CA1121497A - System for protecting power distribution circuit against ground faults - Google Patents
System for protecting power distribution circuit against ground faultsInfo
- Publication number
- CA1121497A CA1121497A CA000310430A CA310430A CA1121497A CA 1121497 A CA1121497 A CA 1121497A CA 000310430 A CA000310430 A CA 000310430A CA 310430 A CA310430 A CA 310430A CA 1121497 A CA1121497 A CA 1121497A
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- ground fault
- control power
- solenoid
- gfci device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
- H02H3/34—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors of a three-phase system
- H02H3/347—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors of a three-phase system using summation current transformers
Abstract
ABSTRACT OF THE DISCLOSURE
A conventional residential ground fault circuit interrupting (GFCI) device is utilized to control a tradi-tional circuit breaker in protecting a large power distri-bution circuit against ground faults. The GFCI device is adapted with a switch which closes incident to tripping of the GFCI device. The switch controls energization of a shunt trip solenoid adapted to the circuit breaker. A
ground fault sensor responds to ground faults on the distribution circuit by injecting a current imbalancing signal into the GFCI device, causing it to trip. The switch then closes to energize the solenoid, shunt tripping the circuit breaker to clear the distribution ground fault.
A conventional residential ground fault circuit interrupting (GFCI) device is utilized to control a tradi-tional circuit breaker in protecting a large power distri-bution circuit against ground faults. The GFCI device is adapted with a switch which closes incident to tripping of the GFCI device. The switch controls energization of a shunt trip solenoid adapted to the circuit breaker. A
ground fault sensor responds to ground faults on the distribution circuit by injecting a current imbalancing signal into the GFCI device, causing it to trip. The switch then closes to energize the solenoid, shunt tripping the circuit breaker to clear the distribution ground fault.
Description
~21~ 7 ~1 PR 3217 Ground fault protection for personnel and electrical equipment is an ever increasing concern in both home and industry. For residential circuit applications, ground fault circuit interrupting (GFCI) devices are now widely available in compact circuit breaker and receptacle configurations for convenient installation in existing ser-vice entry equipment and wall receptacle boxes. These GFCI devices are primarily intended to protect people from the hazards of electrical shock caused by leakage current emanating from ground faults, however they do afford a measure of equipment protection in terms of acting to halt ground fault current which can be damaging to insulation.
For high current applications found in industry, ground fault protection is available in basically two configurations. With the event of so-called "static trip" circuit breakers, it has become economically possible to combine overcurrent and ground fault signal processing circuitry in a compact electronic trip unit package which can be integrated with the circuit breaker to achieve comprehensive circuit protection. Alternatively, traditional circuit breakers having thermal-magnetic and `
dual-magnetic trip units for overcurrent protection can be utilized with so-called "ground fault relays" in providing ground fault protection as well. These relays respond to a ground fault signal developed by a suitable sensor, such as a zero sequence transformer coupled with the load carrying conductors, by energizing (or de-energizing) a solenoid which, in turn shunts trips the breaker to initiate circuit interruption.
U. S. Patent No. 4,044,395, issued August 23, 1977 `
and assignecl to the assignee of the instant application, discloses a system for protecting relatively large power ~ 7 41 PR 3217 distribution circuits against ground faults by utilizing as its principle operating component a conventional GFCI
device normally used in low power, residential circuit applications. As disclosed and claimed therein, the GFCI
device is installed in a control circuit for an under-voltage release solenoid adapted to a conventional circuit breaker protecting the distribution circuit or in the control circuit for the holding coils of a contactor operating in the distribution circuit. A ground fault sensor in the form of a zero sequence transformer coupled with the load current carrying conductors of the distribu-tion circuit develops a current signal in its secondary winding in response to a ground fault on -the distribution circuit. This current signal is injected into one side of the control circuit to create a current imbalance of the natu~e to which the GFCI device is responsive. The GFCI
device trips to interrupt the control circuit, and the undervoltage release solenoid drops out to trip the circuit breaker or the holding coil becomes de-energized to open the contactor. In either case, the distribution circuit is interrupted to clear the ground fault.
The system configuration of this patent, while quite satisfactory for most application, has one drawback in that it is sensitive to control circuit voltage fluxuations.
That is, should the control circuit voltage drop to an abnormally low level, the undervoltage release solenoid could drop out, causing the circuit breaker to trip despite the fact there is no ground fault on the distribution circuit.
