Abstract: A ground fault detector employs a current feedback loop which makes use of a differential current sensing configuration to in essence increase the gain of the current feedback signal, thereby lowering the detector trip level when ground fault currents are present. In a preferred embodiment, ground faults are detected in a circuit having an AC-to-AC converter and a useful load by positioning a differential sensing configuration in the DC link of the AC-to-AC converter.

Abstract: In the overcurrent tripping unit for a circuit breaker, current transformers are provided for detecting currents flowing through respective phases of a main circuit, the secondary outputs of the current transformers are star connected, the primary outputs are polyphase full-wave rectified, the voltage drop based on the rectified positive/negative direct output of each phase is directed by first and second resistances to be applied to the control means, and a ground fault current is detected based on the secondary outputs of the current transformers to be applied to the control means.

Abstract: An electrical apparatus for magnetothermal and differential protection, of the type comprising a device for sensing differential currents associated with a magnetothermal protection switch, comprises a differential current sensor connected to an input of a controlled gain signal amplifier, in turn connected to a plurality of light indicators arranged to go on progressively in dependence on the sensor. The apparatus provides a quantitative and qualitative measurement of the stray current.

Abstract: An apparatus for detecting an accident of electric wire lines a single light emitting element, a plurality of optical sensor heads arranged respectively to the lines to be observed, for modulating a light supplied form the light emitting element through a light transmission line in response to electric variations in the line, and a single light receiving element for receiving the synthetic light. Therefore, since the light transmission line is used instead of electric wires, the apparatus has good insulation characteristics and thus the apparatus is not affected by an electromagnetic induction from the electric wire lines. Moreover, since use is made of single light emitting element and single light receiving element, high S/N ratio is realized.

Abstract: High resistance ground faults on a transmission line of an electrical power transmission network are detected with the aid of a device comprising a travelling wave model of the line located in measuring stations (P, Q) at either end of the line, which permits the voltage distribution along the line, seen both from P and from Q, to be obtained. A voltage .DELTA.U.sub.Qp is formed as the difference between a votlage in station P, calculated in the travelling wave model in Q, and the corresponding voltage one period earlier. A voltage .DELTA.U.sub.Pp is formed as the difference between a voltage calculated in the travelling wave model at P and the corresponding voltage one period earlier. The corresponding voltage differences .DELTA.U.sub.Pq and .DELTA.U.sub.Qq are calculated for station Q. The voltage difference .DELTA.P is then formed as the difference between .DELTA.U.sub.Qp and .DELTA.U.sub.Pp, and the corresponding .DELTA.Q is formed as the difference between .DELTA.U.sub.Pq and .DELTA.U.sub.Qq.

Abstract: A method for location of a fault on a transmission line in a network for distribution and transmission of electric power uses a travelling wave model of the transmission line positioned in measuring stations (P, Q) at either end of the transmission line, to obtain the voltage distribution along the transmission line, seen from both station P and station Q. A voltage .DELTA.U.sub.Qp is generated as the difference between the voltage in station P, calculated in the travelling wave model in station Q, and the corresponding voltage one period/half period earlier. A voltage .DELTA.U.sub.Pp is generated as the difference between the voltage, calculated in the travelling wave model in station P, and the corresponding voltage one period/half period earlier. The corresponding voltage differences .DELTA.U.sub.Pp and .DELTA.U.sub.Qq are calculated for station Q. The voltage difference .DELTA.P is then generated as the difference between .DELTA.U.sub.Qp and .DELTA.U.sub.Pp and the corresponding voltage difference .DELTA.

Abstract: An electric shock protector apparatus includes a circuit for detecting an electric shock current signal which has a frequency substantially higher than the line frequency of a power distribution system. The current of the power system is passed through a filter which eliminates the power supply frequency and produces a signal indicative of an electric shock current. The electric shock current signal is passed to positive and negative half-cycle operation signal circuits which transmit signals to a logic gate for operating a relay to disconnect the power source from the line conductors.

