Abstract:
The present invention is a method and apparatus for protecting a power supply from ground faults. The present invention operates substantially independently of the current drawn by the load. In addition, the present invention includes a time delay circuitry for preventing false detection of ground faults when the power source is connecting to the load. In a preferred embodiment, the apparatus of the present invention includes a control relay for connecting the power supply to the load. The apparatus also preferably includes a sensor diode for detecting ground faults and triggering the control relay to disconnect the power source from the ground fault as well as the load when a ground fault is detected. The apparatus also preferably includes a time delay relay to prevent false detection of ground faults by shielding the sensor diode from any current spikes that may occur when the power source is connecting to the load. Finally, the apparatus also preferably includes a fault protection condition indicator to indicate whether the circuit breaker circuitry is working properly.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a circuit breaker circuitry for protecting a power source from ground faults. 
     BACKGROUND OF THE INVENTION 
     Many devices known in the art are useful for protecting power sources from ground faults. Ground faults occur when grounded conductors come into contact with electrical circuitry, causing an excessive current flow in that circuitry. As a result, power supply can become overloaded, and the load that the power supply is meant to power ends up receiving little or no current at all. 
     The existing devices for protecting power sources from ground faults use thermal sensors, magnetic sensors, or current sensors to detect ground faults. For these devices, it is necessary to select and calibrate their sensors to accommodate the current drawn by the load for proper operation, making the existing fault protection devices load dependent. The process of selecting and calibrating particular sensors to the current drawn by the load is time consuming and expensive. Furthermore, these sensors must be recalibrated when the current drawn by the load changes significantly or if a different load is used. 
     Accordingly, there exists a need for a ground fault detection and protection device which operates independently of the load so that no calibration of the sensor is needed and is cost-effective to construct. 
     SUMMARY 
     The present invention relates to a circuit breaker circuitry for protecting a power source from ground faults. More specifically, the circuit breaker circuitry operates independently of the load to which the power source is connected. In addition, the preferred circuit breaker circuitry includes a time delay circuitry to prevent false detection of ground faults resulting from current spikes that may occur when the power supply connects to the load. 
     Preferably, the circuit breaker circuitry includes a control relay that connects a power source to its load. The control relay is powered by the power source through a circuit breaker so that, when the circuit breaker overloads and opens, the control relay loses power and severs the connection between the power source and the load. 
     Preferably, the circuit breaker circuitry also includes a sensor diode that detects ground faults by monitoring the voltage drop across the control relay. The sensor diode connects to the power supply side of the control relay through a time delay relay and the circuit breaker and connects directly to the load side of the control relay. When a ground fault occurs in the circuit, the ground fault draws a high current that causes the potential drop across the control relay to exceed the forward voltage of the sensor diode, activating the sensor diode. As a result, the sensor diode begins to conduct current through the circuit breaker, causing the circuit breaker to overload and open. Consequently, the control relay loses power and disconnects the power source from the load as well as the ground fault. 
     After removing the ground fault and manually resetting the circuit breaker, power returns to the control relay and the connection between the power source and the load is restored. However, the time delay relay delays the connection between the sensor diode and the power supply side of the control relay. This delay functions to shield the sensor diode from any current spikes that may occur when connecting the power source to the load so that no false detection of ground faults can occur. 
     Preferably, the circuit breaker circuitry also includes a fault protection condition indicator for indicating whether the circuit breaker circuitry is working properly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a block diagram of the present invention; 
     FIG. 2 depicts a schematic of a preferred embodiment according to the present invention with power switching time delay relay; 
     FIG. 3 depicts the temporal relationship between a current spike caused by connection of power supply to its load as compared to time delay caused by time delay circuitry; 
     FIG. 4 depicts a detailed schematic of the alternate embodiment according to the present invention with ground switching time delay relay; 
     FIG. 5 depicts a schematic of the preferred embodiment according to the present invention which works with AC signals; 
     FIG. 6A depicts an AC signal from a AC generator; 
     FIG. 6B depicts the AC signal of FIG. 6A after the signal passes through the control relay; 
     FIG. 6C depicts the difference in AC signals of FIG.  6 A and FIG. 6B; 
     FIG. 6D depicts the AC signal of FIG. 6C in further detail; 
     FIG. 7 depicts a schematic of the preferred embodiment according to the present invention that protects against arcing and transient faults as well as ground faults; and 
     FIG. 8 depicts a schematic of a circuitry for powering various parts of a helicopter that uses the preferred embodiment for protection against ground faults. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention involves a circuit breaker circuitry that detects ground faults and isolates a power source from the ground fault. The disclosed circuit breaker circuitry operates independently of the load. 
