Note: Descriptions are shown in the official language in which they were submitted.
`` 10667t70
This invention relates to load selective power
systems and more particularly to a power system in which dangers
such as accidental electrocution are prevented.
DESCRIPTION OF T~E PRIOR ART
There have been many attempts in the prior art to
prevent accidental electrocution of a person caused by the person
~eing the load, by quickly detecting and reacting to the result-
ant ovexload and/or by detecting and reacting to shorting between
a supply conductor or terminal and an external ground, or a
short occuring in the load where the person may be connected
between the shorted load and ground. There have also been
many attempts at providing overload and/or over voltage pro-
: . , .,:
tection for circuits. Illustrative of such prior art are thefollowing U.S. Patent Nos. 3,197,676 - Jones; 3,312,862 - Currin;
3,449,635 - Staples; 3,543,090 - Pfister et al; 3,566,198 - Del-
ahunty; 3,573,550 - Baker; 3,602,773 - Berstein; and 3,617,808 - -
~ Yoder. None of these prior art patents, found in the search
-'` on the invention herein disclosed, either alone or in any appro-
~'~; priate combination, anticipates or renders the disclosed invention
'~! 20 unpatentable, nor does the prior art function in the manner here-
in disclosed to solve the heretobefore problems of the prior art.
SUMMARY OF_THE INVENTION
The present invention is used in a power system and
relates to the combination comprising a load and a supply circuit
` ~ connected to the load and adapted to connect the loaa to an al-
ternating current source. The suppl~ circuit includes a uni-
directionally triggered switching means connected between the
load and one terminal of an alternating current source for sup-
~, plying current from an alternating current source to the load
J 30 in one direction, the system including a unidirectional blocking
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means. The supply cixcuit further includes control means
connected to the switching means and one terminal of an alterna-
ting current source and connected to another terminal of an
alternating current source through the unidirectional blocking
means for supplying triggering current in tne one direction to
turn-on the switching means. The control means is operative
substantially to reduce the current flow in the one direction
through the switching means whenever a current flow in the
opposite direction is permitted by any shunting connection of
the blocking means causing a minor current flow in both direc-
tions through the control means.
In one o~ the aspects of this invention the power
system includes a supply circuit having a pair of terminals
including a unidirectionally triggered switching means adapted
`
to be connected to an alternating current source for supplying
`` current in one direction. The supply circuit also includes means
operatively connected to the switching means for substantially
^`l
reducing the current flow through the switching means in the one
direction whenever an improper load ~ircuit omitting a unidirec-
, 20 tional blocking means is connected to the supply circuit across
~' the terminals. A proper load circuit includes a load and a
"~` unidirectional ~locking means connected in series to the load
for passing substantial current in said one direction through the
load and passing substantially no current in the opposite direc-
tion.
Other aspects include various specifics of the system
i 27 wherein the ~loc~ing means is a rectifier and the sw_tching means
, '
i
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106670
is a reverse blocking thyristor. The means for substantially
reducing the current flow includes a capacitor for triggering the
gate of the thyristor, with the capacitor discharging below the
firing potential whenever an improper load circuit is connected.
` The means for substantially reducing the current flow also includes
a rectifier coupled between the gate and anode of the thyristor
and oriented in a direction opposite to the one direction. The
supply circuit also includes a resistor connected between the gate
and anode of the thyristor which has a resistance value sufficiently
high to maintain the firing angle of the thyristor substantially
at 180 degrees, the RC time constant of the resistor and capacitor
being greater than one half-cycle of the alternating current source.
In other aspects of the invention, another load circuit
:~ .
`~` having a pair of input terminals and another load is connected to
one of the input terminals, with a pair of unidirectionally
triggered switching means, in parallel and having the orientation
of each reversed from the other, connected between the other load -
.,, ~ .
and the~other input terminal so that current may pass through the
other load in either direction depending upon the manner of
connection which may exist at the time between the pair of input
terminals and respective supply circuit terminals. Other details
of this bidirectional other load circuit is seen where the pair
~ of unidirectional switching means are thyristors, and a pair of
`~, means are connected respectively between the gate and anode of
each thyristor for controlling the firing potential thereof, each
such means including a resistor and a rectifier oriented in the
,i same direction as its associated thyristor and being of values
determined by individual thyristor gate characteristics for
adjusting sensitivities thereof and permitting only one thyristor
of the other load to be conducting at any particular time when
attached to the terminals of the supply circuit.
` In accord with another embodiment of t~e invention
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full-wave power may be supplied to a proper load circuit having
three input terminals and a pair of unidirectional blocking means
respectively connected to two of such input terminals and oriented
in the same current carrying direction. The load circuit includes
a load connected between the pair of blocking means and adapted to
be coupled to the other input terminal. A supply circuit having
three output terminals and including a pair of unidirectionally
triggered switching means adapted to be connected to an alternat-
ing current source supplies current in such direction with one
unidirectional blocking means passing one half-cycle of current
from the source through the load and through one of the unidirec-
ti~ly triggered switching means back to the source, while the
other unidirectionally triggered switching means passes the other
half-cycle of current from the source through the other unidirec-
tional blocking means and through the load back to the source
whereby substantially full wave current is delivered to the load
from the source. Connected to the pair of switching means is a
means for substantially reducing the current flow through the
pair of switching means to effectively terminate current flow
through the load whenever an improper load circuit omitting a
unidirectional blocking means is connected to the supply circuit
across any two of the three output terminals or whenever an im-
proper load circuit omitting a pair of unidirectional blocking
means is connected to the three output terminals of the supply
circuit.
Other aspects of the above full wave embodiment include
the connection of an auxiliary load circuit, having another load
in series with another unidirectional blocking means and oriented
in the same direction, is connected in parallel with the load and
~0 one unidirectional blocking means so that substantially half-wave
current is delivered to the other load. The full-wave
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embodiment also includes additional means for substantially reduc-
ing the current flow and includes a resistor and capacitor in se-
ries across two output terminals. A gaseous discharge bulb and
a series connected reset switch are located in parallel with the
above capacitor.
Monitor circuits in accord with other aspects are disclosed
and are operable upon functioning failure of the thyristors to in-
dicate such failure and to warn of the more normally dangerous con-
dition of the supply circuit. The supply circuit includes current
interrupting means connected in series with the thyristors, and
the monitor means, indicative of such failure, may include means
for activating the interrupting means to prevent current flow from
the alternating current source. Delay means preferably should be
included in such~ monitor for delaying activation of the interrupt-
ing means a predetermined time greater than the time in which the ``
monitor would be made operable by transient conditions.
The monitor circuits could include means, such as a relay,
for audibly indicating such failure and means, such as a bulb,for
visually indicating such failure.
In yet other aspects the power system may include a proper
load circuit including a load with at least two terminals and at
` least one unidirectional blocking means connected between the
terminals and in series with the load. A supply circuit for such
proper load circuit may include at least two supply terminals
connected to the load terminals, and at least one controlled
unidirectional blocking means connected to the load circuit ~`
through the supply terminals, the controlled blocking means being `~
adapted to be connected to an alternating current source so that `
.,
a series circuit between the load circuit and the controlled block- `
` 30 ing means and the alternating current source is established. ~ ~
.' . , '.
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The supply circuit includes a control circuit in parallel with the
controlled blocking means which is turned on and turned off by the
control circuit according to the direction of current flow determined
by the proper load circuit and any improper other load which may
be connected. The proper load circuit is operative to eliminate
the current in the turn-off direction due to the series inclusion
of the unidirectional blocking means with the load, and being
operative to pass both turn-on current and power current from the
source which are flowing in the same direction and causing
substantial current from the source to flow in said proper load
circuit, while the supply circuit causes no substantial current
flow to any improper other load circuit in which appreciable current
in the reverse turn-off direction is permitted to flow in such
other improper load. The control circuit is a resistor-capacitor
phase control circuit which controls the firing potential of the
` gate of the controlled unidirectional blocking means.
A general object of the present invention is to provide
a novel load selective power system.
