same power supply; preferably removing
water from the stunner tube
for disposal and fish for further processing. Optionally, transport of the
fish may be via the water flow
and/or by conveyor means.
In a further aspect of the invention there is provided a power supply for use
in flow-through fish
stunner apparatus and methods, e.g. especially in saltwater, configured to
deliver at least one high
power alternating voltage for stunning fish e.g. stunning fish unconscious
swiftly and maintaining the
stun until death (which may be via other means e.g. ice or bleeding). The
power supply may be used
in various flow-through arrangements and also be used in batch (tank based)
and re-circulation fish
stunning methods, and may also be used in other animal stunning apparatus and
methods.
6
In a further aspect there is provided use of a power supply as described
herein, for stunning fish
and/or other animals.
In a further aspect there is provided a method of stunning fish or other
animals comprising: using a
power supply as described herein, to stun fish and/or other animals.
In a further aspect there is provided a method and a stunner for stunning fish
or other animals
comprising:
- stunning, or means for stunning, fish (or other animals) using at least
one high power
alternating electric field;
wherein the electric field is configured to alternate at 125Hz, and/or 100Hz,
and/or 50Hz,
and/or 25Hz and/or between 10 to 50Hz, and/or between 20 to 40Hz, and/or
between 25 to
50Hz, and/or at 25Hz, and/or at 50Hz.
Any feature of any embodiment of any aspect may be used in any embodiment of
any other aspect of
the invention as would be understood by someone skilled in the art.
Preferably the fish stunner comprises at least four stunning electrodes or at
least five stunning
electrodes. Preferably the stunning electrodes are annular stunning
electrodes.
Preferably the first electrode and at least the second electrode in the
direction of flow form a stun
station. Preferably the last electrode and at least the next to last electrode
in the direction of flow form
a stun maintenance station. Preferably the fish stunner comprises a stun
station and a stun
maintenance station and the stun station is upstream of the stun maintenance
station. Preferably in
the direction of flow, the last electrode of the stun station forms the first
electrode of the stun
maintenance station. Preferably, the electric field at the upstream end (e.g.
in the stun station) has a
higher strength electric field able to render a fish rapidly unconscious and
an electric field at the
downstream end (e.g. in the stun maintenance station) which is of lower
strength and so able to
maintain the state of unconsciousness but not typically strong enough to
render a conscious fish
rapidly unconscious. Where provided a stun station is preferably adjacent, and
more preferably
contiguous with a follow on stun maintenance station. Preferably the same
stunning tube provides
both.
Preferably at least two neighbouring stunning electrodes in the direction of
flow within the stun station
are at a first predetermined separation Ll and at least two neighbouring
stunning electrodes in the
stun maintenance station in the direction of flow are at a second
predetermined separation L2, and in
which L2 is greater than Ll. Preferably, L2 is in a predetermined ratio to Ll
whereby the electric fields
in at least part of the stun station have a predetermined ratio to the
electric field in the stun
maintenance station (e.g. to provide a lower electric field). Preferably the
length of L2 is over one
times, two times or three times or four times the length of Ll. This
arrangement facilitates the use of a
limited number of alternating voltage(s) from the same high power alternating
voltage power supply to
7
Date Recue/Date Received 2020-06-22
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
be used over larger lengths of stunner tube by varying the distances between
stunning electrodes to
produce different electric fields e.g. a lower stun maintenance field.
Optionally at least two
neighbouring stunning electrodes in the stun maintenance station are at a
third predetermined
separation L3. For example, L2 may be greater than L3, particularly when the
stunning electrodes
defining L2 have greater voltage difference than those of separation L3. It
will be understood that it is
the electric field strength developed in the volume that is important for
stunning and stun maintenance
and this depends on a number of factors including number of stunning
electrodes, applied voltage and
phase of the voltage as well as electrode separation. It will be understood
that the speed of water flow
in a flow-through stunner is necessarily quite swift and so to ensure
sufficient duration of stun e.g. in a
stun station and in a later stun maintenance section, the fish stunner must be
quite long. Therefore to
ensure sufficient duration of stun (stun conditions and timings depend upon
species) e.g. 2-30s, 5-
30s, 2-25s, 10-30s, 15-30 sand so on, for example in the stun maintenance
section, the stunner tube
must be commensurately long in total, even if the stunner tube is presented in
two stunner tube
sections one after the other. This requirement for a lengthy stun presents
unique challenges for
stunning in water in general and saltwater in particular, which the present
invention seeks to address.
Preferably the fish stunner comprises stunning electrodes in the stun
maintenance station which are
equi-spaced. This is particularly effective when using an odd number of
stunning electrodes.
Preferably an alternating electric field is provided between each stunning
electrode (e.g. by providing
it with Ov, V1, V2 or different phases) and its neighbouring electrode
upstream and/or its neighbouring
electrode downstream. Preferably for an even number of stunning electrodes,
each electrode
between first and last is powered differently from its neighbours (optionally
with different voltages
and/or different phases) so as to provide an alternating electric field along
part or substantially all of
the length of the stunner tube.
Preferably the stunning electrodes are grouped into groups; a first group with
stunning electrodes at
Ov, and at least one further group with stunning electrodes at a first
alternating voltage so as to
provide an alternating field between each pair of neighbouring stunning
electrodes.
Preferably the fish stunner comprises an odd or even number of stunning
electrodes and comprises a
first group of two or more stunning electrodes at Dv, a second group of
stunning electrodes at a first
alternating voltage and a third group of one or more stunning electrodes at a
second alternating
voltage.
Preferably an odd number of stunning electrodes are provided and the first
group at Ov comprises the
first and last stunning electrodes and each alternate electrode between first
and last stunning
electrodes.
Preferably the high power alternating supply comprises one or more
transformers.
Preferably the high power alternating voltage power supply is powered by a
single phase power
supply and comprises one, two or three single phase transformers.
8
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
Preferably the high power alternating voltage power supply is provided by a
three phase supply and
comprises a three phase transformer and/or at least two single phase
transformers.
Preferably an odd or even number of four or more stunning electrodes are
provided and neighbouring
stunning electrodes are connected to different phases and/or Ov so that each
pair of neighbouring
stunning electrodes are provided with an alternating electric field
therebetween and/or so that no two
neighbouring stunning electrodes are provided with the same voltage at the
same time.
Preferably the power supply supplies two different high power alternating
voltages. One of these may
be for the stun station and one for the stun maintenance station provided e.g.
by different single
phase transformers or different phases and/or taps from a three phase
transformer.
Preferably the power supply comprises two single phase transformers of
different power ratings (e.g.
so that one transformer can deliver more, e.g. a multiple (e.g. twice) the
current than that of the
second transformer).
Preferably the distance between stunning electrodes in the stun station is
less than that between
stunning electrodes in the stun maintenance station so that when the same
alternating voltage is used
in each of the stations, the electric field (voltage gradient) is
commensurately different between their
respective stunning electrodes.
Preferably the high power alternating voltage power supply is configurable so
that the peak output
voltage and/or RMS output voltage and/or frequency and/or output voltage
waveform can be selected,
and comprises an output inverter configured to provide at least one
predetermined alternating voltage.
Preferably the power supply provides an alternating voltage with a sinusoidal,
and /or square, and/or
smooth square, and/or quasi-square waveform. Preferably the alternating
voltage has a frequency of
5Hz to 10000Hz and/or 5Hz to 2000Hz and/or 5Hz to 1000Hz and/or 5Hz to 250Hz
and/or 100Hz to
200Hz and/or 5125Hz. More, preferably the alternating voltage has a frequency
lower than 125Hz.
More preferably, the alternating voltage has a frequency of 10 to 50Hz and/or
20 to 40 Hz, and/or 25
to 50Hz, and/or 10Hz, 0r20 Hz or 25Hz. It is thought these lower frequencies
may be particularly
suitable for certain embodiments of this invention. Preferably the alternating
voltage alternates about
Ov.
Preferably the peak voltage of the voltage output is between 100V and 600V or
is between 200V and
600V or is between 250V and 600V or is between 300V and 600V. Preferably the
rms voltage per
meter is between 12 Vrms/m and 800 Vrms/m or is between 15Vrms/m and
500Vrms/m, or is greater
than or equal to 12Vrms/m or is greater than or equal to 15Vrms/m or or is
greater than or equal to
15Vrrns/m or is less than or equal to 800Vrms/m or is less or equal to
500Vrms/m or is less than or
equal to 400Vrms/m.
Preferably the high power alternating voltage power supply is configured to
deliver at least 3kW
and/or at least 5kW and/or at least 7 kW and/or at least 12kW and/or at least
14kW and/or at least
15kW and/or at least 16kW or 5kW to 40kW or 5kW to 25kW or 7kW to 20kW.