Abstract: A device for continuous supervision of the attenuation (d), dissymmetry (k) and mismatch (v) system parameters in impedance earthed power systems. The parameters are calculated from the circle diagram uEN=f(v), i.e., the relative neutral point voltage as a function of the mismatch. The circle diagram is in turn defined by two measuring points for uEN which are derived by connection or disconnection of a reactance complement between system neutral and earth. The invention improves known devices for control of the condition of impedance-earthed power systems. Then the continuous supervision of the mentioned power parameters enables a better detecting of high-resistive earth connections.The invention can be implemented in any computer system capable of providing the necessary measurement, control and calculating functions.

Abstract: A residual current detector capable of detecting an earth leakage current, e.g. for use in a circuit breaker, includes a toroidal core through which passes the live and neutral wires of an electrical installation, to form the primary windings of a differential transformer. At least one secondary winding is wound on to the core and driven with an alternating voltage by a generator. A phase sensitive detector identifies a residual current by detecting the change in phase of the voltage across the at least one secondary winding. The secondary winding may comprise two coils, a first coil driven by the generator and a second coil adapted to pick up an induced voltage from the toroidal core. The phase sensitive detector, which may form part of a phase locked loop, compares the phase of the signal from the second coil with that of the alternating voltage of the generator.

Abstract: A self-contained test feature for ground fault protection systems in circuit breakers. The ground fault protection system includes a sensing transformer having a primary winding that sums the currents through the phase current transformers. Upon the occurrence of an actual ground fault, the sensing transformer will transmit a signal to cause the breaker to trip. The test feature includes a test transformer having its secondary winding electrically connected in parallel with the primary winding of the sensing transformer. The current path between the test transformer secondary winding and sensing transformer primary winding is completed only upon the activation of a test switch. The primary winding of the test transformer is hooked to an external current source to provide the necessary current to simulate the ground fault.

Abstract: A ground-fault circuit interrupter is provided with an additional current-sensing element that responds to a net value of current through the power wires in an ac circuit. The winding may be wound on a ferromagnetic core of its own or it may be placed as a separate winding on a core that is used to sense imbalance in a GFCI. In the latter case the extra winding must be insulated electrically from the main sense winding. The additional coil is connected to a rectifying diode and a capacitor, so that an imbalance of current in the power wires charges the capacitor. The voltage thus developed across the capacitor is used to operate the tripping mechanism of the ground-fault circuit interrupter. The fault-powered signal thus attained in the added winding will enable the GFCI to operate despite the existence of heavy fault currents that reduce the operating voltage to the rest of the GFCI to a level that would otherwise prevent its operation.

Abstract: A current sensor for use in a three phase ac system for producing a signal indicative of the average value of the sum of the squares of the ac current and of the phase imbalance between the three phases using two current transducers and an associated method.

Abstract: The electronics of a residual differential device is powered by several sources derived from the electrical system (14, 16, 18). A supply anomaly detector (36) signals the failure of one of the supply sources caused, for example, by a break in one of the wires (14, 16, 18). The anomaly detector signals the break in this wire and sends a tripping order to the protection circuit breaker (10). Voltage in the phase conductors is monitored, and an alarm device is energized, for example, if one of the phase conductors is open.

Abstract: Differential current static trip circuits interconnected with upstream and downstream current sensing transformers in a protected system provide automatic coordination of the downstream static trip circuit breakers. The differential current transformer associated with the breakers vectorially sense the difference between the upstream breaker currents and the sum of the downstream breaker currents. The output is processed within the trip circuits for I.sup.2 t and fixed time band delays to insure that the downstream breakers clear the fault.

Abstract: A current monitoring circuit of a ground fault detector which receives its input from the secondary winding of an annular core transformer through which extends the current carrying leads being monitored. A resistor and capacitor are connected in series between the secondary winding and an AC amplifier to form an RLC band pass filter to minimize the circuits sensitivity to noise outside of the band of frequencies of interest. The sensitivity of the circuit to temperature changes due to fluctuations of the inductance is reduced by choosing an inductance value sufficiently high to ensure that it is not reduced to below a critical level at which sensitivity is effected.