` Another general object is to provide a power system
in which accidental electrocution and the like is prevented.
A particular object is the provision of an improved
supply circuit having unidirectionally triggered switchi~g means
with control circuitry to prevent accidental electrocution in
... . .
which a ground path for current through a body is provided or the
body becomes connected across the supply circuit output terminals. ~ ~
Another particular object is to provide an improved - -
supply circuit in which a more convenient but safe exposure of
electrical output terminals or conductors may be employed, ~ ~-
particularly for use in supplying power to moving contacts for
cranes, tramways, railways, trolleys and personal conveyances and
the like.
; A specific object is the provision of an improved
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supply circuit in which power transmission from a source to a
load is more safely delivered than presently employed in the art
and which alleviates many problems of the prior circuit
arrangements considered to be overly hazardous.
; Another specific object is to provide an improved
selective supply system, which may be connected, for example, `
between the normal house fuses or circuit breakers and the various
outlets or loads, whereby any short or improper load across the
outlets or loads will interrupt the current flow to the various
outlets or loads and only proper loads may derive power therefrom.
Other specific objects are to provide an improved load
selective power system that is simple in design and easily
constructed inexpensively manufactured and maintained, and
reliable and efficient in use.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features which are believed to be characteristic
of this inventio~ are set forth with particularity in the appended
claims. The invention itself, however, both as to its organization
and method of operation,together with further objects and advantages
thereof, may best be understood by reference to the following
description taXen in connection with the accompanying drawings, in
which:
FIG. 1 is a circuit diagram of the first embodiment of
s :.
the load selective power system in accord with this invention, in
which the half-wave power is delivered to the load; -:
~ FIG. 2 is a circuit diagram of a bidirectional load
-~ circuit in accord with this invention and usable with the system
of FIG. l; -
FIG. 3 is a circuit diagram of the second embodiment of
30 the load selective power system in accord with this invention, in
which full-wave power is delivered to the load;
FIG. 4 is a circuit diagram of a unidirectional load -
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1066770
circuit which may be used in a sli~htly modified circuit of FIG.
3, in which full wave unidirectional power is delivered to the
load;
FIG. 5 is a circuit diagram of the third embodiment of
the load selective power system in accord with this invention,
in which full wave power is delivered to the load with the circuit
being able to supply much more power than the circuit of FIG.3;
FIGS. 6A and 6B are circuit diagrams of two different
fault monitors in accord with this invention which may be used in
either of the circuits of FIGS. 3 or 5;
FIGS. 7 and 8 are circuit diagrams of load circuits
in accord with this invention usable with the system of FIG.l;
FIG. 9 is a circuit diagram of a fourth embodiment of
the load selective power system in accord with this invention,
- similar to FIG. 8, but not affording as many protective features;
\j
FIGS.10-13 are circuit diagrams of load circuits in -
~: accord with this invention usable with the systems of FIGS. ~ -
`: 3 or 5;
FIGS. 14-16 are circuit diagrams of load circuits
;'. 20 usable with the systems of FIGS. 1, 3 or 5 with simple circuit ~
testing incorporated therein; .
` FIGS. 17 and 18 are circuit diagrams of alternative ~.
`~, circuit testing arrangements usable with the load circuits of
FIGS. 14-i6; ~ ;
` FIGS. 19 and 20 are diagrammatic views of two different
component arrangements for eliminating surge currents to the -.
load when the supply circuit is turned on by a switch or by being ~:~
~ plugged into a supply;
,` FIG. 21 is a fi~th embodiment of the load selective .
.~ 30 power system in accord with this invention;
FIGS. 21A and 21B are modifications of FIG. 21;
FIG. 22 is a circuit diagram of a load circuit in accord
~ ' ! . . . `
~667 70
with this invention usable with the system of FIG. 1, but
providing a modified alternating current to an A. C. load;
FIG. ~3 is a circuit diagram of a load circuit usable
with, for example, the system of FIG. l; and
FIG. 24 is a circuit diagram of a bidirectional load
circuit similar to FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
. .
The essential feature of this invention is the
recognition that one direction of current flow, for example,
10 the positive half cycles of an alternating current supply, could
be employed as the source of power while the other direction of
current flow, the negative half cycles could be used to discriminate
between a proper and an improper load. Thus, a half-cycle
directional blocking means in the form of a simple rectifier 10
can be intentionally included in the load circuit, generally
` depicted by 11, with the load terminals 12 and 13 as shown. Therectifier 10 is in series with DC load 14 and functions to block
a discriminator current flow in one direction, for example,
during the negative half cycles, and to permit power current
flow during the positive half cycles from the alternating -
.
current source 15 connected across terminals 16 and 17. It is
apparent that rectifier 10 can be located on the other side of
DC load 14, and, when so located, additional ground fault
protection obviously would be provided between such diode and
the load. The depiction of rectifier 10 on the hot side of
~i .
the DC load 14 was primarily to facilitate a ready comparison ~-
and recognition of its inclusion în the hereina~ter described -~
full wave AC circuit of FIG.3.
If an improper load, one without such rectifier 10 is
also connected in parallel with the proper load circuit 11, a
discriminator current flows during the next negative half-cycle
after connecting such improper load. Such discriminator current
_9 _
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1(~66770
is effective to temporarily or permanently cause substantially no
further current flow during the next or subsequent positive half
cycles. The discriminator current thus may effect control by acti-
vating or deactivating a unidirectionally triggered switching
means or gate controlled rectified means in the form of a direc-
tionally triggered thyristor or SCR 18, in the basic power supply
circuit, generally depicted by 20, having output terminals 21 and
22 to which the load circuit 11 is connected and wherein termi-
nals 22 is connected by switch 23 to the ground or neutral to
ground side 17 of AC source 15. Rectifier 10 is oriented to pass
current in the same direction as SCR 18 thereby permitting power
current flow through load 14, but when an improper load is connect-
ed in parallel with the proper load circuit 11, a reverse discrim-
inator current is also permitted to flow, and power current flow
ceases, as hereinafter more fully described.
Consider the DC load 14 and diode 10 connected by their input
terminals 12 and 13 respectively to output terminals 21 and 22,
switch 23 is initially closed and the capacitor 24 charges on the
positive half cycle of SCR anode voltage to the trigger point of
20 SCR 18 in a time determined by the RC time constant of resistor -~
25 and capacitor 24 and the rising anode voltage. Diode 26 blocks
reverse gate voltage on the negative half cycle of the AC supply
voltage. Once the capacitor 24 is sufficiently charged, a trig- -~
gering current for turning on the SCR 18 is supplied to the gate
` 27 through diode 26 and resistor 25. The DC load 14 will be
supplied a current during one-half of the AC supply cycle. If the
output terminals 21 and 22 are shorted for example, the capacitor
24 discharges during the next one-half negative cycle through diode
28 thereby cutting off SCR 18, diode 28 providing very little
30 resistance as compared with the resistance of resistor 25 to
discharge capacitor 24 very quickly, and if the short is by the
:~ human body, for example, capacitor 24 discharges before any
electrocution of the human body, and depending upon contact
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conditions, most often with little or no sensation of shock by
the body. The power to the load is thereby discontinued during
such a short because SCR 18 is made non-conducting.
The system according to this invention is seen to
include a proper load circuit 11 having a load 14 and a half-
cycle directional blocking means in the form of a diode 10 or
other rectifying device in series with the load 14 and an
improper load circuit cannot derive power from the system in accord
with this invention. SCR 18, capacitor 24, diodes 26 and 28 and
resistor 25 may be confused with ~ simple half-wave RC-diode SCR
phase control circuit because of many similarities, but the
component values for resistor 25 and capacitor 24, in accord with `
this invention, are selected to provide a relatively long time
constant, namely longer than the time of one-half cycle, to
prevent charging of capacitor 24 sufficiently to the trigger point
: , .