9
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
Preferably the elongate stunner tube comprises a pipe (or two or more, or
preferably several, in-line
pipe sections). Optionally, the elongate stunner tube may comprise multiple
separate sections, e.g.
pipe sections that are adjacent and contiguous with one another to form the
pipe or which are in line
but not contiguous forming two separate stunner tube sections. Typically, the
pipe forming the stunner
tube may have for example a continuous periphery (e.g. closed pipe).
Preferably the elongate stunner
tube is circular in cross section. Preferably the elongate stunner tube has a
substantially fixed cross-
sectional area, or average cross-sectional area e.g. when corrugated, along
part or all of its length
(e.g. between the first and last stunning electrodes).
It will be understood by those skilled on the art that saltwater can have
various salinities and
associated conductivities. For example, Wikipedia ("Fresh Water" retrieved 23
Sept 2015) describes
fresh water as less than 500ppm (<0.05%) of dissolved salts, brackish water as
500-30,000ppm
(0.05%-3%) which is roughly equivalent to conductivity of around 800-50,000
pS/cm, saline water as
30,000-50,000ppm (3-5%) which is roughly equivalent to conductivity of around
50,000-80,000 pS/cm
and brine as more than 50,000ppm (>5%) which is roughly equivalent to
conductivity of greater than
around 80,000 pS/cm. Sr is used by oceanographers as a measure of the total
salt content of
seawater. Practical salinity, symbol S, is determined through measurements of
the electrical
conductivity and temperature of seawater, which are interpreted by an
algorithm developed by the
Unrted Nalions Educational Scientlfic and Cultural Orearuzaten (UNESCO). The
measure of practical
salinity (psu although strictly this is a unit-less quantity) was originally
developed to provide an
approximate measure of the total mass of salt in one kilogram of seawater.
Seawater with S equal to
35 contains approximately 35 grams of salt and 965 grams of water, or 35 ppt
(35 psu).
So for example, tap water is typically 20 - 560 ppm, and this is equivalent to
0.02 - 0.56 psu and
conductivities of 30 - 800p5/cm at 10 C. The salt concentration limit in the
US for drinking water is
1000ppm which is 1 psu or equivalent to a conductivity of 1400pS/cm at 10 C.
The typical limit for
agricultural irrigation is 2000 ppm which is 2 psu or equivalent to a
conductivity of 2700 pS/cm at
C. Sea water is typically 35,000 ppm and this is equivalent to 35 psu and
conductivity of
38000pS/cm at 10 C.
In this application the term saltwater is, unless the context indicates
otherwise, intended to exclude
water having those ranges of dissolved salts and conductivities attributable
to fresh, or useable
agricultural, water. Thus saltwater is intended to cover water having salinity
and corresponding
conductivity which starts to present a problem for stunning in that type of
water (at the temperature at
which it is expected to be used). Therefore, the term saltwater water includes
more brackish water,
saline and brine water, unless the context indicates otherwise, having
dissolved salts and associated
conductivities over generally accepted limits for fresh water, and optionally
also over generally
accepted limits for agricultural water, for example having conductivities of
greater than around 3000
pS/cm at 10 C.
Preferably the fish stunner, and/or stunner tube, is adapted for use with
saltwater of conductivity
greater than 30001Js/cm, or greater than 50001Js/cm, or greater than
10,0001Js/cm, or greater than
20,0001Js/cm or greater than 30,000ps/cm or greater than 40,0001Js/cm or
greater than 50,0001Js/cm.
Preferably the fish stunner, and/or stunner tube, is adapted for use with
saltwater of salinity between
to 50p5u, or between about 10psu to about 50p5u. The power requirements are
now significant to
have an effective stun, and preferably also maintenance of stun, in a flow
through fish stunner.
It will of course be understood that conductivity of water varies greatly with
temperature, but that
salinity and temperatures of water sources, e.g. sea water, sea lochs, fresh
water lochs, do not vary
significantly over the course of a day, month, or year (except in some more
unusual geographic
situations), therefore in a particular location the conductivity of the water
can be predicted to be
generally the same. It is intended that the conductivities for which the fish
stunner is adapted will
provide for, or preferably encompass, the typical conditions e.g. salinity and
temperature of a
particular location, since it is preferred that the water in which the fish
are found is the same water
that is used in the fish stunner so as to stress the fish less.
Preferably the stunner tube comprises an elongate tube of diameter 200mm,
250mm, 300mm or 8"
10" or 12" or 14" or 15". The greater the length or width of the stunner tube,
then the greater are the
power requirements. Preferably, the fish stunner is configured to cooperate,
preferably, in-line, with an
inlet of a fish pump. Alternatively or in addition, the fish stunner is
configured to cooperate, preferably,
in-line, with an outlet of a fish pump. Thus, the stunner tube may be adapted
to connect directly to the
inlet and/or outlet pipes of a fish pump. Alternatively or in addition fish
pump (vacuum pump) could be
configured to allow the fish to be stunned early in the transportation
process, so that fish will be
unconscious at the point they enter the pump, reducing stress and improving
quality.
Preferably the stunning electrodes are located in an internal recess about the
internal surface of the
elongate stunner tube. Preferably the stunning electrodes are substantially
perpendicular to the
direction of water flow through the passage.
Preferably the fish stunner comprises: a stun station of a first predetermined
length having a first
predetermined alternating electrical field therein for stunning fish into an
unconscious state; and, a
stun maintenance station of a second predetermined length and a second
predetermined alternating
electric field therein for maintaining fish in an unconscious state.
Preferably, the method comprises any of the features of described herein.
Preferably, the method comprises: providing an elongate stunner tube
configured so that water can
be flowed (e.g. pumped) through the stunner tube in a flow-through manner;
providing at least three
stunning electrodes, more preferably four or five stunning electrodes, at
least one of the stunning
electrodes being at Ov (e.g. the first and/or last): the first and second
stunning electrodes in a direction
of flow forming a stun station; at least the next to last and last stunning
electrodes in a direction of
11
Date Recue/Date Received 2020-06-22
flow forming a stun maintenance station; providing and powering a high power
alternating voltage
power supply to power the stunning electrodes so as to provide an alternating
(preferably
substantially longitudinal) electric field along part, or substantially all,
of the tube; and powering the
stunning electrodes to provide the said alternating electric field so as to
cause the fish to be rendered
unconscious in the stun station and maintained in an unconscious state in the
stun maintenance
station.
Preferably the power supply comprises at least one transformer configured to
deliver at least 3kW, or
at leats 5kW, or at least 7kW or at least 10kW or indeed 12kW or at least 14kW
or at least 16kW.
Preferably the power supply comprises a single phase power supply and one, two
or three single
phase transformers. Preferably, the power supply comprises a three phase
supply and a three phase
transformer and/or at least two single phase transformers.
Preferably the power supply comprises: an AC to DC rectifier module configured
to convert at least
one industrial supply (mains AC and/or generator AC/DC supply) to low voltage
DC output; an
isolated DC to DC converter configured to step up the low voltage DC input to
a high voltage DC
output; and, an output inverter module configured to convert DC to at least
one predetermined
alternating voltage (e.g.AC) waveform.
Preferably the power supply is configurable and can supply at least one
alternating voltage of varying
configuration (configurable in e.g. peak voltage and/or rms voltage and/or
frequency and/or
waveform).
Preferably the power supply comprises any of the features of described herein.
The power supply(ies)
of one or more embodiments of the invention can be used in various stunning
applications e.g. as
described herein.
A flow-through fish stunner is one in which water (preferably bearing fish to
be stunned) is flowed, e.g.
pumped, from an entrance of a stunner tube to an exit after which it is
disposed of e.g. at a de-
watering station. Thus, water is not recirculated. Optionally, further fish
transporting means (e.g. a
conveyor belt) may be provided but this is less preferred. To avoid fish
swimming out of the stunner
tube, preferably the flow of water is quite fast, so the tube is necessarily
quite long to ensure sufficient
stun time, increasing the power requirements drastically. Some de-watering
before the flow-through
fish stunner may take place. Preferably, the stun maintenance station is from
the second to the last
electrode but it may be from a later electrode to the last electrode in the
direction of flow. A fish pump
may be provided before or after the fish stunner, i.e. before or after the
elongate stunner tube. This
may be an air pump, vacuum pump, centrifugal pump or similar pump. The stunner
tube is preferably
in line with the pump inlet/outlet pipes. The stunner tube may be provided by
one or more circular
plastic pipe(s) e.g. flexi-pipe of PVC or HDPE). Typically the pipe is of
consistent diameter along the
stunning length. It may be of 50-300mm in diameter and is preferably 150-250mm
or more or
preferably 200mm in diameter. Preferably, some of the water after
transportation (or removal from a
12
Date Recue/Date Received 2020-06-22
fish farm etc) and immediately before the fish stunner is removed to reduce
the volume of water going
into the stunner.
