Abstract:
A leakage current protection device, such as a ground fault circuit interrupter (GFCI), is provided that can be used in single phase or polyphase systems, with a range of input voltages from 70 to 264 volts AC, frequencies of 50 or 60 hertz, and ground fault trip currents of 6 to 30 milliamperes. A leading power factor circuit is connected to the secondary winding of the GFCI differential transformer to permit the magnetic circuit to respond to pulsating DC signals. Provision is made for continuing to provide GFCI protection in the event of an open neutral lead, with a timing circuit to prevent current flow to the ground lead until current flow in the neutral lead is completely discontinued. Various types of circuit interrupting devices, such as a circuit breaker or a power converter, may be selectively utilized.

Description:
This application is a continuation of U.S. application Ser. No. 08/381,293 filed Jan. 31, 1995 which is a continuation of U.S. application Ser. No. 07/918,664 filed Jul. 22, 1992, both are now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a leakage current protection device, such as a ground fault circuit interrupter (GFCI), and more specifically, this invention relates to a leakage current protection device adapted to function effectively over a wide range of operating conditions both domestically and internationally. 
     2. Description of the Prior Art 
     GFCIs protect against undesired current paths to ground that may create hazardous conditions. A common form of such a GFCI includes a differential amplifier having a core with opposed primary windings, one primary winding having current from the power line lead passing through it, while the other primary winding has return current from the neutral lead passing through it. These primary windings produce magnetic fluxes in the core that flow in opposite directions, known as “bucking.” If all of the power line current going to the load returns through the neutral lead, then the fluxes will be equal and will cancel out one another. However, if some of the load current is drawn off through an undesired path to ground, the bucking fluxes will not cancel out and there will be a resulting flux flow in the core. 
     A secondary winding is also located on the magnetic core. The resulting flux flow when an imbalance occurs in the currents flowing through the primary winding will induce a signal in the secondary winding. The signal induced in the secondary winding is conveyed to the control circuitry of the GFCI to open the power line lead, thus preventing the development of a dangerous condition. 
     This type of GFCI has been utilized for some time, and various modifications and improvements have been made from time to time to meet particular conditions. For example, in applicant&#39;s U.S. Pat. No. 4,598,331, an arrangement is disclosed in which the power line lead is opened if an open neutral or an open ground lead is detected. However, there are other situations in which it would be preferable to maintain GFCI protection even if the neutral lead is broken. 
     Around the world the applications for GFCI&#39;s involve a wide variety of conditions. For example, in the United States it has been decided that to insure personal protection a ground fault current in excess of 6 milliamperes cannot be permitted. However, in other countries the permissible ground fault current may be as high as 30 milliamperes. Accordingly, a GFCI for use in all international situations must be able to provide protection against ground fault currents in the range of 6-30 milliamperes. 
     Also, not all countries utilize the 60 hertz frequency of AC power that is utilized in the United States. Therefore, a GFCI for international applications must be able to provide protection for a frequency range of 50-60 hertz. Further, the GFCI, for maximum flexibility in application should be able to handle both single and polyphase input power, with either balanced or unbalanced phase loading, and input line to neutral voltages ranging from 70-264 volts (AC). All of these features should be achievable with load current capabilities of up to 100 amperes or more. 
     In some situations the magnetic circuitry of the GFCI must be able to respond to pulsating DC requirements. GFCIs in the art do not presently meet this requirement in a satisfactory manner. 
     Another problem that arises is in connection with multiple GFCIs connected to a power line. If one GFCI is being tested by simulating a ground fault circuit for that GFCI, the other GFCIs in the series may detect the test as a ground fault and be actuated in response thereto. A similar situation may occur when a GFCI having an alternate lead to ground is actuated and arcing of the contact opening the neutral lead maintains current flow through the neutral lead until after there is current flow through the alternate path to the ground lead. This is also detected by other GFCIs as a ground fault, and they may be undesirably actuated. 
     In still other situations, it may be desirable to have a choice between a circuit breaker and a power contactor to open the power line lead or leads. Prior art devices do not provide such a feature. 
     SUMMARY OF THE INVENTION 
     The present invention provides a GFCI which meets the requirement of being able to function under a wide range of operating conditions to prevent dangerous ground fault currents from occurring. The basic GFCI operation is that disclosed in connection with the prior art devices, with a number of additional features. 
     Also, it should be recognized that this description, although directed to a GFCI, may be equally applicable to other types of leakage current protection devices, such as an appliance leakage current interrupter (ALCI), an equipment leakage current interrupter (ELCI), or an immersion detection circuit interrupter (IDCI). 