~` of the SCR 18 upon closure of switch 23, particularly when the
` supply circuit 20 is connected to an improper load. While SCR -
18 is in an unfired condition, substantially no current initially
flows through the proper load circuit, including diode 10. If a
`` 20 short initially occurs, while SCR 18 is unfired, between the
terminals 21 and 22 or across the proper load circuit 11, the
only current which would pass through the short would be the
`~ rather small current resulting from the charging and discharging
of capacitor 24 and any small leakage through SCR 18. The amount
of this small current may be varied, as would be apparent to those
skilled in the art, by ehanging the circuit parameters without
changing the basic functioning of the supply circuit 20, to
discourage careless habits of people regarding the touching of
possibly exposed conductors or the like.
Even with a proper load circuit 11 connected and the
SCR 18 in fired condition, a short across terminals 21 and 22 or
12 and 13 would cause quick discharge of capacitor 24 through
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diode 28 thereby de-activating SCR 18, and therafter any current,
but the very small current her~inabove set forth, is inhibited.
If a low resistance contact is provided by the short
at the same time that a high power surge pulse is experienced in
the conducting direction of the fired SCR 18, the higher current
during such half-cycle will flow through such short, but
electrocution of a human whose body may constitute the short
would not occur, as would be obvious to a person skilled in the
art.
The small current passed by capacitor 24 through an
improper load provides for continued non-conductance of SCR 18.The
shorting of the proper load circuit 11 negates the blocking -
function of diode 10, and the entire curcuit 11 and 20 thus becomes
a simple half-wave rectifying power source which is non-conducting
due to the lack of a sufficient charge on capacitor 24 for firing
SCR 18.
The series connected diode 10 must be oriented in the
~ame c~nductive direction as the direction of conduction of SCR
18 for proper flow of current. If the diode 10 were connected
oppositely, i.e., opposite to the conducting direction of SCR 18,
SCR 18 will not be fired due to the fact that capacitor 24 is
provided a discharge path having less resistance than its charging ;~
path and will not store a charge sufficient to being the control
` or gate electrode 27 of SCR 18 up to firing potential.
An improper load applied in parallel to a proper load
circuit 11 serves to restore the firing angle of the SCR 18 to
; a non-conducting state and effect a termination of the power being
supplied to the proper load circuit 11. -~-
Except for the aforementioned possibility of initial
` 30 surge or at the most a generally one-half cycle of current, the
very small currents passed by non-rectifying loads permit even ;
` direction shorting across the proper load circuit 11 without harm
' ' . ~
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to the power supply system 20, proper load circuit 11 or the
element or person causing the direct short.
In the simplest summary of function it may be stated
that the capacitor 24 connecting the SCR gate 27 to the SCR cathode
29 through the protective diode 26 acquires a firing potential
through resistor 25 which is connected to the SCR anode 30 and
at a rate inversely proportional to the value of resistor 25. It
may be discharged or reduced to a point below the firing potential
required by SCR 18 during the negative half cycles through the
diode 28 that parallels resistor 25 at a rate thus made independent
of resistor 25 and made dependent upon other resistances in
series with diode 28, such as the diode 10 and load 14. Discharge
` through diode 28 by capacitor 24 would be blocked by diode 10,
but a short in parallel with the proper load circuit 11 would
permit quick discharge of capacitor 24 and as long as the short
. were present the SCR 18 would not conduct due to the inability
of capacitor 24 to charge sufficiently to cause firing of the SCR
18.
~`. A circuit of this general type, which has a great deal
in common with the prior art phase control circuits, may be made
to supply non-rectifying or conventional loads wherein the ~ -
resistance 25, in parallel with the discharge diode 28, would be
made to be variable and capable of a range that permits a .
regulation of the comparative charge-discharge rate that would be
effective within the half-cycle with a resultant retardation from :
.i essentially zero to 180 degrees or from full "on" to full "off"
respectively for conventional loads, all of which is common in ~;~
~; the art as shown for example at page 69 of SCR Manual, 4th Edition,
- 1967, General Electric Company.
When the load circuit 11 is given an efficient rectifying
quality by connecting the load 14 in series with a diode 10 of
good reverse blocking resistance, an external control of the . :
~. . - . , . : ~ - . .
1066~70
internal circuitry is provided, i. e., an external proper load
circuit 11, including a diode 10, can derive power from supply
circuitry adjusted to an off condition, but an improper load
cannot derive power therefrom. If the diode 10 is arranged
to have its polarity in a direction opposing that of the SCR
18, the discharge rate of the phasing capacitor 24 is undiminished
but the charge rate is essentially reduced to zero and the SCR
gate 27 is not raised to a firing potential. If the load circuit
11 is a proper one, i.e. load 14 is in series with diode 10 and
diode 10 has polarity like that of the SCR 18, the discharge rate
is effectively reduced to æero and the charge rate is normaly
determinable by the resistance 25. In a supply circuit 20 where
an external control is to be exercised, the charge capability to
the triggering potential for the SCR 18 within a half-cycle is no
longer a requirement. In fact the protective features of the
;- system in accord with this invention cannot be realized if the
triggering potential is achieved within one-half cycle. Higher -~
resistance for resistor 25 coupling the SCR gate 27 to anode 30
~` becomes highly desirable and should be of a fixed value to
insure that it does not drop low enough to cause a firing potential
to be achieved within one-half cycle. Thus, a capacitor
triggered phase control prior art circuit can be altered to
maintain a full "off" condition and may be turned "on" by a
rectifying load 11 kaving a properly directed polarity of diode
.. :.
10 and power will not be supplied to a non-rectifying load or to
a rectifying load of improper polarity. The only small current
provided to improper load is that which is passed by the gate
resistor 25 and diode 28 caused by the charging and discharging
of capacitor 25, other than a possible initial half-cycle pulse,
hereinabove mentioned. Where human contact may be expected this
small continuous current should be reduced to a subjectively
endurable level, although an appreciable level may be of some
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~alue in possibly discouraging the adoption of careless habits
regarding exposed conductors in general.
The restoration of firing potential is delayed by
increased resistance of resistor 25, but may be advanced by
reducing the value of capacitor 24 within the limitations set by
the current demands of the SCR gate 27.
Turn-off should occur within one-half cycle to minimize
any danger to a person shorting the load. The possibility of a
hal~-cycle pulse of great magnitude, before turn-off, is present
when conditions permit a very low resistance completion of an
improper load circuit during an instant of forward conduction in
the supply circuit. Establishment of such a low resistance contact
re~uiring more than the half-cycle of time avoids the possibility
of the sizeable half-cycle pulse by accomplishing turn-off within
a half cycle and during the initial time of higher resistance.
To cushion the possible pulse overload effects of
immediate and direct shorts, a current reactive negative thermal ~
~ coefficient thermistor 31 is placed in series with the SCR 18. ~ -
`` Thermistor 31 should be mounted at the AC supply end if stud -
mounted heat sink exposure is planned for the SCR 18, but may be
alternately located at the supply terminal 16, if isolation is
possible. Such protective thermistor 31 at the AC end has littlè `~`
effect upon the basic circuit performance. The fuse 32 is
`~ included in a manner common in the art.