The same nuisance interruption of the distribution circuit could likewise result from control circuit voltage dips if a contactor is substituted for the circuit breaker.
It is accordingly an object of the present ~ !7 41 PR 3217 invention to provide an inexpensive ground fault protection system suitable for high current, industrial circuit applications.
An additional object of the present invention is to provide a ground fault protection system of the above character which utilizes as its fault clearing component a circuit interrupting device of the more traditional, non-static trip design.
A further object of the present invention is to provide a ground fault protection system of the above character which utilizes as one of its principle components a low-cost ground fault circuit interrupting (GFCI) device of the type presently enjoying wide use in the low-power residential circuitry.
Other objects of the invention will in part be obvious and in part appear hereinafter.
In accordance with the present invention, there is provided a ground fault protection system ideally suited for application to high current, high voltage power distri-bution circuits, wherein the system utilizes as its principle operating component a ground fault circuit interrupting (GFCI) device of the type used in low voltage residential-type circuits. As is well known, such GFCI
devices utilize a differential current transformer to sense imbalances in the currents going out to and returning from a load, as would be occasioned by leakage current returning to the source through an unintended ground path. The differential current transformer develops an analog signal proportional to this leakage current which is processed by electronic circuitry, and, if of a predeter-mined magnitude and duration, an electronic switch is triggered to complete ~n energization circuit for a shunt ~ 7 41 PR 3217 trip solenoid. Upon energization, the solenoid plunger strikes a latch to release a spring powered mechanism which is freed to open contacts,, clearing the ground faul~ through which the leakage current originates.
In accordance with the present in~ention, the GFCI device is equipped with switch means ln the form of an auxiliary switch or a bell alarm switch for controlling the energization of a shunt trip solenoid operative to trip a circuit ~reaker protectiny the power distribution circuit. The switch means is normally open, but is operatively coupled to the GFCI device such as to be closed incident to the tripping of the GFCI device. Closure of the switch means completes an energization circuit for the solenoid which then acts to trip the circuit breaker, interrupting the distribution circuit.
- To sense the existence of a ground fault on the distribution circuit, a ground fault sensor is coupled with the load current carrying conductors of the distribution circuit for developing a current signal indicative of the ground fault current magnitude. This current signal is impressed across one side of a control power circuit for energizing the GFCI device, thereby creating a current imbalance sensible by the differential current transformer of the GFCI device. The GFCI device trips, and the switch means closes to fire the shunt trip solenoid, thereby tripping the circuit breaker and clearing the ground fault on the distribution circuit.
As an incidental, but nevertheless signi~icant feature of the present invention, the control power circuit may be utilized to power loads connected downstream from the GFCI device. Such loads may include alarms, signal lights, etc. traditionally found in motor control centers, ~ 4~ 41 PR 3217 for example. Since these loads are wired through the GFCI device, they are afforded ground fault protection, a significant advantage in terms of operating personnel safety.
The invention accordingly comprises the features of construction and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the seope of the invention will be indicated in the claims.
For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawing, in which the sole figure is a circuit diagram, partially in bloek form, of a ground fault proteetion system eonstrueted in accordance with the present invention.
Turning to the drawing, the ground fault protection system of the present invention is depieted in its application to a high voltage, industrial-type electrical distribution circuit ineluding a grounded neutral source 10 supplying three-phase power over phase or line eonductors 12 to a load 14. Ineluded in this distribution circuit is a conventional three-pole eireuit breaker, generally indicated at 16, having separable contacts 18 connected in series with each line eonduetor 12. The cireuit breaker also ineludes, as diagrammatieally illustrated in FIGURE 1, a trip unit 20 of known eonstrue-tion responsive to the levels of eurrent flowing in the three line conductors for effecting automatie opening of the breaker contacts 18 under overload and short eir-cuit conditions.
Operatively associated with eircuit breaker 16 in a well known manner is shunt trip solenoid 22. As is ~ 7 41 PR 3217 well understood in the art, a shunt trip solenoid in its adaption to a circuit breaker is normally de-energized, but when it is desired to trip the circuit breaker, its coil is energized. Its plunger is magnetically attracted from an inactive to an actuated position, in the process striking a latch associated with the trip unit. The latch releases the breaker mechanism which operates under the power of a mechanism spring to abruptly open the breaker contacts.
