Note: Descriptions are shown in the official language in which they were submitted.
CA 02245420 1998-08-24
BACKGROUND OF THE INVENTION
This invention relates to a g1-ound fault circuit interrupter having the
capability to successfully interrupt ground faults on systems having different
alternating
current line voltages.
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There has been a great need for means for detecting when an abnormal
current is flowing through line to ground and for immediately interrupting the
fault to
halt such an abnormal flow to protect people from electric shock, fire, and
explosion.
As known in the prior art, the "differential" circuit breakers previously
utilized in
certain European countries have been generally unsatisfactory for such
purposes
because they have been too insensitive to ensure complete protection to human
life. A
prior art arrangement attempts to solve the aforementioned problem by
providing a
differential circuit breaker whose current interrupting contacts, in the event
of a line to
ground short circuit or an abnormal leakage current to ground, are operated by
a
semiconductor device which in turn is energized by the secondary of a
differential
transfonner through whose core two conductors of the electrical circuit being
monitored pass to effectively function as primary windings for the
differential
transformer.
Known is a ground fault circuit interrupter with an inadvertent ground
sensor wherein a circuit breaker connected between a power source having a
neutral
conductor and a phase conductor and a load is operated when the differential
transformer senses that more current is flowing into the load from the source
through
the conductors than is flowing back to the source through the conductors. A
power
transformer is connected across the neutral conductor and a phase conductor
and has in
its magnetic field a winding for inducing a sniall voltage between the neutral
conductor
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and ground to sense an inadvertent grounding of the neutral conductor at or
near the
load. A tertiary winding of the power transformer is connected into the
neutral
conductor in the vicinity of the load whereby, in the event of a grounding of
the neutral
conductor in the vicinity of the load, a current is thus induced in the
neutral conductor
which passes into the ground in the vicinity of the load, and then into the
ground for the
neutral connector at the power line side of the differential transformer
whereupon it
passes through the prilnary of the differential transformer and, if large
enough, causes
the circuit breaker to open.
Also known is a ground fault protective system comprising a differential
transformer having a toroidal core through which each of two line conductors
and a
neutral conductor pass to form primary windings of at least one turn. The
secondary
winding of the transformer serves as an output winding and is connected to a
ground
fault interrupter circuit which energizes the trip coil of a circuit breaker
having a
plurality of contacts connected to the conductors of the distribution circuit.
The
protective system further includes pulse generator means coupled to the
neutral
conductor for producing a high frequency current therein upon grounding of the
neutral
conductor between the differential transfornier and the load. The high
frequency
current is produced by the periodic firing of a diac when the voltage on a
capacitor
connected thereto reaches a certain level. Thus, a continuous train of voltage
pulses is
applied to a winding of an output transformer and these pulses induce voltage
pulses in
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the neutral conductor which passes through the transformer core. The voltage
pulses
induced on the neutral conductor have no effect upon the current balance in
the
distribution system as long as the neutral conductor is not grounded on the
load side of
the transformer. When such grounding does occur, the voltage pulses produce a
current in the neutral conductor which does not appear in either of the line
conductors.
This imbalance is detected by the ground fault sensing means and causes the
contacts to
open, interrupting the flow of current in the distribution system.
Another known arrangement discloses an electric circuit breaker including
highly sensitive ground fault responsive means for protecting human life from
electrical
shock. Reference is inade to the fact that prior art electric circuit breakers
were not
suitable for protecting human life which requires the detection of fault
currents on the
order of 3 to 50 milliamperes with load currents in the order of 10 to 100
amperes.
Sensitivity adequate to protect against ground faults is achieved by a circuit
breaker
comprising highly sensitive ground fault responsive means including a
differential
transformer having a toroidal core fabricated of a magnetic material. A line
conductor
and a neutral conductor pass through the opening in the toroidal core, forming
single
turn primary windings. The differential transformer also includes a secondary
winding
comprising a plurality of turns wound on the toroidal core. This secondary
winding is
connected to the remainder of the ground f'ault responsive means which
includes a
solenoid assembly comprising an armature, an operating coil, and a frame
mounted on
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a casing. The armature is adapted for movement between an extended position
and a
retracted position in response to energization of the operating coil. A latch
hook is
attached to the armature and disposed for engaging the armature member of the
actuator
assembly. Thus, energization of the operating coil causes the latch hook to
draw the
armature away from a latch member to initiate tripping of the circuit breaker.