In FIG. 1, if the proper load circuit 11, including the
DC load 14 and diode 10, is connected to the supply circuit 20,
i. e., terminals 12 and 21 are connected and terminals 13 and 22 ~-`
. are connected, the non-polarized load circuity 40 of FIG. 2
could be connected in parallel with the proper load, i.e., terminal
41 connected to terminal 42 or 44 and terminal 43 connected to the
other terminal 44, or 42, the non-polarized or non-directionalized
load circuit 40 would receive half-cycle power in either
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direction connection to supply circuit 20. With terminals 41 and
43 connected respectively to terminals 42 and 44, the positive
half-cycles will turn on SCR 45 through its gate resistor 46 and
diode 47 so that power is supplied to the DC load. The negative
half-cycles will be blocked by SCR 45 and will be inhibited from
passing through SCR 49 since its gate resistor 50 will be chosen
large enough to prohibit SCR 49 from firing, i.e., the reverse
discriminator current is smaller than the current in the forward
direction through SCR 18, whereby current is supplied to the load
48 from terminal 43 to 41, only. Since the negative half-cycles
are blocked in the manner aforementioned, the functioning of the
circuit of FIG. 1 is unaltered, and if a short occurs across
terminals 41 and 43 current flow in the entire circuit is
substantially reduced to the aforementioned small currents of
charging and discharging of the capacitor 24 every half-cycle
~' and the very minute leakage current through the SCR 18. With -
terminals 43 and 41 connected respectively to terminals 42 and
X! 44, the positive half-cycles will turn on SCR 49 through its gate
resistor 50 and diode 51 so that pcwer is supplied to the DC load
~ 20 48. The negative half-cycles will be blocked by SCR 49 and will be
`` inhibited from passing though SCR 45 since its gate resistor 46
will be chosen large enough to prohibit SCR 45 from firing in
response to the comparatively smaller discriminator current,
~ whereby current is supplied to the load 48 from terminal 41
;~ to 43, only. A triac or other triggered bidirectional equivalent
could be substituted for SCR's 45 and 49, as would be apparent to
persons skilled in the art. ~ -
It would be readily apparent that the entire circuit
of FIG. 1, i.e., circuits 20 and 11, could be used as the power
30 source in electrically powered "Go-Cart" track racers or in an --
arrangement similar to the common bumper car system at amusement
fairs, zoos and the beaches, for example, with such power source
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feeding conveniently exposed conductors alternately, connected to
terminals 42 and 44. The cars would be provided with the proper
non-polarized or non-directionalized load circuit 40 of FIG.2 with
terminals 41 and 43 being constituted by spaced, wiping contacts
engageable with such exposed conductors. Of course, a speed control
or the like of proper type would normally be provided for the DC
motor load, as would be apparent to those skilled in the art. Since
a short by a person across such exposed conductors would be
effective to cut-off power to all of the cars, substantially
greater safety would be provided by a system in accord with this
invention than is presently provided.
In the power system shown in FIG. 3, an AC supply
circuit 60 for powering an AC proper load circuit 61 is depicted
in accord with another embodiment of the invention. It is
believed to be easily recognized that SCR 62, thermistor 63,
capacitor 64, resistor 65, diodes 66 and 67, fuse 68 and switch
69 correspond to similar components identified and described in
FIG. 1, and that SCR 72, thermistor 73, capacitor 74, resistor
` 75 and diodes 76 and 77 also correspond to similar components
20 in FIG. 1.
The AC proper load circuit 61 includes a pair of diodes
80 and 81 which conduct in the same directions as SCR's 62 and 72.
The AC load 82 is connected in common line 83 with AC load circuit
61 thus having three input terminals 84,85, and 86.
When the switch 69 is closed and the output terminals
87, 88, and 89 of the supply circuit 60 are connected to respective
input terminals 84,85, and 86 of the AC load circuit 61, the SCR's
62 and 72 will begin to conduct after the firing is obtained in
the same manner, as hereinbefore described in connection with SCR
30 18 of FIG. 1. Current will thus flow in the conventional
J direction through switch 69, terminal 88, terminal 85, line 83,
AC load 82, diode 81, terminal 84, terminal 87, SCR 62, thermistor
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63 and fuse 68 during the positive half-cycles from the source 90.
During the negative half-cycles, current will flow throught fuse
68r thermistor 73, SCR 72, terminal 89, terminal 86, diode 80,AC
load 82, line 83, terminal 85, terminal 88, switch 69 back to the
source 90. Accordingly, with a three wire system between AC supply
circuit 60 and AC proper load circuit 61, AC power may be supplied
to the AC load 82, whereas a two wire system in accord with this
invention can only be used to supply power to a proper DC load
circ~it, as specifically shown in FIG. 1.
With the AC load circuit 61 connected to supply circuit
60, the switch 69 is initially closed and the positive half-cycles
:~ raise the capacitor 64 to a firing potential to cause SCR 62 to
conduct, in the same manner as described with respect to FIG. 1.
The negative half-cycles, prior to conduction of SCR 62, cause
current flow in the conventional direction from suppiy 90 through
fuse 68, resistor 75, capacitor 74, terminals 89 and 86 diode 80,AC
load 82, line 83, terminals 85 and 88 and back through switch 69 to
supply 90, thus raising the potential of capacitor 74 to the
firing potential of SCR 72. With both SCR's 62 and 72 conducting,
~:
AC power from supply 90 is supplied to the AC load 82 in the
.` manner hereinabove set forth.
When a short occurs between terminals 87 and 89 of
~- supply circuit 60, with proper load circuit 61 connected, both ~
capacitors 64 and 74 discharge through load diodes 80 and 81 ~ -
` respectively, and SCR's 62 and 72 become non-conducting and :~.
i remain non-conducting until after the short is removed. In ::
accord with the invention, transmitting bridge means, in the ::
form of resistor 91 and capacitor 92, are connected preferably
within the supply circuit 60 between the two hot lead terminals v~
87 and 89. The function of such bridge means is to effect
substantially simultaneous cut-off, for example, of SCR 62 when
a short occurs across terminals 88 and 89, such short causing
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.
~ :: . , . ,. :
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turn-off of SCR 72 in a manner hereinbefore explained in
connection with FIG. 1. Similarly, if a short occurs between
terminals 87 and 88, SCR 62 will be cut-off in the manner set
forth in FIG. 1, while SCR 72 will be cut-off due to the bridge
means 91 and 92.
The bridge means does not interfere with the aforesaid
cutting-off of both SCR's 62 and 73 when the two hot leads 87
and 89 are shorted. Consider the circuit of FIG. 3 without
bridge means 91 and 92 (and without the neon tube and connecting
10 resistors and switch thereinafter described), a short between
terminals 87 and 89, by a non-directional conductance, i.e., a
resistor, or a directional conductance, i.e., a diode, oriented
in the direction opposite to the conducting direction of SCR's
~ 62 and 72 and diodes 80 and 81, provides for a reverse current
`~ path to ground terminal 88 to terminal 89 through the AC load 82
and its pick-up diode 81, and a reverse current path to terminal
87 from ground terminal 88 through the AC load 82 and its pick-up
Z diode 80. If such a short is by a sufficiently high resistance,
for example, 10 megohms, turn-off may not be effected and such
20 high resistance may have no effect or a slight effect to reduce
~` the current being supplied to the AC load 82 without effecting
~ cut-off of the SCR's 2 and 72. If a capacitance of any
-~ appreciable value is connected across terminals 87 and 89,immediate
turn-off of SCR's 62 and 72 is accomplished. If a resistor and
capacitor are employed in series across terminals 87 and 89, a
lower resistance value ~which would cause turn-off, if employed
without the capacito-~) can be included without any apparent
effect.
'i Thus, it would appear that both a full-wave rectified
DC current and an AC current effect are encountered, in the
circuit for the bridge means 91 and 92. Thecapaoitor 92 functions
to block the DC current which exists between terminals 87 and
-19
~`
~066~70
and 89 while passing the smaller AC current which may also effect
turn-off of the SCR's 62 and 72. ~ resistor 91 must be included
and app~r.ently be sufficient to reduce the AC current to a
value below that causing turn-off of the SCR's 62 and 72 whereupon
the capacitors 64 and 74.discharge below the firing potential.
Thus, with the resistor 91 in series with capacitor 92
adjusted slightly above the value required to eliminate a turn-off
reaction of the SCR's 62 and 72, in its shorting between terminals
87 and 89, substantially simultaneous turn-off may be accomplished
~y shorting between terminals 87 and 88 or between terminals 88 ~ :~
and 89, and establishment of an alternating current path is
provided by the transmitting bridge means 91 and 92. If either of : ~
`~ the load diodes 80 or 81 is respec~ively shorted out of the .
circuit, cut-off of the SCR 72 or 62 (where the short exists) ;
~, occurs in the same manner as described in FIG. 1, and the other
.~ SCR respectively 62 or 72, is cut-off by the AC current increase
.~. . through the bridge means 91 and 92. In other words, if a short : .