It will be understood by those skilled in the art that fish may be stunned
along their bodies from head
to tail (preferably head first) or across their bodies. In a flow-through fish
stunner with pumped water
flowing through a stunner tube, elongate fish typically travel with their
elongate body in-line with the
longitudinal axis of the stunner tube and preferably head first. Where
conveyors are used, e.g. with
flat fish, this is not necessarily the case, so a longitudinal field along the
stunner tube may provide a
transverse field across a fish if the fish is lying transverse to the long
axis of the conveyor belt.
Optionally, the invention comprises various aspects and embodiments of the
invention, such as the
fish stunner, stunner apparatus, method(s), power supply(ies), in which any
feature which cannot,
explicitly or implicitly, be directly and unambiguously derived using common
general knowledge from
the priority application GB1511850.8 as filed, is expressly excluded from that
aspect or embodiment.
In a further aspect of the invention, the fish stunner(s), stunning method(s)
and power supply(ies) as
described may be used or configured for use with fresh water. This
configuration may be minimal as
the power requirements for fresh water are so much less onerous.
Brief Description of the Invention
The invention will now be described by way of example only with reference to
the following Figures in
which like reference numerals refer to like features. It will be understood by
those skilled in the art that
the following descriptions represent examples of how the invention may be
carried out in practice and
other embodiments can be envisaged from the description herein. Any feature
from any one or more
aspects of the invention may be combined with any other feature in any one or
more aspects and/or
embodiment of the invention.
Figure 1 shows a schematic view of a flow-through fish harvest production line
illustrating a flow-
through fish stunner operating in line with the fish transportation pipe in a
harvest production process
(here, on-site adjacent a fish farm).
Figure 2 shows a schematic diagram of a fish stunner with a fish stunner
passage, in the form of an
elongate electrifiable stunner tube comprising a tube and three stunning
electrodes spaced along it
and powered using a three phase supply, a three phase transformer and two
conductor arrangement.
Figure 3 shows a schematic diagram of a three electrode flow-through fish
stunner powered by a
single phase supply and a single transformer using two conductors.
Figure 4 shows a schematic diagram of a four electrode flow-through fish
stunner comprising a power
supply powered by a three phase supply and comprising a three phase
transformer for powering four
stunning electrodes using three conductors.
13
Date Recue/Date Received 2020-06-22
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
Figure 5A shows a schematic diagram of a flow-through fish stunner with five
stunning electrodes
comprising a power supply powered by a three phase supply and comprising a
three phase
transformer for powering the five stunning electrodes using three conductors.
Figure 5B shows a similar arrangement to Figure 5A but using a three phase
transformer (not shown)
to power five stunning electrodes using two conductors (cf. also to Figure 2).
Figure 6 shows a schematic diagram of a flow-through fish stunner with four
stunning electrodes and
a power supply powered by a three phase supply and comprising two single phase
transformers to
power the four stunning electrodes via three conductors.
Figure 7 shows a schematic diagram of a five electrode flow-through fish
stunner having a power
supply powered by a three phase supply and comprising two single phase
transformers for powering
the five stunning electrodes using two conductors.
Figure 8 shows a schematic diagram of a five electrode flow-through fish
stunner having a power
supply powered by a single phase supply and comprising a single phase
transformer to power the five
stunning electrodes using two conductors.
Figure 9 shows a schematic diagram of a five electrode flow-through fish
stunner comprising a power
supply powered by a single phase supply and comprising two single phase
transformers to provide
power to the five stunning electrodes using three conductors.
Figure 10 shows a schematic diagram of a fish passage, in the form of an
elongate stunner tube 90
for a five electrode flow-through fish stunner comprising spaced annular
stunning electrodes and
illustrating alternating electric field lines between the stunning electrodes
along substantially the entire
length of the tube.
Figure 11 shows a schematic of a configurable high power alternating voltage
power supply for
powering stunning electrodes in a flow-through fish stunner, according to one
or more aspects of the
invention.
Figures 12A and 12 B show example waveforms capable of being delivered by the
one or more
embodiments of the high power alternating voltage power supply of the
invention for use in flow-
through fish stunner(s) and method(s) of the invention.
Detailed Description of the Invention
Most commercial fish harvesting methods do not make use of electric stunning.
Depending on
species and other factors, methods of harvesting include asphyxiation,
exsanguination, CO2 and
percussive stunning. Large fish can be percussively stunned with mechanical
apparatus, but smaller
fish are more difficult to handle and are often put straight into ice buckets.
Supermarkets and
consumers consider this unethical. Electric stunners are available but
typically for limited volumes of
water. Batch methods using small tanks with a limited volume of water are
unsuitable for commercial
14
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
harvesting. Electric stunners designed to render fish unconscious in 1 second,
prior to a slaughter
method, such as ice or bleeding, are considered more humane.
Precise electrical parameters (in terms of electricity type (AC and/or DC),
frequencies (Hz) and
voltages must be applied to the fish to render them unconscious. In batch
methods in a small tank,
the required voltage and currents can be easily applied because the power
required to electrify that
volume of water is relatively small. As the system is up-scaled to include
larger quantities of water,
then the power requirements go up drastically. Furthermore, if the tank is
inappropriately designed,
fish closer to the stunning electrodes may be heavily stunned whilst those
further away may only be
lightly stunned.
The present applicant developed the first electrical pipeline stunner in 2004
to stun trout ¨ a fresh
water fish. In a flow-through process, a pump moves fish from cages and passes
these into a
specially constructed pipe with opposing stunning electrodes providing
transverse electric fields
across the diameter of the pipe. Because of the low conductivity of fresh
water, low power suffices
and the stunning electrodes can be powered with a class D amplifier or
multiple class D amplifiers.
This works for low power stunning in fresh water.
To slaughter fish in saltwater is an entirely different proposition in terms
of power, the conductivity of
fresh water being in the range typically of 50ps/cm to 600ps/cm whereas the
conductivity of sea water
can be in the range typically of 50,000p5/cm to 60,000ps/cm, an increase of 2
to 3 orders of
magnitude (100 to 1000 times greater). Higher conductivity means that for the
same electric field,
more current will flow, increasing the power requirements drastically.
A D class amplifier approach would require multiple such amplifier units
attached to a great many
stunning electrodes to provide the required electric fields in saltwater of
very high conductivity. To get
round this, one embodiment of the present invention proposes using industrial
single or industrial
three phase power, which requires more skill and knowledge to manipulate into
the appropriate
voltages and frequencies to render the particular fish species unconscious in
the particular
conductivity of the transporting water.
In one or more embodiments, the present invention does not rely on
recirculating water supply of
limited volume nor on controlled salinity to reduce the power required to
generate the precise
electrical voltages and frequencies required between the stunning electrodes.
In at least one
embodiment the present invention creates the required electric field in
whatever water supply the fish
are pumped.
One or more embodiments of the present invention provide high power modules
that meet the low
voltage and electromagnetic induction (EMI) regulations as well as providing a
robust system capable
of managing high voltages (e.g. 600 volts) and currents (e.g. 50 amps).
Thus, in one embodiment, a high power alternating voltage power supply
provides voltages of the
required parameters to render species unconscious within 1 second in
saltwater, and to maintain the
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
stun period to create the required lengths of insensibility for them to be
killed humanely e.g. in ice. In
at least one embodiment the invention will be flexible enough to be extended
to other larger fish
species, (salmon, seatrout, yellowtail etc.) bringing the fish stunner
apparatus into direct competition
with percussive stunners. In at least one embodiment, flexible power input
will allow the systems to
operate in many countries, using for example pulse width modulation (PVVM)
electrical conversion and
controls to enable a vast range of parameters (AC, DC, frequency, voltage and
timing controls) to be
applied to help improve quality after stunning.
To date the transportation and stunning of fish has been a two stage
processes, with the latter
occurring subsequent to pumping into the harvesting station and dewatering;
however fish are
inevitably stressed, which has a knock on effect for quality. The present
invention proposes a
stunning system to offer a strategy for stunning fish as soon as they leave
the holding pen, stunning
them quickly and in water, making it an attractive system for all commercial
fish species and to
welfare legislators.
KNOWLES et al (2007) "and LAMBOOIJ et al. (2008), provide comment on the
parameters required
to stun seabass and bream both in small tubs using modest power amplifiers,
and in a recirculation
system where the conductivity of the water is carefully controlled.