     FIG. 1 illustrates the circuit breaker circuitry according to the present invention. It includes a control circuitry  100 , a sensor circuitry  400 , and a time delay circuitry  500 . Control circuitry  100  connects power source  200  to load  300 . Sensor circuitry  400  triggers control circuitry  100  to isolate power source  200  from circuit breaker  25  circuitry  10  when sensor circuitry  400  detects a ground fault. When the ground fault is removed and the control circuitry  100  is reset, control circuitry  100  reconnects power source  200  to circuit breaker circuitry  10 . While control circuitry  100  is being reset or when control circuitry  100  initially connects power source  200  to its load, a current spike may occur as a result of connecting load  300  to power source  200 . Time delay circuitry  500  operates to isolate sensor circuitry  400  from the current spike so as to prevent false ground fault detection. Control circuitry  100 , sensor circuitry  400 , and time delay circuitry  500  interact in such a way that circuit breaker circuitry  10  operates independently of load  300 , as will be illustrated by the preferred embodiment below. 
     A preferred embodiment according to the present invention is shown in FIG.  2 . In the preferred embodiment, control circuitry  100  includes a control relay  102  and a circuit breaker  104 . Although various relays and circuit breakers may be used, the preferred control relay  102  and circuit breaker  104  are the Cutler Hammer SM150D2 relay and the Klixon 7277-2-1/2 circuit breaker respectively. Control relay  102  includes a control coil  106 , a control armature  108 , resistive contacts  110 , and a time delay circuitry switch  112 . Control armature  108  connects power source  200  to load  300  when it engages resistive contacts  110 . Although biased away from resistive contacts  110 , control armature  108  engages resistive contacts  110  when control coil  106  creates a magnetic field that pulls control armature  108  to resistive contacts  110 . Similarly, time delay switch  112 , which is biased to engage an open circuit, connects to time delay circuitry power supply  508  when control coil  106 &#39;s magnetic field pulls time delay switch  112  to time delay circuitry power supply  508 , powering time delay relay  502 . Circuit breaker  104  connects power source  200  to control coil  106  to supply control coil  106  with the necessary current to create its magnetic field. Circuit breaker  104  also connects power source  200  to time delay relay  502  and sensor diode  402 . 
     Sensor circuitry  400  (see FIG. 1) includes a sensor diode  402  (see FIG. 2) that monitors the voltage drop across control relay  102  at points A and B. Although various diodes may be used, a preferred sensor diode  402  is the Motorola 1N4005 diode. Sensor diode  402  connects to point A on one terminal via sensor circuitry switch  506  and circuit breaker  104 . Sensor diode  402  connects to point B directly on the other terminal. Sensor diode  402  is biased to allow current to flow from point A to point B, but it will only allow current to flow through when the voltage drop across control relay  102  is greater than sensor diode  402 &#39;s forward voltage, typically 0.6 volts. Since resistive contacts  110  have very low resistance, the voltage drop across control relay  102  exceeds sensor diode  402 &#39;s forward voltage only when a high current is drawn from power source  200 , which occurs when there is a ground fault. When sensor diode  402  allows current to flow through it, that same current flows through circuit breaker  104 , causing circuit breaker  104  to overload and become an open circuit. 
     Also shown in FIG. 2, time delay circuitry  500  (see FIG. 1) includes a time delay relay  502 , a time delay circuitry power supply  508 , a fault protection diode  510 , and a fault protection condition indicator  514 . Although various time delay relay may be used, the preferred time delay relay  502  is the NCC L1F-00010-562 time delay relay. Time delay relay  502  includes a timing resistor  516 , a timing circuit  518 , a time delay coil  504 , and a sensor circuitry switch  506 . Timing resistor  516  and timing circuit  518  operate together to delay switching of sensor circuitry switch  506  when time delay relay  502  is activated. The resistance value of timing resistor  516  determines the length of the time delay. In the NCC L1F-00010-562 time delay relay, the period of time delay may be varied from 10 ms to 10 s. 