~' occurs between 88 and 89, SCR 72 will be turned-off because
~ capacitor 74 discharges in the afore established manner, as well
~ 20 as causing discharge of capacitor 64 by its non-directional
connection with terminal 88 through resistor 91, capacitor 92 and
the shorting means which assures turn-off of SCR 62.
The neon glow lamp 93 is in parallel with capacitor
92 which controls the firing potential of lamp 93 in a manner ~ .
~ familiar in the àrt, particularly with respect to the common
-1 relaxation oscillator circuits. A turn-off of the SCR's 62 -
: ~ and 72 caused by a short across any two of the three terminals 87,
88 snd 89, will cause lamp 93 to fire and to subsequently conduct
.~ a portion of the turn-off current. Without the resistor 95, i. e.
with switCh 96 closed, the voltage level across the lamp 93 is
sufficient to maintain lamp 93 in an on or latched c~ndï.tio~
even after the short is removed whereby no power is delivered to
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the load until the neon lamp 93 is momentarily turned-off to
reestablish the original state. Opening re-set switch 96
momentarily causes the voltage to drop to a level to extinguish
lamp 93 and after charging of capacitors 64 and 74, power is
restored to the AC proper load 61, whereupon switch 96 may again
be closed to reset for automatic latching.
If resistor 95 is included in series with resistor
94, i.e. the switch 96 is in open condition, a reduction of the
voltage across lamp 93 may be made sufficient to avoid the
aforementioned latching effect, after a short has been removed
which causes a turn-on of glow lamp 93 and subsequent shunt
conductance of turn-off current. Thus, when the short has been
removed, the voltage drops across lamp 93 sufficiently to cause
cut-off of lamp 93 and automatically reestablishes the conditions
of the supply circuit 60 to deliver power to the proper AC load
circuit 61, i.e., after refiring of SCR's 62 and 72. Any short
in the brid~e means 91 and 92 or in lamp 93, effects a-cut-off of
the SCR's 62 and 72.
It is to be noted that in practice, a greater resistance
value of resistor 91 in series with the capacitor 92 is required
to avoid unwanted turn-off when a lower AC source 90, for example,
105 volts, is encountered and a lesser resistance value may be
- used when a higher source is used, for example 120 volts. It
should be apparent that certain other electrical devices having
similar breakdown trigger characteristics could be employed
rather than the neon tube.
The capacitor 92 in the bridge arrangement of FIG.3
connected between 87 and 89, may be eliminated when the neon glow
lamp 93 is included. Such an arrangement may provide simultaneous
turn-off of the two SCR circuit sides when one side is shorted,
and provide both automatic reset and latching functions. At levels
of higher series resistance permitting automatic reset, i.e. 400K
.
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.
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ohms and higher, turn-off is incomplete and unsatisfactory for
most purposes. Appreciable motor starting load surges and the
like, at both latching and automatic reset levels of resistance,
tend to trigger turn-off. This is advantageous whenever a
sensitive means of surge protection is required, but is considered
undesirable in the normal instance particularly when inductive
load effects are present. Use of the neon lamp in the bridge
circuit produces similar results even when the capacitance is
included, but since the resistance-capacitance series combination
10 alone can be relied upon to accomplish simultaneous turn-off,
higher resistances, such as the value of the FIG. 3 resistor 95
(500,000) ohms) may be employed to control the neon response
or it may be omitted if latching is not desired. A neon lamp in
a low series resistance circuit for latching purposes provides -
substantially complete turn-off and reset may be conveniently
accomplished by the tool or appliance ~control switch if turned
off and then on agaln.
If a proper DC load circuit 98, as shown in FIG.4, were
to be connected to a supply circuit in accord with this invention,
- 20 such circuit could be identical to supply circuit 6~ shown in FIG.
3, except resistors 91,94 and 95, capacitor 92, neon lamp 93, and
switch 96, together with their connections, could be safely
eliminated. Thus, a full-wave DC supply circuit would be produced
`` for powerQng~- load circuit 98. In this system, shorting of one
side would leave the other side functional and capable of supplying
half-wave current to the load. Caution must be exercised however,
since connecting a proper AC load circuit 61 accid~tly into such
' a supply circuit intended for DC only could produce hazardous
1 conditions due to the omission of the aforementioned bridge means
i 30 91 and 92 and its protective function. While an AC circuit
including the bridge means may be tested by shorting any two of the
three terminals, two switches, one between terminals 87 and 88
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. . . . . . .
i06~770
and the other between 88 and 89 could be employed in such a
modified full-wave DC supply circuit for testing between hot and
ground on each side to verify individual functioning and steps
should be taken in either case to make certain that the ground is
connected to terminal 85 of the proper load circuit 61 and terminal
99 of the proper load circuit 98. Other protective factors have
and should be considered, but are not disclosed herein due to the
emphasis on the basic arrangements.
Another embodiment of the invention is shown in FIG.5
in which SCR's 100 and 101 when fired provide slave triggering for
respective SCR's 102 and 103, as is common in the art. In this
manner SCR's 100 and 101 may have small current capacities, for
example, 6 amps, while SCR's 102 and 103 may carry very large
current, for example, 500 amps. The operation of the circuit
shown in FIG. 5 is thus essentially the same, as previously
described in FIG 3. The resistances 104 and 105 are added in
series with anodes 106 and 107 of respective SCR's 100 and 101
to provide current limiting for the gates of the slave SCR's 102
and 103 and to provide a proper voltage range for the operation
20 Of component failure monitors, as hereinafter more fully described
in connection with FIGS. 6A and 6B.
The component failure monitor circuits 120 and 121,
generally depicted in respective FIGS. 6A and 6B, in accord with
this invention, may be coupled across the AC load 122 at terminals
~ 123 and 124 and are shown in their off conditions with the power
< switch 119 in open condition. The monitor circuit 120 is seen to
include a pair of incandescent bulbs 125 and 126 and series
connected diodes 127 and 128. With the power on, the relay 130 `
closes the contacts and bulbs 125 and 126 are activated. When a
30 component failure causing a short then occurs in the supply circuit,
particularly, shorting of either diodes 116 and 117, or any of
SCR's 100, 101, 102, and 103, the armature contacts in the relay
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'~ .
.~. .. . : . .: ..
.
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130 will chatter and provide an audio indication of a shorting
component fault in the supply circuit and the frequency and phase
of such contact chatter tends to eliminate or greatly diminish
the current flow to one of the bulbs 125 or 126, depending on
whether such shorting component fault occurred in left half or
the right half of the full wave supply circuit, as seen in FIG.5,
thus providing a visual indication of the location of such fault
or shorting failure.
The monitor circuit 121 of FIG. 6B employs relays rather
than bulbs of FIG. 6A and functions to generally pass a high
enough current, indicative of the component shorting fault, to
both sides of the supply circuit thereby interrupting the current
supply as by blowing or destroying the fuse means 114 and 115, such
fuse means being in the nature of fuses circuit breakers, or other
overload protection devices known in the art.
If a shorting fault occurs in the supply circuit, -
particularly, shorting of either of the diodes 116 and 117, of any
of the SCR's 100,101,102 and 103, relay 131 will buzz or chatter
causing same to alternately open and close circuit apparently at
or near current frequency and either relay 132 or 133 would be
permitted to close which puts a short across the load blowing
out both fuses 114 and 115. It is to be appreciated, that with 121
connected across the AC load 122, and the AC load and supply ~
circuits are coupled prior to closing switch 119, the monitor is `
in a shorting indicative condition. Thus a delay means, in the
form of a negative thermal coefficient thermistor 134, permitting
full shorting only after a predetermined and brief hesitation, is
required to permit proper charging of the gate capacitors which
fire SCR's 100 and 101, which in turn fire SCR's 102 and 103 to ~;
energize the coils of relays 132 and 133 thereby removing the~short -
Diodes 135 and 136 are series connected to the coils of the `
respective relays 13Z and 133 and provide proper selective current
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,
1~66770
paths for the monitor 121.