The
highly sensitive ground fault responsive means of this arrangement comprising
the
aforementioned solenoid assembly is capable of opening the circuit breaker
contacts in
response to ground fault current on the order of 3 to 5 amperes, and thus is
desirable
from the standpoint of protecting human life against electrical shock.
Yet another ground fault circuit interrupter comprises a differential
transformer connected to an AC source which produces a voltage output when an
imbalance in current flow between the power lines connected to the AC source
occurs.
This AC signal voltage is coupled to a differential amplifier through a
coupling
capacitor, rectified, current limited, and applied to a gate of an SCR. When
the SCR
conducts, the winding of a transformer connected across the power line is
energized,
causing two circuit breaker switches to open. Also provided is a ground fault
circuit
for closing the switch when the line becomes unbalanced.
Still another known arrangement uses a ground leakage protector
including a ground fault release coil controlled by a ground fault detector.
The ground
fault release coil is normally energized, and is deenergized when a ground
fault appears
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which disables a restraining latch which results in the opening of the circuit
breaker.
Yet another known arrangement uses a unitary circuit breaker of the
molded case type including, within its casing, means sensitive to ground
faults, means
sensitive to overcurrents, and means sensitive to short circuit currents, all
of which act
on a common trip latch of the breaker to cause automatic opening. The ground
fault
sensitive means comprises a current imbalance detecting coil which energizes a
tripping
solenoid, releasing a normally latched plunger to cause tripping.
Also known is a ground fault protection system that employs a dormant
oscillator which is triggered into oscillation to initiate disconnection of
the protected
distribution circuit upon occurrence of a neutral to ground type of fault.
Prior art ground fault circuit interrupters are limited to dedicated
protection at their rated voltage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide ground fault protection
for systems with voltages as high as 240 volts AC line to line or line to
ground.
It is an object of the present invention to provide ground fault protection
for systems with voltages as high as 277 volts 3 phase wye. The GFCI of the
present
invention differs from the prior art in that, while it requires 120 volts AC
for operation,
it can protect 120 volt, 240 volt, and 277 volt wye, etc., systems. As shown
in Fig. 3
and explained hereinafter, through the use of 2 contactors, protection is
provided for
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more than a single voltage system, i.e., 120 volts and 240 volts.
When 120 volts does not exist in the system, a transformer may be used
to step down the voltage to the 120 volts required by the GFCI. For example, a
transformer may be used to supply power for the GFCI on a 3 phase wye circuit
with
no neutral.
It is another object of the present invention to provide such ground fault
protection for systems carrying current as high as 50 amps.
Yet another object is to provide protection for neutral to ground faults.
A further object of the present invention is to provide ground fault
protection for line to ground faults.
These and other objects, which will become apparent hereinafter, are
accomplished by a ground fault circuit interrupter comprising a differential
transformer
and a neutral transformer mounted adjacent to each other in a compartment
separate
from the compartment housing the ground fault interrupter circuits while
providing the
aforementioned current carrying capabilities, the ground fault interrupter
circuitry
being controlled by an integrated circuit and functioning to open the
distribution cables
being protected upon a fault indication input by one of the transformers for
line to
ground faults and the other transformer for neutral to ground faults. Current
carrying
capability is provided by a contactor whose coil is deenergized by the ground
fault
circuit interrupter circuitry and whose contactor contacts thereupon open the
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distribution system being protected.
The housing compartment for the differential transformer and the neutral
transformer provides a magnetic shield which reduces extraneous field
influence on the
differential transformer. Such fields would otherwise be particularly
bothersome in the
system of the present invention because of the high currents involved.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of the high current ground fault circuit
interrupter of the present invention;
Fig. 2 is a schematic diagram of the basic system of the present invention;
Fig. 3 is a schematic diagram of the system of the present invention when
used to protect distribution systems having different voltages;
Fig. 3A is a schematic diagram of an alternative manner of implementing
the device of Fig. 3 fol- use with distribution systems having different
voltages.
