CA1104243A - Ground fault circuit interrupter module - Google Patents
Ground fault circuit interrupter moduleInfo
- Publication number
- CA1104243A CA1104243A CA229,059A CA229059A CA1104243A CA 1104243 A CA1104243 A CA 1104243A CA 229059 A CA229059 A CA 229059A CA 1104243 A CA1104243 A CA 1104243A
- Authority
- CA
- Canada
- Prior art keywords
- ground fault
- circuit interrupter
- output
- amplifier
- potential
- 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
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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
- H02H3/33—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 using summation current transformers
- H02H3/331—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 using summation current transformers responsive to earthing of the neutral conductor
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/06—Arrangements for supplying operative power
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
GROUND FAULT INTERRUPTER MODULE
Abstract of the Disclosure The module is composed of the internal electronic circuitry and components of a ground fault circuit interrupter, and is designed for use with a power supply system having a neutral conductor and at least one line conductor and carry-ing current between a source and a load, with the neutral conductor being grounded at the source and the supply system including a system circuit interrupter or circuit breaker operable responsive to application of a potential to an operating element such as a solenoid. The module includes first and second current transformers embracing the neutral conductor and at least one line conductor of the power supply system. A resistor is connected across the terminals of the secondary winding of the first current transformer so that a potential appears across the resistor responsive to inequality of the currents carried by the neutral and line conductors, as a result of a ground fault. An operational amplifier has its input connected across the resistor and a feedback network is connected between the input and output of the amplifier to control the gain thereof. The output of the amplifier is connected to the base of a transistor controlling triggering of an SCR which, when conductive, acts as a switch across terminals connected to the solenoid so as to energize the solenoid to trip the power system circuit breaker. The secondary winding of the second current transformer is coupled by a capacitor to the output of the amplifier. When the volt-age across the resistor at the input of the amplifier reaches a predetermined value, responsive to a ground fault, the amplifier output is sufficient to trigger the transistor con-ductive. If the neutral conductor becomes grounded on the load side of the two current transformers, it forms an ef-fective loop extending through the cores of both current transformers, so that the two current transformers form a magnetic coupling between the output and the input of the amplifier. The amplifier then breaks into high frequency oscillation and the high frequency signal on the transistor triggers the same conductive to trigger the SCR conductive.
Thus, only one electric circuit performs both basic functions of a ground fault circuit interrupter with a corresponding substantial reduction in components and increase in relia-bility and economy of operation.
Abstract of the Disclosure The module is composed of the internal electronic circuitry and components of a ground fault circuit interrupter, and is designed for use with a power supply system having a neutral conductor and at least one line conductor and carry-ing current between a source and a load, with the neutral conductor being grounded at the source and the supply system including a system circuit interrupter or circuit breaker operable responsive to application of a potential to an operating element such as a solenoid. The module includes first and second current transformers embracing the neutral conductor and at least one line conductor of the power supply system. A resistor is connected across the terminals of the secondary winding of the first current transformer so that a potential appears across the resistor responsive to inequality of the currents carried by the neutral and line conductors, as a result of a ground fault. An operational amplifier has its input connected across the resistor and a feedback network is connected between the input and output of the amplifier to control the gain thereof. The output of the amplifier is connected to the base of a transistor controlling triggering of an SCR which, when conductive, acts as a switch across terminals connected to the solenoid so as to energize the solenoid to trip the power system circuit breaker. The secondary winding of the second current transformer is coupled by a capacitor to the output of the amplifier. When the volt-age across the resistor at the input of the amplifier reaches a predetermined value, responsive to a ground fault, the amplifier output is sufficient to trigger the transistor con-ductive. If the neutral conductor becomes grounded on the load side of the two current transformers, it forms an ef-fective loop extending through the cores of both current transformers, so that the two current transformers form a magnetic coupling between the output and the input of the amplifier. The amplifier then breaks into high frequency oscillation and the high frequency signal on the transistor triggers the same conductive to trigger the SCR conductive.
Thus, only one electric circuit performs both basic functions of a ground fault circuit interrupter with a corresponding substantial reduction in components and increase in relia-bility and economy of operation.
Description
~i~4Z~3 Field and Background of the Invention This invention relates to ground fault circuit interrupters and, more particularly, to a novel and improved ground fault circuit interrupter modu:Le using only one elec-trical circuit to perform two basic functions with a sub-stantial reduction in com onents and with a more economical and reliable circuit.
A ground fault circuit interrupter module is the internal electronic circuitry and components of a ground fault circuit interrupter. Ground fault circuit interrupters are intended primarily to protect normal human beings from harmful effects of electric shock by sensing ground faults, leakage currents, or both, and by interrupting the electric circuit to a load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device, or circuit breaker, of a supply circuit or system.
Basical]y, ground fault circuit interrupters must perform two functions. In the first place, they must sense ground faults and/or leakage currents to ground and interrupt the electric circuit to the load when a fault current ex-ceeds the predetermined value. The second function involves grounding of the neutral conductor of a power supply system.
Such neutral conductors are grounded at the source of electric potential and, if the grounded conductor of the system, otherwise known as the neutral conductor, becomes grounded at points on the load side of a ground fault current inter-rupter, the ground fault current interrupter must sense this conduction and interrupt the electrical circuit to the load.
Such grounds of neutral conductors on the load side of a ` 3 ~l~g243 ground fault current interrupter are not allowed by the National Electric Code.
Ground fault circuit interrupters having various circuitry configurations are presently in commercial use.
