Abstract: An apparatus and method for detecting a single-phase-to-ground fault on a three-phase electrical power system and for identifying the faulted phase conductor. Each phase conductor is monitored by evaluating three phasor signals associated therewith, i.e., the zero sequence current of the electrical power system, the negative sequence voltage on the phase conductor rotated 90 electrical degrees counterclockwise (or the negative sequence current on the phase conductor), and the quadrature phase voltage for the phase conductor rotated 30 electrical degrees counterclockwise. The coincidence of these three signals for a predetermined time indicates the occurrence of a single-phase-to-ground fault on the monitored phase conductor.

Abstract: A system is provided for early detection of leakage currents through ground connections of loads such as three-phase motors connected to isolated secondary windings of supply transformers. An alarm device is energizable when leakage current is a small fraction of a predetermined value which might present a potential hazard, the point of energization being adjustable by an operator until the predetermined value is reached. Thereafter, it is adjustable only by a supervisor, after operation of a key switch. Circuitry is provided to obtain sensitive, stable and reliable operation.

Abstract: A power supply system comprising an a.c. voltage source (ACS), a load (LL) and a detachable (DCC) cable connection (CC). In order to prevent a dangerously high a.c. voltage from occurring between cable conductors (CC1, CC2) when the cable connection is loose, a safety circuit (CITSR) is provided which includes an on/off switching circuit (S1, SR1, S2, SR2). The safety circuit (CITSR) includes a parallel arrangement (CI) of at least one capacitor (C) and a direct current source (I). The parallel arrangement (CI) is part of a direct current circuit (CC2, DC2, CC1, S1, DC1, CC2) which is closed via the cable conductors (CC1, CC2), the a.c. voltage source (ACS) and the load (LL). The parallel arrangement (CI) is coupled to the on/off switching circuit (S1, SR1, S2, SR2) via a threshold circuit (TC). When a controllable a.c.

Abstract: A secondary arc extinction device is disclosed for an electrical power system which includes a bus bar, an electrical power line connected to the bus bar and a protective relay device. A first reactance is provided with each phase so that one terminal of the first reactance is connected to a respective phase of the power line. A transformer which has a primary winding connected between the second terminal of the first reactance and ground is further provided and a second reactance is connected to the secondary winding of the transformer. A control device provides for control of the second reactance in response to a signal from the protective relay.

Abstract: A three-phase power transmission line phase-to-ground fault responder wherein voltage coils of respective responder relays are energized by respective phase-related voltages and wherein current coils of such relays are serially connected across the composite voltage source comprising the three serially composite voltage source comprising the respective phase-related voltages applied in series. In one embodiment the phase-related voltages are proportional to the transmission line phase voltage itself whereas in a second embodiment, less sensitive to location of fault in relation to the instrument takeoff voltage location, the phase-related voltage is the vector sum of voltages of the other two phases.

Abstract: A monitoring system for detecting earth contact of at least one phase of a polyphase network. Each of the phases in the network is connected by a capacitive-inductive filter to a neutral node which is connected to earth. In one embodiment of the invention, the current flowing from the neutral node to earth is detected by an induction current transformer which provides a signal responsive to said earth current. The output signal of the induction current transformer is conducted through at least one low pass filter for suppressing harmonics, and rectified to produce a direct current voltage signal, the amplitude of which is proportional to the amplitude of the fundamental frequency component of said signal. A fault indicating signal is produced when the direct voltage signal exceeds a predetermined value.

Abstract: Apparatus for monitoring the fault current in the ground conductor of a polyphase AC electrical power system. When the fault current exceeds a predetermined level, the magnetic field produced causes a magnetic reed switch to close and open at twice the AC frequency. Pulse producing circuitry connected to the reed switch responds to the switch action to produce pulses at the same frequency. The pulses are counted by logic circuitry, and when a predetermined number of pulses have been counted, an output signal triggers circuitry which trips circuit breaker apparatus in the power system. The delay period between first detecting the fault current and tripping of the circuit breaker apparatus can be adjusted by changing the number of pulses to be counted by the logic circuitry before it produces an output signal.

Abstract: Methods and apparatus for detecting a single-phase-to-ground fault on a three-phase electrical power system, and for identifying a faulted phase. A single-phase-to-ground fault is correctly distinguished from other faults, including phase-to-phase-to-ground faults, even with transmission lines which utilize series capacitors, by taking into consideration the phase-to-phase voltage which is in quadrature with the voltage to ground of the monitored phase.

