Multiphase motor control system with overcurrent and undercurrent protection

Claim 2

A control system for regulating energization of a multiphase motor from a multiphase power input circuit, including a main switch relay having a winding and main switch contacts for transferring multiphase energy to the motor, and a current transformer connected to provide current signals each of which is a function of the current flowing over one phase conductor to the motor, the improvement which comprises: an indicator and detector assembly coupled to said current transformer, including a meter relay for each phase circuit, which relay has first and second semiconductor switches, the first semiconductor switch in each meter relay being conductive when the respective phaSe current is below the preset high level and the second semiconductor switch in each meter relay being conductive when the respective phase current is above the preset low level, a first series circuit including a first conductor coupled in series with all the first semiconductor switches to provide a first control signal indicating all the phase currents are below the preset high level, and a second series circuit comprising a second conductor coupled in series with all the second semiconductor switches to provide a second control signal indicating all the phase currents are above the preset low level, a control circuit, including a primary start relay having a winding coupled in series with a start button and a normally closed delayed contact set, a delayed start relay for actuating said delayed contact set after the phase currents exceed the preset low level, which delayed start relay has its winding coupled in parallel with a series circuit including the primary start relay winding and said delayed contact set, said main switch relay winding being connected for energization responsive to closure of a contact set of the primary start relay to close the main switch contacts and energize the motor, and relay means connected to operate in the absence of either of said first and second control signals to effect deenergization of said main switch relay and deenergize the motor, and means for energizing said control system.

Claim 3

A control system as claimed in claim 1 in which said meter relay for each phase circuit comprises a pair of lamps, and in which said first and second semiconductor switches are connected to be normally conducting when said lamps are illuminated, said first series circuit further comprises a first control relay winding which is energized when all the phase currents are below the preset high level, said second series circuit further including a second control relay winding which is energized when all the phase currents are above the preset low level setting.

Claim 4

A control system as claimed in claim 2 in which said control circuit further comprises a first trip relay having a winding coupled in series with a contact set of the first control relay such that the first control relay contact set closes responsive to deenergization of the first control relay to complete an energizing circuit for the first trip relay, said first trip relay further comprising a contact set connected to close responsive to operation of the first trip relay to deenergize the primary start relay which deenergizes the main switch relay and correspondingly deenergizes the motor, and a second trip relay having a winding coupled in series with a contact set of the second control relay such that the second control relay contact set opens responsive to deenergization of the second control relay to interrupt an energizing circuit for the second trip relay, said second trip relay further comprising a contact set, coupled in parallel with said delayed contact set, and connected to open responsive to deenergization of the second trip relay to deenergize the primary start relay which deenergizes the main switch relay and correspondingly deenergizes the motor.

Claim 5

A control system for regulating energization of a three-phase motor from a three-phase power input circuit, including a main switch relay having a winding and main switch contacts for transferring three-phase AC energy to the motor, and a current transformer connected to provide current signals each of which is a function of the current flowing over one phase conductor to the motor, the improvement which comprises: an indicator and detector assembly coupled to said current transformer, including a meter relay for each phase circuit, which meter relay has first and second light-sensitive semiconductor switches, a first lamp in the meter relay connected to apply a gating signal to the first semiconductor switch and render the first switch conductive when the respective phase current is below the preset high level, and a Second lamp in the meter relay connected to apply a gating signal to the second semiconductor switch and render the second switch conductive when the respective phase current is above the preset low level, a first series circuit including a first control relay winding coupled in series with a first conductor and with all the first semiconductor switches to provide a first control signal which energizes the first control relay when all the phase currents are below the preset high level, and a second series circuit including a second control relay winding coupled in series with a second conductor and with all the second semiconductor switches to provide a second control signal which energizes the second control relay when all the phase currents are above the preset low level, a control circuit, including a primary start relay having a winding coupled in series with a start button and a normally closed delayed contact set, a delayed start relay for actuating said delayed contact set after the phase currents exceed the preset low level, which delayed start relay has its winding coupled in parallel with a series circuit including the primary start relay winding and said delayed contact set, said main switch relay winding being connected for energization responsive to closure of a contact set of the primary start relay to close the main switch contacts and energize the motor, and trip relay means connected to change state in the absence of either of said first and second control signals to effect deenergization of said main switch relay and deenergize the motor, and means for energizing said control system.

Claim 6

A control system for regulating energization of a three-phase motor from a three-phase power input circuit, including a main switch relay having a winding and main switch contacts for transferring three-phase AC energy to the motor, and a current transformer connected to provide current signals each of which is a function of the current flowing over one phase conductor to the motor, the improvement which comprises: an indicator and detector assembly coupled to said current transformer, including a meter relay for each phase circuit, which meter relay has first and second light-sensitive semiconductor switches, a first lamp in the meter relay connected to apply a gating signal to the first semiconductor switch and render the first switch conductive when the respective phase current is below the preset high level, and a Second lamp in the meter relay connected to apply a gating signal to the second semiconductor switch and render the second switch conductive when the respective phase current is above the preset low level, a first series circuit including a first control relay winding coupled in series with a first conductor and with all the first semiconductor switches to provide a first control signal which energizes the first control relay when all the phase currents are below the preset high level, and a second series circuit including a second control relay winding coupled in series with a second conductor and with all the second semiconductor switches to provide a second control signal which energizes the second control relay when all the phase currents are above the preset low level, a control circuit, including a primary start relay having a winding coupled in series with a start button and a normally closed delayed contact set, a delayed start relay for actuating said delayed contact set after the phase currents exceed the preset low level, which delayed start relay has its winding coupled in parallel with a series circuit including the primary start relay winding and said delayed contact set, said main switch relay winding being connected for energization responsive to closure of a contact set of the primary start relay to close the main switch contacts and energize the motor, and trip relay means connected to change state in the absence of either of said first and second control signals to effect deenergization of said main switch relay and deenergize the motor, and means for energizing said control system.

Claim 7

A control system as claimed in claim 4 in which said trip relay means comprises a first trip relay having a winding coupled in series with a contact set of the first control relay such that the first control relay contact set closes responsive to deenergization of the first control relay to complete an energizing circuit for the first trip relay, said first trip relay further comprising a contact set connected to close responsive to operation of the first trip relay to deenergize the primary start relay which deenergizes the main switch relay and correspondingly deenergizes the motor, and a second trip relay having a winding coupled in series with a contact set of the second control relay such that the second control relay contact set opens responsive to deenergization of the second control relay to interrupt an energizing circuit for the second trip relay, said second trip relay further comprising a contact set, coupled in parallel with said delayed contact set, and connected to open responsive to deenergization of the second trip relay to deenergize the the primary start relay which deenergizes the main switch relay and correspondingly deenergizes the motor.