     Sensor circuitry switch  506  connects sensor diode  402  to circuit breaker  104  when sensor circuitry switch  506  engages sensor diode  402 . Although biased to connect to fault protection diode  510 , sensor circuitry switch  506  connects to sensor diode  402  under the force of the magnetic field created by time delay coil  504 . Time delay circuitry power supply  508 , which is connected to control relay  102 , provides time delay coil  504  with the necessary current to generate its magnetic field. Fault protection diode  510  is biased to conduct current from the power source  200  to fault protection indicator  514 . 
     In operation, the preferred embodiment of FIG. 2 functions as follows. When no ground fault is detected, control armature  108 , which is in engagement with resistive contacts  110  under the force of control coil  106 &#39;s magnetic field, connects power source  200  to load  300 . Power source  200  supplies the necessary current via circuit breaker  104  to the control coil  106  for generating the magnetic field. Control coil  106 &#39;s magnetic field also engages time delay circuit switch  112  with time delay relay power supply  508 , supplying power to time delay relay  502 . 
     Sensor diode  402  monitors the voltage drop across control relay  102  via points A and B. Sensor diode  402  is in voltage contact with point A on one terminal via sensory circuitry switch  506  and circuit breaker  104  and is directly connected to point B on the other terminal. Sensor circuitry switch  506  is held in contact with sensor diode  402  by time delay coil  504 &#39;s magnetic field. Time delay circuitry power supply  508  provides the necessary current to time delay coil  504  via time delay circuit switch  112  to generate the magnetic field. 
     The voltage drop across points A and B is caused by resistive contacts  110  of control relay  102 . Normally, load  300  does not draw enough current from power source  200  to cause enough voltage drop across points A and B to activate sensor diode  402 , which typically requires a forward voltage of 0.6 volts for activation. However, when a ground fault occurs, the ground fault draws a high quantity of current from power source  200 , causing the voltage drop across resistive contacts  110  and, consequently, the voltage drop across points A and B to exceed the forward voltage of sensor diode  402 . In alternate embodiments, sensor diode  402  can be made more sensitive to current drawn by a ground fault by using a diode with a lower forward voltage rating. Sensor diode  402  can also be made more sensitive to current drawn by a ground fault by placing a shunt resistor in series with resistive contacts  110  between points A and B so as to raise the potential drop across points A and B. As a result of exceeding it forward voltage, sensor diode  402  becomes active and begins to conduct current from power source  200  to the ground fault through circuit breaker  104 . 
     Circuit breaker  104  responds to the surge in current by opening the circuit, disconnecting power source  200  from control coil  106 . Without current from power source  200 , control coil  106  loses its magnetic field, releasing control armature  108  from resistive contacts  110 . As a result, power source  200  is isolated from the ground fault as well as most of the circuit breaker circuitry  10 . The loss of magnetic field in the control relay  102  also releases time delay circuitry switch  112  disconnecting time delay relay  502  from time delay circuitry power supply  508 . Consequently, time delay coil  504  also loses its magnetic field, disconnecting sensor circuitry switch  506  from sensor diode  402 . 
     At this point, power source  200  is isolated from the ground fault and time delay relay  502  is without power. In order to reactivate the circuit breaker circuitry  10  and allow current to again flow from power source  200  to load  300 , the ground fault needs to be removed and the circuit breaker  104  needs to be manually reset. 
     After circuit breaker  104  is manually reset, power source  200  restores current to control coil  106 , generating a magnetic field in control relay  102 . The magnetic field engages control armature  108  and time delay circuit switch  112  to resistive contacts  110  and time delay circuitry power supply  508  respectively. As a result, power source  200  is again connected to load  300  and time delay relay  502  is activated. 