Abstract: There is disclosed a monitoring system for insuring the continuity and integrity of a power distribution system comprising a plurality of trailing cables, each trailing cable connected at a central station to a common power source and transmitting a power energizing signal to a load disposed at a remote location. In particular, the monitoring system comprises a transmitter and receiver for each trailing cable of the power distribution system whereby a monitoring signal is transmitted from the central station to the remote location and returned to be detected by the receiver. If there is a fault condition within the trailing cable, the receiver provides a signal indicative thereof to be applied to a circuit breaker or coupling switch actuating the coupling switch to its open position thereby disconnecting the power from the trailing cable and its load.

Abstract: A solid state load protection system whereby the current supplied to a load is monitored enabling ground fault sensing to be used. A current sensor is utilized so as to produce an output current which is proportional to the current in the electrical circuit. Attached to the current sensing function is a resistive load which converts the current produced by the current sensing function to a voltage which is also proportional to the current utilized by the motor. Attached between two resistors which comprise the resistive load is a ground fault resistor which has its remaining end connected to the neutral leg of the current transformers of the current sensing function. The ground fault sensor monitors the voltage across the resistors in the resistive load and the current in the neutral leg of the current sensors.

Abstract: An improved ground monitoring circuit for detecting the integrity and proper connection of the ground conductors in an electrical cable of an electrical power distribution system of a type that is commonly used at a surface mining site. A complete conductive loop is established between the ground conductor, or conductors, and the ground check, or pilot wire of the cable. A sensing signal at a frequency higher than the power frequency is coupled onto the ground monitoring loop. The monitoring loop includes a terminating resistor of predetermined value. The sensing signal on the ground conductor in the loop is isolated from local ground by means of an impedance element that presents a high impedance at the sensing signal but not at the power frequency. The impedance element is connected between the ground conductor of the power cable and the local ground.

Abstract: A technique for detecting high impedance faults on distribution circuits with delta connected loads is disclosed herein. This technique bases its detection on the status of the third harmonic component in each of the three-phase line currents of the distribution circuit and specifically on a predetermined minimum increase in the amplitude of any one of these components over a continuous predetermined period, whereby to discriminate between a true high impedance fault and a transient disturbance.

Abstract: An electronic control system and associated circuit breaker is taught in which the effect of in-rush current on mining equipment, for example, in regard to tripping is minimized even though a single phase fault of an equal magnitude is adequately provided for. This is done even though the same circuit breaker system and circuit breaker for both situations is utilized. A resistive capacitive series network is utilized to separate the ripple frequency from the DC value of the overload current being sensed. If the ripple component is relatively high for a given amount of overload current in the lines to be protected, then that is indicative of a single-phase fault for which circuit breaker tripping should be provided. If on the other hand the same amount of current causes a ripple component of a relatively low value, that is indicative of balanced three-phased overload which is usually indicative of in-rush or spurious transients.

Abstract: A ground monitoring circuit for detecting the existence and proper connection of the ground wires in an electrical power cable of a type commonly used at a surface mining site. A complete conductive loop is established between the ground conductor, or conductors, and the ground check, or pilot, wire of the cable. A sensing signal at a frequency higher than the power frequency is coupled onto the ground monitoring loop. The voltage and current in the loop are separately sampled. Various comparisons of the voltage and current samples are made to detect any deviation in the resistance and/or reactance characteristics of the loop. Any deviation from desired conditions in the loop produce one or more output signals that change the condition of a trip relay. The trip relay initiates action that ultimately opens circuit breakers to remove power from the cable.

Abstract: A method, and apparatus for, protecting an object, and specifically detecting ground shorts in the rotor circuit of a generator, wherein for essentially completely detecting a ground short the phase of an alternating signal is modulated to produce an alternating injection or test signal which is delivered to the object to be protected, i.e. the rotor circuit. A response signal corresponding to the injection signal and indicative of the ground short is derived from the rotor circuit. The modulated alternating signal may be at the network frequency and modulation of the phase thereon preferably encompasses continuously switching the phase of the alternating signal between two phase positions in the sense of a phase oscillation. The alternating signal is preferably in the form of an alternating voltage.

Abstract: Three voltage transformers have primary windings whose first ends are connected, respectively, to three a-c leads of a static converter and whose second ends are connected together to form an artificial neutral point. A high value resistor is connected between the neutral point and ground and a current-measuring means measures the current flowing in the resistor and generates an alarm signal in the event such current indicates a ground in the converter. Also disclosed is an arrangement including two high voltage converters connected to each other through smoothing chokes to form a frequency changer or converter in which the two converters have substantially identical circuit arrangements for detecting grounds with the circuit arrangements for detecting grounds having their outputs connected to each other.