Abstract: An electrical apparatus that is adapted to be connected between a source of alternating current supply and a load is designed to achieve automatic correction of hot and neutral lines at the output should the supply lines at the input be reversed, and is arranged to be utilized in connection with a ground wire. To achieve the result, a change-over switch is provided in each of the phase wires and a logic circuit is provided for operating the switch, the logic circuit being arranged to detect a voltage change between one of the phase wires and the ground wire so that when a voltage change is detected, the logic circuit will energize the switch to reverse the connection of the supply lines to the load. Two types of change-over switches are disclosed, one in the form of a relay and the other in the form of solid state triacs.

Abstract: Apparatus is provided for detecting the presence of a high impedance arcing fault on an electrical circuit, particularly a high voltage power line. Detection of a high impedance fault is realized by monitoring the high frequency components of the alternating current in the circuit, and evaluating the high frequency components of each cycle of the alternating current using a microcomputer operating in accordance with a program of instructions, to determine the occurrence of a significant increase in magnitude of the high frequency components, and then to determine whether the increase exists for a prescribed period of time and follows a prescribed pattern. The high frequency components are monitored using a current-to-voltage transducer coupled to the electrical circuit, bandpass filters coupled to the transducer, and an analog-to-digital converter providing digitized samples of the filtered transducer output voltage signal.

Abstract: A low voltage circuit breaker with a current sensing unit having a magnetic circuit with three branches, the secondary winding being mounted on the intermediate branch and the primary winding being formed by a conductor selectively passing through one or two of the openings provided between the secondary winding and the outer branches. The circuit breaker comprises an instantaneous electromagnetic trip mechanism and a static long time and short time delay trip unit, the latter unit being governed by a signal attenuated by a rating selection device.

Abstract: A protection device has first and second differential transformers each with a toroidal magnetic core through which pass the neutral and phase conductors of an alternating current distribution network, and a secondary winding. The secondary winding of the first transformer is coupled to the input of an amplifier followed by a rectifier, a threshold comparator and a control device adapted to release a circuit-breaker. The secondary winding of the second transformer is coupled to the output of the amplifier. The improvement is constituted by an auxiliary amplifier inserted between the output of the first amplifier and the terminals of the secondary winding of the second differential transformer.

Abstract: The invention concerns a solid state trip unit having long time delay, short time delay and ground fault trip circuits. It comprises a metering resistor (40) electrically connected in a series circuit (42) including additionally a power supply (44) for the trip circuits LR, CR and H, and a trip coil (22). A switch (52) connected in parallel with the coil (22) which may be either in an ON-state to shunt the coil (20), or in an OFF-state after a trip signal is delivered from one of the trip circuits, so as to cause an increase of the impedance of the series circuit (42) and the excitation of the trip coil (22). The trip unit can be applied to low-voltage circuit breakers.

Abstract: A motor protection device is provided that monitors motor currents and motor temperatures and provides protective functions whose characteristics are based on field settable data and motor operating conditions. The protective functions provided are overtemperature, overload, instantaneous overcurrent, ground fault, phase unbalance, and phase reversal. Field settable data is entered by means of a keyboard and consists of motor trip points for the protective functions, and motor and system parameters.

Abstract: An electric current detector circuit for sensing a leakage of electrical current in a particular system and then providing a signal to control the operation of the system. The circuit is also adapted to receive a signal upon the occurrence of fire, in and around the system attached thereto, and then provide a signal to further control the operation of the system.

Abstract: A method and apparatus for monitoring conductor currents for a fault current which changes the magnetic bias of a magnetic circuit in which the magnetization of the magnetic core is alternatingly reversed by sequences of magnetizing pulses and a determination made of the number of pulses up to which the pulse amplitude exceeds predetermined voltage reference value, with the change of this number of pulses used to derive an output signal.

Abstract: For optimizing the manufacturing cost of the magnetic torus of a differential transformer, the volume is reduced in that the free volume of the central aperture is fully filled: only one turn for each primary conductor, the section of which is reduced, the adjacent parts of larger section forming heat sinks, the central part of the conductors having the form of circular sectors. An important saving is secured on the most expensive part of the relay.

