Protection system for electric motors
AssigneeEaton Corporation
InventorsRichard J. Kuntner, James C. Vander Meer
Life of this patent
Estimating the term…
Abstract
A solid state protection system for AC electric motors driving high inertia loads requiring long acceleration times. An electroresponsive relay (OL) is separately responsive to permissible acceleration time, circuitry (DT, DC), acceleration overload current circuitry (ACA), and to normal running overload current circuitry (ACR). Up-to-speed detector and latch circuits (USD, USL) deactivate the acceleration time circuitry and overload current circuitry, and activate the running overload current circuitry upon attainment of normal running speed by the motor. The response levels of the overload and time response circuits are individually settable.
Claims14
In an overload protection system for an electric motor which is connectable to an electric supply source by electroresponsive means, the combination with an electroresponsive relay which when energized causes said electroresponsive means to disconnect said motor from said supply source, of
- (a) means providing a control signal which varies in accordance with current drawn by said motor,
- (b) means responsive to connection of the motor to said supply source to provide a timed output signal upon elapse of a preset timed interval,
- (c) current overload responsive means activated by connection of said motor to said supply source to be responsive to a predetermined value of said control signal of said first mentioned means to provide an overload output signal,
- (d) second current overload responsive means responsive when activated to provide another overload output signal whenever said control signal of said first mentioned means exceeds another predetermined value,
- (e) means responsive to said motor attaining a predetermined running speed for deactivating said means providing said timed output signal and said first mentioned current overload responsive means, and for activating said second overload responsive means, and
- (f) means responsive alternatively to said timed output signal, or either of the first mentioned or said other overload control signals to energize said electroresponsive relay.
The combination with a polyphase alternating current motor, of
- (a) means including an electromagnetic contactor for connecting and disconnecting said motor from a source of polyphase AC supply,
- (b) an electromagnetic relay having normally closed contacts in circuit with the energizing coil of said contactor and having an operating coil which when energized effects deenergizaton of said contactor to disconnect said motor from the AC source of supply,
- (c) means including current transformers in the supply connections between said contactor and the motor primary terminals for providing a unidirectional control signal proportional to the current drawn by said motor,
- (d) means responsive to energization of said contactor to provide a timed output signal upon elapse of a preset timed interval,
- (e) current overload responsive means activated by energization of said contactor to be responsive to a predetermined value of said control signal to provide an overload output signal,
- (f) second current overload responsive means which when activated provides another overload output signal whenever said control signal exceeds another predetermined value,
- (g) means responsive to said motor attaining a predeterined running speed for deactivating said means providing said timed output signal and the first mentioned overload responsive means, and activating said second overload responsive means, and
- (h) means responsive alternatively to said timed output signal or to either of the first mentioned or said other overload output signals to effect energization of the operating coil of said relay.
Dependencies are inferred from the claim text.