The system of the present invention further includes a ground fault circuit interrupting (GFCI) device, generally indicated at 26, of the type widely available for use in low voltage residential-type circuits for pro-tecting humans from the hazards of electrical shock due to ground faults. As diagrammatically illustrated in FIGURE 1, the GFCI device 26, energized from a conventional 120 volt AC source 24, includes a differential current transformer consisting of a toroidal core 28, a first single turn primary winding 30a connected in series with the line side of a control power circuit fed from source 24, a second single turn primary winding 30b connected in series with the neutral side of the control power circuit, and a multi-turn secondary winding 32 connected to the input of an electronic module 34. As is well understood in the art, the differential~transformer develops a signal in its secondary winding 32 in response to a differential in the currents flowing in the primary windings 30a and 3Ob, as would be occasioned by an imbalance in the currents flowing in the two sides of the control power circuit.
This signal is processed by electronic module 34, and, if found to exceed a predetermined magnitude and duration, an electronic switch is triggered to complete an energization circuit for a solenoid (not shown). Energiza-tion of this solenoid initiates the opening of contacts 36 to interrupt the control power circuit.
It will be understood that the GFCI device may be constituted in either a single pole circuit breaker configuration or a receptacle configuration. The GFCI
device is illustrated as being equipped to breaker both sides of the control power circuit as is typical in receptacle configurations. To break both sides of the control power circuit using a circuit breaker configura-tion, a conventional single pole GFCI circuit breaker is equipped with one or more additional breaker poles which may or may not have overcureent tripping capability. So-called "switching neutral" GFCI circuit breakers are now being offered by assignee's Circuit Protective Devices Department, Plainville, Connecticut provide the capability of breaking both sides of th`e control power circuit.
To sense a ground fault on the distribution circuit downstream from circuit breaker 16, a ground fault sensor, generally indicated at 38 and typically a zero sequence transformer, is utilized. Thus, as illustrated in FIGURE 1, sensor 38 comprises a toroidal core 40 which embraces the three line conductors 12 of the distribution circuit. As long as the vectorial sum of the currents flowing in the three line conductors 12 equals zero, the net flux induced in core 40 is also zero and no voltage is induced on its multi-turn secondary winding 42, which is connected across either primary winding (winding 30b in the illustrated embodiment) of GFCI device 26. It is seen that in the absence of an induced voltage in sensor secondary winding 42, the GFCI
differential current transformer remains balanced. On the ~`4~i97 other hand, if a ground fault should exist on the dist~ibu-tion circuit, such as illustrated at 44, the vertical sum of the currents in line conductors 12 no longer equals zero, and a voltage is induced in secondary winding 42. This induced voltage, as impressed across primary winding 30b, causes additional current to flow therethrough, and the GFCI differential transformer becomes unbalanced, resulting in the opening of the GFCI device contacts 36. While the distribution circuit is illustrated as simply a three phase, three wire circuit,`it will be appreciated that it may also include a fourth, neutral wire, in which case all four wires would be embraced by core 40. Moreover, the sensor 38 may be constituted by separate current transformers inductively coupled with each distribution circuit wire and with their secondary windings connected in parallel, residual circuit fashion.
To translate the tipping of GFCI device 26 in response to a ground fault on the distribution circuit into tripping of circuit breaker 16 to clear the ground fault, the GFCI device is adapted with a switch 50. This switch may be in the form of an auxiliary switch mechani-cally coupled with the GFCI circuit breaXer mechanism and operated thereby to assume a normally open condition while the GFCI breaker contacts are closed and to assume a closed condition whenever the GFCI breaker contacts are opened. Preferably however, switch 50 is of the so-called "trip or bell alarm" type physically adapted to a GFCI
circuit breaker in the same manner as currently being adapted to conventional residential-type circuit breakers. A
bell alarm switch is mechanically adapted to a circuit breaker so as to be insensitive to manual opening of the circuit breaker, but is actuated to i-ts closed condition ; .
~ 9 7 41PR 3217 in response to tripping of the circuit breaker. In this connection, reference is made to the disclosure in U.S.
Patent No. 3,256,407 - K.W. Klein, dated June 14, 1966.