     With respect to being able to continue providing GFCI protection even when a neutral lead is open, control means in the form of unidirectional current devices, such as diodes, are utilized to direct the GFCI actuating current to ground, when the neutral lead is open. In normal operation, code requirements preclude a current return path to ground. However, in the case of an open neutral, a very short pulse of current to ground may be utilized to actuate the GFCI without creating hazardous or dangerous conditions. An important aspect of the control means is that the diodes permitting current flow to ground have a higher forward voltage drop than the diodes permitting current flow to neutral. This is necessary in order to preclude current flow to ground during normal operation. 
     This approach may be utilized with either a single phase or polyphase arrangement, as illustrated in the preferred embodiments disclosed herein. In one of the preferred embodiments, provision is made to permit the GFCI to be used with either a single phase or a polyphase system without modification or adjustment of the device. 
     In order to permit the magnetic circuit of the differential transformer to respond to pulsating DC requirements, means are utilized to provide a leading power factor for the circuit. A preferred embodiment to achieve this leading power factor is to attach a suitable capacitor across a secondary winding of the differential transformer. Limitation of peak voltage on the secondary winding may be achieved by connecting a pair of clamping diodes in opposite directions across the winding in parallel with the leading power factor capacitor. 
     In order to protect other GPCIs from being actuated unnecessarily, a time delay means is utilized to prevent current flow to the ground lead until current flow has been discontinued in the neutral lead. The time delay of the time delay circuit is sufficiently long to permit the discontinuance of arcing as the neutral lead is opened, before permitting current flow to the ground lead. This time delay circuit is also useful in preventing undesired actuation of other GFCIs when a test circuit is utilized to provide a simulated ground fault to one of the GFCIs. 
     This test circuit may be formed by placing a supplemental secondary winding on the core of the differential transformer. When the test circuit is closed, such as by a manually actuated switch, current flow through the supplemental secondary winding will create a flux flow that simulates the existence of a ground fault current. Energization of the test circuit may be achieved either directly from the line lead or from a regulated output of the GFCI control circuitry. To have these GFCIs respond to various levels of permitted ground fault currents, as determined in different nations, an adjusting means may be utilized to determine the trip level of the ground fault current. At the present time, trip levels of 6, 10 and 30 milliamperes would seem to suffice, although more or less can be provided as required or desired. The adjusting means may be provided by a replaceable or variable resistor in the GFCI control circuitry. 
     By utilization of a regulator circuit, the GFCI may be adapted to work over a wide range of input voltages, such as 70 to 264 volts AC line-to-neutral. The voltage regulator may be of a cascade type with a pair of switching devices being forced to share the voltage drop over the desired range of input voltages. 
     Various circuit opening devices may be utilized such as, for example, a circuit breaker or a power contactor. Normally closed circuit breaker contacts in the power line and neutral may be actuated to open the power line and neutral leads. This is achieved by providing power to a shunt trip coil. On the other hand, if it is desired to utilize a normally energized power contactor, switching arrangements can be provided to open the line to the solenoid coil of the contactor, thus permitting the contacts to return to the normally open position. 
     In this way, a GFCI may be provided that operates effectively in a great number of different operating conditions, while also providing a variety of different features. Of course, it should be realized that not all of the features or operating condition versatility disclosed herein need be utilized in every situation. In many situations, less than all of the features and advantages may suffice. Hench, each of the claimed features may have significance apart from the others. 
    
    
     These and others objects, advantages, and features of this invention will hereinafter appear, and for purpose of illustration, but not of limitation, exemplary embodiments of the subject invention are shown in the appended drawing. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a simplified schematic circuit diagram of a first preferred embodiment of the present invention. 
     FIG. 2 is a simplified schematic circuit diagram of a second preferred embodiment of the present invention. 
     FIG. 3 is a simplified schematic circuit diagram of a third preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a GFCI with a power line lead  11 , a neutral lead  13  and a ground lead  15 . A circuit opening contact  17  is located in power line lead  11 , while a similar circuit opening contact  19  is located in the neutral lead  13 . Metal oxide varistors  21  and  22  are connected between power line lead  11  and the neutral and ground leads  13  and  15  to provide transient voltage protection. 
     The GFCI has a differential transformer  23 . Differential transformer  23  has a magnetic core  25 , with the portions  27  and  29  of leads  11  and  13 , respectively, passing through core  25  form the primary windings of the differential transformer. The primary windings  27  and  29  are connected to produce opposing or “bucking” fluxes. Accordingly, if all of the load current returns through the neutral lead, the fluxes of the primary windings will cancel one another. 
     A secondary winding  31  is also located on the transformer core  25 . If a ground current in excess of a predetermined size (e.g., 6 milliamperes) occurs, the fluxes produced by the primary windings  27  and  29  will not cancel and there will be a resulting flux flow in the core  25 . This flux flow will induce a signal in the secondary winding  31 , which is then conveyed to the GFCI control circuitry to open the power line and neutral leads. 
