Abstract A circuit breaker including separable contacts, an operating means for opening and closing the contacts and a trip coil responsive to a static control circuit for tripping the circuit breaker when instantaneous power in one of the phases of a three phase alternating current circuit exceeds adjustable predetermined levels for adjustable predetermined times as well as ground faults. A separate non-saturated iron core current transformer detects the current in each of the phases independently and powers independent cascaded current transformers having outputs of the same polarity connected to form OR circuits and provide a voltage signal correlated with the instantaneous current in a single one of the protected lines with the highest signal back biasing the others. This signal is amplified and delivered to a plurality of independent solid state adjustable time delay circuits for instantaneous time delay, short time delay and long time delay actuation of the trip coil dependent upon the extent to which the current levels in the protected line providing the signal exceeds a predetermined level of line current. Ground fault protection is also provided. Also disclosed is a light weight power supply whose power requirements are determined by the electronic power requirements of the control circuit but nonetheless provides the power level energy needed to actuate the trip coil. The static control circuit further includes fail-safe features so that a poor circuit connection or malfunction will not render the circuit breaker inoperative.
In a circuit breaker for protecting a polyphase circuit comprising separable contacts, operating means for opening and closing said contacts, a latch for maintaining said contacts in their closed position, a trip coil for tripping said latch, and a control circuit for energizing said trip coil upon the occurrence of a predetermined condition in any one of the phases; said control circuit including: A. overcurrent detection circuitry for independently detecting an overcurrent condition in each phase; B. ground fault protection circuitry for detecting a fault condition on any of the phases; C. power supply circuitry having a separate input per phase and a common output; D. a separate first current transformer coupled with each phase, each said first transformer having a secondary winding for developing an output current proportional to the current flowing in the associated phase; E. a separate second current transformer for each phase, each said second transformer having a primary winding and a secondary winding providing a discrete input to said overcurrent protection circuitry; F. a third current transformer having a primary winding per phase and a common secondary winding coupled to the input of said ground fault protection circuitry, and G. means connecting together in separate series circuits different ones of said first transformer secondary windings, said second transformer primary windings, said third transformer primary windings and said power supply inputs.
Claim 2
Dependent Claim
225 words
In a circuit breaker for protecting a polyphase circuit comprising separable contacts, operating means for opening and closing said contacts, a latch for maintaining said contacts in their closed position, a trip coil for tripping said latch, and a control circuit for energizing said trip coil upon the occurrence of a predetermined condition in any one of the phases; said control circuit including: A. overcurrent detection circuitry for independently detecting an overcurrent condition in each phase; B. ground fault protection circuitry for detecting a fault condition on any of the phases; C. power supply circuitry having a separate input per phase and a common output; D. a separate first current transformer coupled with each phase, each said first transformer having a secondary winding for developing an output current proportional to the current flowing in the associated phase; E. a separate second current transformer for each phase, each said second transformer having a primary winding and a secondary winding providing a discrete input to said overcurrent protection circuitry; F. a third current transformer having a primary winding per phase and a common secondary winding coupled to the input of said ground fault protection circuitry, and G. means connecting together in separate series circuits different ones of said first transformer secondary windings, said second transformer primary windings, said third transformer primary windings and said power supply inputs.
Claim 3
Dependent Claim
42 words
The combination defined in claim 1, wherein said primary windings of said third transformer are wound in differential current transformer fashion, whereby the current induced in said secondary winding thereof is the result of unbalanced currents flowing in said separate series circuits.
Claim 4
Dependent Claim
62 words
The combination defined in claim 2, wherein said overcurrent detection circuitry includes means for deriving a single output signal indicative of the current in the phase experiencing the most serious overcurrent condition, said control circuit including means interconnecting said overcurrent protection circuitry and said power supply circuitry for referencing said output signal to a predetermined power supply voltage at said common output.
Claim 5
Dependent Claim
42 words
The combination defined in claim 3 wherein said overcurrent detection circuitry includes a separate rectifying network connected with each said second transformer secondary winding, and each said power supply circuitry input includes a separate rectifying network included in each said series circuit.