~ost of the known devices utilize a differential transformer having a magnetic core and primary windings of at least one turn connected in series with the conductors of the distribution system. The differential transformers also include a secondary winding which is typically connected to means for visually indicating the presence of a ground fault or for interrupting the flow current in the distribution system or for both. In a power supply system having a neutral conductor and at least one line conductor carrying current between a source and a load, with the neutral conductor being grounded at the source, the total current flowing through the line conductors, under normal conditions, is equal to the current flowing through the neutral conductor. This produces a zero net magnetic flux in the differential transformer core and thus there is no output from the secondary winding.
When a ground fault occurs, the current in the line conductors differs from that in the neutral conductor by an amount equal to the magnitude of the fault current, and the difference produces a net magnetic flux in the transformer core which induces a fault signal in the secondary winding. An arrangement of this type is disclosed in Dalziel U.S. Patent No. 3,213,321, issued October 19, 1965. The differential transformer may be a so-called "zero sequence" current transformer.
The known ground fault circuit interrupters operate satisfactorily under most conditions, particularly for i~Q4Z~3 detecting ground faults. However, the detection of a low impedance ground on the neutral conductor between the trans-former and the load has presented some difficulty due to the fact that, while the current produced by a ground fault returns to the source through the ground, in bypassing rela-tion to the portion of the neutral conductor passing through the differential transformer, when the neutral conductor is grounded on the load side of the transformer there is pro-vided an alternate path to the source for a ground fault current so that a portion of the current returns to the source through the neutral conductor and the transformer. This makes it extremely difficult to detect the level of fault current required to produce tripping of an overcurrent circuit breaker or the like in the power supply system, as the increase in fault current required is dependent upon the magnitude of the impedance between the neutral conductor and ground.
Various approaches have been posed for solving this problem. Thus, U.S. Patent No. 3,506,906 discloses an arrangement in which a voltage is induced on the neutral conductor, and this voltage causes a current imbalance in the conductors whenever the neutral conductor is grounded.
The voltage is induced on the neutral conductor by means of a transformer having a secondary winding connected in series with that conductor and a primary winding which is energized by current taken from the distribution system. For proper operation, the transformer core must have a fairly large cross-sectional area, and such large cores are not suitable for use in miniaturized ground fault protectors.
To solve this latter problem, Douglas U.S. Patent No. 3,611,035, issued October 5, 1971, discloses an 1~4Z~;~
oscillator circuit for generating a high frequency signal necessary for detection of a grounded neutral, the high fre-quency signal having a frequency substantially higher than that of the line current and being induced in the neutral conductor.
Upon grounding of the neutral conductor, the high frequency signal produces a current in the neutral conductor causing an imbalance in the currents in the line and neutral con-ductors. The arrangement includes additional circuitry to amplify the high frequency signal, or the fault current signal, and to trip the mechanism of the ground fault circuit interrupter. A disadvantageous feature of this latter arrangement is that the high frequency signal is always present on the conductors of the power supply system, and must be present always on the conductors in order for the arrangement to operate properly to detect grounding of a neutral conductor between the transformer and the load.
Summar of the Invention y In accordance with the invention, the disadvantages of the prior art ground fault circuit interrupters are avoided by using only a single electric circuit to perform both basic functions of a ground fault circuit interrupter, namely:
(1) sensing ground fault and/or leakage current to ground and interrupting the electric supply to the load when a fault current exceeds a predetermined value, and
A ground fault circuit interrupter module is the internal electronic circuitry and components of a ground fault circuit interrupter. Ground fault circuit interrupters are intended primarily to protect normal human beings from harmful effects of electric shock by sensing ground faults, leakage currents, or both, and by interrupting the electric circuit to a load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device, or circuit breaker, of a supply circuit or system.
Basical]y, ground fault circuit interrupters must perform two functions. In the first place, they must sense ground faults and/or leakage currents to ground and interrupt the electric circuit to the load when a fault current ex-ceeds the predetermined value. The second function involves grounding of the neutral conductor of a power supply system.
Such neutral conductors are grounded at the source of electric potential and, if the grounded conductor of the system, otherwise known as the neutral conductor, becomes grounded at points on the load side of a ground fault current inter-rupter, the ground fault current interrupter must sense this conduction and interrupt the electrical circuit to the load.
Such grounds of neutral conductors on the load side of a ` 3 ~l~g243 ground fault current interrupter are not allowed by the National Electric Code.
Ground fault circuit interrupters having various circuitry configurations are presently in commercial use.
~ost of the known devices utilize a differential transformer having a magnetic core and primary windings of at least one turn connected in series with the conductors of the distribution system. The differential transformers also include a secondary winding which is typically connected to means for visually indicating the presence of a ground fault or for interrupting the flow current in the distribution system or for both. In a power supply system having a neutral conductor and at least one line conductor carrying current between a source and a load, with the neutral conductor being grounded at the source, the total current flowing through the line conductors, under normal conditions, is equal to the current flowing through the neutral conductor. This produces a zero net magnetic flux in the differential transformer core and thus there is no output from the secondary winding.
When a ground fault occurs, the current in the line conductors differs from that in the neutral conductor by an amount equal to the magnitude of the fault current, and the difference produces a net magnetic flux in the transformer core which induces a fault signal in the secondary winding. An arrangement of this type is disclosed in Dalziel U.S. Patent No. 3,213,321, issued October 19, 1965. The differential transformer may be a so-called "zero sequence" current transformer.
The known ground fault circuit interrupters operate satisfactorily under most conditions, particularly for i~Q4Z~3 detecting ground faults. However, the detection of a low impedance ground on the neutral conductor between the trans-former and the load has presented some difficulty due to the fact that, while the current produced by a ground fault returns to the source through the ground, in bypassing rela-tion to the portion of the neutral conductor passing through the differential transformer, when the neutral conductor is grounded on the load side of the transformer there is pro-vided an alternate path to the source for a ground fault current so that a portion of the current returns to the source through the neutral conductor and the transformer. This makes it extremely difficult to detect the level of fault current required to produce tripping of an overcurrent circuit breaker or the like in the power supply system, as the increase in fault current required is dependent upon the magnitude of the impedance between the neutral conductor and ground.