Abstract: A ground fault detecting circuit interrupter is taught. A ground fault is sensed by utilizing a summing transformer interconnected with the three-phase current transformers for normal fault detection. The turns ratio between the primary winding and the secondary winding of the summing transformer is kept purposely high so that the excitation current for the current transformers is made relatively small when compared to the normal secondary current of the current transformers. This has the effect of improving the accuracy of the normal fault detecting portion of the circuit breaker. The relatively high turns ratio between the primary and second of the summing transformer usually supplies insufficient current to directly actuate the trip coil of the circuit interrupter on the occurrence of a ground fault. However, this latter current is utilized to charge a capacitive storage element after a ground fault has been sensed.

Abstract: A unique ground fault circuit interrupting (GFCI) device is utilized to control either an industrial circuit breaker or a contactor in protecting a large power distribution circuit against ground faults. The GFCI device is equipped with plural sets of switch contacts which are actuated incident with tripping of the GFCI device. The particular switch contacts are selected to control energization of an actuator adapted to the circuit breaker or contactor, depending on the actuator type. A ground fault sensor responds to ground faults on the distribution circuit by injecting a current imbalancing signal into the GFCI device, causing it to trip. The consequent switch contact actuation initiates operation of the circuit breaker or contactor to interrupt the distribution circuit.

Abstract: A ground fault circuit interrupting (GFCI) device is utilized to control either an industrial circuit breaker or a contactor in protecting a large power distribution circuit against ground faults. The GFCI device is equipped with switch contacts which are actuated incident with tripping of the GFCI device. The switch contacts control energization of an actuator adapted to the circuit breaker or contactor. A ground fault sensor responds to ground faults on the distribution circuit by injecting a current imbalancing signal into the GFCI device, causing it to trip. The consequent switch contact actuation initiates operation of the circuit breaker or contactor to interrupt the distribution circuit.

Abstract: A three-phase electrical transformer utilizes a conductor independent of the transformer windings for sensing zero sequence current upon the occurrence of a ground fault. A current transformer coupled with the independent conductor provides polarization to protective relay devices. One embodiment utilizes the transformer internal tank shield in combination with the current transformer for providing zero sequence current.

Abstract: In the absence of a ground fault, a triac completes an AC energization circuit for a relay whose contacts then close to provide load circuit continuity. Gate drive for the first triac is obtained from a secondary winding of a transformer whose primary is driven by an oscillator for the purpose of producing a differential transformer unbalancing current signal in the event of a desensitizing ground fault on the load circuit neutral conductor. When the differential transformer senses a ground fault, the oscillator is disabled, and the resulting loss of gate drive renders the triac non-conductive to drop out the relay.

Abstract: A sensor develops a ground fault signal in response to a ground fault on a power distribution circuit, which signal is processed by a signal processor of a conventional, residential ground fault circuit interrupter (GFCI) pursuant to developing a trip signal resulting in energization of a light emitting device. The light signal emitted by this device triggers a solid state, light activated switch to complete an energization circuit for a solenoid acting to shunt trip a power circuit breaker operating to interrupt the distribution circuit.

Abstract: A circuit interrupter is secured to a mounting pan together with an insulative block in turn mounting a transverse array of fuse load terminals in individual, spaced alignment with associated interrupter load terminals. A differential current transformer is mounted to the pan with its window located in the space between the interrupter and fuse load terminals. Plural fuses extend through the transformer window with their opposed end terminals in respective electrical connection with associated interrupter and fuse load terminals, whereby the transformer monitors the vectorial sum of the phase currents flowing through the fuses.

Abstract: A ground fault and fire detector system for an A.C. electrical power distribution apparatus including a multi-pole circuit interrupter to disconnect a poly-phase electrical power supply from a load. A single-pole circuit device is operatively connected to the circuit interrupter for controlling its operation. Ground fault sensing circuitry is operatively positioned with respect to at least one wire for initiating a fault current. The single-pole circuit device is responsive to the fault current for activating the circuit interrupter to disconnect the power supply from the load.