Fig. 4 is a schematic diagram of the system of the present invention when
used to protect 3 phase circuits; and
Fig. 5 is a detailed schematic of the system shown in prior art circuitry
which can be used to implement the ground fault circuit interrupter diagrams
of FIGS.
2 to 4.
FIG. 6 is a side elevational view of the high current ground fault circuit
interrupter of FIG. 1 but inverted.
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FIG. 7 is a bottom plan view of the device of FIG. 6 taken along the lines
7-7, partially in section.
FIG. 8 is a combined front elevational view and prospective view of
separated portions of the device of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Identical elements are identified by the same reference numerals
throughout the application.
Figs. 1, 6 and 7 shows the high current ground fault circuit interrupter A
comprising a housing compartment B in which the ground fault interrupter
circuitry is
located, and a sensor compartment C in which a differential transformer and a
neutral
transformer are located (see Fig. 7). Mounting ears D and E, as well as test
push-
button F, are also shown. The separate compartmentalization of the ground
fault
interrupter circuitry and the transformers allows a plurality of high current
cables G to
be passed through the sensor housing C of the ground fault circuit interrupter
whereas,
in the prior art, such high current carrying cables, i.e., around 20 to 50
amps, could
not be used with ground fault circuit interrupters having the size of the
present one,
which has contacts rated at only 20 amps.
The differential transformer DT and the neutral transformer NT, as seen
as in Fig. 7 are placed in a compartment C made up of two half shells Sl and
S2 which
when joined at their open long sides form a hollow toroid about the cores of
the
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transformers DT and NT, which are held parallel to each other by a separator
or spacer
1. The half shells S 1 and S2 may be held in assembly by any conventional
fastener,
adhesive, welding, swaging, upsetting, etc.
Compartment C can be fastened to the back of compartment B by any
conventional means including welding, adhesives, fasteners, etc. The secondary
windings on the transformers DT and NT (not shown) are connected to the ground
fault
circuit interrupter circuitry in housing compartment B. The individual
conductors G
can be fed through aperture W in compartment C, where they act as the primary
winding (one turn) for the transformers DT and NT.
The arrangement of Figs. 1, 6 and 7 places the conductors G in
compartment C close to the compartment B where the ground fault circuit
interrupter
circuitry is located, but this proximity is not required. In Fig. 8, the
ground fault
circuit interrupter circuitry is in a compartment B' located at control panel
P at one
location, while the compartment C' is located remote from panel P at a
location closer
to the load and contactor contacts as will be further discussed below.
One of the salient features of the ground fault circuit interrupter system
shown in Fig. 2 is the inductance loop 10 inounted in sensor compartment C.
This
inductance loop 10 comprises two transformers the differential transformer DT
and the
neutral transformer NT mounted adjacent to each other, as shown in Fig. 7, and
having
a voltage carrying capability of 277 volts 3 phase wye. As shown in Fig. 2,
two phase
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lines L1, L2, and a neutral line N pass through inductance loop 10. Each of
these lines
provides a primary winding for each of the two transformers of inductance loop
10.
The secondary windings of each of these transformers are connected to
respective
points in GFCI 12, as shown in detail in Figure 5. Also shown in Fig. 2 are
terminals
marked HOT and NEUTRAL which can be suitably connected to a 120 volt, 60 Hz
source needed to power the ground fault circuit interrupter.
When either a line to ground or neutral to ground fault is sensed by GFCI
12, contacts 14 and 16 open whereupon contactor coil 18 is deenergized. This
permits
the spring loaded to the normally open position contactor contacts 20 and 22
of the
contactor to respectively open lines Ll and L2, thus disconnecting load 24
from the
circuit.
A slight modification in the schematic of Fig. 2 is required if the GFCI
load, i.e., the contactor coil 18, is to be protected. In this instance, the
lines labeled
"HOT" and "NEUTRAL" should be fed through the inductance loop 10 comprising
the
two transformers first (see Fig. 3).