Various approaches have been posed for solving this problem. Thus, U.S. Patent No. 3,506,906 discloses an arrangement in which a voltage is induced on the neutral conductor, and this voltage causes a current imbalance in the conductors whenever the neutral conductor is grounded.
The voltage is induced on the neutral conductor by means of a transformer having a secondary winding connected in series with that conductor and a primary winding which is energized by current taken from the distribution system. For proper operation, the transformer core must have a fairly large cross-sectional area, and such large cores are not suitable for use in miniaturized ground fault protectors.
To solve this latter problem, Douglas U.S. Patent No. 3,611,035, issued October 5, 1971, discloses an 1~4Z~;~
oscillator circuit for generating a high frequency signal necessary for detection of a grounded neutral, the high fre-quency signal having a frequency substantially higher than that of the line current and being induced in the neutral conductor.
Upon grounding of the neutral conductor, the high frequency signal produces a current in the neutral conductor causing an imbalance in the currents in the line and neutral con-ductors. The arrangement includes additional circuitry to amplify the high frequency signal, or the fault current signal, and to trip the mechanism of the ground fault circuit interrupter. A disadvantageous feature of this latter arrangement is that the high frequency signal is always present on the conductors of the power supply system, and must be present always on the conductors in order for the arrangement to operate properly to detect grounding of a neutral conductor between the transformer and the load.
Summar of the Invention y In accordance with the invention, the disadvantages of the prior art ground fault circuit interrupters are avoided by using only a single electric circuit to perform both basic functions of a ground fault circuit interrupter, namely:
(1) sensing ground fault and/or leakage current to ground and interrupting the electric supply to the load when a fault current exceeds a predetermined value, and
(2) sensing if the grounded neutral conductor of the system becomes grounded at points on the load side of a ground fault circuit interrupter and interrupting the electrical 42~3 supply to the load.
Furthermore, the present invention is directed to a novel and improved ground fault circuit interrupter module resulting in an approximately 30% reduction in components as well as in a more economical and reliable circuit. Most importantly, with the ground fault circuit interrupter module of the present invention, there is no high frequency signal present on the conductors of the power supply system during normal operation of that system, which means that no signal can be radiated from the conductors of a branch circuit, for example, being protected by a ground fault circuit inter-rupter embodying the invention.
The module forming the subject matter of the invention is designed for use with a power supply system having a neutral conductor and at least one line conductor, such as a single phase or polyphase AC system, carrying current between a source and a load and with the neutral conductor being grounded at the source. Furthermore, as is the usual case, the supply system includes an overcurrent circuit breaker or the like which is operable, responsive to applica-tion of a potential to an operating element thereof, to interrupt or open the supply system between the source and the load. In accordance with the invention, a first zero sequence current transformer is arranged to embrace the neutral conductor and at least one line conductor of the supply system, and an operational amplifier has an input connected across the secondary winding of the first current transformer and has an output, the operational amplifier providing an amplified output potential responsive to a potential developed across the secondary winding of the ~ -7-l~U~Z4~
first currenttransformer responsive to a ground fault in the supply system resulting in inequality of the currents carried by the neutral and line conductors. Circuit means connected to the amplifier output are operable, when activated responsive to a preselected amplified output potential, to apply a potential to the operating element of the system circuit interrupter. The arrangement so far described senses ground faults in the supply system and interrupts supply of power to the load when a ground fault current exceeds a predetermined magnitude.
For the purpose of sensing grounding of the neutral conductor between the ground fault circuit inter-rupter and the load, a second zero sequence current trans-former, serving as a feedback transformer, is arranged to embrace the neutral conductor and at least one line conductor of the supply system, and has a secondary winding coupled to the operating amplifier output for inducing a magnetic field in the secondary winding. This magnetic field is at power line frequency and is ineffective unless and until the neutral conductor of the supply system becomes shorted on the load side of the two current transformers. When this happens, there is effectively one turn of wire through both transformer cores, and the output of the amplifier is then magnetically coupled, in phase, to the amplifier input so that the amplifier breaks into high frequency oscillation. The resulting high frequency signal applied to the circuit means activates the circuit means to apply a potential to the operating element of the power supply system circuit interrupter to open the power supply to the load. Thus, it will be noted that a high frequency 1~4Z43 oscillation is present on the conductors of the power supply system when and only when the neutral conductor is grounded between the two current transformers and the load, and otherwise is not present on the conductors of the system.
The circuit means connected to the amplifier output includes a transistor receiving a triggering signal from the amplifier output and, in turn, supplying a gating signal to an SCR. The SCR, when conductive, acts like a switch between a pair of terminals connected to the operating element, such as a solenoid, of the system circuit inter-rupter, so that the solenoid is energized.
An object of the invention is to provide an improved ground fault circuit interrupter module.
Another object of the invention is to provide such a ground fault circuit interrupter module utilizing only one electrical circuit to perform both basic functions of a ground fault circuit interrupter.
A further object of the invention is to provide a ground fault circuit interrupter module in which the components are substantially reduced and a more economical and reliable circuit is provided.
Yet another object of the invention is to provide a ground fault circuit interrupter module in which there is no high frequency signal present on the conductors of an electrical supply system during normal operation of the system, that is, in the absence of a ground fault and in the absence of grounding of a neutral conductor between the ground fault circuit interrupter and the load.
For an understanding of the principles of the invention, reference is made to the following description ~4Z43 of a typical embodiment thereof as illustrated in the accompanying drawing.