Switch 50 may be adapted to a GFCI receptacle by positioning its contacts for closure in response to engagement by the receptacle movable contact carrier as it springs to its open circuit position incident to a ground fault trip function. In either case, switch 50 is mechanically coupled to the GFCI device contacts 36 such that the switch is left open as long as the device contacts are closed. When the device contacts are tripped open, the switch is incidentally actuated to its closed condition. Switch 50 is wired into an energization circuit for the shunt trip solenoid 22 which, in the illustrated embodiment of the invention, is tapped into the control power circuit at the line side of the GFCI device, but could be fed from a source separate from source ~4. It is thus seen that until the GFCI device is tripped, the switch is open and -thus energization of the shunt trip solenoid from source 26 is inhibited.
However, when the GFCI device trips in response to a ground fault on the distribution circuit, switch 50 closes to effect energization of the shunt trip solenoid and tripping of circuit breaker 16.
From the foregoing description of the disclosed embodiment of the invention, it is seen that by using the combination of three low-cost components, namely, a residential-type GFCI device equipped with a trip alarm or auxiliary switch, a shunt trip solenoid and a ground fault sensor, to control a conventional industrial circuit breaker, economical ground fault protection is afforded to a high current power distribution circuit.
~, _ g _ , .: ;
~i~2~ ~9 ~ 41 PR 3217 As an additional feature of the present inven-tion, the control power circuit is utilized to power an electrical load 52 connected downstream from the GFCI
device. This load may include indicator lights, alarms, and other devices as may be incorporated in typical industrial electrical power delivery installations.
Since load 52 is fed via the GFCI device, it, as well as the control power circuit downstream from the GFCI device, is afforded ground fault protection. This is a significant feature as well from a personnel safety standpoint. If the GFCI device is in a circuit breaker configuration, then load 52 is also afforded overcurrent protection.
It will be appreciated that control power source 24 may be in the form of a 120/240 AC volts supply feeding two line conductors and a grounded neutral conductor. In this case, the GFCI device 26 would be provided by a two pole GFCI circuit breaker, such as is offered by assignee's Circuit Protecti~te Devices Department, Plainville, Connecti-cut. This can be desirable from the standpoint that load 52 may require a 240 volt supply or be constituted by a ^
variety of 120 and 240 volt loads. In practice, it would be preferable to connect secondary winding 42 of sensor 38 directly across one of the primary windings 30a, 30b, rather than across the one primary winding and one set of GFCI contacts 36 as shown, so as to avoid open-circuiting the sensor secondary winding.
Also to be noted is the fact that the GFCI device contacts 36 are not electrically involved in the shunt trip solenoid energization circuit and need not be directly mechanically involved with switch 50, as in the case of a bell alarm switch. Consequently, if a particular installa-tion does not call for a load 52 or that such load and its associated circuit does not require ground fault, then the GFCI device may be devoid of contacts 36. I~ this case, the shunt trip solenoid energization circuit including switch 50 could be connected to the load side of the GFCI device.
It will thus be seen that the objects set forth, among those made apparent in the preceding descrip-tion, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying dra~ings shall be interpreted as illustrative and not in a limiting sense.
-- 11 -- .,
For high current applications found in industry, ground fault protection is available in basically two configurations. With the event of so-called "static trip" circuit breakers, it has become economically possible to combine overcurrent and ground fault signal processing circuitry in a compact electronic trip unit package which can be integrated with the circuit breaker to achieve comprehensive circuit protection. Alternatively, traditional circuit breakers having thermal-magnetic and `
dual-magnetic trip units for overcurrent protection can be utilized with so-called "ground fault relays" in providing ground fault protection as well. These relays respond to a ground fault signal developed by a suitable sensor, such as a zero sequence transformer coupled with the load carrying conductors, by energizing (or de-energizing) a solenoid which, in turn shunts trips the breaker to initiate circuit interruption.
U. S. Patent No. 4,044,395, issued August 23, 1977 `
and assignecl to the assignee of the instant application, discloses a system for protecting relatively large power ~ 7 41 PR 3217 distribution circuits against ground faults by utilizing as its principle operating component a conventional GFCI
device normally used in low power, residential circuit applications. As disclosed and claimed therein, the GFCI
device is installed in a control circuit for an under-voltage release solenoid adapted to a conventional circuit breaker protecting the distribution circuit or in the control circuit for the holding coils of a contactor operating in the distribution circuit. A ground fault sensor in the form of a zero sequence transformer coupled with the load current carrying conductors of the distribu-tion circuit develops a current signal in its secondary winding in response to a ground fault on -the distribution circuit. This current signal is injected into one side of the control circuit to create a current imbalance of the natu~e to which the GFCI device is responsive. The GFCI
device trips to interrupt the control circuit, and the undervoltage release solenoid drops out to trip the circuit breaker or the holding coil becomes de-energized to open the contactor. In either case, the distribution circuit is interrupted to clear the ground fault.