     Since the magnetic circuitry of the differential transformer  23  must be able to respond to certain pulsating DC requirements, a capacitor  33  is connected across the secondary winding  31 . Capacitor  33  provides a leading power factor that permits the magnetic circuit to respond to its pulsating DC requirements. In order to limit the amplitude of voltage peaks across the secondary winding  31 , clamping diodes  35  and  37  are connected in opposite directions across the secondary winding  31 , in parallel with capacitor  33 . 
     The signal induced in secondary winding  31  is conveyed to terminals  1  and  3  of an integrated circuit that linearly amplifies and provides a stable output control or trip signal under varying conditions. A phase adjusting resistor  39  and a DC blocking capacitor  41  are connected in series from secondary winding  31  to terminal  1  of the integrated circuit  43 . A damping resistor  45  is connected from one side of the secondary winding  31  to terminal  6  of the integrated circuit  43 . 
     Resistors  47  and  49  are connected in the feedback loop from terminal  7  of integrated circuit  43  to terminal  1  thereof. Resistor  47  is utilized to limit asymmetry in the potential signals of the different polarities. Resistor  49  is the feedback gain control, and it is this resistor that may be varied to adjust the ground current tripping level for the GFCI. This may be achieved by making the resistor  49  replaceable so that different magnitude resistors may be selectively utilized, or, alternatively, by using a variable resistor with selectable discrete settings. At the present time, settings for trip levels of 6 milliamperes, 10 milliamperes and 30 milliamperes are probably all that are required, but the number of discrete settings may be altered as needed or desired. Transistor  51 , resistor  53 , Zener diode  55 , resistor  57 , diode  59  and capacitor  61  provide a voltage regulator circuit that permits the GFCI to operate over a wide range of input voltages from 70 to 264 volts AC line-to-neutral. In addition, the circuit essentially forms a constant current device that reduces power dissipation. 
     Resistor  63 , connected to terminal  6  of the integrated circuit  43 , is also a part of this voltage regulator circuit. The output of the integrated circuit, at terminal  5 , is conveyed to the gate of an SCR  67  to trigger it into conduction. As SCR  67  conducts, the current flow through solenoid  65  opens the contact  17  and  19  to break the power flow to the load. Capacitor  69  connected across the SCR  67  serves to suppress DVDT (transient voltage attitude) characteristics, while capacitor  71  provides a time constant to eliminate nuisance tripping. 
     A test circuit has a test switch  73  that completes a circuit through a supplemental secondary winding  75  located on the core  25  of differential transformer  23 . A current limiting resistor  77  is located in the test circuit. Actuation of test switch  73  to complete the circuit through the supplemental secondary winding simulates the effect of a ground fault circuit so that the operation of the GFCI may be tested. 
     As may be seen, the embodiment of FIG. 1 is a single phase AC circuit. Diodes  72 ,  74 ,  76  and  79  form a rectified half-wave power supply for the GFCI control circuitry, with alternate returns to the neutral and ground leads, and with direct current connections between the neutral and ground leads. 
     The diode  79  is connected from the ground lead to the output side of the GFCI control circuitry. Diode  79  provides an alternate path to ground in the event that the neutral lead should be open. Similarly, if there is a potential above a predetermined minimum level from the neutral lead to the ground lead, or from the ground lead to the neutral lead, diodes  74  and  79  provide a current path for energizing the GFCI, even if the power line lead is open or not connected. In order to ensure that there is no current flow to ground when the neutral lead is intact (during normal operation), diode  79  is selected to have a greater forward voltage drop than diode  76 . Thus, as opposed to the automatic opening of the contacts  17  and  19  when an open neutral is detected, as in U.S. Pat. No. 4,598,331, the GFCI may still be actuated in the event of an open neutral. Also, the current flow in the ground lead for actuation of the GFCI is of sufficiently short duration that it does not create any health hazards. 
     Connected in series with diode  79  is a timing circuit formed by an SCR  81 , capacitor  83  and resistor  85 . In the event of an open neutral, DC gating for the SCR  81  is achieved through diode  79 . During opening of contact  19 , there will be some arcing during the initial opening phase. This arcing creates an impedance such that the forward voltage drop across diode  76  and the contact  19  may become greater than the forward voltage drop of diode  79 . Any current flow through diode  79  to ground would appear as a ground fault to other GFCIs upstream of this particular GFCI. The result would be to cause actuation of such a GFCI. 
     The timing circuit of SCR  81 , capacitor  83  and resistor  85  is set to introduce a time delay in the forward current flow through diode  79  that is sufficiently long to permit the arcing at contact  19  to fully clear. In this way, there will be no current flow through the diode  79  unless there is an actual ground fault condition, when energy is being supplied to the load through the power line lead  11 . This timing circuit also prevents inadvertent tripping of other GFCI circuits when the test circuit is actuated by closing switch  73 . 