Brief Description of the Drawing In the drawing, the single Figure is a schematic wiring diagram of a ground fault circuit interrupter module embodying the invention.
Description of the Preferred Embodiment Referring to the drawing, the ground fault circuit interrupter module of the invention is illustrated, solely by way of example, as associated with a two-wire power supply system having a neutral conductor _ and a line conductor L, and carrying current between a source of potential connected to terminals 1 and 2 and a load connected to terminals 3 and 4. Neutral conductor _ extends between terminals 2 and 4, and is grounded at the source as indicated by the ground connection to terminal 2. This two-wire system is illustrat-ed solely by way of example, as the ground fault circuit interrupter module of the invention is applicable equally to two-wire circuits, to single phase AC circuits and to polyphase AC circuits, having a conductor grounded at the source and usually referred to as a "neutral conductor".
In the usual manner, the power supply system is provided with a circuit breaker 5, which may be an overcurrent-responsive circuit breaker, and circuit breaker 5 has an operating element such as a solenoid 6 which, when energized, opens the circuit breaker to disconnect the load from the source.
In accordance with the invention, the first zero sequence current transformer CT-l has a secondary winding 10 wound on a core 11 embracing the conductors L and _.
1~4243 Secondary winding lO has terminals 12, one of which is con-nected by a conductor 13 directly to an input terminal of amplifier 25 and the other of which is connected by a con-ductor 14 to a junction point 15 connected by a resistor R-2 to the other input terminal of amplifier 25. Reversely poled diodes Dl and D2 are connected between conductors 13 and 14, as is also a resistor R-l. A resistor R-3 is connected in series between resistor R-2 and the output terminal of amplifier 25.
For a purpose to be described, the ground fault circuit interrupter module includes a second zero sequence current transformer CT-2, serving as a feedback transformer, having a secondary winding 20 wound on a core 21 embracing the conductors L and _, between transformer CT-l and load terminals 3, 4. Secondary winding 20 of transformer CT-2 has terminals 22, one of which is connected by a conductor 23 to a junction point 16 connected by a conductor 17 to the junction point 15 of resistors R-l and R-2. The other terminal 22 is connected through a capacitor C-l to a con-ductor 24 connected, at a junction point 26, to a conductor 27 connecting the output terminal 28 of amplifier 25 to the base of an NPN transistor Q. It will thus be noted that the output of amplifier 25 is coupled, through capacitor C-l, to the second current transformer CT-2, for a purpose to be described hereinafter.
A full wave rectifier bridge BR has its input ;
connected to terminals 31 and 32, terminal 31 being connected to conductor L through solenoid 6, and terminal 32 being connected to the load neutral. The output of full wave rectifier bridge BR is applied to conductors 33 and ~ -11-~1~4Z43 34. Bridge BR rectifies the AC voltage across terminals 31 and 32 and which, as stated, is obtained from the supply system through the solenoid 6 of the circuit breaker 5.
If no trip signal is present at amplifier 25, the DC output voltage of rectifier bridge BR is divided into plus and minus 12vDC by resistors R-7, R-8 and R-9, resistor R-7 being connected in series in conductor 33 and resistors R-8 and R-9 being connected in series between a junction point 36 and conductor 33 and a junction point 37 in conductor 34, the two resistors being connected in series at a junction point 38. Through a conductor 41 connected to junction point 36 and a conductor 42 connected to junction point 37, the plus and minus 6vDC is used to power operational ampli-fier 25. A conductor 43 connects junction point 16 to junc-tion point 38 and a capacitor C-4 is connected between this junction point and conductor 34.
A resistor R-6 connects junction point 38 to the emitter of transistor Q, and a conductor 44 connects the collector of transistor Q to the gate of a silicon con-trolled rectifier SCR whose anode is connected to conductor33 and whose cathode is connected to conductor 34. A capa-citor C-2 and a Zener diode D-3 are connected between con-ductors 33 and 34 between bridge BR and control rectifier SCR. Finally, a capacitor C-3 and a resistor R-5 are connected, in parallel with each other, between conductors 34 and 44.
Ground Fault Sensing The operation of the thus described circuit during ground fault sensing will now be described. When a ground fault occurs in the electrical supply system, a ~-~ -12-..~ .
116~4Z43 signal is developed across resistor R-l by zero sequence current transformer CT-l. This signal is then amplified by operational amplifier 25. Resistors R-2 and R-3 constitute a feedback network that controls the gain of operational amplifier 25. Diodes D-l and D-2 protect amplifier 25 by clipping any voltage spikes that may be developed due to current or voltage transients on the electrical supply system. The output of amplifier 25 is supplied to the base of transistor Q.
When the ground fault is at or above the trip level, the signal voltage applied to the base of transistor Q is sufficient to trigger transistor Q conductive on the negative half cycle of signal voltage. Capacitor C-3 is then charged through transistor Q and resistor R-6. Capa-citor C-3 and resistors R-5 and R-6 provide the proper noise immunity and response time to prevent nuisance trips.
When the charge on capacitor C-3 reaches the firing voltage of silicon controlled rectifier SCR, this rectifier conducts and acts as a switch across terminals 31 and 32 to energize the solenoid 6 in the ground fault circuit interrupter trip mechanism or circuit breaker 5.
Capacitor C-2 is provided to prevent silicon con-trolled rectifier SCR from firing prematurely from voltage transients developed on the conductors of the electrical supply system. Zener diode D-3 clips any voltage transients produced by the electrical system that are in excess of 200v, to prevent damage to silicon controlled rectifier SCR.