The system configuration of this patent, while quite satisfactory for most application, has one drawback in that it is sensitive to control circuit voltage fluxuations.
That is, should the control circuit voltage drop to an abnormally low level, the undervoltage release solenoid could drop out, causing the circuit breaker to trip despite the fact there is no ground fault on the distribution circuit.
The same nuisance interruption of the distribution circuit could likewise result from control circuit voltage dips if a contactor is substituted for the circuit breaker.
It is accordingly an object of the present ~ !7 41 PR 3217 invention to provide an inexpensive ground fault protection system suitable for high current, industrial circuit applications.
An additional object of the present invention is to provide a ground fault protection system of the above character which utilizes as its fault clearing component a circuit interrupting device of the more traditional, non-static trip design.
A further object of the present invention is to provide a ground fault protection system of the above character which utilizes as one of its principle components a low-cost ground fault circuit interrupting (GFCI) device of the type presently enjoying wide use in the low-power residential circuitry.
Other objects of the invention will in part be obvious and in part appear hereinafter.
In accordance with the present invention, there is provided a ground fault protection system ideally suited for application to high current, high voltage power distri-bution circuits, wherein the system utilizes as its principle operating component a ground fault circuit interrupting (GFCI) device of the type used in low voltage residential-type circuits. As is well known, such GFCI
devices utilize a differential current transformer to sense imbalances in the currents going out to and returning from a load, as would be occasioned by leakage current returning to the source through an unintended ground path. The differential current transformer develops an analog signal proportional to this leakage current which is processed by electronic circuitry, and, if of a predeter-mined magnitude and duration, an electronic switch is triggered to complete ~n energization circuit for a shunt ~ 7 41 PR 3217 trip solenoid. Upon energization, the solenoid plunger strikes a latch to release a spring powered mechanism which is freed to open contacts,, clearing the ground faul~ through which the leakage current originates.
In accordance with the present in~ention, the GFCI device is equipped with switch means ln the form of an auxiliary switch or a bell alarm switch for controlling the energization of a shunt trip solenoid operative to trip a circuit ~reaker protectiny the power distribution circuit. The switch means is normally open, but is operatively coupled to the GFCI device such as to be closed incident to the tripping of the GFCI device. Closure of the switch means completes an energization circuit for the solenoid which then acts to trip the circuit breaker, interrupting the distribution circuit.
- To sense the existence of a ground fault on the distribution circuit, a ground fault sensor is coupled with the load current carrying conductors of the distribution circuit for developing a current signal indicative of the ground fault current magnitude. This current signal is impressed across one side of a control power circuit for energizing the GFCI device, thereby creating a current imbalance sensible by the differential current transformer of the GFCI device. The GFCI device trips, and the switch means closes to fire the shunt trip solenoid, thereby tripping the circuit breaker and clearing the ground fault on the distribution circuit.
As an incidental, but nevertheless signi~icant feature of the present invention, the control power circuit may be utilized to power loads connected downstream from the GFCI device. Such loads may include alarms, signal lights, etc. traditionally found in motor control centers, ~ 4~ 41 PR 3217 for example. Since these loads are wired through the GFCI device, they are afforded ground fault protection, a significant advantage in terms of operating personnel safety.
The invention accordingly comprises the features of construction and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the seope of the invention will be indicated in the claims.
For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawing, in which the sole figure is a circuit diagram, partially in bloek form, of a ground fault proteetion system eonstrueted in accordance with the present invention.
Turning to the drawing, the ground fault protection system of the present invention is depieted in its application to a high voltage, industrial-type electrical distribution circuit ineluding a grounded neutral source 10 supplying three-phase power over phase or line eonductors 12 to a load 14. Ineluded in this distribution circuit is a conventional three-pole eireuit breaker, generally indicated at 16, having separable contacts 18 connected in series with each line eonduetor 12. The cireuit breaker also ineludes, as diagrammatieally illustrated in FIGURE 1, a trip unit 20 of known eonstrue-tion responsive to the levels of eurrent flowing in the three line conductors for effecting automatie opening of the breaker contacts 18 under overload and short eir-cuit conditions.
