Showing papers on "Fault current limiter published in 1977"

Overcurrent and ground fault responsive trip unit for circuit breakers

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.

Saturable reactor limiter for current

Abstract: A saturable reactor device for limiting alternating and direct current in an external electric circuit. In one form, the required magneto-motive force (mmf) bias for the saturable reactor is provided by a controllable flux bias element in order to minimize the required bias power. A current sensor provides a control signal representative of the alternating or direct current passing between the source and the load. This signal is used to control the magnitude of the bias so that the mmf provided by the bias element is a function of the current driving the load, permitting a current limiting threshold at a predetermined percentage of the current applied to the load. In an alternate form, the device may be adapted to limit bipolar current in the external circuit. In this form, the device includes an input circuit and an associated direct current saturable reactor limiter. In response to direct current of either positive or negative polarity passing through the external circuit, unidirectional current is driven through the input coil of the direct current limiter. The magnitude of the unidirectional current passing through the input coil is proportional to the magnitude of the current provided by the source. When the unidirectional current exceeds a predetermined threshold, the direct current limiter effectively provides a relatively high current-limiting impedance between the source and load of the external electric circuit. When the unidirectional current is below that threshold, the direct current limiter has minimal effect on the external electric circuit.

Fault current limiter

Abstract: A current limiting network is connected in a power line between an AC power supply and a load, and has a pair of series connected resonant branch circuits, each of which include a capacitance and an inductance tuned to the power supply frequency. Under normal operation virtually no impedance is offered by the network. Each branch circuit has a circuit node between the capacitor and inductor contained therein. A switch, having a resistance in series therewith, is connected between the circuit nodes in the branch circuits. The branch circuits are connected in parallel, and a resistance is connected in parallel with the branch circuits. The switch is responsive to a fault current in the power system and when actuated, detunes the series resonant branch circuits to thereby present a high impedance to the power line. The parallel resistance reduces the level of any transient surges and the time of any oscillation appearing on the capacitors when the switch is actuated by a fault current. Another embodiment selectively suppresses transients and reduces oscillation on the branch circuit capacitors.

High voltage d-c vacuum interrupter device with magnetic control of interrupter impedance with movable contact

Abstract: A circuit interrupter which can be used as a high voltage d-c breaker or fault current limiter transfer switch or the like contains a pair of cooperable contacts disposed in an evacuated container. One of the contacts also serves as the cathode of a magnetically modulated vacuum arc discharge device. This cathode is spaced from an anode disposed in the wall of the evacuated housing. The anode is surrounded by a winding which is capable of producing a magnetic field which can increase the impedance of the arc plasma between the cathode and anode in order to decrease the arc current and extinguish the arc. The cooperable contacts within the interrupter serve to carry load current and also serve to create the inital arc which is transferred between the anode and cathode structures.

Programmable fault detecting relay for a transformer

Abstract: A programmable fault detecting relay for fluid cooled electrical apparatus utilizes a pressure transducer to provide an electrical input to an electronic discriminating circuit. The circuit discriminates between through fault pressures and internal fault pressures and provides an output upon the occurrence of an internal pressure fault.

Power system short circuit planning for superconducting power transmission

Abstract: Short circuit capacity of large power generation facilities is limited by the internal reactance of the generator and the impedance of connecting bus work and transformers. In the event of a fault on a generator get away circuit, d-c offset could double the short circuit current on the cable for a period of from 3 to 5 cycles after the fault initiation. High performance circuit breakers (PCBs) can shorten this fault duty time to 1 cycle (17 msec). If a superconducting cable is arbitrarily designed for 10X rated current fault withstand, its capital and operating cost may be dramatically increased. What can be done? First, a careful look at generator step up transformers and circuit breaker capability shows a marked tendency for this equipment to have very high costs if the generator bus connection scheme is planned to allow very large fault currents. However, the power system designer can set up the circuit arrangement so that massive fault currents are avoided. Second, the development of fault current limiting devices promises the possibility of holding fault current levels below 2X or 3X rated current. DC superconducting cables do not require this extra fault duty consideration, because the rectifier inverter system protects them. Usual fault conditions on d-c cable are such that less than 2X rated current will occur on the cable during a fault. Because a-c superconducting cables include very high fault current capability in their design, a careful trade-off study with current limiters, generator bus layout alternatives and possible d-c cable application should be done to assure that the final design may more readily achieve reasonable economics.