Grounded Neutral Sensing As stated, the output of amplifier 25 is coupled through capacitor C-1 to the secondary winding 20 of feed-11~4z4;~
back transformer CT-2. The resultant magnetic field in-duced in feedback transformer CT-2 is at power line frequency and, since it has no path to the input of amplifier 25, it has no effect. If the neutral conductor N becomes grounded at the load side, which is at terminal 4, feedback trans-former CT-2 is magnetically coupled to transformer CT-l by neutral conductor N and the ground path from terminal 2 to terminal 4, which can be viewed as one turn of wire through the transformer cores 11 and 21. This magnetic coupling establishes a regenerative feedback path from the output of amplifier 25 to the input of amplifier 25. This re-generative or positive feedback causes amplifier 25 to oscillate in a very predictable manner. In the preferred embodiment, the frequency of oscillation is 5 to 6 KHZ and the frequency can be controlled by the value of capacitor C-l and the number of turns of winding 20 on the core 21 of feedback transformer CT-2.
In actual conditions, with the neutral conductor grounded at terminal 4, there is impedance in the ground path from terminal 4 to terminal 2, caused by ground con-nectors, etc. This impedance is in series with the regenerative feedback path for amplifier 25, so that the amplitude of oscillations at the output of amplifier 25 is inversely proportional to the impedance in the ground path from terminal 2 to terminal 4 of neutral conductor N.
In the circuit embodying the invention, the circuit components are selected to trigger transistor Q conductive to charge capacitor C-3 and thus to fire the SC~ to trip the solenoid in the ground fault interrupter mechanism when the impedance from the ground path, between terminal 4 and terminal 2, is ~4Z43 4 ohms or less to pass the UL requirement of 4 ohms.
In summary, amplifier 25 oscillates when a positive feedback path from its output to its input is com-pleted by grounding of neutral wire N at the load side with resultant coupling of transformers CT-2 and CT-1 and the input of amplifier 25. The amplifier 25, which is used to perform the basic function of ground fault sensing, thus also functions as an oscillator when ground conductor or neutral N becomes grounded on the load side of the ground fault circuit interrupter. This results in a 30~ saving in electrical components and in a more reliable circuit which is especially important since, in a standard circuit breaker type ground fault circuit interrupter, there is very little space available for the electrical circuitry.
As a convenience, a test resistor R-4 is provided and is connected in the ground fault circuit interrupter in such a manner that, when a test button on the ground fault circuit interrupter is pressed, a fault is applied to the electrical supply system to test the ground fault circuit interrupter and its internal circuitry. Test button 35 is connected between the panel neutral and a terminal 46, and resistor R-4 is connected at one end to terminal 46 and at its opposite end in parallel to terminals 47 and 48.
Terminal 47 is connected to the load power and terminal 48 is connected to solenoid 6.
While a specific embodiment of the invention has been shown and described in detail to illustrate the applica-tion of the principles of the invention, it will be under-stood that the invention may be embodied otherwise without departing from such principles.
Furthermore, the present invention is directed to a novel and improved ground fault circuit interrupter module resulting in an approximately 30% reduction in components as well as in a more economical and reliable circuit. Most importantly, with the ground fault circuit interrupter module of the present invention, there is no high frequency signal present on the conductors of the power supply system during normal operation of that system, which means that no signal can be radiated from the conductors of a branch circuit, for example, being protected by a ground fault circuit inter-rupter embodying the invention.
The module forming the subject matter of the invention is designed for use with a power supply system having a neutral conductor and at least one line conductor, such as a single phase or polyphase AC system, carrying current between a source and a load and with the neutral conductor being grounded at the source. Furthermore, as is the usual case, the supply system includes an overcurrent circuit breaker or the like which is operable, responsive to applica-tion of a potential to an operating element thereof, to interrupt or open the supply system between the source and the load. In accordance with the invention, a first zero sequence current transformer is arranged to embrace the neutral conductor and at least one line conductor of the supply system, and an operational amplifier has an input connected across the secondary winding of the first current transformer and has an output, the operational amplifier providing an amplified output potential responsive to a potential developed across the secondary winding of the ~ -7-l~U~Z4~
first currenttransformer responsive to a ground fault in the supply system resulting in inequality of the currents carried by the neutral and line conductors. Circuit means connected to the amplifier output are operable, when activated responsive to a preselected amplified output potential, to apply a potential to the operating element of the system circuit interrupter. The arrangement so far described senses ground faults in the supply system and interrupts supply of power to the load when a ground fault current exceeds a predetermined magnitude.
For the purpose of sensing grounding of the neutral conductor between the ground fault circuit inter-rupter and the load, a second zero sequence current trans-former, serving as a feedback transformer, is arranged to embrace the neutral conductor and at least one line conductor of the supply system, and has a secondary winding coupled to the operating amplifier output for inducing a magnetic field in the secondary winding. This magnetic field is at power line frequency and is ineffective unless and until the neutral conductor of the supply system becomes shorted on the load side of the two current transformers. When this happens, there is effectively one turn of wire through both transformer cores, and the output of the amplifier is then magnetically coupled, in phase, to the amplifier input so that the amplifier breaks into high frequency oscillation. The resulting high frequency signal applied to the circuit means activates the circuit means to apply a potential to the operating element of the power supply system circuit interrupter to open the power supply to the load. Thus, it will be noted that a high frequency 1~4Z43 oscillation is present on the conductors of the power supply system when and only when the neutral conductor is grounded between the two current transformers and the load, and otherwise is not present on the conductors of the system.
The circuit means connected to the amplifier output includes a transistor receiving a triggering signal from the amplifier output and, in turn, supplying a gating signal to an SCR. The SCR, when conductive, acts like a switch between a pair of terminals connected to the operating element, such as a solenoid, of the system circuit inter-rupter, so that the solenoid is energized.
An object of the invention is to provide an improved ground fault circuit interrupter module.
