DISTRIBUTION TRANSFORMER SECONDARY CIRCUIT RRUPTER HAVING MPROVED BIMETAL

摘要

45,781 DISTRIBUTION TRANSFORMER SECONDARY CIRCUIT INTERRUPTER HAVING AN IMPROVED BIMETAL A distribution transformer having a secondary circuit breaker utilizing a bimetal thermal trip for opening the circuit breaker upon the occurrence of overload currents wherein the power dissipation is concentrated in the base of the bimetal. The teachings of this invention are particularly adaptable for an oil immersed circuit breaker, as utilized with distribution transformers wherein a given oil temperature change must produce a required deflection and a given current flow for a predetermined period of time must also produce the required deflection, Standard bimetal thermal trip elements are generally constructed with a linear power distribution along their lengths to provide a predetermined deflection, The total power dissipation in the bimetal can be reduced and the predetermined deflection still obtained by concentrating the power dissipation in the base of the bimetal trip element, A movable bridging contact is spring biased towards an open position separated from the stationary contact, but with the circuit breaker in the normally closed position is held in engagement with the stationary contact. by a latching mechanism which is responsive to a bimetal trip element to allow the circuit breaker to trip open during selected overloads, The conducting bridging contact completes a series circuit through the circuit breaker which opens during circuit interruption, The secondary circuit breaker can also, if desired, be provided with a signal light circuit which activates the signal light, on the exterior housing of the transformer, when current through the circuit breaker exceeds a low signal overload value which is less than the trip value. A single signal light provided for each multipole circuit breaker can be activated by the bimetals of any one of the individual poles.