US 4,072,997 A · Overtemperature protective circuit for switching devices

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.

Claims10

Dependent claims

A circuit for monitoring the temperature of the contacts of an electrical switching device, said circuit comprising:

an electrical, resistance-capacitance analogue circuit of the thermal system of said switching device;
at least one switch for modifying said analogue circuit to account for different methods of cooling said switching device;
a current controller in series circuit relationship with said analogue circuit for controlling the flow of current through said analogue circuit;
a load sensing means, both for obtaining a control signal that is proportional to the magnitude of the current conducted by said switching device, and for applying said signal to said controller for controlling the current conduction thereof;
and at least one voltage level detector connected across the capacitance of said analogue circuit for measuring the voltage level thereof, said voltage level being representative of the temperature of the contacts of said switching device.

2 more elements

A circuit for monitoring the temperature of the contacts of a circuit breaker, said circuit comprising:

an electrical, resistance-capacitance analogue circuit of the thermal system of said circuit breaker;
at least on switch for modifying said analogue circuit to account for different methods of cooling said switching device;
a current controller in series circuit relationship with said analogue circuit for controlling the flow of current through said analogue circuit;
a load sensing means, both for obtaining a control signal that is proportional to the current conducted by said circuit breaker, and for applying said signal to said current controller;
said current controller functions such that the current passing through it, and consequently also through said analogue circuit, is proportional to the square of said control signal;
and at least one voltage level detector connected across the capacitance of said analogue circuit for measuring the voltage level thereof, said voltage level being representative of the temperature of the contacts of said circuit breaker.

3 more elements

Dependencies are inferred from the claim text.

Overtemperature protective circuit for switching devices

Life of this patent

Overtemperature protective circuit for switching devices

Life of this patent

Abstract

Claims10