Another object of the invention is to provide such a ground fault circuit interrupter module utilizing only one electrical circuit to perform both basic functions of a ground fault circuit interrupter.
A further object of the invention is to provide a ground fault circuit interrupter module in which the components are substantially reduced and a more economical and reliable circuit is provided.
Yet another object of the invention is to provide a ground fault circuit interrupter module in which there is no high frequency signal present on the conductors of an electrical supply system during normal operation of the system, that is, in the absence of a ground fault and in the absence of grounding of a neutral conductor between the ground fault circuit interrupter and the load.
For an understanding of the principles of the invention, reference is made to the following description ~4Z43 of a typical embodiment thereof as illustrated in the accompanying drawing.
Brief Description of the Drawing In the drawing, the single Figure is a schematic wiring diagram of a ground fault circuit interrupter module embodying the invention.
Description of the Preferred Embodiment Referring to the drawing, the ground fault circuit interrupter module of the invention is illustrated, solely by way of example, as associated with a two-wire power supply system having a neutral conductor _ and a line conductor L, and carrying current between a source of potential connected to terminals 1 and 2 and a load connected to terminals 3 and 4. Neutral conductor _ extends between terminals 2 and 4, and is grounded at the source as indicated by the ground connection to terminal 2. This two-wire system is illustrat-ed solely by way of example, as the ground fault circuit interrupter module of the invention is applicable equally to two-wire circuits, to single phase AC circuits and to polyphase AC circuits, having a conductor grounded at the source and usually referred to as a "neutral conductor".
In the usual manner, the power supply system is provided with a circuit breaker 5, which may be an overcurrent-responsive circuit breaker, and circuit breaker 5 has an operating element such as a solenoid 6 which, when energized, opens the circuit breaker to disconnect the load from the source.
In accordance with the invention, the first zero sequence current transformer CT-l has a secondary winding 10 wound on a core 11 embracing the conductors L and _.
1~4243 Secondary winding lO has terminals 12, one of which is con-nected by a conductor 13 directly to an input terminal of amplifier 25 and the other of which is connected by a con-ductor 14 to a junction point 15 connected by a resistor R-2 to the other input terminal of amplifier 25. Reversely poled diodes Dl and D2 are connected between conductors 13 and 14, as is also a resistor R-l. A resistor R-3 is connected in series between resistor R-2 and the output terminal of amplifier 25.
For a purpose to be described, the ground fault circuit interrupter module includes a second zero sequence current transformer CT-2, serving as a feedback transformer, having a secondary winding 20 wound on a core 21 embracing the conductors L and _, between transformer CT-l and load terminals 3, 4. Secondary winding 20 of transformer CT-2 has terminals 22, one of which is connected by a conductor 23 to a junction point 16 connected by a conductor 17 to the junction point 15 of resistors R-l and R-2. The other terminal 22 is connected through a capacitor C-l to a con-ductor 24 connected, at a junction point 26, to a conductor 27 connecting the output terminal 28 of amplifier 25 to the base of an NPN transistor Q. It will thus be noted that the output of amplifier 25 is coupled, through capacitor C-l, to the second current transformer CT-2, for a purpose to be described hereinafter.
A full wave rectifier bridge BR has its input ;
connected to terminals 31 and 32, terminal 31 being connected to conductor L through solenoid 6, and terminal 32 being connected to the load neutral. The output of full wave rectifier bridge BR is applied to conductors 33 and ~ -11-~1~4Z43 34. Bridge BR rectifies the AC voltage across terminals 31 and 32 and which, as stated, is obtained from the supply system through the solenoid 6 of the circuit breaker 5.
If no trip signal is present at amplifier 25, the DC output voltage of rectifier bridge BR is divided into plus and minus 12vDC by resistors R-7, R-8 and R-9, resistor R-7 being connected in series in conductor 33 and resistors R-8 and R-9 being connected in series between a junction point 36 and conductor 33 and a junction point 37 in conductor 34, the two resistors being connected in series at a junction point 38. Through a conductor 41 connected to junction point 36 and a conductor 42 connected to junction point 37, the plus and minus 6vDC is used to power operational ampli-fier 25. A conductor 43 connects junction point 16 to junc-tion point 38 and a capacitor C-4 is connected between this junction point and conductor 34.
A resistor R-6 connects junction point 38 to the emitter of transistor Q, and a conductor 44 connects the collector of transistor Q to the gate of a silicon con-trolled rectifier SCR whose anode is connected to conductor33 and whose cathode is connected to conductor 34. A capa-citor C-2 and a Zener diode D-3 are connected between con-ductors 33 and 34 between bridge BR and control rectifier SCR. Finally, a capacitor C-3 and a resistor R-5 are connected, in parallel with each other, between conductors 34 and 44.
Ground Fault Sensing The operation of the thus described circuit during ground fault sensing will now be described. When a ground fault occurs in the electrical supply system, a ~-~ -12-..~ .
116~4Z43 signal is developed across resistor R-l by zero sequence current transformer CT-l. This signal is then amplified by operational amplifier 25. Resistors R-2 and R-3 constitute a feedback network that controls the gain of operational amplifier 25. Diodes D-l and D-2 protect amplifier 25 by clipping any voltage spikes that may be developed due to current or voltage transients on the electrical supply system. The output of amplifier 25 is supplied to the base of transistor Q.
When the ground fault is at or above the trip level, the signal voltage applied to the base of transistor Q is sufficient to trigger transistor Q conductive on the negative half cycle of signal voltage. Capacitor C-3 is then charged through transistor Q and resistor R-6. Capa-citor C-3 and resistors R-5 and R-6 provide the proper noise immunity and response time to prevent nuisance trips.