In at least one embodiment the present invention proposes scaling up the power
of the system
significantly so that the same electrical parameters can be achieved across a
200mm pipe in
saltwater drawn from a fish pen along a 30m transport pipe. In at least one
embodiment the present
invention provides for a 15Kw system to supply voltages for insensibility to
two stunning electrodes
and power to a further three stunning electrodes supplying the required
maintenance field. Typically, a
series of alternative electric fields supply AC electricity to stun fish;
however in at least one
embodiment the present invention uses a range of DC (e.g. pulsed DC) and/or AC
options for specific
species.
Figure 1 shows a flow-through fish harvest production line 100 incorporating
an in-line flow-through
fish stunner 32 situated part way along the fish transport pipe(s) 22, 28
(here before a fish pump 24).
Fish production line 100 is provided on working platform 40. The in-line
nature of the fish stunner 32
enables the production line 100 to be located adjacent to a body of water 21,
such as a fresh or sea
water loch or the sea, in which fish are farmed. The production line 100
comprises a pump inlet hose
22 leading to fish stunner 32 and then fish pump 24 (although the fish stunner
could be provided after
the pump). Fish 20 are pumped from a body of water 21 via pump inlet hose 22
and via flow-through
fish stunner 32 and fish pump 24 into a pump outlet hose 28. A further portion
of pump outlet hose 28
leads to a dewatering box 36. Water is not re-circulated, although the power
supplies described
herein may find application in re-circulating fish stunners and other stunning
apparatus and methods.
Once stunned in the flow-through fish stunner 32, fish may be dispensed onto a
working platform 34
or straight into bins 38 loaded with ice water. A generator or a mains power
supply (not shown) may
be used to provide power to flow-through fish stunner 32.
16
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
Examples of flow-through fish stunners are shown in Figures 2 to 11 comprising
mains or generator
powered high power alternating voltage power supplies and various numbers and
configurations of
stunning electrodes arranged into groups so as to be powered by a given number
of conductors 54
(54A, 54B, 54C). Each flow-through fish stunner 32 comprises a stunner tube
90. Stunner tube 90 is
elongate and comprises at least part of or substantially all of an elongate
tube 42 and at least three or
more preferably at least four or five stunning electrodes 10 (numbered in the
direction of flow as
stunning electrodes 1, 2, 3, 4, 5, etc.) spaced longitudinally along tube 42
to form an electrifiable
stunner tube 90. Elongate tube 42 may be formed from a single (e.g. plastic
circular) pipe or from a
series of joined plastic pipe sections. Elongate tube 42 (forming stunner tube
90) is shown linearly in
Figures 2 to 11. Nevertheless, it would be understood by someone skilled in
the art and as shown in
Figure 1 that elongate tube 42 may be curved and may follow a circuitous
route. For example,
elongate tube 42 may comprise a number of generally horizontal loops
superimposed one upon the
other. The loops may be circular as shown in Figure 1 or indeed may be oval or
elliptical or spiral etc.
The entrance to elongate tube 42 may be low down and the exit e.g. into fish
pump 24 may be high
up or vice versa although this is less preferred. Thus, elongate tube 42 may
thus be looped to provide
a smaller footprint.
Nevertheless, even if stunner tube 90 (elongate tube 42) is formed into loops,
it is possible to define a
longitudinal central axis substantially equally spaced from the inner walls of
stunner tube 90.
Preferably, the electric field(s) will be a longitudinal electric field along
the longitudinal central axis and
substantially symmetrically (and more or less evenly) dispersed about this
axis in a plane transverse
to it, e.g. by the provision of annular stunning electrodes. When stunner tube
90 is curved, or formed
into loops, its central longitudinal axis is similarly curved or formed into
loops. Stunner tube 42 is
preferably continuous about its periphery and also preferably circular in
cross section although other
shapes of cross section such as oval or square or rectangle can be envisaged.
Whilst less preferred,
elongate tube 42 of stunner tube 90 may be provided by open passages or
channels such as U or V
shaped channels or pipes, but preferably with a lid to prevent inadvertent
human access to the
(relatively) high voltages present within. Thus, the stunner tube may comprise
a fish channel or fish
passage or other water carrying channel or passage of any suitable shape of
cross-section capable of
carrying water (especially saltwater) and fish or other animals to be stunned
in a flow-through manner.
The term "tube" should therefore be interpreted in a broad manner.
Nevertheless, a preferred
embodiment of the stunner tube and in particular the elongate tube of stunner
tube 90, is a pipe (or
pipe sections) having a continuous circumference. Any shape of cross-section
of pipe may be used,
but circular is preferred. The pipe typically has a constant diameter (or
average diameter). The pipe
may be corrugated to facilitate the formation of curves and loops.
Stunning electrodes 10 (stunning electrodes 1, 2, 3, 4, 5, etc.) are
preferably annular stunning
electrodes e.g. formed from rings of conductive material such as metal.
Preferably, the annular
stunning electrodes have a constant cross sectional area and shape around the
annulus, and are
continuous about the circumference of the tube 42. Alternatively, annular
stunning electrodes may be
provided by multiple spaced stunning electrodes placed in an annular fashion
about the
17
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
circumference or periphery of elongate tube 42 e.g. a pair of crescent shaped
stunning electrodes
connected together or stunning electrodes on opposing side walls of the tube
42, also connected
together electrically to form a single electrode. Stunning electrodes 10 are
typically recessed into
electrode housings 44 on elongate tube 42 (typically circular pipe) to provide
stunner tube 90.
In a further aspect, the power supply(ies) of the present invention may be
used with other types of
stunner (e.g. re-circulation stunners or fresh water stunners) or with
stunners such as those
comprising partly, or substantially, transverse electric fields across the
tube (between more or less
directly opposing stunning electrodes). Indeed, in a further aspect the power
supply(ies) of the
invention could be used with a diagonal electric field within the tube (with
transverse and longitudinal,
perhaps even substantial longitudinal, components) between longitudinally
spaced apart opposing
(facing but not directly opposite) stunning electrodes on the opposing
internal side walls of the tube.
In a further aspect the power supply(ies) of the invention could be used with
batch (tank based)
and/or recirculation stunning apparatus for stunning other types of fish such
as flat fish which would
typically need to be conveyed on an endless belt (conveyer) belt through water
e.g. in a tank or re-
circulation apparatus.
Preferably, stunning electrodes 10 (1, 2, 3, 4, 5, etc.) are configured so
that when powered a
substantially longitudinal electric field is provided along part, most or
substantially all the stunner tube
90. This is shown in more detail in Figure 10. Typically, the longitudinal
electric field runs along
substantially all of the elongate tube 42 with minimal or few gaps. This can
be achieved by preferably
ensuring all the stunning electrodes 10 (1, 2, 3, 4, 5, etc.) are all
continuously powered and interlinked
so that electric fields are always present between each neighbouring pair of
stunning electrodes.
Nevertheless, as can be seen in Figure 10, regions of low electric field
(fewer field lines) around the
centre of the annular electrodes can be seen. Preferably, the annular
electrodes are configured so
that these regions of low field round their centre are not so long (along the
tube), and/or so wide
(across the tube) and/or so numerous that fish are likely to regain
consciousness as they pass
through these. Indeed, it is conceivable that there might be other short gaps
of reduced or minimal
field along the stunner tube 90. For example, neighbouring stunning electrodes
powered by the same
output from the power supply will, if provided, have no electric field between
them. Preferably, any
such gaps are sufficiently small in length along the tube that that in passing
through any such regions,
the fish do not have time to regain consciousness. For example, if one
intermediate (or end) electrode
has a closely spaced electrode next to it, and both of these electrodes are
connected to the same
output of the power supply (e.g. V, or V1 or V2 or Ov) then no alternating
field is provided between
these closely spaced neighbouring electrodes. Preferably, the alternating
field is provided along
sufficient length of the stunner tube 90 that at typical flow speeds and
fields for that species, fish do
not have time to regain consciousness as they travel through the tube from
entrance to exit, even if
one or more short regions of the tube have low or no field present along it.
The length of time during
which the absence of an electric field may allow fish to regain consciousness
will depend on the
species and the initial stunning electric field, and any later stun
maintenance electric field, and other
factors. In this way, alternating electric field sufficient to stun fish for
their journey through the stunner
18
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
tube is therefore provided preferably along at least part or substantially all
of stunner tube 90. The
stunning electrodes may be configured so as to provide a swift stun in 1-2
seconds in a stun station
and a maintenance stun of for example, 5-25s, or 10-30s, or 15-30s, or 15-20s,
or similar in a
downstream stun maintenance station.
