Siemens Energy & Automation, Inc.

Siemens Aktiengesellschaft

Siemens-allis, Inc.

William E May

William A King

Jerry M Green

Von G Pardue

James O Alexander

Rex J McColloch

Janerio N Morgan

Curtis J Ayers

Peter N Pang

James S Wells

John P Halferty

Ronald W McKinney

William R Taylor

An arrangement for producing a signal representative of the vectorial sum of the currents in a plurality of electric conductors in an electrical system. The arrangement includes a current transformer associated with each of the electrical conductors, and a differential current transformer for summing the current produced by each of the current transformers in response to currents in the electrical conductors. The differential current transformer is coupled to a rectifier and resistor arrangement which allows a voltage signal to be produced which is representative of the sum of the currents in the current transformers. The voltage signal is also representative of the sum of currents in the phase conductors of the electrical system.

Current summing arrangement for ground fault detection

An arrangement for opening a circuit coupled to an electrical power source associated with a neutral circuit. The arrangement includes a bi-stable latch for electrically engaging and disengaging a pair of contacts in response to the value of the sum of currents in the circuit and the neutral circuit exceeding a predefined limit. The arrangement also includes a mechanism for opening and closing a pair of main contacts which are used to open and close the circuit. The mechanism can be operated by a shunt trip solenoid such that the solenoid causes the operating mechanism to open the contacts when the contacts of the bi-stable latch are closed.

Arrangement for providing ground fault protection

An apparatus for monitoring alternating currents and providing a signal representative of the current. The signals are rectified by a modified full wave rectrifier to provide a power source, a positive signal associated with the positive range of the current, and a positive signal associated with the negative range of the current. The two positive signals serve to preserve the polarity information associated with the current being monitored. The apparatus also provides for combining the negative signals to produce other signals useable by a microprocessor and an analog logic circuit.

Ground fault current rectification and measuring circuit

Ground fault interrupting circuit breaker (10) includes a sensing coil (20) which is the secondary winding of a current transformer having a core (18) and includes a test coil (22) also wound about the core with load conductors passing through the core. A current sensing circuit (30) compares the output from the sensing coil to a reference voltage which is adjustable to set the sensitivity of the breaker. A test circuit (42) generates in the test coil a test current whch has its magnitude determined by the same reference voltage which determines the sensitivity of the breaker, thus causing the test current to automatically track the sensitivity of the breaker without separate adjustment.

Current sensing relay circuit with adjustable sensitivity and tracking

A magnetic actuating or trip mechanism for use with a circuit breaker including an armature, a permanent magnet for biasing the armature to a biased position, a first magnetic member having an armature guide, a second magnet member, an electromagnetic coil including a first winding for urging the armature from the biased position and a second winding for urging the armature from the biased position, a compression spring for urging the armature from the biased position, a fastener for fastening the first and second members to the permanent magnet, and recesses for locating the electromagnetic coil relative to the first and second members. The coil includes an armature opening and the first and second members each include a permanent magnet mounting surface and a coil mounting surface, the permanent magnet mounting surface includes a ridge for preventing the members from rotating relative to the permanent magnet.

Magnetic actuating mechanism

A molded case circuit breaker has control terminals mounted on the front of the breaker and accessible from the front. A transparent plexiglass cover is positioned over the terminals to prevent inadvertent contact with the terminals and an opening is provided in the side of the casing for the egress of the control wires. With the control terminals on the front of the circuit breaker, an inspection can be performed without disconnecting power from the breaker.

Molded case circuit breaker with front accessible control panel

A microprocessor based trip unit for a circuit breaker is disclosed. The instantaneous current magnitudes in each phase and in the neutral of the circuit being protected are simultaneously and sequentially sampled by respective sample and hold circuits. The measured values are then applied to a respective analog-to-digital converter and the digitized values are sequentially applied to a microprocessor. The microprocessor calculates true RMS current and sums the signals of all phases and neutral to determine presence and magnitude of a ground fault current. To permit use of an 8-bit microprocessor, while maintaining high resolution of measured current over a large range, novel automatic scale adjustment is provided. The memory of prior thermal history of the circuit breaker is provided electronically by a capacitor circuit which is discharged at a rate representative of the rate of cooling of the circuit breaker. The output of the capacitor circuit is loaded into the microprocessor when the circuit breaker comes back onto the line after a prior opening operation. Any desired number of trip units can be remotely located from a switchboard frame containing a respective plurality of circuit breakers without local trip units.

Microprocessor controlled circuit breaker trip unit

A current transformer is provided for the electronic trip unit of a molded case circuit breaker. The current transformer has a core with a winding encoiled about the core and a bus spiraled about the core. The spiral bus establishes a current path from one end of the bus to the other which will conduct current through the core in a spiral fashion. The spiral bus design effectively rotates the bus 90 degrees achieving a narrow transformer design which fits into the electronic trip unit without increasing the width of the trip unit.

Molded case circuit breaker current transformer with spiral bus

A ground fault accessory for a molded case circuit breaker is provided by converting a shunt trip accessory to automatically trip the breaker when a ground fault occurs. A printed circuit mounted in the housing with the shunt trip eliminates the need for a separate ground fault relay. The ground fault relay and the shunt trip are made available in the same accessory requiring no additional mounting of equipment or external wiring while conserving space which is scarce in load centers and other locations where both ground fault and shunt trip are desired.

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Lawrenceville, GA, United States of America

William E May