Overtemperature protective circuit for switching devices

Details Overtemperature protective circuit for switching devices Overtemperature protective circuit for switching devices

1976-10-08

1978-02-07

Moose, Jr., Harry E.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Circuit interruption by thermal sensing

361 24, H02H 504

Patent

active

040729974

ABSTRACT:
A circuit for monitoring the temperature of the contacts of an electrical switching device (such as a circuit breaker), comprises an electrical analogue circuit of the thermal characteristics of the switching device. The analogue circuit comprises electrical resistance and capacitance, interconnected so as to form an electrical model of the heat flow paths and capacitances respectively, in the switching device. The preferred embodiment also provides a temperature sensing device to introduce to the analogue circuit a voltage signal the magnitude of which is proportional to the exterior temperature of the switching device. The analogue circuit is connected in a series circuit relationship with a current controller. The current controller controls the amount of current flowing through the analogue circuit. The current controller is in turn controlled by a voltage control signal proportional to the amount of current being carried by the switching device. The current controller is operated in such a fashion that the current it lets flow through the analogue circuit is proportional to the square of the voltage control signal.

REFERENCES:
patent: 3643130 (1972-02-01), Liska et al.
patent: 3808503 (1974-04-01), Hentschel
patent: 3808516 (1974-04-01), Hentschel
patent: 3845354 (1974-10-01), Boothman et al.
"Thermal Tracking-A rational Approach to Motor Protection", IEEE Paper, T 74 029.5, 11/73.

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