It will be understood by those skilled in the art that by "alternating
voltage" is meant a varying voltage
that oscillates in a time varying manner between at least two voltage levels
of any polarity, including,
but not limited to, AC and pulsed DC. Examples of this include the voltage
waveforms described
herein. Similarly, an "alternating electric field" is an electric field that
oscillates in a time varying
manner, for example between two electrodes; the alternating electric field
being generated by an
alternating voltage oscillating between at least two voltage levels of any
polarity, the alternating
voltage applied to one electrode with, typically, the other electrode earthed
at Ov or oscillating at a
different phase between at least two voltage levels of any polarity. By
"alternating voltage power
supply" is meant a power supply capable of delivering at least one varying
voltage that oscillates in a
time varying manner between at least two voltage levels of any polarity. By
"high power alternating
voltage power supply" is meant a power supply capable of delivering 3kW to
40kW or more preferably
5kW-40kW.
It is desirable that the electric fields between each pair of neighbouring
stunning electrodes is
alternating and of predefined voltage and frequency as it is this alternating
field which induces a
stunning seizure in the fish to render them unconscious swiftly and humanely.
Referring now to the figures, it can be seen from Figures 2 to 11 that a high
power alternating voltage
power supply 70, 170 may be powered by single phase or triple phase supply and
may comprise 1, 2
or 3 transformers and/or a power inverter module (preferably configurable) for
delivering specific
predetermined voltages and frequencies to the stunning electrodes 10 (1, 2, 3,
4, 5, etc.). Whilst only
stunning electrodes are shown, the principles of the present invention can be
extend to 6, 7 or more
stunning electrodes to ensure sufficient stun over longer distances.
By providing a stunner tube 90 comprising an elongate tube 42 (even when
circuitously arranged in
loops) and annular stunning electrodes disposed therealong, alternating
electric fields can be
provided which have electric field lines substantially evenly and
symmetrically dispersed across the
tube so that fish are within the presence of the electric field no matter
their location with respect to the
side walls of the tube.
Preferably the stunning electrodes are arranged into a stun station 60
comprising at least two
stunning electrodes and a stun maintenance station 62 comprising at least two
or three or more
stunning electrodes. Typically, one electrode (e.g. electrode 2) is common
between the stun station
and the stun maintenance station 62.
Typically, the first stunning electrode (e.g. electrode 1 connected to the
power supply 70, 170 in the
stunner tube 90) is the first electrode in the fish stunner e.g., the first
electrode in the elongate tube (in
the direction of water flow). However, one or more further electrodes (not
shown) may be provided
19
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
upstream of the first stunning electrode 1 may be provided. This may be
connected to ground.
Similarly, the last stunning electrode (e.g. electrode 3, 4 or 5 connected to
the power supply 70, 170
in the stunner tube 90) is the last electrode in the fish stunner e.g., the
last electrode in the elongate
tube (in the direction of water flow). However, one or more further electrodes
(not shown) may be
provided downstream and may be connected to ground. These further electrodes,
typically not
connected directly to the power supply, may be provided to sweep up any stray
currents.
Turning to the drawings in more detail now, in Figure 2, a flow-through fish
stunner apparatus 32 is
shown. This stunner apparatus 32 comprises a three phase transformer, adapted
to receive power
from a three phase supply, two conductors 54 (54A, 54B), an elongate tube 42
having spaced
electrode housings 44 spaced there along with individual stunning electrodes
1, 2, 3 located within
and form an electrified stunner tube 90. In this case, a fish pump 24 delivers
transport water and fish
(not shown) in direction 200 into the entrance of tube 42 passing first
electrode 1 and electrode 2 and
electrode 3 before exiting the elongate tube 42 into a de-waterer 36 and on to
further processing.
Typically, this further processing may include for smaller fish asphyxiation
whilst lying unconscious in
ice water whereas larger fish may be bled and gilled. In Figure 2, three
stunning electrodes are
provided although preferably four or more stunning electrodes are provided.
Having four or more
stunning electrodes is helpful to provide the required electric fields over
the long stunner tubes
needed in flow-through designs, but it is problematic to provide alternating
electric fields between
multiple especially four or more stunning electrodes, e.g.especially when for
safety reasons the first
and last stunning electrodes connected to the power supply are at Ov.
Particularly in flow through fish stunning apparatus, stunner tube 90 is
typically very long, for example
over 12m or more preferably over 14m or more preferably over 16m or more
preferably over 18m
long. The flow of water through stunner tube 90 is typically quite high to
ensure that fish cannot swim
upstream and escape from the apparatus. Therefore, to ensure sufficient
duration within the fish
stunner 32, and therefore sufficient time within the stun maintenance fields
64 in stun station 60 and
stun maintenance station 62 to ensure unconsciousness, stunner tube 90 is
typically much longer
than in recirculation fish stunners. In a stun station, a volume of water is
provided with a high electric
field sufficient to generate rapid onset of insensibility. In a stun
maintenance station, a volume of
water is provided with an electric field sufficient to maintain insensibility
and prolong duration of
unconsciousness so that it persists after leaving the electric field (as
explained elsewhere herein).
Even for the flow through arrangement a shorter stunner tube may be provided
e.g. by removing
some of the water before stunning. Preferably, the stunner tube has a minimum
length of 5- 7 m. In a
recirculating fish stunner, the stunner tube may be quite a lot shorter.
Preferably, the fish stunner apparatus is arranged to provide from 1-2s to
30s, preferably 5 to 30 sec
of exposure depending on the species and post stun treatment (in the stun
maintenance station), so
fora water speed range of 1 to 2 m/s, the stunner tube may be 5 m to 60 m.
However, preferably, the
stunner tube is 5 to 30 m in length. Typically the initial stun rendering the
fish unconscious happens
within 1-2s, preferably within Is.
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
For various species, preferably the fish stunner apparatus and stunner tube
are configured to provide
between 12V rms per meter and 800V rms per meter, or more preferably between
15 V rms per meter
and 500V rms per meter (from the AC components). Typically, 400V rms per meter
may be used.
To extend the stun duration or increase the field, shorter distances between
the stunning electrodes
may be used and/or a slower water flow and/or a longer stunner tube (using
more pipes or more
conjoined pipe sections).
In the stun station 60, high fields of up to 500 or up to 800 V/m may be
required with the aim to
expose the fish to this for only 1 or 2 seconds and then the field strength
may be reduced by a factor
of 2 or 3 (preferably not more than 3) in the stun maintenance station 62. The
stun maintenance
station may have 1, 2, 3, 0r4 or more of these longer tubes (e.g. 42
optionally lengths of pipe) to
make up the remaining length of stunner tube 90.
In one example, 400V rms over the first 3m may be provided, then three more
lengths of 9m each
offering 400V rms along the 9m length (400V/9m). The total stunner tube length
would be 30m.
In another example, 600V over the first 1.2m may be provided followed by 3
lengths of about 3m also
with 600V rms along each 3m length. The total stunner length may be 10.2m.
In another example, 80V rms over the first 4m may be provided and then 1 or 3
more lengths of 8 to
10m with 80V rms along each 8 or 10m length. The total stunner length may be
12m or 28m or 13m
or 31m or 14 or 34m or even 15m or 35m or preferably 12m or 14m or 28m or 34m.
Whilst less, preferred, in one particular embodiment, stunning in stun station
60 can take place in
water, and stun maintenance in stun maintenance station 62 could take place in
air (after passing a
dewatering) station.
Additional or alternative transport means (to water), such as a conveyer belt,
may be provided in, for
example, the stun maintenance and/or stun maintenance station to co-operate
with stunner tube 90
for transporting fish within it. Thus, whilst flow-through fish stunners may
typically use water alone for
transporting fish, some embodiments (e.g. for flat fish) may use a conveyer
belt as an alternative or in
addition to water as a transport medium. For flow-through fish stunners, the
fish are transported
through it in flowing water and water is not recirculated. For flat fish, the
stun and maintenance
section, or just the stun section, would typically be provided in a fish
passage (e.g. stunner tube 90)
with a conveyor belt lying in slower flowing electrified water.
In Figure 2, a three phase supply 46 is converted by power supply 70
comprising a three phase
transformer 48 into two voltage lines namely conductors 54A and 54B. Conductor
54A powers a first
group of stunning electrodes, here the first and last stunning electrodes 1
and 3, of stunner tube 90.
Conductor 54B powers a middle electrode 2 at a varying alternating voltage V.
Thus, first and last
stunning electrodes 1 and 3 are held at zero volts and middle electrode 2
varies in a predetermined
alternating manner (peak voltage and/or rms voltage and/or waveform and/or
frequency) depending
upon the species of fish to be stunned. It is preferred that first and last
stunning electrodes in the
21
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
direction of flow are held at Ov. Optionally, the first and last stunning
electrodes are substantially at or
very near to (<0.5m) to the end of the elongate tube 42. Alternatively, the
first and last stunning
electrodes are spaced apart from the entrance and exit of the elongate tube
42. The stunner tube 90
comprises that part of the elongate tube 42 that is provided with stunning
electric field(s). Elongate
tube 42 may extend beyond stunner tube 90. Elongate tube 42 may comprise one
or more non-
stunning electrodes (not shown) upstream and/or downstream of and spaced apart
from the stunning
electrodes. The one or more non-stunning electrode(s) may be attached to
ground, so as to stop stray
currents e.g. near the open ends of elongate tube 42.