When the charge on capacitor C-3 reaches the firing voltage of silicon controlled rectifier SCR, this rectifier conducts and acts as a switch across terminals 31 and 32 to energize the solenoid 6 in the ground fault circuit interrupter trip mechanism or circuit breaker 5.
Capacitor C-2 is provided to prevent silicon con-trolled rectifier SCR from firing prematurely from voltage transients developed on the conductors of the electrical supply system. Zener diode D-3 clips any voltage transients produced by the electrical system that are in excess of 200v, to prevent damage to silicon controlled rectifier SCR.
Grounded Neutral Sensing As stated, the output of amplifier 25 is coupled through capacitor C-1 to the secondary winding 20 of feed-11~4z4;~
back transformer CT-2. The resultant magnetic field in-duced in feedback transformer CT-2 is at power line frequency and, since it has no path to the input of amplifier 25, it has no effect. If the neutral conductor N becomes grounded at the load side, which is at terminal 4, feedback trans-former CT-2 is magnetically coupled to transformer CT-l by neutral conductor N and the ground path from terminal 2 to terminal 4, which can be viewed as one turn of wire through the transformer cores 11 and 21. This magnetic coupling establishes a regenerative feedback path from the output of amplifier 25 to the input of amplifier 25. This re-generative or positive feedback causes amplifier 25 to oscillate in a very predictable manner. In the preferred embodiment, the frequency of oscillation is 5 to 6 KHZ and the frequency can be controlled by the value of capacitor C-l and the number of turns of winding 20 on the core 21 of feedback transformer CT-2.
In actual conditions, with the neutral conductor grounded at terminal 4, there is impedance in the ground path from terminal 4 to terminal 2, caused by ground con-nectors, etc. This impedance is in series with the regenerative feedback path for amplifier 25, so that the amplitude of oscillations at the output of amplifier 25 is inversely proportional to the impedance in the ground path from terminal 2 to terminal 4 of neutral conductor N.
In the circuit embodying the invention, the circuit components are selected to trigger transistor Q conductive to charge capacitor C-3 and thus to fire the SC~ to trip the solenoid in the ground fault interrupter mechanism when the impedance from the ground path, between terminal 4 and terminal 2, is ~4Z43 4 ohms or less to pass the UL requirement of 4 ohms.
In summary, amplifier 25 oscillates when a positive feedback path from its output to its input is com-pleted by grounding of neutral wire N at the load side with resultant coupling of transformers CT-2 and CT-1 and the input of amplifier 25. The amplifier 25, which is used to perform the basic function of ground fault sensing, thus also functions as an oscillator when ground conductor or neutral N becomes grounded on the load side of the ground fault circuit interrupter. This results in a 30~ saving in electrical components and in a more reliable circuit which is especially important since, in a standard circuit breaker type ground fault circuit interrupter, there is very little space available for the electrical circuitry.
As a convenience, a test resistor R-4 is provided and is connected in the ground fault circuit interrupter in such a manner that, when a test button on the ground fault circuit interrupter is pressed, a fault is applied to the electrical supply system to test the ground fault circuit interrupter and its internal circuitry. Test button 35 is connected between the panel neutral and a terminal 46, and resistor R-4 is connected at one end to terminal 46 and at its opposite end in parallel to terminals 47 and 48.
Terminal 47 is connected to the load power and terminal 48 is connected to solenoid 6.
While a specific embodiment of the invention has been shown and described in detail to illustrate the applica-tion of the principles of the invention, it will be under-stood that the invention may be embodied otherwise without departing from such principles.
Claims (10)
1. A ground fault circuit interrupter module for use with a power supply system, having a neutral con-ductor and at least one line conductor, carrying current between a source and a load, the neutral conductor being grounded at the source and the supply system including a system circuit interrupter operable responsive to applica-tion of a potential to an operating element thereof, said ground fault circuit interrupter module comprising, in combination, a first zero sequence current transformer embracing said neutral conductor and at least one line conductor of said supply system and having a first secondary winding; an operational amplifier having an input, connected across said first secondary winding, and an output, said operational amplifier providing an amplified output potential responsive to a potential developed across said first secondary winding responsive to a ground fault in said supply system resulting in inequality of the currents carried by said neutral and line conductors; circuit means connected to said amplifier output and operable, when activated responsive to a preselected amplified output potential, to apply a potential to the operating element of said system circuit interrupter; and a second zero sequence current transformer, serving as a feedback transformer, embracing said neutral conductor and at least one line conductor of said supply system and having a second secondary winding coupled to the operational amplifier output for induction of a magnetic field in said second secondary winding; said first and second current transformers, responsive to a short in said neutral conductor on the load side of said current transformers effectively providing a single turn primary winding extending through both current transformers, magnetically coupling the output of said operational ampli-fier to its input for high frequency oscillation of said operational amplifier to provide a high frequency signal activating said circuit means.
2. A ground fault circuit interrupter module, as claimed in Claim 1, including a first resistor connected across said first secondary winding in advance of said operational amplifier, and having a potential developed thereacross responsive to a ground fault in said supply system resulting in inequality of the currents carried by said neutral and line conductors.
3. A ground fault circuit interrupter module, as claimed in Claim 1, including a feedback network connected to said operational amplifier and controlling the gain thereof.
4. A ground fault circuit interrupter module, as claimed in Claim 1, including circuitry connected between a source of DC potential and said operational amplifier and operable, when no potential is developed across said first secondary winding, to apply an operating potential to said operational amplifier.
5. A ground fault circuit interrupter module, as claimed in Claim 1, in which said circuit means includes an SCR operable, when gated conductive, to apply a potential to the operating element of said system circuit interrupter, and further includes a transistor having an input connected to the output of said operational amplifier and an output connected to the gate of said SCR, said transistor, when triggered conductive responsive to a preselected amplified output potential, gating said SCR
conductive.
conductive.