Operatively associated with eircuit breaker 16 in a well known manner is shunt trip solenoid 22. As is ~ 7 41 PR 3217 well understood in the art, a shunt trip solenoid in its adaption to a circuit breaker is normally de-energized, but when it is desired to trip the circuit breaker, its coil is energized. Its plunger is magnetically attracted from an inactive to an actuated position, in the process striking a latch associated with the trip unit. The latch releases the breaker mechanism which operates under the power of a mechanism spring to abruptly open the breaker contacts.
The system of the present invention further includes a ground fault circuit interrupting (GFCI) device, generally indicated at 26, of the type widely available for use in low voltage residential-type circuits for pro-tecting humans from the hazards of electrical shock due to ground faults. As diagrammatically illustrated in FIGURE 1, the GFCI device 26, energized from a conventional 120 volt AC source 24, includes a differential current transformer consisting of a toroidal core 28, a first single turn primary winding 30a connected in series with the line side of a control power circuit fed from source 24, a second single turn primary winding 30b connected in series with the neutral side of the control power circuit, and a multi-turn secondary winding 32 connected to the input of an electronic module 34. As is well understood in the art, the differential~transformer develops a signal in its secondary winding 32 in response to a differential in the currents flowing in the primary windings 30a and 3Ob, as would be occasioned by an imbalance in the currents flowing in the two sides of the control power circuit.
This signal is processed by electronic module 34, and, if found to exceed a predetermined magnitude and duration, an electronic switch is triggered to complete an energization circuit for a solenoid (not shown). Energiza-tion of this solenoid initiates the opening of contacts 36 to interrupt the control power circuit.
It will be understood that the GFCI device may be constituted in either a single pole circuit breaker configuration or a receptacle configuration. The GFCI
device is illustrated as being equipped to breaker both sides of the control power circuit as is typical in receptacle configurations. To break both sides of the control power circuit using a circuit breaker configura-tion, a conventional single pole GFCI circuit breaker is equipped with one or more additional breaker poles which may or may not have overcureent tripping capability. So-called "switching neutral" GFCI circuit breakers are now being offered by assignee's Circuit Protective Devices Department, Plainville, Connecticut provide the capability of breaking both sides of th`e control power circuit.
To sense a ground fault on the distribution circuit downstream from circuit breaker 16, a ground fault sensor, generally indicated at 38 and typically a zero sequence transformer, is utilized. Thus, as illustrated in FIGURE 1, sensor 38 comprises a toroidal core 40 which embraces the three line conductors 12 of the distribution circuit. As long as the vectorial sum of the currents flowing in the three line conductors 12 equals zero, the net flux induced in core 40 is also zero and no voltage is induced on its multi-turn secondary winding 42, which is connected across either primary winding (winding 30b in the illustrated embodiment) of GFCI device 26. It is seen that in the absence of an induced voltage in sensor secondary winding 42, the GFCI
differential current transformer remains balanced. On the ~`4~i97 other hand, if a ground fault should exist on the dist~ibu-tion circuit, such as illustrated at 44, the vertical sum of the currents in line conductors 12 no longer equals zero, and a voltage is induced in secondary winding 42. This induced voltage, as impressed across primary winding 30b, causes additional current to flow therethrough, and the GFCI differential transformer becomes unbalanced, resulting in the opening of the GFCI device contacts 36. While the distribution circuit is illustrated as simply a three phase, three wire circuit,`it will be appreciated that it may also include a fourth, neutral wire, in which case all four wires would be embraced by core 40. Moreover, the sensor 38 may be constituted by separate current transformers inductively coupled with each distribution circuit wire and with their secondary windings connected in parallel, residual circuit fashion.
To translate the tipping of GFCI device 26 in response to a ground fault on the distribution circuit into tripping of circuit breaker 16 to clear the ground fault, the GFCI device is adapted with a switch 50. This switch may be in the form of an auxiliary switch mechani-cally coupled with the GFCI circuit breaXer mechanism and operated thereby to assume a normally open condition while the GFCI breaker contacts are closed and to assume a closed condition whenever the GFCI breaker contacts are opened. Preferably however, switch 50 is of the so-called "trip or bell alarm" type physically adapted to a GFCI
circuit breaker in the same manner as currently being adapted to conventional residential-type circuit breakers. A
bell alarm switch is mechanically adapted to a circuit breaker so as to be insensitive to manual opening of the circuit breaker, but is actuated to i-ts closed condition ; .