In Figure 3, a stunner tube 90 similar to that shown in the Figure 2 having
three stunning electrodes
is provided. However, here a single phase supply 50 is converted by a single
transformer 52 to
provide the required voltage difference. The voltage on one output is set at
zero volts by earthing it.
This is connected by conductor 54A to the first and last stunning electrodes 1
and 3. The voltage on
the other output is connected by conductor 54B to middle electrode 2.
Figures 4, 5A, 5B and 6 to 12 show further embodiments of the invention. In
Figure 4, a stunner tube
90 comprising an elongate tube 42 of substantially constant circular cross
section is provided between
fish pump 24 and dewatering station 36, although as described elsewhere the
fish pump may be
provided after the fish stunner. Elongate tube 42 may be wound into loops to
provide a smaller
footprint shown in Figure 1. Spaced along elongate tube 42 are four stunning
electrodes 1, 2, 3, and 4
housed in electrode housings 44 forming stunner tube 90. A first pair of
neighbouring stunning
electrodes 1 and 2 forms a stun station 60. These are neighbouring in the
direction of flow. Stunning
electrodes 1 and 2 are spaced by distance L1. The last three stunning
electrodes 2, 3 and 4 form two
pairs of neighbouring stunning electrodes each pair may be spaced at a
distance L2. Alternatively,
stunning electrodes 2 to 3 may be spaced differently than stunning electrodes
3 to 4. By providing
extra tapping in the transformers, different voltages may be provided for use
with different spacings of
stunning electrodes to produce the same fields, or with the same spacings to
produce different fields.
Stunning electrodes 2, 3 and 4 provide a stun maintenance station 62.
Typically, fish passing through
stun station 60 experience a relatively high alternating electric field
(voltage gradient) so as to render
them immediately unconscious (via an epileptic-type seizure). Stun maintenance
station 62 typically
provides a lower alternating electric field to maintain the fish in an
unconscious state. Typically, the
stun maintenance station retains the fish in an unconscious state during their
transport through the
stun maintenance station 62 but also for a period of time after they exit.
This ensures that if fish are
subsequently placed in ice water for example they do not regain consciousness
before expiring.
By providing stunning electrodes at one or more predetermined but different
distances, e.g. L1 and
L2, then a more limited number of voltages can be used to provide different
electric fields (voltage
gradients) along stunner tube 90. As the number of stunning electrodes 10
increases this becomes
more important as stunning electrodes can be grouped together (e.g. 1+3,
1+3+5, 2+4, 2, 4) to
receive particular voltages from particular conductors, but fewer voltages
overall are needed to be
provided. This facilitates provision of different electric fields in the stun
station and in the stun
maintenance station without requiring additional voltages to be provided by
the power supply as the
22
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
different physical arrangements if the stun and stun maintenance station
allows the voltages to be
used in both to provide the desired different electric fields.
In Figure 4, a specially wound three phase transformer 48 provides three
voltages to four stunning
electrodes. This is achieved by grouping the stunning electrodes; in this case
a first group is formed
from first and last stunning electrodes 1 and 4 which are held at zero volts.
These are preferably near
the entrance and exit of the elongate tube 42. Thus, conductors 54A provide
zero volts to stunning
electrodes 1 and 4. Conductor 54B provides a first alternating voltage V1 to
second electrode 2.
Conductor 54C provides a second alternating voltage V2 to third electrode 3.
Whilst the peak voltages
of alternating voltages V1 and V2 may be the same, these are not in phase and
therefore there will be
a potential difference between stunning electrodes 2 and 3 providing an
appropriate alternating
electric field for the stun maintenance station. Stunning electrodes 2 and 3
and 3 and 4 may be
equally spaced as this is the simplest arrangement or may be differently
spaced one from the other
(e.g. to provide the same or different electric fields between each pair of
neighbouring stunning
electrodes). By selection of distances L2 with respect to L1, lower electric
field may be provided
between later stunning electrodes 2, 3 and 4 in stun station 62 than between
stunning electrodes 1
and 2 in stun station 60. This arrangement advantageously reduces the number
of voltages that need
to be supplied. A higher alternating electric field can be provided between
stunning electrodes 1 and 2
whilst a reduced electric field (voltage gradient) can be provided between
stunning electrodes 2 and 3
and 3 and 4 by using similar voltages but extending the length of the section
in a predetermined
manner. Thus, for particular species and particular flow rates and salinity of
water, the distance ratio
of L2 to L1 may be predetermined to provide a predetermined ratio of stun
station electric field to stun
maintenance station electric field.
Figure 5A shows a similar system to that of Figure 4 using a three phase
supply and a three phase
transformer but providing power to five stunning electrodes 10 (stunning
electrodes 1, 2, 3, 4 and 5).
Here, stunning electrodes 10 are formed into three groups, a first group
comprising stunning
electrodes 1 and 5 held at zero volts and a second group (stunning electrodes
2 and 4) provided with
alternating voltage V1 and a third group comprising a single middle electrode
3 held at an alternating
voltage V2. Conductors 54A are earthed and provide zero volts to stunning
electrodes 1 and 5.
Conductors 54B are common to another phase of the three phase transformer 48
to provide
alternating voltage V1. Finally, conductor 54C is connected to another phase
of three phase
transformer 48 to provide alternating voltage V2. Stunning electrodes 2, 3, 4
and 5 are equi-spaced at
a predetermined distance L3 which is between 1 and 2 times the distance L1
between stunning
electrodes 1 and 2. This is unlike Figure 4 in which distance L2 is over twice
L1.
In Figure 5B an alternative arrangement is shown in which only two phases from
three phase
transformer 48 are used (as in Figure 2) . In this embodiment stunning
electrodes 1, 3 and 5 are
grouped together and powered by earthed conductor 54A from one phase of
transformer 48 and
stunning electrodes 2 and 4 are grouped together and powered at alternating
voltage V1 by another
phase of three phase transformer 48.
23
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
Figure 6 shows an alternative embodiment of flow-through fish stunner
apparatus 32 comprising two
single phase transformers 52 (52A and 52B) and/or stunning electrodes 10 in
elongate tube 42
(forming stunner tube 90), stunning electrodes 1 and 2 forming stun station 60
and stunning
electrodes 2, 3 and 4 forming stun maintenance station 62. Here, stunning
electrodes 2 and 3 are
spaced at a distance L4 which is less than a distance L5 between stunning
electrodes 3 and 4
although it may be more. Alternatively, stunning electrodes 2, 3 and 4 may be
equi-spaced a distance
L4. A first single transformer 52A is connected to a single transformer 52B
and provides, at a common
electrode, an earthed conductor 54A for first and last stunning electrodes 1
and 4. Second electrode 2
is powered by the other phase from first transformer 52A via conductor 54B. A
third electrode 3 is
powered by the other phase of second single phase transformer 52B via
conductor 54. Thus, stunning
electrodes 2 and 3 are at respective alternating voltages V1 and V2 which may
have similar peak
voltages but which are out of phase with respect to one another.
Figure 7 shows a three phase supply being used to power a flow-through fish
stunner apparatus 32
comprising two single phase transformers 52A and 52B. Here, first, third and
last electrode 1, 3 and 5
are connected to a common conductor from first and second transformer 52A and
52B and are held at
zero volts. The other phase of first single phase transformer 52A powers
second electrode 2 at first
alternating voltage V1, and the other phase of second single phase transformer
52B provides second
alternating voltage V2 to electrode 4. Voltages V1 and V2 may have the same or
similar, or indeed
different, peak voltages but in any case are out of phase with one another
thereby providing
alternating electric fields in the corresponding section of stunner tube 90.
Figure 8 shows a flow-through fish stunner comprising a single phase
transformer 52 powered by a
single phase supply 50 delivering power to five stunning electrodes 1, 2, 3, 4
and 5. A first group of
conductors 1,3 and 5 are connected together to one end of transformer 52 by
conductors 54A and
are grounded at zero volts. The other end of transformer 52 is connected to a
second group of
stunning electrodes 2 and 4 by conductors 54B and are provided with a
predetermined alternating
voltage V. Different alternating electric fields are provided in stun station
60 and stun maintenance
station 62 by stunning electrodes 1 and 2 being differently (more closely)
spaced than stunning
electrodes 2, 3, 4 and 5. A variable voltage may be provided by providing an
alternate or variable
voltage tap via conductor 154B or multiple taps on the transformer may be
provided to offer a variety
of voltages.