Abstract: The present invention contemplates an improved method and control apparatus for indicating the leakage resistance in an electrical system wherein the electrical system generally includes an alternating current power source connected to a load via a conductor assembly, and wherein the control apparatus generally includes: a direct current power source connected to the electrical system for impressing a direct current control signal on the electrical system, and a portion providing an output indication of the leakage resistance in the electrical system.

Abstract: A method of, and apparatus for, protecting electrical devices, such as generators connected in parallel against ground faults or shorts, wherein when there arises a ground short at one of the parallely connected generators a ground or earth current (response signal) flows between the fault location and a ground location. The network is grounded at the ground location by means of a ground transformer and a ground resistance. In order to essentially completely detect the ground short the phase of an alternating signal is modulated to produce an alternating injection or test signal which is delivered to the network containing the parallely connected generators. A response signal corresponding to the injection signal and indicative of the ground short is derived from the electrical network.

Abstract: To detect system ground faults in a dual Y-connected output winding group polyphase alternator to direct current power supply system having direct current output circuitry isolated from a selected point of reference or ground potential, an electrical potential is applied across a selected point of reference or a ground potential and the alternator output winding group neutrals. A system ground fault completes a circuit through which this potential energizes the operating coil of an electrical relay having a pair of normally closed contacts connected in series in the alternator exciting field winding energizing circuit to effect the interruption of the alternator exciting field winding energizing circuit. To detect single phase operation faults, an auxiliary polyphase full-wave rectifier circuit is provided for each of the two alternator output winding groups.

Abstract: Separate current transformers sense the individual currents flowing in each conductor of a distribution circuit. A full wave rectifying network includes a plurality of parallel pairs of like poled, series diodes connected between a pair of buses. One corresponding side of each transformer secondary is connected to the junction between a different diode pair. A series circuit consisting of an additional pair of like poled diodes and a burden resistor is also connected between the buses. The corresponding other sides of the transformer secondaries are connected in common to the junction between the additional diode pair. A voltage is developed across the burden resistor only upon the existence of an imbalance in the currents flowing in the distribution circuit.

Abstract: The present invention relates to a security apparatus connected to the circuit of a machine in order to detect the presence of a fault therein such as a short circuit or loss of insulation between a power line and ground. The security apparatus comprises a tripping circuit having at least one transistor which is normally nonconductive and becomes conductive only when a fault current is fed to its base. The collector current activates a circuit breaking device and/or a signalling device which are continuously energized. The security apparatus operates, depending on its mode of connection, in response to a relatively small detected fault current resulting, for example, from defective insulation or from a short circuit. The security provided is irrespective of the state of the ground of the apparatus being protected.

Abstract: An electrical power system safety monitor for monitoring the continuity of an electrical power distribution system and including signal generators for generating a monitoring signal and a simulated fault signal; an impedance bridge; a three-phase coupler connected between the impedance bridge and the system's three-phase electrical conductors for impedance coupling the bridge to the conductors; a second three-phase coupler connected between the three-phase electrical conductors and the ground connector for impedance coupling the three-phase electrical conductors to the ground conductor; a reactor in series with the ground conductor for impedance isolating the ground conductor; and a signal comparator for developing a control signal whenever the relationship between the simulated fault signal and the monitoring signal indicates the occurrence of an electrical fault in the system.

Abstract: Process and apparatus for detecting electrical phase to ground or phase to phase fault currents occuring in enclosures retaining electric switch gear, switchboards, panel boards, and the like providing ionization chamber sensing of the particulate and/or ionized matter generated by the electrical fault, and generating a signal as a result of the parameter. The signal is transmitted to a means for opening the circuit and the circuit is opened to stop further current flow and damage to the devices to which it is connected. Audio or visual alarms as well as sensor status readouts may also be used with the invention.

Abstract: A ground wire monitoring circuit particularly adapted for use in connection with mining machinery that is supplied with alternating current through a flexible cable from a power source remote from the machine. The cable contains phase conductors, a ground wire and a pilot wire. The ground wire is energized through the pilot wire from a voltage derived from the alternating current power supply at the remote source. Any failure of the pilot wire or ground wire is detected by circuit means adjacent the remote power source and in the event of such failure the power circuit leading to the machine is immediately opened. The power circuit is opened in the event of failure of the ground wire even though there may be low resistance parallel ground paths between the machine frame and the remote power source.