A sensitivity range of voltages to permit proper operation
of either of the monitors 120 and 121 can be determined by vary-
ing the AC source voltage 118. Similarly with a predetermined
range of source voltage, resistors 104 and 105 can be selected to
drop the voltage to a proper value within such range of voltages.
Failure of one SCR 100 or 102 in one side and 101 or 103 in the
other side, either by shorting or with ret~ntion of its rectifi-
cation capacity without being capable of turn-off, will effect an
apparent depressive condition in the performance of the SCR's in
the other side. This effect is not fully understood but is read-
ily detectable by a simple AC relay, such as relay 130 of FIG 6A,
connected in parallel with the AC load 122 of a full wave AC
supply circuit. The relay 130 thus buzzes or chatters to indi-
cate a loss of protective function apparently at the frequency of
the AC supply 118. While there is no apparent power loss in an
incandescent load, or in a universal motor, a synchronous motor
ceased operating in the component failure testing thereon thus
far accomplished. Regardless of how or why the monitor 120
operates, the results are valuable in that warning reaction is -
obtained by the monitor to indicate a shorting of either diodes
116 and 117 or any of the SCR's 100,101,102 and 103. Thus, any
shorting failure that would normally be encountered and result in
a restoration of normally dangerous circuit conditions, which
could result in the electrocution of a person who became the
short across any two or three of such terminals or exposed conduc-
,~ .
tors between the supply circuit and the load circuit, would be
indicated by the monitor 120, or result in immediate cut-off of
the current from source 118 in accordance with the effect of mon-
` itor 121. Corrective action would then be taken to restore the
safe or protecting properties of the circuits in accord with this
; invention and in accord with generally recognized safe electrical
25- ~
. ' ~' ~.
.
.. . .: . ~: : : .
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1066770
practices.
The designations of "DC Load" and "AC Load" in the drawings
is not intended to unnecessarily limit the types of loads which
would or would not operate in the various circuits disclosed.
; For example, an inductor and resistor could be connected as the
"DC Load" 14 in the FIG.l. If an AC motor were connected as the
load 14, the motor would not operate, but current would pass
therethrough. Thus, the designations "DC Load" and "AC Load" are
intended to mean respectively that substantially half-wave direct
; 10 current and full-wave alternating current are available to the
respective loads from the supply circuits 20 and 60. It is also
understood that current from the alternating current sources may
be changed or adjusted in the relative magnitude and/or duration
of forward and reverse cycles or positive and negative cycles for
obtaining various design advantages therefrom.
It is to be noted that protection against component failure ~ -
may be achieved by, for example, use of two or more SCR's in
series in a single trigger circuit, or in paralleled separate
. .
trigger circuits, or by two or more complete circuits in series,
the latter arrangement requiring more sensitive SCR gates, as
" would occur to those persons skilled in the art. Furthermore, an -
increase in the gate circuit resistance of a given SCR increases
its sentitivity to turn-off and requires less fault current to
trigger a turn-off while a decrease in the resistance lessens the - -
sensitivity of a given SCR and requires a greater fault current
for triggering a turn-off. With a fixed gate circuit resistance,
increase~ inherent gate sensitivity in an SCR decreases sensitiv- -~
,
ity to turn-off fault currents while decreased inherent gate sen- -~
sitivity increases sensitivity to fault currents.
-
., , ' .
-26-
.
., .
~L~366770
An exemplary embodiment of the circuit components of
FIG. 1 is seen to include the following parameters:
diode 10 -------- 3 amp,~rcher, 400 PIV
diodes 26 and 28- 1 amp,Archer, 400 PIV
SCR 18 ---------- Archer E/c/c 331,BO 1052,6amp,Thermotab
capacitor 24 ---- 0.033 mfd
resistor 25 ----- 740,000 ohms
thermistor 31 ---Globar Fr. 49
fuse 32 ---------3 ampere
The parameters of FIG. 2 are as follows:
SCR's 45 and 49 ---- same as SCR 18
resistor 46 -------- 3.3 megohms
resistor 50 -------- 3.8 megohms
diodes 47 and 51 --- same as diodes 26 and 28
The parameters of FIG. 3 are:
SCR's 62 and 72 --~---------- same as SCR 18
resistors 65 and 75 --------- 1.2 megohms
capacitors 64 and 74 -------- same as capacitor 24
diodes 66,67,76, and 77 ----- same as diodes 26 and 28 -
; 20 diodes 80 and 81 ------------ same as diode 10
resistor 91 ----------------- 330,000 ohms
resistor 94 ----------------- 100,000 ohms
resistor 95 ----------------- 500,000 ohms
capacitor 92 ---------------- 0.022 mfd.
" thermistor 63 and 73 -------- same as thermistor 31
fuse 68 --------------------- 5 ampere
; Neon lamp 93 ---------------- NE2 neon glow tube
. .
: :-
The FIG. 4 diodes are all the same ad diode 10.
FIG. 5 parameters are the same as the FIG.3 parameters.
30 except as follows:
.
SCR 102 ------------------------Motorola HEP 306,15 amps
SCR 103 ------------------------Motorola HEP 307,15 amps
resistor 104------------------- 45,000 ohms
resistor 105 -------------------52,000 ohms
diodes 108 and 109--------------15,amps
diodes 110,111,116 and 117 -----same as diodes 26 and 28
thermistors 112 and 113 --------15 amp thermistor(special
order)
fuses 114 and 115---------------15 amp fuses
:. : .
.
-27-
. :
:..
~)66'770
The parameters of FIGS. 6A and 6B are:
diodes 127 and 128 --------same as diodes 26 and 28
lamps 125 and 126 --------7 1/2 watt incandescent
pilot or NE 2 neon glow tube
relay 130 ------------------Archer, 115 v AC,coil/2200
ohms-current 20 ma;
contactS/3amps
thermistor 134 -------------same as thermistors 112
and 113
diodes 135 and 136 ---------same as diodes 26 and 28
relay 131 ------------------same as relay 130
relay 132 and 133 ----------same as relay 130 but with
contacts 15 amps
FIGS. 7 through 13 are directed to circuit modifications in-
cluding protective connections for conductive load housingc to be
employed with the circuits disclosed in FIGS. 1,3 and 5 as an al-
ternative to simple grounding of the normal load housing, including
14', as is common in the prior art. Such a connection is consid-
ered advantageous in accord with this invention in providing for
automatic shut-off of the supply in the event of an internal short
to the load housing and prevents the housing from p~viding a dan-
gerous ground path if other current sources should be contacted by
the housing or the person holding same. While the protective con- ;--
nection is discussed in reference to the load housing 14' or other ~-
enclosure, it should be noted that the supply housing may also be
.... .
connected with the load housing or be substituted therefor. In
each instance, the load housing, for example 14', is connected to
the supply circuit in such a way that the grounding of the housing
either directly or through a shorting medium, such as the human
body, permits a current flow in a direction opposite to the direc-
tion of the load powering flow. This reverse current flow of com-
paratively small or feeble current triggers a turn-off of the SCR
switching means thereby terminating power current flow until the
~,
SCR again fires. Inadvertent contact of a tool (drill or saw or
the like) with concealed water pipes, conduits and other grounded
obstructions, which is powered and connected in accord with FIG.7,
causes a turn-off of the tool before any appreciable damage occurs.
Internal shorting of the power leads to the tool housing also per-
mits the reverse
-28-
, .
~066770
current flow that triggers the protective turn-off of the SCR
switching means in the manner fully explained in connection with
FIG. 1.
The housing connection may be made by means other than
the indicated resistance 14", such as a small value capacitance
98''' (FIG. 13) or a reverse oriented unidirectional blocking
diode 98" (FIG. 12), i.e. a blocking diode conductive in a
direction opposite to the conduction of the SCR. A resistance
14" with a nominal value of, for example, lOOK ohms, is the
preferred means because of its reliability and its mode of normal
failure. Coupling may consist of a simple connecting lead in -
many instances, but use of such a resistance 14" or other current
limiting coupling offers protection for any substantial current
flow therethrough even in the event of shorting of the SCR or
insensitivity thereof to turn-off conditions.