Abstract: A circuit for detecting line-to-ground and neutral-to-ground faults and in response thereto interrupting the line conductor. Included in the circuit is a magnetic core about which the neutral conductor and line conductor are wound to produce a zero net magnetomotive force in the core in the absence of a line fault and a non-zero net magnetomotive force in the presence of a line fault. A secondary winding wound on the core has at least one diode or thermistor connected thereacross. The diode or thermistor has a dynamic impedance, which is reflected back to the neutral winding, which decreases when current flows through the diode or temperature rises in the thermistor in response to an induced voltage in the secondary winding caused by non-zero net magnetomotive force in the core produced by a current imbalance in the line and neutral conductors due to a line fault.

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: Ground fault protective systems are disclosed in which fault signals are generated in response to differential currents carried by electrical supply lines. A circuit breaker interrupts power on the supply lines when the fault signals exceed a given magnitude and duration. Downstream reactances to ground from one or more supply lines give rise to spurious fault signals which do not characterize true ground fault conditions. These spurious fault signals are cancelled prior to detection by means of neutralizing auxiliary circuits. The resulting fault signals exhibit a high signal-to-noise ratio.

Abstract: A fault current protection switch detects fault currents from conductors of a supply means to ground. The system uses at least one difference transformer connected to the conductors of the supply mains. An oscillation generator circuit is connected to the difference transformer through feedback windings. The oscillation generator circuit checks the magnetization of a core of the difference transformer, and, in the event of a change in the transforming properties of the core due to "mis" magnetization caused by a fault current, the oscillation generator circuit triggers a control and switching member connected in the supply mains to disconnect the same.

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: A circuit breaker electronic trip unit is equipped with a plurality of current transformers for sensing overcurrent and ground fault conditions in a distribution circuit. A ground fault signal voltage is applied to a differential amplifier together with an adjusted voltage establishing a desired ground fault signal pick-up level. The differential amplifier controls a variable duty cycle switch to establish charging versus discharging rates for a timing capacitor in accordance with the ground fault signal amplitude. When the voltage across the capacitor exceeds a predetermined threshold, a thyristor is triggered to draw a safe level of energizing current through a trip coil. Secondary open circuited protection is provided for any of the current transformers disposed externally of the circuit breaker.

Abstract: Ground fault detection apparatus improved to include detector circuiry for providing an output current responsive to imbalance in the alternating currents flowing to and from a load only if it be of sustained character and of sufficient amplitude. The detector circuitry discriminates against responses to imbalance current primarily consisting of infrequent short-duration high-amplitude spikes characteristic of transient disturbances in favor of responses primarily consisting of the sustained, relatively long-duration rectified sinusoidal waveforms characteristic of ground fault conditions, even where the average level of the transient disturbance component of the imbalance current is equal to or in excess of the average level of ground fault component.

Abstract: Various embodiments of a ground fault protection system are disclosed for protecting a multiple source distribution network consisting of at least two sources having their neutral points interconnected by main neutral and tie neutral bus and also typically by separate ground connections. The system operates to selectively trip a ground fault circuit interrupter by distinguishing between normal neutral loading regardless of the routes taken by neutral currents in returning to the sources and a ground fault regardless of the routes taken by ground fault currents in returning to the source feeding the fault.

Abstract: A field test set for static trip circuit breakers is electrically connected to the static trip unit and to the circuit breaker trip coil and phase current sensor transformers. The test set, powered from a low voltage source, is equipped to shunt feed the trip unit power supply, bringing the trip unit up to power preparatory to the injection of selected levels of overcurrent and ground fault simulating test signal current for verifying the time-current characteristics and current pickup calibrations of the various trip functions of the trip unit. A lockout circuit automatically terminates a test signal current whose magnitude and duration represents potential harm to the trip unit. The test set is also equipped to test the trip coil energization level developed by the trip unit and also the continuity of the breaker current transformers.

Abstract: A circuit for detecting arcing in a vacuum contactor in a polyphase system, caused by development of an air leak. A current transformer and sensing means, which may be independent of or which may work in conjunction with a conventional ground fault relay, senses the unbalanced leakage current and activates warning and protection circuits so as to prevent damage to the rest of the system. The protection system is activated or switched into a higher sensitivity mode when the vacuum contactor is supposed to be open so as to detect relatively small leakage currents. When the vacuum contactor is supposed to be closed, the system is disabled or is operated in a lower sensitivity mode so as to detect ground faults, but so as not to be tripped by normal surges and transients during operation of the system.

