Apparatus and method for thermal protection of electric motors

Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits

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361 25, 361 31, 361 33, H02H 708

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active

055396011

ABSTRACT:
An apparatus for thermal protection of an electric motor is provided, including a monitoring device for generating a signal representative of the current in a conductor supplying electrical power to the electric motor. A control circuit processes the current signal and utilizes the processed signal and motor thermal parameters, including the thermal resistance and thermal capacitance of the rotor, to generate signals representative of the temperature of at least the rotor. A comparator circuit, which may be part of the control circuit, compares the temperature signals to reference maximum temperature signals and produces a control signal when the temperature signals and reference signals satisfy a predetermined relationship. The control signal may be applied to a contactor to interrupt current to the motor. A method for thermal protection of an electric motor is also provided, including thermal modeling of the rotor temperature.

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ABB ProStar Motor Protection Relay, pp. 28-33 (no date).

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