Square D Company

Joseph M Khalid

Clark L Oster

James W Cook

Richard T Dickens

A current limiting iron wire resistor having a transformable resistance for a current limiting circuit breaker. Each pole of the circuit breaker includes said resistor in parallel with a pair of auxiliary contacts for current limiting which are in series with a pair of main contacts to open the circuit. The main contacts are separable upon operation of a thermally and electromagnetically operable tripping mechanism, and the auxiliary current limiting contacts separate only on occurrence of a high amplitude fault current above a preselected threshold value. When that value of fault current is reached, the tripping mechanism and associated components which operate the auxiliary current limiting contacts serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the current limiting resistor. The resistor is formed in a bent-back serpentine shape to reduce inductance of the parallel resistor circuit which would otherwise be very high with the magnitudes of fault current involved, and to also balance the mutual electromagnetic forces among various sections of the resistor. The resistor also includes integrally formed flattened terminals, and intermediate terminal pieces welded to the flattened terminal of the iron wire resistor between the resistor and the copper conductors leading to and from the resistor at each terminal end. The intermediate terminal pieces have a resistivity characteristic between that of the copper conductors and the iron wire resistor.

Current limiting circuit breaker

A current limiting circuit breaker having for each pole, a pair of main contacts separable upon operation of a thermally and electromagnetically operable tripping device and a pair of auxiliary contacts for current limiting in series with the main contacts and in parallel with a transformable resistor having a positive temperature coefficient of resistance. The auxiliary contacts are separable when an electromagnet is energized by a fault current which simultaneously energizes a field magnet to produce a transverse magnetic field across the auxiliary contacts and the arc formed between them when separating. This simultaneous action of electromagnet and field magnet coacting for rapid contact separation and lengthening of the arc upon flow of a fault current serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the resistor. The auxiliary contacts are carried on a pair of minimum inertia movable contact blades to facilitate rapid separation of the auxiliary contacts. The minimum inertia contact blades are elongated between a pivot point and the point at which the contacts are mounted, where they terminate without providing an arc runner portion.

An iron wire resistor connected in shunt with the current limiting contacts of a circuit breaker. The current limiting contacts are in series with the main contacts of the breaker, and are separated by extremely high fault currents before the main contacts can respond. Opening of the limiting contacts shunts the high fault current through the resistor. The resistor has a positive temperature coefficient of resistance and heats rapidly to sharply reduce the magnitude of the high fault current. To prevent the connection between the resistor and a low resistance copper conductor from being destroyed by the high fault current an intermediate resistance value terminal of copper clad stainless steel is employed between the resistor and the copper conductor. The use of oppositely directed segments or a serpentine shape in the resistor substantially reduces inductance in the resistor circuit which would tend to impede transfer of the fault current into the resistor circuit and thus maintain the arc across the contacts. The wire is potted in a ceramic compound utilizing alumina or silica.

A current limiting circuit breaker having for each pole, a pair of main contacts separable upon operation of a thermally and electromagnetically operable tripping device and a pair of auxiliary contacts for current limiting in series with the main contacts and in parallel with a transformable resistor having a positive temperature coefficient of resistance. The auxiliary contacts are separable when an electromagnet is energized by a fault current which simultaneously energizes a field magnet to produce a transverse magnetic field across the auxiliary contacts and the arc formed between them when separating. This simultaneous action of electromagnet and field magnet coacting for rapid contact separation and lengthening of the arc upon flow of a fault current serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the resistor. The field magnet is rectangular and tubular, with the auxiliary contacts approximately centered within the cavity defined by the tubular magnet walls. It may be formed preferably of two L-shaped magnet portions, one reversely positioned with respect to the other, to form a rectangular tube.

Current limiting circuit breaker having for each pole, a pair of main contacts separable upon operation of a thermally and electromagnetically operable tripping device and a pair of auxiliary contacts for current limiting in series with the main contacts and in parallel with a transformable resistor having a positive temperature coefficient of resistance. The auxiliary contacts are separable when an electromagnet is energized by a fault current which simultaneously energizes a field magnet to produce a transverse magnetic field across the auxiliary contacts and the arc formed between them when separating. This simultaneous action of electromagnet and field magnet coacting for rapid contact separation and lengthening of the arc upon flow of a fault current serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the resistor. A conductor system is associated with the electromagnet which includes two conductor turns, the first being connected in parallel with the auxiliary contacts and the second being connected in series with the auxiliary contacts and with the other conductor turn. The second produces magnetic flux in the magnet core when a fault current appears and while the auxiliary contacts are closed. The first and second conductor turns together continue to produce magnetic flux in the magnet core after the auxiliary contacts have opened to hold them apart and prevent contact welding.

A current limiting circuit breaker having for each pole, a pair of main contacts separable upon operation of a thermally and electromagnetically operable tripping device and a pair of auxiliary contacts for current limiting in series with the main contacts and in parallel with a transformable resistor having a positive temperature coefficient of resistance. The auxiliary contacts are separable when an electromagnet is energized by a fault current which simultaneously energizes a field magnet to produce a transverse magnetic field across the auxiliary contacts and the arc formed between them when separating. This simultaneous action of electromagnet and field magnet coacting for rapid contact separation and lengthening of the arc upon flow of a fault current serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the resistor.

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Cedar Rapids, IA, United States of America

Joseph M Khalid