Figure 9 shows further alternative arrangements for a transformer based
solution of a flow-through
fish stunner apparatus 32. Here, apparatus 32 comprises two single phase
transformers 52A and 52B
connected to a single phase supply 50 and arranged to power five electrode
stunner tube 90.
Conductors 54A are provided grouping stunning electrodes 1, 3 and 5 to a
common ground between
first and second single phase transformers 52A and 52B. The other phase of 52A
is connected to
electrode 2 to provide a first alternating voltage V1. The other phase of
second single phase
transformer 52B is connected to fourth electrode 4 by conductor 54C to provide
a second alternating
voltage V2.
24
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
The arrangements described above provide the ability to offer bespoke
solutions for particular species
of fish and salinities (conductivities of water) by varying one or more of the
power supplied, and/or the
distances between stunning electrodes in the stun station, and/or the distance
between one or more
pairs of neighbouring stunning electrodes in the stun maintenance station,
and/or the separation of
stunning electrodes in the stun station with respect to separation of stunning
electrodes in the stun
maintenance station 62.
For illustration purposes, examples of field lines 64 developed between
neighbouring stunning
electrodes are shown in Figure 10. Here, five annular stunning electrodes are
shown. Electrode 1 has
one neighbouring electrode. Electrode 2 has two neighbouring stunning
electrodes that is electrode 1
and electrode 3. Electrode 3 similarly has two neighbouring stunning
electrodes that is electrode 2
and electrode 4. Electric field lines 64 are substantially continuous and
substantially longitudinally
arranged along elongate tube 42 of stunner tube 90. Furthermore, the annular
nature of stunning
electrodes 10 (1, 2, 3, 4 and 5) ensure that the electric field is
substantially symmetrical (about a
central longitudinal axis) and substantially evenly distributed across the
cross section of elongate tube
42 through which water and fish pass.
Single phase power: Where single phase power is available one or two single
phase transformers can
be used with a single phase supply to provide the required voltage steps for
the species of interest.
Single phase ac power comprises a pair of conductors where the voltage of one
conductors oscillates
from +310 to -310 V relative to the other (assuming normal 220 V rms power).
By setting the voltage
of one of these conductors to zero the other is forced to oscillate between
+310 and -310 [N.B.220 x
N/2 = 310].
One or more embodiments of the present invention uses a stun tube with an odd
number of stunning
electrodes, the first and the last connected Ov and the middle one connected
to the oscillating
voltage (when the number of stunning electrodes = 3, 7, 11, etc.) or to Ov
(zero volts) (when the
number of stunning electrodes = 5, 9, 13, etc.). Therefore at the start of the
tube, between the outside
world and the 0 V electrode there is no voltage gradient (electric field).
This is therefore safer.
Between the first and the second stunning electrodes the voltage rises from 0
V to the voltage of the
second electrode. There is therefore a voltage gradient between these two.
Between the second to
last and last stunning electrodes the voltage drops from the oscillating
voltage back to 0 V. There is
therefore a voltage gradient between these two. Between the last electrode and
the end of the tube
which is at 0 V there is no voltage gradient. This is therefore safer. To make
the system longer, two
more stunning electrodes can be added. The second to last electrode is again
at the osculating
voltage and the first and last stunning electrode(s) are preferably at 0
volts.
Three Phase Power: Where three phase power is available three phase
transformer or two single
phase transformers can be used with a triple phase supply to provide the
required voltage. In three
phase power systems there are 4 conductors, one of which is set to 0 V and the
other three that all
carry an oscillating voltage as with single phase. However the voltages of
these three conductors
reach +310 and -310 vat different times. They are each separated by a phase
lag of 120 degrees.
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
This means that while there is a voltage difference of between +310 and -310 v
between any one of
them and the 0 v conductor, there is also a voltage difference between any two
of the three power
conductors which oscillates between +538 and -538 V [N.B. 220 x x I3 =
538]. In this
implementation, it is possible therefore to have a first and last stunning
electrode set at 0 V and then
any number of intermediate stunning electrodes attached to the other three
conductors ensuring
that no two adjacent stunning electrodes are attached to the same conductor
(otherwise their voltage
is the same and so voltage gradient between them is zero).
Using transformers is a very simple way to achieve the "power" required on the
stunning electrodes
for a narrow and precise set of parameters ¨ but it is not very flexible. In
an example embodiment of a
further aspect, a highly flexible alternative is provided (see Figure 11)
which uses switches (e.g. IGBT
(insulated-gate bipolar transistors) or MOSFET switches) to provide pulse
width modulation to create
precise electrical waveforms in which all aspects of the waveform, voltage and
frequency can be
adjusted.
Preferably, in both approaches, feedback for conductivity changes, and/or
density or crowding of fish
in the tube, and/or change of flow rate, can be used to adjust the alternating
voltage output e.g. on the
fly during processing. Thus, preferably monitoring in real time is provided
and the power supply can
make the adjustments accordingly, either automatically (e.g. in during the
next offline period or more
preferably in real time e.g. within 30 seconds), or manually (e.g. during set
¨up). Typically the
transformer power supply would be switched off, adjusted and switched on
again.
Turning now to Figure 11, another aspect of the invention is shown. Here a
configurable high power
alternating voltage power supply 170 is shown. The configurable high power
alternating voltage power
supply 170 has been designed to be configurable to provide varying alternating
voltages of one or
more required parameters (peak voltage, rms voltage, frequency, waveform etc.)
for use in stunning
e.g. a flow through fish stunner for particular species in salt (typically
>50000p5icm conductivity)
and/or fresh water (typically 50ps/cm to more brackish 1000ps/cm). Typically,
power supply 170 will
be capable of providing up to 14 or even 16kW or more but in another
embodiment at least 5kW or at
least 7kW or at least 10kW or indeed 12kW may be provided. Whilst this is less
desirable, one or
more configurable high power alternating voltage power supplies 170 may be
provided.
Configurable power supply 170 comprises an AC protection control module 172,
an AC-DC rectifier
module 174, an isolated DC-DC converter 176, an output inverter module 178
(converting DC to AC)
and a control module 180. Control module provides overall control but local
control is typically pushed
down to individual modules 172, 174, 176 and 178.
AC protection and control module 172 provides front end power correction and
safety features for
connecting to mains grid AC power supply (not shown). This module delivers an
appropriate AC
supply to AC-DC rectifier module 174. Most of the protection and control is
provided by module 172
on the AC input side of AC-DC rectifier module 174. A 15kW system with PFC
will require around 16
26
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
to 17kVA of power supply capability. AC and protection module 172 and AC-DC
Rectifier module 174
may be provided by a single module (not shown) e.g. on a single PCB.
AC-DC rectifier module 174 functions as an active front end to provide an
adjustable, stabilised DC
output with a very high power factor on the AC input side. Typically this is
configured to convert a pre-
selected mains supply (or more than one mains supply by swapping in and out
modules 172 or
providing a configurable input module 172 (e.g. 230 or 110 V 50 01 60 Hz
input) into DC using a full
wave rectifier. AC-DC rectifier module 174 (module A) may also provide an
isolated DC supply to
power the control system 180 (module D) as well as providing a DC link voltage
to power DC to DC
converter 176 (module B).
Module 176 is an isolated DC-DC converter to step up the voltage. The DC from
module 174 is
chopped into AC using switches to enable use of a transformer to increase the
voltage. Then a DC
bridge is provided on the secondary side of the transformer to produce high
voltage DC. The high
voltage DC (here 600V DC) is provided to output inverter module 178. Module
176 functions as an
intermediate line converter to provide isolation from input to output so as to
allow for a fully floating
output stage minimising the risk of electric shock and unwanted earth
currents. The output system
may need to have one side tied to earth and galvanic isolation between the
three phase AC input and
the output of this module is virtually a necessity. Module 176 may be based on
phase shifted full
bridge topology for a high power, high voltage isolated converter. Isolated DC-
DC converter module
176 may comprise one, two or more converters e.g. two 8kW converters running
in parallel to provide
full 16kW capability. For example, the primary side of each converter may
comprise a full bridge on
the primary side and a bridge rectifier on the secondary side which allows the
transformer to use a
single secondary winding. The converter bridge on the primary side typically
may comprise MOSFETs
and IGBTs. The secondary side may comprise a bridge rectifier. Isolated DC-DC
converter 176
provides an isolated/regulated 600Vdc DC link to feed the output inverter
stage.