     A polyphase arrangement similar to that of the embodiment of FIG. 1, with some additional features depicted, is shown in the embodiment of FIG.  2 . For ease of reference the components of FIG. 2 that are the same as those of FIG. 1 have been marked with the same numerals primed. 
     In this multi-phase embodiment, there are three power line leads  87 ,  89  and  91 . As this GFCI is arranged to be connected to either a poly-phase or single phase source, power line lead  91  would correspond to power line lead  11  in the FIG. 1 embodiment, if a single phase source were utilized. In this poly-phase circuit, a full wave power supply, rather than the half wave power supply of the FIG. 1 embodiment, is utilized. The rectified full wave power is obtained through diodes  93 ,  95 ,  97 ,  99 ,  101 ,  103 ,  105  and  107 . In function, these diodes correspond to the diodes  72 ,  74  and  76  of the FIG. 1 embodiment. As an example, it may be seen that on the positive half cycles for the power on lead  87 , the path is through diode  93  to the GFCI control circuitry and back to neutral through diode  107 . On the negative half cycles, the path of current flow is through diode  95  to the GFCI control circuitry and back to neutral through diode  105 . Each of the other power line lead routes are through the associated diode pairs  97 ,  99  and  101 ,  103 . 
     Diodes  108  and  110  provide an alternate path to ground corresponding to the function of diode  79  in the FIG. 1 embodiment. Accordingly, the GFCI will still function in the presence of an open neutral lead  15 ′. A cascade voltage regulator circuit is provided by breakdown devices  113  and  115  (shown here as metal oxide semiconductor field effect transistors—NOS FET&#39;s—although any suitable device could be used); Zener diodes  117 ,  119  and  121 ; resistors  123 ,  125 ,  127  and  63 ′; and capacitor  61 ′. With this arrangement, the MOS FET  113  regulates the voltage from approximately 50 volts to approximately one half of the maximum DC voltage of 650 volts. The MOS FET  115  continues the regulation up to the maximum voltage. 
     As this embodiment utilizes a modular approach to permit utilization of different circuit interrupters, as well as other options, such as a remote module for testing and resetting, lines  87 ,  89 ,  91 ,  13 ′ and  15 ′ are shown ending in a terminal board  129 . Similarly, various connections from the GFCI control circuitry are made to the terminal board  131 . Alternative circuit interrupters are shown as a circuit breaker  133  or a power contactor  135 . If the circuit breaker option is utilized, the power line leads  87 ,  89  and  91  would be connected as shown in the device  133 , while the normally closed contacts  137 ,  139  and  141  would be controlled by the shunt trip coil  143 . It may be seen that the solenoid  65 ′, which in the FIG. 1 embodiment would control the opening of the normally closed switches  17  and  19 , controls contacts  145  and  147 , as well as contact  149  for the shunt trip coil  143 . Upon energization of the solenoid  65 ′, contact  149  would be closed so that shunt trip coil  143  can be energized through the terminals  5  and  7  of the terminal board  131 . Energization of shunt trip coil  143  opens the contacts  137 ,  139  and  141  (as well as the neutral lead contact  19 ′ not shown). 
     If the power contactor  135  is connected to terminal board  139  solenoid coil  150  is energized from power line lead  91  through the normally closed contact  147 . In the event of energization of solenoid  65 ′, contact  147  is opened to de-energize the coil  150 . De-energization of the solenoid coil  150  permit the normally closed contacts  151 ,  153  and  155  in leads  87 ,  89  and  91 , respectively, to return to the normally open position. 
     A remote module  157  may be connected to the terminal board  131 , as shown. Various different features could be included as desired. Shown here are a light emitting diode (LED)  159  that would be energized upon production of a GFCI trip signal to give a visual indication of tripping. Another feature included in this remote module  157  is a reset button for resetting the GFCI after actuation by the presence of a ground fault current. The final feature shown here is the placing of test switch  73 ′ in the remote module, rather than having it in the GFCI itself. 
     FIG. 3 is a simplified embodiment of the GFCI of FIG. 1, in which the open neutral line protection feature has been eliminated. For some applications, this simplified version without open neutral protection will suffice to provide the necessary protection at a significantly lower cost. 
     For ease of reference, the components of the circuit of the FIG. 3 embodiment are identified by utilizing the same numerals as in the FIG. 1 embodiment, but with a double prime. It may be seen that this embodiment utilizes a full wave rectifier power supply with diodes  163 ,  165 ,  167  and  169 , rather than the half-wave rectified power supply of the FIG. 1 embodiment. Other than that, the basic operation of this circuit is substantially the same as that of the FIG. 1 embodiment, but without features such as the open neutral lead protection, the associated timing circuit and the particular voltage regulator of the FIG. 1 embodiment. 
     It should be understood that various modifications, changes and variations may be made in the arrangement, operation and details of construction of the elements disclosed herein without departing from the spirit and scope of this invention.