Fig. 3 shows the ground fault circuit interrupter of the present invention
as it can be used with loads of two different voltages. In the event of a line
to ground
or neutral to ground fault, inductance loop 10 sends respective signals to
different
points in GFCI 12. GFCI contacts 14 and 16 in GFCI 12 thereupon open, thus
deenergizing contactor coils 26 and 28. Contactor coil 26 permits spring
loaded to the
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open position contactor contacts 30 and 32 connected to the 240 volt AC load
40 to
open, whereas contactor coil 28 permits spring loaded to the open position
contactor
contacts 34 and 36 connected to the 120 volt AC load 38 to open.
As in the circuit of Fig. 2, if contactor coils 26 and 28 are to be
protected, the "HOT" and "NEUTRAL" lines should be fed through the inductive
loop
comprising the two transformers first.
Fig. 3A shows an alternative arrangement where the sets of contactor
contacts are separately operable by their respective contactor coils. Thus, it
is possible
to open one set of contactor contacts while retaining the other set of
contactor contacts
in their closed condition so that only the faulted circuit is caused to open
without
affecting other circuits. A first inductance loop 10' receives conductors Li
and N
therethrough and is coupled to a GFCI 12. A second inductance loop 10" or
merely
different windings upon a common inductance loop 10' is connected to a second
GFCI
12' or to a different portion of the same GFCI 12. GFCI 12 is coupled to
contactor
coil 26 and in the presence of a fault signal from inductance loop 10' permits
the GFCI
contacts 14, 16, which are biased to the open position, to open and deenergize
contactor coil 26. This permits the contactor contacts 34, 36, biased to the
open
position, to open the circuit to the 120 Volt AC load 38. This has no effect
on the
contactor contacts 30, 32 which remain closed and conduct current to load 40.
Alternatively, a fault could exist between conductors Ll and L2 which is
detected by
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inductance loop 10" connected to GFCI 12'. The signal to GFCI 12' permits GFCI
contacts 14' and 16' to open and deenergize contactor coil 28. The
deenergization of
contactor coil 28 permits contacts 30, 32 to open and cut off the current to
240V AC
load 40. A fault that affects conductors L1, L2 and N will cause all the
contactor
contacts 30, 32, 34 and 36 to open thus removing all current to both the 120
VAC and
240 VAC loads.
Fig. 4 shows a ground fault interrupter system of the present invention as
applied to a 3 phase system. This arrangement functions similarly to that of
Fig. 2 in
that, in the event of a line to ground or neutral to ground fault, inductive
loop 10 sends
respective signals to different points in GFCI 12. GFCI 12 contacts 14 and 16
thereupon open and deenergizes contactor coil 110. Contactor coil 110 permits
the
spring loaded to the open position contactor contacts 112, 114, and 116 to
open the
connections of lines L1, L2, and L3 to the load 118.
Figure 5 is a prior art schematic which shows basic circuitry which can be
used to implement the ground fault circuit interrupter portions of Figures 2-
4. It should
be emphasized, however, that the circuitry of Figure 5 lacks the features of
the present
invention of orienting the transformer coils in an inductance loop separately
compartmentalized from the ground fault interrupter circuitry capable of
carrying up to
277 volts, utilizing a first set of contacts in the ground fault circuit
interrupter to
deenergize the coils of one or more contactors having the capability of
interrupting
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currents of up to 50 amps, and then using the contacts of respective
contactors to
interrupt respective load currents.
The circuit of Figure 5, which is limited to a single phase application with
120 volts line to ground and which, though it can be found in the prior art,
is
explanatory of the electronic features of the present invention except as
modified by
Figures 2-4, operates in the following manner:
Differential transformer 50 monitors the flow of current in the line and
neutral conductors, 52 and 54, respectively, and produces in its secondary a
fault signal
when the total current in the line conductor or conductors 52 does not equal
the current
in the neutral conductor 54. The output from the secondary of differential
transformer
50 is conveyed to integrated circuit 56 through diode 58, capacitors 60, 62
and 64, and
resistor 66. Integrated circuit 56 may be a type ML 1851 Ground Fault
Interrupter
manufactured by National Semiconductor Corporation.