     When control armature  108  connects power source  200  to load  300 , a current spike may occur which results in a temporary high potential drop across points A and B that may falsely activate sensor diode  402 . Time delay relay  502  functions to isolate sensor diode  402  from effects of the current spike by connecting sensor diode  402  to point A only after enough time has passed for the current spike to subside. The period of time delay is determined by timing resistor  516  and timing circuit  518 . FIG. 3 illustrates the current spike as a function of time in relation to the time delay created by time delay relay  502 . 
     If, during the process of resetting circuit breaker circuitry  10 , sensor circuitry switch  506  fails to engage the sensor diode  402 , fault protection diode  510  is activated, conducting current from the power source  200  to the fault protection condition indicator  514 . Fault protection condition indicator  514  then warns of improper resetting of the circuit breaker circuitry  10 . If, however, sensor circuitry switch  506  properly connects to sensor diode  402 , circuit breaker circuitry  10  resumes normal conditions, where control relay  102  connects power source  200  to the load  300  and sensor diode  402  monitors the voltage drop across points A and B. 
     In an alternate preferred embodiment illustrated in FIG. 4, time delay relay  502  can be ground switching rather than power switching, as was described above. In the ground switching embodiment, time delay circuitry power supply  508  connects to time delay relay coil  504  via time delay coil switch  510 , and ground  512  is connected to control relay  102 . 
     Operation of the alternate preferred embodiment depicted in FIG. 4 is similar to the operation of the preferred embodiment of FIG.  2 . They differ only in the following two ways. First, when circuit breaker  104  becomes an open circuit in response to a ground fault and, consequently, control coil  106  loses its magnetic field, time delay switch  112  switches from ground  512  to an open circuit rather than from the time delay circuitry power supply  508  to open circuit as is done in the power switching relay embodiment above. Second, when circuit breaker  104  is manually reset, time delay relay  502  initially draws current from power source  200  rather than from time delay circuitry power supply  508  as is done in the power switching relay embodiment above. Only after the time delay caused by timing resistor  516  and timing circuit  518  does time delay coil  504  generate a magnetic field to pull time delay coil switch  510  to engage time delay circuitry power supply  508 , powering time delay relay  502  in steady state. 
     The preferred embodiment can also be modified to operate with AC signals. One such embodiment is shown in FIG.  5 . The preferred circuitry depicted in FIG. 5 is similar to the one depicted in FIG. 2; the differences exist only in components used. Specifically, relays  114  and  520  are AC relays rather than DC relays so that no chattering occurs when handling AC signals. In addition, power source is an AC power source  204 , and the load is an AC load  304 . 
     Operationally, the AC embodiment of FIG. 5 functions similarly to the DC embodiment of FIG.  2 . The only difference is that an AC power source  204  powers control coil  106  and an AC signal activates sensor diode  402 . FIG. 6A depicts the AC signal seen at point A, which is the signal from of AC power source  204 . FIG. 6B depicts the signal seen at point B, which is the AC signal seen at point A reduced by voltage drop across resistive contacts  110 . FIG. 6C depicts the difference between the two AC signals. If a ground fault occurs, the voltage difference between points A and B becomes large enough to activate sensor diode  402 . This condition is depicted in FIG. 6D, where the positive peak of the AC signal exceeds the forward voltage of sensor diode  402 , causing the sensor diode  402  to activate and conduct current through circuit breaker  104 . Consequently, circuit breaker  104  becomes an open circuit. 
     In yet another alternate embodiment, the preferred embodiment can be modified to protect power source  200  from transient or arching faults in addition to ground faults. One such embodiment is shown in FIG.  7 . The circuitry depicted in FIG. 7 is similar to one depicted in FIG. 2; the difference is that sensor circuitry  400  (see FIG. 1) is modified to detect transient and arcing faults in addition to ground faults. The modified sensor circuitry  400  (see FIG. 1) includes a optocoupler emitting diode  404 , optocoupler detecting diode  406 , a sample and hold circuitry  408 , a sensor circuitry relay  410  and a transient protection device  416 . Sensor circuitry relay  410  includes a sensor circuitry coil  412  and a circuit breaker switch  414 . 