-- FIG. 7 depicts the load arrangement of FIG. 1 with the
resistance 14" coupled to the housing 14' enclosing both the
DC load 14 and blocking diode 10. A ground fault turn-off
reaction is produced when connection is made between ground and
any point in the circuit between diode 10 and the SCR with
trigger circuit that constitutes the supply. It is apparent
that diode rectifier 10 could be located on the other side of -~-
load 14 and that some obvious advantage would be gained by such
. location, since ground fault protection would be extended to
load 14 and any point between the diode 10 and load 14. The
depiction of the diode 10 on the hot side of DC load 14 in FIG. -
1 was made to facilitate a ready recognition of half-wave
circuit inclusion in the full wave AC supply circuit 60 shown in
FIG. 3. Location of the diode 10 on the ground side of the DC
load 14 is restricted to the half-wave circuitry, as will be
apparent to those skilled in the art in consideration of FIGS.3
and 5. FIG. 8 depicts the half-wave load circuit with preferred
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.:
: - . : - , , :. , . ,:,,
~066770
half-wave placement of diode 10 and a resistance 14" coupling
load housing 14' which encloses both load 14 and diode 10.
While ground access may be provided as a convenience within
the supply enclosure, it may also be advantageous to provide
ground access externally, for example, for a single conductor
transmission line.
If it were desired to have only a simple "ground fault"
protector without the line-to-line load fault protection, i.e.
between 21 and 22, that can be obtainad in accordance with this
invention, the blocking diode 10 can be located between contact
22 and the ground side of source 15 and most conveniently within
the supply enclosure 20' of supply circuit 20 thereby preventing
housing 14' and/or 20' from providing a live source or a danger-
` ous ground path. FIG. 9 depicts the half-wave arrangement of
FIG.l, modified for "ground fault" protection only and having a
resistance 14" coupling load housing 14', which encloses only
the DC load 14, and coupling supply housing 20' thereto. ~-
FIG. 10 depicts the AC full-wave load circuit of FIG.3
; with a resistance 82" coupling the housing 82f enclosing AC
` 20 load 82 and bridge diodes 80 and 81.
.
FIG. 11 depicts the AC load circuit of FIG. 3 modified
to provide a system in which the housing 82' encloses the
AC load only and the diodes 80 and 81 may be provided within the
socket at the end of an extension cable connected to the supply
at its plug end, or otherwise repositioned or transferred to the
supply circuit and/or its enclosure, as would be obvious to a
person skilled in the art. This system provides no direct
ground or line-to-line fault protection for the load circuitry,
except to the end of such extension cable, but in providing a
housing 82' properly coupled by resistance 82" to the supply
circuit, protection is provided against load circuit shorting
to the housing 82' and ground-fault protection is also provided
.~ .
-30-
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.
1~66770
for such housing.
FIG. 12 depicts the DC load circuit 98 of FIG.4 with
a reverse oriented blocking diode 98" coupling housing 98' which
encloses the DC load and the four diodes of its bridge circuit.
FIG. 13 depicts the DC load circuit of FIG.4 with a
capacitance 98 " ' coupling housing 98' which encloses the DC
load only, with the four diodes of the bridge repositioned or
transferred to the supply circuit and/or its enclosure.
Intentional shorting of supply leads to ground in the
protective circuitry, described in connection with FIGS.1,3 and
5 may be accomplished by means of a test switch, including
switch 200, to confirm proper circuit functioning. Such testing
shorts should be made through a cushioning resistance,including
resistance 201, in order to minimize the possible 1/2 cycle surge
that may occur when a shorting contact is immediately established
-~ during a period of forward conductance. An additional advantage is
obtained if the cushioning resistance is a Negative Thermal
Coefficient type with appropriate characteristics, such as the
Globar Fr. 49, also employed as series surge limiter 31 in FIG.
1. If test shorting is made through such a resistance and the
:~.
circuit turns off in a normal manner, negligible heating effect
is produced. If the turn-off does not occur, as in the event of
a circuit malfunction, the N.T.C. resistance element 201 heats
rapidly dropping the resistance to near zero to overload the fuse
of the circuit, such as fuse 32 of FIG. 1, thereby disarming the
circuit automatically. If the test switch 200 is employed as the
on-off circuit control, testing with an automatic disarming
capability is accomplished with and during each turn-off when the
test switch is closed. In many instances, such as the control of
a hand tool, a normally closed pushbutton switch may be empl~yed,
with turn-on of the tool accomplished upon opening such a switch.
FIG. 14 depicts the load circuit of FIG. 1 with N.T.C~resistance
-31-
.. .. -
;. , . , : : - : . .. . , ,;: :
`` 1066770
201 and nonE~lY closed control-test switch 200 in series across
load terminals 12 and 13. Such an arrangement would normally be
enclosed within the load housing, but the resistance and switch
could also be placed across the supply terminals 21 and 22 and
placed within the housing enclosing the supply, if desired.
FIG. 15 depicts the N.T.C~ resistance 203 and control-test
switch 202 positioned across load terminals 84 and 85 although
they could be connected across the other pair of load terminals
85 and 86 or either pair of supply terminals 87 and 88 or 88 and
89.
FIG. 16 depicts the full-wave DC load and diode bridge circuit
98 of FIG. 4 with dual N.T.C., resistances 204 and 206 and dual
switches 205 and 207, which obviously may be combined in a D.P.D.T.
type switch controlling the testing of both sides simultaneously.
While one switch 202 and resistance 203 is effective in testing
and providing disarming potential for both sides of the AC arrange-
~ .
` ment of FIG. 15, dual provision must be made in the DC full-wave
;
circuit of FIG. 16, since the two sides are isolated from each
~. other by the four diodes of the DC bridge.
`~`` 20 Where large current requirements prohibit a practical use of
the N.T.C. resistance, an initial higher resistance shorting
followed by a rapid establishment of either a short or a low
.~
~ ~ resistance short may be accomplished in any well known manner,
~`
such as those illustrated in FIGS. 17 and 18. FIG.17 depicts a
switch 210 having two contact leaves 211 and 212 designed to make ~ `
. .
'~ successive closure in a make-then-make arrangement so that the re-
sistance 213 coupled to leaf 212 establishes contact a short time
~i, before the essentially zero resistance contact by leaf 211. FIG.
3 18 depicts a thermostatically closed switch 215 of the type com-
monly employed as a lamp blinker connected in series with the
control-test switch 216. Closing of the control-test switch 216
will accomplish turn-off
., : -32-
. . .
. 1066770
of an operative circuit through the resistance 217 of the heating
element without appreciable heating, but if turn-off does not
' promptly and properly occur due to a faulty circuit, the element
will rapidly heat and create a near zero resistance short of
sufficient duration to disarm the faulty circuit.
Sometimes, a plug-in or switch controlled turn-on of the
supply circuit momentarily results in a surge of current being
supplied to the load even with a shorting turn-off resistance
placed across the load terminals. This surge of current may be
effectively eliminated if full empowerment of the supply circuit
is slightly preceeded by a limited current connection to establish
an off-state. FIG. 19 depicts one manner of accomplishing the
above - a supply control switch 220, which corresponds to either
switch 23 of FIG. 1 or switch 69 of FIG. 3, with a small capacit-
ance 221 in shunt position to assure limited current flow in the
"; circuit before full switch closure. A resistance, if desired, may
` be employed rathex than capacitor 221 to accomplish substantially
`~ the same results. FIG. 20 depicts a grounded type 3 prong wall
plug 225 with a slightly shortened ground side blade 226. This
plug 225 permits an initial limited current flow through the
longer hot side blade 227 and the round grounding prong 228 which ~
, ; connects the circuit through a capacitor 229 to ground, or, as `
; previously stated, a resistance may be used rather than capacitor `
~` ~ 229. Full current flow is thus available slightly later as the
shortened ground side blade 226 also makes contact with the ground-
ed side of the current source. ; -
FIG. 21 depicts a circuit similar to that of FIGS.l and
` 7, but with a particular location of the proper load diode 230,
i ~ corresponding to diode ~0 of F~æS.l and 7, positioned between the !:'''
load and SCR 18 and its trigger circuit, either made adjacent to
.. .