6. A ground fault circuit interrupter module, as claimed in Claim 5, in which said operating element of said system circuit interrupter is connected at one end to a line conductor of said power supply system; said circuit means including a first terminal connected to the other end of said operating element and a second terminal connected to the load neutral; and means connecting said SCR across said first and second terminals.
7. A ground fault circuit interrupter module, as claimed in Claim 6, including a full wave rectifier bridge having an input connected across said first and second terminals; first and second conductors connecting respective output terminals of said full wave rectifier bridge to said operational amplifier; said full wave rectifier bridge, when no potential is developed across said first secondary winding, applying an operational potential to said amplifier through said first and second conductors; and a voltage divider connected between said first and second conductors and dividing the voltage there-across into equal positive and negative potentials with re-spect to a junction point; said transistor having a base connected to said amplifier output and an emitter connected to said junction point.
8. A ground fault circuit interrupter module, as claimed in Claim 7, including a third conductor connecting the collector of said transistor to the gate of said SCR; and a capacitor and a resistor connected, in parallel with each other, between said third conductor and one of said first and second conductors, to provide a time constant circuit for charging of said capacitor responsive to conduction of said transistor to a potential sufficient to gate said SCR conductive; said SCR being connected between said first and second conductors.
9. A ground fault circuit interrupter module, as claimed in Claim 3, including a conductor connecting one terminal of said second secondary winding to said feedback network at the input side of said operational amplifier, and a capacitor connecting the other terminal of said second secondary winding to the output of said operational amplifier.
10. A ground fault circuit interrupter module, as claimed in Claim 1, in which said neutral conductor, responsive to a short therein on the load side of said current transformers, constitutes an electrical loop ex-tending through the cores of said current transformers and having impedance therein due to the resistance of ground connectors and the like; the amplitude of the high fre-quency oscillation at the output of said operational amplifier being inversely proportional to such impedance in such ground loop.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US48010474A | 1974-06-17 | 1974-06-17 | |
| US480,104 | 1983-03-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104243A true CA1104243A (en) | 1981-06-30 |
Family
ID=23906689
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA229,059A Expired CA1104243A (en) | 1974-06-17 | 1975-06-11 | Ground fault circuit interrupter module |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5132934A (en) |
| CA (1) | CA1104243A (en) |
| DE (1) | DE2526649B2 (en) |
| FR (1) | FR2275047A1 (en) |
| GB (1) | GB1517352A (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4929822U (en) * | 1972-06-14 | 1974-03-14 | ||
| CA1101533A (en) * | 1976-04-08 | 1981-05-19 | Raymond H. Legatti | Ground fault system with noise immunity |
| FR2453490A1 (en) * | 1979-04-06 | 1980-10-31 | Telemecanique Electrique | DEVICE FOR PROTECTING PEOPLE FROM DIRECT CONTACTS WITH ONE OF THE PHASE CONDUCTORS OF AN ELECTRICAL DISTRIBUTION NETWORK AND FOR PROTECTING AGAINST NEUTRAL CONDUCTOR ISOLATION FAULTS |
| DE3048785A1 (en) * | 1980-12-23 | 1982-07-15 | Brown, Boveri & Cie Ag, 6800 Mannheim | CIRCUIT ARRANGEMENT FOR DETECTING A FAULT CURRENT |
| DE3315190A1 (en) * | 1983-04-27 | 1984-10-31 | Felten & Guilleaume Energietechnik GmbH, 5000 Köln | Triggering system for protection circuit breakers, especially for earth-leakage current protection circuit breakers |
| GB8404766D0 (en) * | 1984-02-23 | 1984-03-28 | Delta Electrical Holdings | Earth leakage protective circuit |
| JPS61117977A (en) * | 1984-11-13 | 1986-06-05 | Sanyo Electric Co Ltd | Vertical deflecting circuit |
| DE3836275A1 (en) * | 1988-10-25 | 1990-04-26 | Asea Brown Boveri | Method for preventing an operating current from flowing through human bodies |
| DE10163016A1 (en) * | 2001-12-20 | 2003-07-10 | Siemens Ag | DI-guard |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3213321A (en) * | 1963-05-31 | 1965-10-19 | Charles F Dalziel | Miniature differential circuit breaker |
| US3506906A (en) * | 1967-12-18 | 1970-04-14 | Rucker Co | Ground fault circuit interrupter with inadvertent ground sensor |
| US3611035A (en) * | 1970-06-08 | 1971-10-05 | Rucker Co | Ground fault protective system having grounded neutral protection |
| US3772569A (en) * | 1972-09-05 | 1973-11-13 | Rucker Co | Ground fault protective system |
| US3800189A (en) * | 1972-11-28 | 1974-03-26 | Amf Inc | Apparatus for detecting a ground connection on load side of neutral conductor |
-
1975
- 1975-06-11 CA CA229,059A patent/CA1104243A/en not_active Expired
- 1975-06-14 DE DE19752526649 patent/DE2526649B2/en active Granted
- 1975-06-16 FR FR7518701A patent/FR2275047A1/en active Granted
- 1975-06-16 GB GB2558275A patent/GB1517352A/en not_active Expired
- 1975-06-17 JP JP7363975A patent/JPS5132934A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2526649B2 (en) | 1980-05-29 |
| FR2275047A1 (en) | 1976-01-09 |
| DE2526649C3 (en) | 1987-04-16 |
| JPS5132934A (en) | 1976-03-19 |
| JPS5727647B2 (en) | 1982-06-11 |
| DE2526649A1 (en) | 1976-01-02 |
| FR2275047B1 (en) | 1982-03-19 |
| GB1517352A (en) | 1978-07-12 |
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| MKEX | Expiry |