Electric motor fault and dynamic braking protection system

An electric motor fault protection system for electric motor circuits having a normal operating mode in which the motor circuit input and output carry total motor current comprising

• saturable reactor means for sensing current imbalance between the motor circuit input and output in the normal mode;
• detector means coupled to said saturable reactor means for producing fault signals when the reactor means sense a current imbalance of a predetermined magnitude in the operating mode;
• bistable control means having first and second operating states selectively coupled to said detector means to receive the fault signals therefrom, said control means being operable in the first state thereof to energize the motor circuit and operable in the second state thereof to deenergize the motor circuit, the operating states of said control means being shiftable from said first state to said second state in response to said fault signals and from said second state to said first state in response to either a first reset signal or a second reset signal;
• first manually operable reset signal producing means for producing said first reset signal;
• second manually operable reset signal producing means for producing a second reset signal;
• counting means having first and second operating conditions selectively coupled to said detector means and said first reset signal producing means, said counting means being operable in the first condition thereof to couple said first reset signal producing means to said control means so that said control means may be shifted from said second operating state to said first operating state in response to said first reset signal and operable in the second condition thereof to decouple said first reset signal producing means and said control means to thereby prevent shifting of said control means from said second state to said first state in response to said first reset signal, the operating conditions of said counting means being shiftable from said first condition to said second condition after receipt of a predetermined number of said fault signals and from said second operating condition to said first operating condition upon receipt of said second reset signal.

A dynamic braking protection system for electric motor circuits having a dynamic braking operating mode in which motors are opposed to dissipate energy comprising

• saturable reactor means for sensing current imbalance between opposing motors in the dynamic braking mode;
• detector means coupled to said saturable reactor means for producing fault signals when the reactor means sense a current imbalance of a predetermined magnitude in the operating mode;
• bistable control means having first and second operating states selectively coupled to said detector means to receive the fault signals therefrom, said control means being operable in the first state thereof to permit dynamic braking and operable in the second state thereof to prevent dynamic braking, the operating states of said control means being shiftable from said first state to said second state in response to said fault signals and from said second state to said first state in response to either a first reset signal or a second reset signal;
• first manually operable reset signal producing means for producing said first reset signal;
• second manually operable reset signal producing means for producing a second reset signal;
• counting means having first and second operating conditions selectively coupled to said detector means and said first reset signal producing means, said counting means being operable in the first condition thereof to couple said first reset signal producing means to said control means so that said control means may be shifted from said second operating state to said first operating state in response to said first reset signal and operable in the second condition thereof to decouple said first reset signal producing means and said control means to thereby prevent shifting of said control means from said second state to said first state in response to said first reset signal, the operating conditions of said counting means being shiftable from said first condition to said second condition after receipt of a predetermined number of said fault signals and from said second operating condition to said first operating condition upon receipt of said second reset signal.