     Optocoupler emitting diode  404  takes the place of sensor diode  402  of the circuitry depicted in FIG.  2 . When activated, optocoupler emitting diode  404  emits a light which optocoupler detector diode  406  detects. Optocoupler detecting diode  406  connects to time delay circuitry power supply  508  on one terminal and connects to sample and hold circuitry  408  on the other terminal. Sample and hold circuitry  408  samples signals from optocoupler detecting diode  406  and outputs the sampled signal in a sustained form. Sample and hold circuitry  408 &#39;s output is connected to sensor circuitry relay  410  through sensor circuitry coil  412 . Sample circuitry relay  410  connects to circuit breaker  104  through circuit breaker switch  414 . Transient protection device  416 , which may be a capacitor, a spark gap, or a solid state device such as a metal oxide varistor, connects to load  300 . 
     In operation, when a transient or arcing fault occurs, transient protection device  416  shorts the transient or arcing fault to the ground, causing a short burst of current to flow through resistive contacts  110  of control relay  102 . This creates a temporary voltage drop across points A and B, activating optocoupler emitting diode  404  for a short period of time which is not long enough to overload circuit breaker  104 . However, optocoupler emitting diode  404  emits radiation during that short period when it is activated. Optocoupler detecting diode  406  captures this brief burst of radiation from optocoupler emitting diode  404  and sends a brief signal to sample and hold circuitry  408  in response. Sample and hold circuitry  408  samples the brief signal from optocoupler detecting diode  406  and sends a sustained signal to sensor circuit relay  410 . The sustained signal causes current to flow through sensor circuitry coil  412  resulting in creation of a magnetic field. The magnetic field pulls circuit breaker switch  414  to engaged circuit breaker  104 , grounding circuit breaker  104 . At this point, current begins to flow from power source  200  through circuit breaker  104  and circuit breaker switch  414  to ground until circuit breaker  104  overloads and opens, setting off a series of events described above in connection to the operation of the circuitry depicted in FIG. 2 that result in isolating power source  200  from further transient or arcing faults. When resetting circuit breaker  104  to reconnect power source  200  to load  300 , sample and hold circuitry  408  is also reset to output zero current to eliminate magnetic field generated by sensor circuitry coil  412 , releasing circuit breaker switch  414 . 
     Importantly, circuit breaker circuitry  10  of the disclosed embodiments operates independently of load  300 ; that is, nothing in circuit breaker circuitry  10  is required to be calibrated to a particular load  300  in order for proper operation. The reason is that, in a typical relay, resistive contacts  110  have resistance on the order of 0.0003 Ohms. In order to activate sensor diode  402 , which typically requires a forward voltage of 0.6 volts, the current drawn would have to be on the order of 2000 Amps. Even with power source  200  supplying a high voltage of about 200 volts, any mechanism that can activate sensor diode would have to have less than 0.1 Ohms resistance. Since most load  300  would have much larger resistance than 0.1 Ohms, voltage drop across points A and B caused by load  300  is negligible to sensor diode  400  such that, without having to specially calibrate a typical relay or diode, circuit breaker circuitry  10  can be connected to most any load  300  and operate properly. 
     Circuit breaker circuitry  10  as described above may be integrated into the circuit depicted in FIG. 8 which is used for powering various parts of a helicopter. Circuit breaker circuitry  10  are designated by 2K6, 2K5, 2K10, 2K16, and 2K15 in the schematic. These circuit breaker circuitries act to protect power sources from ground faults. It should be noted that circuit breaker circuitry  10  can also be employed in circuits powering various parts of an airplane or any other types of aircraft. 
     The disclosed embodiments can be modified by a person skilled in the art without deviating from the scope of the present invention. For example, time delay relay  502  may be replaced with a logic circuit that can isolate sensor diode  402  from current spikes which may occur when connecting power source  200  to load  300 . In addition, sensor diode  402  may also be replace with a logic circuit that conducts current from power source  200  to a ground fault in response to a large voltage drop across points A and B. Other modifications are also possible as by a person skilled in the art. 
     While the invention has been described in conjunction with specific embodiments, it is evident that numerous alternatives, modifications, and variations will be apparent to those skilled in the art in the light of forgoing descriptions. The scope of this invention is defined only by the following claims.