~ 9 7 41PR 3217 in response to tripping of the circuit breaker. In this connection, reference is made to the disclosure in U.S.
Patent No. 3,256,407 - K.W. Klein, dated June 14, 1966.
Switch 50 may be adapted to a GFCI receptacle by positioning its contacts for closure in response to engagement by the receptacle movable contact carrier as it springs to its open circuit position incident to a ground fault trip function. In either case, switch 50 is mechanically coupled to the GFCI device contacts 36 such that the switch is left open as long as the device contacts are closed. When the device contacts are tripped open, the switch is incidentally actuated to its closed condition. Switch 50 is wired into an energization circuit for the shunt trip solenoid 22 which, in the illustrated embodiment of the invention, is tapped into the control power circuit at the line side of the GFCI device, but could be fed from a source separate from source ~4. It is thus seen that until the GFCI device is tripped, the switch is open and -thus energization of the shunt trip solenoid from source 26 is inhibited.
However, when the GFCI device trips in response to a ground fault on the distribution circuit, switch 50 closes to effect energization of the shunt trip solenoid and tripping of circuit breaker 16.
From the foregoing description of the disclosed embodiment of the invention, it is seen that by using the combination of three low-cost components, namely, a residential-type GFCI device equipped with a trip alarm or auxiliary switch, a shunt trip solenoid and a ground fault sensor, to control a conventional industrial circuit breaker, economical ground fault protection is afforded to a high current power distribution circuit.
~, _ g _ , .: ;
~i~2~ ~9 ~ 41 PR 3217 As an additional feature of the present inven-tion, the control power circuit is utilized to power an electrical load 52 connected downstream from the GFCI
device. This load may include indicator lights, alarms, and other devices as may be incorporated in typical industrial electrical power delivery installations.
Since load 52 is fed via the GFCI device, it, as well as the control power circuit downstream from the GFCI device, is afforded ground fault protection. This is a significant feature as well from a personnel safety standpoint. If the GFCI device is in a circuit breaker configuration, then load 52 is also afforded overcurrent protection.
It will be appreciated that control power source 24 may be in the form of a 120/240 AC volts supply feeding two line conductors and a grounded neutral conductor. In this case, the GFCI device 26 would be provided by a two pole GFCI circuit breaker, such as is offered by assignee's Circuit Protecti~te Devices Department, Plainville, Connecti-cut. This can be desirable from the standpoint that load 52 may require a 240 volt supply or be constituted by a ^
variety of 120 and 240 volt loads. In practice, it would be preferable to connect secondary winding 42 of sensor 38 directly across one of the primary windings 30a, 30b, rather than across the one primary winding and one set of GFCI contacts 36 as shown, so as to avoid open-circuiting the sensor secondary winding.
Also to be noted is the fact that the GFCI device contacts 36 are not electrically involved in the shunt trip solenoid energization circuit and need not be directly mechanically involved with switch 50, as in the case of a bell alarm switch. Consequently, if a particular installa-tion does not call for a load 52 or that such load and its associated circuit does not require ground fault, then the GFCI device may be devoid of contacts 36. I~ this case, the shunt trip solenoid energization circuit including switch 50 could be connected to the load side of the GFCI device.
It will thus be seen that the objects set forth, among those made apparent in the preceding descrip-tion, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying dra~ings shall be interpreted as illustrative and not in a limiting sense.
-- 11 -- .,
Claims (4)
1. A ground fault protection system for an electrical power distribution circuit, said system comprising, in combination:
(A) a circuit breaker having contacts connected in the distribution circuit;
(B) a shunt trip solenoid operable upon electrical energization to trip said circuit breaker, opening said breaker contacts to interrupt current flow in the distribution circuit;
(C) an electrical energization circuit for said solenoid;
(D) a control power circuit having a pair of circuit sides;
(E) a GFCI device including (1) contacts connected in at least one said circuit side of said control power circuit, (2) a differential current transformer having a pair of primary windings, one connected in series with each said circuit side of said control power circuit, and a secondary winding in which is developed a ground fault signal indicative of an imbalance in the currents flowing in said primary windings, (3) an electronic module powered from said control power circuit and operating in response to said ground fault signal for initiating a ground fault trip function leading to a physical tripping of said GFCI device to open its contacts, and (4) a normally open auxiliary switch connected in said energization circuit for said solenoid, said switch coupled with said GFCI device and actuated to its closed condition to complete said solenoid energization circuit automatically incident to the tripping of said GFCI device in response to said ground fault trip function initiated by said module; and (F) a ground fault sensor coupled with the distribution circuit and having an output connected across one of said primary windings, said sensor developing in response to a ground fault on the distribution circuit a current signal flowing through said one primary winding to produce a ground fault signal in said secondary winding, whereby said module initiates a ground fault trip function to precipitate opening of said device contacts, closure of said switch and consequent energization of said solenoid to trip said circuit breaker.