A salient feature of the above circuit is the combination of diode 58 and
resistor 66 which are arranged so as to promote quick discharge of capacitor
60. This
discharge of capacitor 60 allows for integrated circuit 56 to be kept
continuously
energized and thus considerably reduces the time required for detection of a
fault. This
continuous energization of integrated circuit 56 from the line side was not
possible in
the earlier arrangements wherein power to the integrated circuit had to be
brought from
the load side or an auxiliary switch had to be employed so that the integrated
circuit
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could only function intermittently. The reason for this is that capacitor 68,
which is
attached to output pin 7 of integrated circuit 56, and which basically
controls the trip
circuit, would otherwise cause SCR 72 to fire frequently, thus frequently
energizing
trip coil 70 and causing the possibility of trip coil burnout.
On a neutral to ground fault the system functions somewhat similarly in
that transformer 74, which together with differential transformer 50 forms
part of the
induction coil 10, which as previously indicated is mounted remotely from the
ground
fault interrupter circuitry in such a fashion that high current cables can be
carried
therethrough, has a signal induced on its secondary windings which is carried
through
capacitors 76 and 78 to input pin 4 of integrated circuit 56.
The trip circuit for both types of faults is identical in that if a fault is
detected by the input pins 2, 3, and 4 of IC 56, a signal is output from pin 7
of
integrated circuit 56 causing capacitor 68 to charge faster. At the same time,
the path
to the gate of SCR 72 including resistors 80 and 84, diode 82, and capacitors
86 and
88, is energized. SCR 72 then conducts and an energization path to trip coil
70 is
created through diode bridge 92, 94, 96, and 98. Capacitor 90 and MOV 106 are
present for surge protection.
Upon energization of trip coil 70, contacts 100 and 102 of the ground
fault circuit interrupter (equivalent to the spring loaded to the open
position GFCI
contacts 14, 16 of Figs. 2 to 4) are opened which in turn causes a load, in
this case,
CA 02245420 1998-08-24
contactor coil 104 (equivalent to contactor coil 18 of Fig. 2) to react and to
use its
contact or contacts (not shown) to open one or more high current lines such as
are
shown in Figures 2-4.
A push-button 106 and resistor 108 are part of a test circuit which
bypasses the transformers 50 and 74. Also, since the ground fault circuit
interrupter is
only sensitive to differences in current flow between the "hot" conductors and
the
neutral conductor or the neutral conductor and ground, unbalanced loading
between
"hot" conductors will not cause "nuisance" tripping.
Among the many advantages achieved by the present invention are the
ability to handle currents of at least 50 amps provided by the construction
wherein the
differential transformer and neutral transformer are mounted adjacent to each
other and
separately compartmentalized from the ground fault interrupter to allow the
passage of
heavy duty cables capable of carrying such high currents therethrough, the
provision
for the capability to interrupt high current loads achieved by using the
intermediary of a
contactor coil or coils as the load for the ground fault circuit interrupter,
the capability
of the transformers of the induction loop 10 to handle 240 volts AC whether
line to
ground or line to line, and the capability to open the lines at remote
distances achieved
by the intermediary of the contactor between the ground fault circuit
interrupter and the
trip points on the lines. This is in contrast with prior art devices wherein
the ground
fault circuit interrupter circuitry was installed in the lines to be monitored
and thus
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limited the current levels that could be monitored. Here the transformers in
inductance
loop 10, in compartment C, can see voltages up to 277 volts but they in turn
pass only
a small current induced in the secondary windings of the transformers DT and
NT to
the GFCI 112.
An additional feature of the invention is that the circuit interrupting means
may be installed at a location remote from the sensing control circuitry. For
example,
as shown in Fig. 8, the GFCI 12 in its housing compartment B' can be mounted
on a
control panel P at a first location and thus made accessible to a user, while
the
contactor 18, 'the transformers DT and NT in compartment C' and the conductors
G is
mounted closer to the load at a location remote from the user. This
arrangement
protects the transformers, particularly the differential transforrner, from
exposure to
electrical noise in the vicinity of the remote location. If desired a switch
23 can be
employed to open the neutral line N. This can be done in both a two and three
phase
system.
The embodiments of the invention disclosed and described in the present
specification and drawings and claims are presented merely as examples of the
invention. Other embodiments, forms and modifications thereof will suggest
themselves from a reading thereof and are contemplated as coming within the
scope of
the present invention.
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