A preferably configurable output inverter module 178 is provided at the output
of the DC-DC converter
module 176. The high voltage DC power (e.g. 600V) provided to an input of
inverter module 178 is
chopped into AC using further switches (such as MOSFETs or IGBTs) to create
pulses and so form
desired waveforms at at least one alternating voltage. Where one alternating
voltage is provided this
can be used (in the same way as the embodiments in Figures 2 to 12 with two
conductors) in
combination with a stun tube 90 and stunning electrodes 10, typically at
predetermined distances
along the tube, to provide the alternating electric field necessary to stun
and preferably also maintain
stun in particular species.
Thus, the function of the output inverter module 178 is to use the high
voltage (e.g. approx. 600V)
isolated DC link from module B (isolated DC to DC converter module 176) to
create the custom output
power profiles required typically using PWM techniques. The inverter output
module 178 voltage will
be controlled using closed loop digital control. Users will be able select pre-
programmed parameters
for particular species by selection of suitable control switches (not shown)
which will be configured to
arrange for delivery of pre-selected program parameters e.g. AC voltage
output, and/or output
27
CA 03023981 2018-11-09
WO 2017/006072 PCT/GB2015/052809
frequency, which the inverter module 178 will then produce. The preferred wave
forms include AC or
pulsed DC with frequencies e.g. from 5Hz to 1000Hz or up to 2000Hz or even
10,000Hz and
preferably around 125Hz or more preferably <125Hz e.g. 10 to 50Hz or 20 to
40Hz or 10Hz or 20Hz
or 25Hz or 40Hz or 50Hz. The shape may be sinusoidal, square, smooth square or
quasi-square
wave. The maximum peak voltage developed across the output is 600V (limited by
the DC link input
voltage). The maximum average output power is around 14kW. The output RMF load
current is
typically a maximum of 50Arms.
Output inverter module 178 (module C) typically will keep the pulse width
modulation (PWM)
generation local to the power devices to avoid noise. Control of the system is
preferably managed by
control module 180 (module D) which will communicate via a bus (CANBUS).
Preferably, all the
inverter timing critical low level control and protection may be done directly
on inverter module 178
(module C) with slower high level communications to the control system over
CANBUS. All monitoring
may be performed locally and then sent digitally to the host control module
180. Anticipating EMI at
such voltage levels, to avoid noise, lower power control electronics will
preferably all sit on one PCB.
Control Module 180 (module D) will provide higher level control of the whole
system and interface to
the user interface front end (not shown).
Example wave forms that might be provided by high power alternating voltage
power sources 70 in
Figures 2 to 1001 using the configurable high power alternating voltage power
source 170 of Figure
11 are shown in Figures 12A and 1213. In Figures 12A and 1213 alternating
voltage wave forms that
may provide voltages V, V1 and V2 in Figures 2 to 11 are shown for saltwater
species and fresh water
species. Use of the quasi-square wave simulation may reduce the power demands
on the system.
Preferably the output impedance of the power supply 70, 170 is continuously
monitored to provide
feedback on the variation of the conductivity in the stunner tube 90.
In the present invention the inventor(s) propose two alternative approaches to
developing a suitable
high voltage power supply for the present invention, one series of embodiments
generates narrow
voltages and frequencies at high power (e.g. around 5 to 40kW, ) (see power
supply 70), the other
series of embodiments generating highly flexible control on the output at high
power (see power
supply 170 in Figure 11). Both approaches can be assisted by careful
consideration of electrode
design (size, shape, location), electrode spacing along the tube and electrode
voltages required for
the particular application.
In one example embodiment of the first approach, one or more single phase or
three phase
transformers are used to generate precise parameters (e.g. voltages)
alternating between the first two
stunning electrodes which are of known spacing and the lower parameters (e.g.
voltages) in the
remaining stunning electrodes which are also of known (usually larger)
spacing. In one example
embodiment a three phase transformer is used to give an isolated supply at the
required voltage. In
one example embodiment, the high voltage power supply is powered from single
phase 230 Volt
supply to provide a sine output of 5Hz to 10,000Hz or 5Hz to 2000Hz, or 5Hz to
1000Hz, or 125Hz to
1000Hz or as described elsewhere herein. As far as the present inventor(s) are
aware a large
28
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
transformer has never been used to generate a stunner for fish. Care is needed
to ensure safety at
these levels.
In an example embodiment of the second approach (see Figure 11). a new
electronics arrangement
in a newly designed configurable high power alternating voltage power supply
is used to generate
flexible control of voltage, waveform, and frequency. All controls and choices
have implications for fish
quality.
Input power supply: In at least one embodiment the present invention include
options for operation on
single phase 220/240 V operation; three phase 200 V; or three phase 380/415 V.
50 Hz 01 60 Hz may
be encountered. The unit may be operated from a generator so a stable voltage
cannot be relied on.
Output: Whilst one preferred example embodiment uses alternating voltage at
frequency 125 5 Hz,
other embodiments using other frequencies can be envisaged including the
option to select a few
other frequencies such as a e.g. 5Hz, 10Hz, 20Hz, 25Hz, 20 to 40Hz, 10 to
50Hz, 50Hz, 125Hz, 100
Hz, 300 Hz, 600 Hz and 1000 Hz is of interest or as described elsewhere
herein.
In one example embodiment, the configurable high power alternating voltage
power supply is capable
of supplying maximum rms voltage of 600 V, a minimum rms voltage of 50 V, a
maximum rms current
of 50 A, and a maximum power of 15 kW. The expected load is resistive with a
minimum 2.5 ohms
and the output is to be floating or to have one pole tied to earth.
Control: The voltage to be generated is determined by parameters set before
start up and may be
modified by the output impedance (e.g. at the low end of the conductivity
range for fresh or brackish
water due to changes in conductivity of water and/or the number and/or
clustering of fish, and/or for
all water conductivities due to changes in volume of water) which may be
continuously monitored. For
example the output impedance across the stunning electrodes may be measured
(e.g. 1-2, 3-4 etc.)
e.g. by measuring the voltage and knowing the current and the geometry, the
impedance can be
deduced. Nevertheless, it is not expected for saltwater in particular (with
such high conductivity) that
other factors will have any significant influence on conductivity requiring
changes to be made during
processing. The delivered voltage is preferably within 5% of the target
voltage to ensure fish are
appropriately stunned according to their species specific requirements.
Following start up or changes
to the impedance, the target voltage should be achieved within a short
predetermined time e.g. 30
seconds. Impedance feedback is provided by measuring impedance directly across
the stunning
electrodes and/or by measuring conductivity and/or salinity, and feeding this
to the control module.
Preferably for the configurable approach at least, feedback on conductivity
and flow rate is ongoing
during operation, whereas for the transformer configuration these
(conductivity and flow rate) may be
manually measured and/or configured at set up so that appropriate electric
fields are delivered for the
species of interest under these conditions.
A user interface (not shown) is typically provided to enable the device to be
started, stopped and
controlled from a purpose built microprocessor based control unit. This
facilitates basic system
29
CA 03023981 2018-11-09
WO 2017/006072
PCT/GB2015/052809
monitoring functions including voltage, current, electronic component
temperature and reason for
system emergency shut down.
In one aspect the present invention provides fish stunner apparatus and
methods for particular use in
stunning in a flow through fish stunner apparatus using saltwater. In further
aspects the present
invention provides bespoke high power alternating power supplies and
configurable high power
alternating power supplies for use in such fish stunners and methods of fish
stunning.
By providing a high power system optionally configurable to different mains
and/or optionally
configurable to deliver different species specific voltage parameters e.g. for
use in flow through
saltwater systems, a more humane approach to fish harvesting is possible in a
wider range of
locations (e.g. loch side), with reduced handling, with a wider range of
species in a wider range of
water types (e.g. fresh water, or preferably saltwater- from salty brackish
water, saline water and
brine). Feedback measurements of water salinity either directly or via output
impedance coupled with
a configurable power supply capable of varying output voltage(s) relatively
rapidly (within around 30s)
can facilitate more continuous operation. The use of feedback can also assist
so that preferably the
voltage to be generated is continuously monitored and adjusted (e.g. adjusting
one or more of peak
voltage, rms voltage, waveform shape, frequency, AC content, ) to enable
species specific electric
fields to be maintained in the stunner tube during operation, e.g. to
compensate for changes in
conductivity and rate of flow of the fish transport medium (water).
High power means relatively high power of 5- 40kW or 4-25kW or 7kW-20kW or as
described
elsewhere herein typical voltage range of up to 1000V or more likely up to
800V or 600V. The
frequency of the alternating voltage may be 5 -10,000Hz or 5-2000Hz or as
described elsewhere
herein.
Other embodiments will be apparent to those skilled in the art from the
information contained herein
and any feature from any embodiment of any aspect of the invention can be
combined with any
features from any other embodiment of any aspect of the invention as would be
understand by a
person skilled in the art from this disclosure.