Abstract: A self-powered self-contained ground fault protective device including a current monitor, an electronic circuit for amplifying the output of the current monitor, and a relay connected to the amplifying circuit and adapted to operate whenever ground fault current through the current monitor rises above a predetermined level. The current monitor, amplifying circuit, and relay are all supported and enclosed by a molded insulating housing.

Abstract: Apparatus for protecting power distribution networks from damage due to ground faults comprises a plurality of groups of zero sequence current monitors, each group surrounding all branches of the network which enter a zone of protection. Each group is electrically connected to produce an output signal corresponding to the vector sum of differential currents flowing into and out of the zone. Each group is connected to a ground fault relay which will trip when the vector sum of the differential currents entering or leaving a zone is above a predetermined level.

Abstract: Three-phase power equipment while still connected to the three-phase line has the insulation qualities of its various phases tested. All ground connections of said equipment except one are disconnected and that one is reconnected through ground current sensing means. Coupling units which may be capacitors are respectively connected between each of the three phases of the power line to which the power equipment is connected and ground. Each coupler unit is a reference phase current sensing means. Adjustable phase and magnitude adjustor means are used to couple the respective phase current sensing means to a summing means so that they are adding. The ground current sensing means is similarly coupled to the same summing means but opposed to phase current effects. A null detector coupled to the summing unit detects when balance occurs.

Abstract: A conventional residential ground fault circuit interrupting (GFCI) device is utilized to control a traditional circuit interrupter in protecting a large power distribution circuit against ground faults. The GFCI device is connected in an energization circuit for a solenoid operable to open the interrupter contacts. A sensor responds to ground faults on the distribution circuit by impressing the current signal on one side of the energization circuit, thus creating a current imbalance effective to trip the GFCI device. Interruption of the energization circuit causes the solenoid to initiate opening of the interrupter contacts. In an alternative embodiment, the GFCI device is adapted to initiate opening of the interrupter contacts upon degradation of ground circuit continuity.

Abstract: Self-powered apparatus for indicating the existence of a fault in any of a plurality of conductors in an multiconductor electrical distribution system. The plurality of conductors pass through the window of a closed loop core structure current transformer, and the current transformer has a power output and a signal output. The power output is connected to, and drives, fault indicating means and starting means. The starting means initiate operation of control signal translation means which are connected to the current transformer signal output. Also included are transmission means connected to the control signal translation means and to prevention means incorporated within the indicating means, and the transmission means transmit the control signal from the signal translation means to the prevention means. The indicating means are responsive to operation of the prevention means, such that only when the control signal is transmitted to the prevention means will the indicating means be allowed to operate.

Abstract: A conventional residential ground fault circuit interrupting (GFCI) device is utilized to control a traditional circuit interrupter in protecting a large power distribution circuit against ground faults. The GFCI device is connected in an energization circuit for a solenoid operable to open the interrupter contacts. A sensor responds to ground faults on the distribution circuit by impressing the current signal on one side of the energization circuit, thus creating a current imbalance effective to trip the GFCI device. Interruption of the energization circuit causes the solenoid to initiate opening of the interrupter contacts. In an alternative embodiment, the GFCI device is adapted to initiate opening of the interrupter contacts upon degradation of ground circuit continuity.

Abstract: Ground to neutral fault protection employing dormant oscillators which are only energized and function on the .[.occurance.]. .Iadd.occurrence .Iaddend.of such type of a ground fault. Combined with known types of two and three wire single phase AC ground fault interrupters to provide circuit interruption regardless of which wire is faulted to ground.

Abstract: A ground fault and fire detector system for an A.C. electrical power distribution apparatus including a multi-pole circuit interrupter to disconnect a poly-phase electrical power supply from a load. A single-pole circuit device is operatively connected to the circuit interrupter for controlling its operation. Ground fault sensing circuitry is operatively positioned with respect to at least one wire for initiating a fault current. The single-pole circuit device is responsive to the fault current for activating the circuit interrupter to disconnect the power supply from the load.