Motor protection circuit unit

A motor protection circuit unit for connection in a motor system including a contactor having a contactor winding and contacts operated when the contactor winding is energized to connect the motor to an electrical source, the circuit unit comprising

• switch means for connection in series with the contactor winding to control the energization of the contactor winding from an AC source;
• current sensing means connected in series with the switch means for producing a signal indicating current flow through the contactor winding;
• timing means responsive to termination of the signal from the current sensing means for preventing operation of the switch means for a predetermined duration;
• said timing means including rectifying means coupled to the current sensing means, a filter capacitance connected to the output of the rectifying means, a timing capacitance, a timing resistance connected in series with the timing capacitance, semiconductor trigger means for changing the voltage on one side of the timing capacitance in response to a predetermined voltage on the filter capacitance, and transistor means connected to the other side of the timing capacitance and to the switch means for preventing operation of the switch means for a predetermined duration;
• and
• said semiconductor trigger means including means connected between an output of the trigger means and an input of the trigger means to change the response of the trigger means so that when the trigger means has changed the voltage on the one side of the timing capacitance to operate the transistor means to prevent the operation of the switch means, the trigger means is responsive only to a first predetermined voltage on the filter capacitance, and so that when the trigger means has change back the voltage on the one side of the timing capacitance, the trigger means is responsive to only a second predetermined voltage, said first predetermined voltage being substantially greater than said second predetermined voltage.

A protection circuit unit for connection in a motor protection system including a contactor having a contactor winding and having contacts operated when the contactor winding is energized to connect the motor to an electrical source, the circuit unit comprising

• a pair of contactor energization terminals adapted to be connected in series with the contactor winding across the AC source,
• a contactor energization circuit connected between the pair of terminals,
• said contactor energization circuit including series switch means for controlling the energization of the contactor winding,
• said contactor energization circuit further including current sensing means connected in series with the switch means in the contactor energization circuit for producing a signal only during current flow through the contactor winding,
• said current sensing means being independent of which terminal of the pair of terminals the contactor winding is connected with,
• oil pressure responsive means including timing means for terminating operation of the switch means in the event that there is an absense of oil pressure during a predetermined duration of operation of the motor, and
• means responsive to the absense of a signal from the current sensing means for preventing the operation of the oil pressure responsive means.

A motor protection circuit unit for connection in a motor protection system including a contactor having a contactor winding and having contacts operated when the contactor winding is energized to connect the motor to an electrical source, the circuit unit comprising

• switch means for connection in series with the contactor winding to control the energization of the contactor winding from an AC source,
• current sensing means connected in series with the switch means for producing a signal indicating current flow through the contact winding,
• oil pressure responsive means including timing means for terminating operation of the switch means in the event that there is an absense of oil pressure during a predetermined duration of operation of the motor,
• means responsive to the absense of a signal from the current sensing means for preventing the operation of the oil pressure responsive means, and
• delay after break means responsive to termination of the signal from the current sensing means for preventing operation of the switch means for a predetermined duration after the termination.