Variable thermal model overload in electrical switching apparatu

Details Variable thermal model overload in electrical switching apparatu Variable thermal model overload in electrical switching apparatu

1996-12-04

1998-06-02

Gaffin, Jeffrey A.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Motor protective condition responsive circuits

361 24, 361103, 361115, 318430, H02H 500

Patent

active

057610185

ABSTRACT:
A motor starter for an electrical circuit includes separable contacts for switching an electrical current flowing between a power source and a motor; an operating mechanism responsive to a trip signal for opening and closing the separable contacts; a separable contact state detection circuit providing an operating signal having two states corresponding to the open and closed positions of the separable contacts; a current transformer sensing the electrical current flowing between the power source and the motor and providing a sensed current value; and an overload relay generating the trip signal as an I.sup.2 t function of the sensed current value and the two states of the operating signal. The overload relay employs a pair of thermal time constants which closely model the motor under both natural convection and forced air cooling conditions.

REFERENCES:
patent: 4528539 (1985-07-01), Forsell et al.
patent: 4547826 (1985-10-01), Premerlani
patent: 4760364 (1988-07-01), Ostby
patent: 4766273 (1988-08-01), Butterworth et al.
patent: 5222009 (1993-06-01), Scharnick et al.

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