(A) a circuit breaker having contacts connected in the distribution circuit;
(B) a shunt trip solenoid operable upon electrical energization to trip said circuit breaker, opening said breaker contacts to interrupt current flow in the distribution circuit;
(C) an electrical energization circuit for said solenoid;
(D) a control power circuit having a pair of circuit sides;
(E) a GFCI device including (1) contacts connected in at least one said circuit side of said control power circuit, (2) a differential current transformer having a pair of primary windings, one connected in series with each said circuit side of said control power circuit, and a secondary winding in which is developed a ground fault signal indicative of an imbalance in the currents flowing in said primary windings, (3) an electronic module powered from said control power circuit and operating in response to said ground fault signal for initiating a ground fault trip function leading to a physical tripping of said GFCI device to open its contacts, and (4) a normally open auxiliary switch connected in said energization circuit for said solenoid, said switch coupled with said GFCI device and actuated to its closed condition to complete said solenoid energization circuit automatically incident to the tripping of said GFCI device in response to said ground fault trip function initiated by said module; and (F) a ground fault sensor coupled with the distribution circuit and having an output connected across one of said primary windings, said sensor developing in response to a ground fault on the distribution circuit a current signal flowing through said one primary winding to produce a ground fault signal in said secondary winding, whereby said module initiates a ground fault trip function to precipitate opening of said device contacts, closure of said switch and consequent energization of said solenoid to trip said circuit breaker.
2. The system defined in claim 1 wherein said solenoid energization circuit is fed from said control power circuit in parallel with said module.
3. The system defined in claim 2, wherein said control power circuit includes a low voltage source and said energization circuit is electrically connected to said control power circuit intermediate said GFCI device and said control power circuit.
4. The system defined in claim 3 wherein said pair of control power circuit sides consists of a line side and neutral side grounded at said low voltage source, said system further including an electrical load connected across said line and neutral sides of said control power circuit downstream from said GFCI device.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US83170977A | 1977-09-09 | 1977-09-09 | |
| US831,709 | 1977-09-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121497A true CA1121497A (en) | 1982-04-06 |
Family
ID=25259676
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000310430A Expired CA1121497A (en) | 1977-09-09 | 1978-08-31 | System for protecting power distribution circuit against ground faults |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5453239A (en) |
| CA (1) | CA1121497A (en) |
| DE (1) | DE2838804A1 (en) |
| FR (1) | FR2402959A1 (en) |
| GB (1) | GB1604711A (en) |
| IT (1) | IT1098755B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104121044B (en) * | 2014-07-24 | 2015-12-30 | 江苏永钢集团有限公司 | The method of controlling security of generator jumped by a kind of turbine emergency protector connection |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4044395A (en) * | 1976-08-02 | 1977-08-23 | General Electric Company | Ground fault protection system |
-
1978
- 1978-05-16 GB GB19698/78A patent/GB1604711A/en not_active Expired
- 1978-08-30 IT IT27131/78A patent/IT1098755B/en active
- 1978-08-31 CA CA000310430A patent/CA1121497A/en not_active Expired
- 1978-09-05 FR FR7825477A patent/FR2402959A1/en not_active Withdrawn
- 1978-09-05 JP JP10818478A patent/JPS5453239A/en active Pending
- 1978-09-06 DE DE19782838804 patent/DE2838804A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5453239A (en) | 1979-04-26 |
| DE2838804A1 (en) | 1979-03-15 |
| IT1098755B (en) | 1985-09-18 |
| IT7827131A0 (en) | 1978-08-30 |
| GB1604711A (en) | 1981-12-16 |
| FR2402959A1 (en) | 1979-04-06 |
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| MKEX | Expiry |