- the supply or included within the supply enclosure 236. A control
and/or a test switch 231 and series N.T.C. resistance 232 connects
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,, , . . . .. .. .. , ~ . . :.. ~
1066770
the ground to the hot side between the load diode 230 and the
SCR 18 with its control circuit that constitutes the supply
circuit. This circuit may be employed to supply a half-wave DC
load without ground-fault protection or line-to-line protection
for the power leads, but with shielding supplied by a housing
233 and a resistance 234 coupled to that point between the load
diode 230 and the SCR 18 with its control circuit, resistance
234 also being connected to enclosure 236 in the same manner
that resistance 14" is connected to load housing 14' and supply
housing 20' in FIG. 9. A rather unusual and unexpected use for
the circuit arrangement of FIG. 21 is that of a shock weapon for
animal or personnel control in which the load is the intended
shock recipient and in which the coupling from resistance 234,
more normally made to the load housing, is made to the operator
most conveniently through contact with supply enclosure 236.
Circuit completion for the shock recipient may be accomplished
by connection through diode 230 with the supply and to its
- contained ground terminal or any other external ground. The
^ coupling supplied to the operator by means of convenient condue-
ti~e contact affords automatic turn-off protection from the ;~
shock effect should the operator contact the supply electrode
21, the ground 22 or a shock recipient which constitutes the
DC load. For such a shock weapon, an optional current limiting `
.. . .
- resistive load 235, such as an incandescent lamp, should be
` placed in series with the SCR circuitry to protect the circuit "~
in the event of overload due to shorting.
` If the load selective blocking diode 230 of FIG. 21 or
diode bridge of some of the other circuits is to be located -
within the supply enclosure in an embodiment of this invention
3~ 30 that provides modified protection, certain by-pass connectio~s
may be conveniently made that relieve the blocking diode or
diode bridge of its major current carrying functions and permit
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the usage of a smaller capacity diode. A portion of the half-
wave circuitry of FIG. 21 is shown in FIGS. 21A and 21B which
would accomplish the intended results (FIG.l could be modified
by transferring the diode to its supply enclosure, as shown by
230 in FIG. 21). If a connection 237 is made between the anode
of the SCR 18 and the anode of diode 230 (and the lead connecting
the anode of the SCR 18' with the cathode of diode 230' is
removed) the major portion of the current is shunted away from
diode 230' which then will carry only the currents of the SCR
trigger circuitry. This modification does not prevent the use
of the test switch 231', but it does eliminate the automatic
diarming function of the N.T.C. resistance, identical to resist-
ance 232 and connected in the same manner. Similarly in FIG.3 if
the anode of SCR 62 and the cathode of SCR 72 are connected
directly to the connection point between diodes 81 and 80 and -
disconnected from that shown in FIG.3, turn-off is still accom- ;
`plished by the usual shorting of any two of the standard three -~
leads, as previously described, but the two additional leads to
the connection point of 80 and 81 are unprotected and cannot be
safely contacted. Such a shunting of the blocking diode or
diode~&Oand 81 by direction connection of the SCR flow of current
to the load 82 is of advantage only in the special circuit in
which a blocking diode or a diode bridge is closely associated
with the supply circuit and most ideally located within the ~
supply enclosure so that such shunting can be accomplished in an ~ -
easy manner therewithin as seen most clearly in FIG. 21B. Neither
~ . . .
ground-fault protection nor line-to-line protection is offered
for the power leads to the load, but the current turn off previ~
:, .-
ously described in accordance with the invention is triggered by
30 fault currents passing through the coupled supply housing 236' `
and/or load housing 233 (FIG.21) through resistance 234' and
lead 238 to the SCR trigger circuit.
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' '
1~6677~) '
Blocking diode 230' of the SCR trigger circuit of FIG.
21B is merely more directly connected to ground than in FIG. 21A,
and this is possible in that the diode 230' connecting the SCR
trigger circuit to ground, as in FIGS. 21A and B no longer car-
ries the load current, as in other circuits previously described;
therèfore smaller capacity diodes (i.e., current carrying) may be
employed.
In summary of the description of FIGS. 21A and B, it is
to be understood that the load current carrying connections from
a proper load, i.e., a load including its identifying proper load
diode, to SCR and the SCR trigger supply circuit are compatible `
and may employ a single conductor (and a ground conductor) thus
affording a fault current control through engagement with the
load current carrying lead. If the load current leads are not to
be given direct protection in the manner hereinbefore described
turn-off capability of the SCR, in accordance with this invention
(by the described shunting of 230' diode providing a reverse flow
of current to the SCR trigger circuitry, may be employed indepe~
~ently and may be adapted to a variety of applications. If the
trigger circuitry on the load side of the SCR, as seen in FIGS
21A and B is disconnected from the power lead and the blocking
diode 230' removed from the power lead, the trigger circuit lead
238 may be reconnected through the blocking diode 230' to the
load connection, as in FIG. 21A, or directly to ground, as in
FIG. 21B, lead 238 retaining its capability of turn-off reaction
to reverse flow, but not its ability to cause a turn-off reaction
to reverse flow in the event of inadvertent ground contact or
external ground fault connections to the power l~ad from the SCR
.~
to the load, as in FIGS. 1, 7,8 and 9. In the more simple switch-
ing arrangements of FIGS. 21A and 21B, the reverse flow to the
SCR trigger circuitry may originate in a load housing 233 (FIG.
21) and/or supply housing 236' through inadvertent contact with
.
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~ ,;.
1066~70
the SCR to load lead 237 or through inadvertent grounding of
either housing.
- The same modifications of blocking diode relocation,
corresponding to diode 230 or 230' of FIGS. 21 or 21A and 21B,
may be made in the full-wave circuits of FIGS. 3 and 5, as would
~; be obvious to a person skilled in the art.
FIG. 22 depicts a load circuit for half-wave DC supply,
such as is shown in FIG. 1, in which a filter capacitor 240 is
used to provide a somewhat modified source of alternating cur
rent . The capacitor is placed in parallel with the DC load 241,
but in series with an AC load 242. The charging and discharging
of the capacitor 240, controlled by the pulsating DC of the
supply, creates the AC availability to the AC load 242. Shorting
of the AC load simply creates a more normal filtering function
for the capacitor 240 with respect to the DC load 241.
- ;
~IG. 23 depicts a load circuit for a supply such as
`~ shown in FIG. 1 in which a time delay relay 250 or the like
controls the power to the DC load. This circuit offers protect-
ion in the event that contact with apartially disconnected proper `~
load is made that places an improper load in series with the
proper one and its identifying diode, i.e., a warning current,
:. .
limited by the delay control circuitry of the relay 250, is
, ..... . .
passed before the switching of the load current and, if the im-
proper load has an appreciable resistance, the closure of the
relay 250 may be delayed indefinitely. Relay 250 may be a
~Iagnecraft W211ACPSOX-~, or any other well known time delay
relay. FIG. 24 depicts a non-polarized half-wave load circuit
260 in which unidirectional current is supplied to a ~C load. -
Such load circuit 260 is an alternative t~ the load circuit of
FIG. 2, which is also non-polarized but which is capable of
.~ . . '
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1066'770
supplying current in either direction to the DC load as deter-
mine~by its orientation with respect to the supply circuit.
While the invention has been described with respect to
certain specific embodiments, it will be appreciated that many
modifications and changes may be made by those skilled in the
art with~ut departing from the spirit of the invention. It is
intended, therefore, by the appended claims to cover all such
modifications and changes as fall within the true spirit and
scope of the invention.
.
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~ '
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. .
. .
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