Motor protection circuit and automatic restart control system

Claim 2

A monitoring system for controlling the state of connection of an electrical load to a three-phase electrical power source, comprising: a. sequence analyzer means for measuring a symmetrical component of input voltages applied thereto; b. input means for connecting said sequence analyzer means to the power source; c. line switching means for controlling the connection of the load to the three-phase power source; d. control means connected to said line switching means and said sequence analyzer means, said control means for causing disconnection of the load from the power source when the magnitude of the symmetrical component varies from a predetermined acceptable range of values and for causing reconnection of the load when the symmetrical component magnitude returns within the acceptable range; e. residual voltage sensing means connected to the load for sensing residual voltages thereat; and f. means connecting said residual voltage sensing means to said control means for inhibiting said control means from reconnecting the load to the power source if the residual voltage exceeds a predetermined value.

Claim 3

A monitoring system according to claim 1, wherein said residual voltage sensing means comprises a relay having a drIver connected to a pair of inputs to the load and having a pair of contacts connected to said control means so as to prevent engagement of the load to the power source if the relay is energized.

Claim 4

A monitoring system according to claim 1, wherein said residual voltage sensing means comprises rectification means connected to said load for providing a DC voltage indicative of the load voltage and logic means connected to said control means for preventing reconnection of the load to the power supply if the load voltage exceeds a predetermined level.

Claim 5

A monitoring system for automatically controlling the connection, disengagement and reconnection of a three-phase electrical load to a power source, comprising: a. sequence analyzer means for measuring a symmetrical component of input voltages applied thereto; b. input means for connecting said sequence analyzer means to the power source; c. line switching means for controlling the connection of the load to the three-phase power source; d. control means connected to said line switching means and said sequence analyzer means, said control means for causing disconnection of the load from the power source when the magnitude of the symmetrical component varies from a predetermined acceptable range of values for a sufficient period of time and for causing reconnection of the load if the symmetrical component magnitude returns to the acceptable range; e. first time delay means connected to said control means for delaying the connection of the load to the power source for a predetermined time period; f. integrating delay means connected to said control means for activation when a connection of the load to the power source is to be made, said integrating delay means having energization and de-energization time constants greater than the energizing and de-energizing time delays of said first time delay means; and g. lockout means connected to said control means and to said integrating delay means, said lockout means operable to inhibit said control means from causing connection of the load to the power source when said integrating delay means has reached a predetermined level of energization, whereby reconnection of the load is prevented when an excessive number of restart attempts have been made in a given time interval.

Claim 6

A monitoring system for automatically controlling the connection, disengagement and reconnection of a three-phase electrical load to a power source, comprising: a. sequence analyzer means for measuring a symmetrical component of input voltages applied thereto; b. input means for connecting said sequence analyzer means to the power source; c. line switching means for controlling the connection of the load to the three-phase power source; d. control means connected to said line switching means and said sequence analyzer means, said control means for causing disconnection of the load from the power source when the magnitude of the symmetrical component varies from a predetermined acceptable range of values for a sufficient period of time and for causing reconnection of the load if the symmetrical component magnitude returns to the acceptable range; e. first time delay means connected to said control means for delaying the connection of the load to the power source for a predetermined time period; f. integrating delay means connected to said control means for activation when a connection of the load to the power source is to be made, said integrating delay means having energization and de-energization time constants greater than the energizing and de-energizing time delays of said first time delay means; and g. lockout means connected to said control means and to said integrating delay means, said lockout means operable to inhibit said control means from causing connection of the load to the power source when said integrating delay means has reached a predetermined level of energization, whereby reconnection of the load is prevented when an excessive number of restart attempts have been made in a given time interval.

Claim 7

A monitoring system according to claim 4, wherein said integrating delay means comprises a thermally insulated time delay relay.

Claim 8

A monitoring system according to claim 4, wherein said integrating delay means comprises a resistance-capacitance charging and discharging circuit.

Claim 9

A monitoring system for a three-phase electrical power for providing automatic disconnection of a motor from the source in the event of unacceptable power source voltages and automatic restart of the motor when the power source voltages return within tolerance, comprising: a. first and second sequence analyzer circuits for providing output voltages having a magnitude proportional to the magnitude of a symmetrical component of three-phase voltages applied thereto; b. means for connecting said three-phase electrical power source to said first sequence analyzer circuit for measurement of the positive sequence symmetrical component; c. means for connecting said three-phase electrical power source to said second sequence analyzer circuit for measurement of the negative sequence symmetrical component; d. voltage responsive switching means connected to receive the output voltages of said first and second sequence analyzers, said voltage responsive switching means for providing control signals indicative of whether the magnitudes of the positive and negative sequence symmetrical components of said three-phase power source are within predetermined tolerances; e. line switching means for controlling the connection of the motor to the three-phase power source; f. logic means connected to said voltage responsive switching means and to said line switching means, said logIc means for causing said line switching means to disconnect the motor when said control signals indicate an out-of-tolerance condition, and for causing said line switching means to connect the motor to the three-phase power source when said control signals indicate an in tolerance condition; g. residual voltage sensing means connected to the motor and to the logic means for inhibiting the logic means from causing reconnection of the motor to the power source if the residual voltage at the motor exceeds a predetermined value; and h. lockout means connected to said logic means for preventing connection of the motor to the power source when a predetermined number of restart attempts have been made in a given time interval.

Claim 10

A monitoring system for a three-phase electrical power for providing automatic disconnection of a motor from the source in the event of unacceptable power source voltages and automatic restart of the motor when the power source voltages return within tolerance, comprising: a. first and second sequence analyzer circuits for providing output voltages having a magnitude proportional to the magnitude of a symmetrical component of three-phase voltages applied thereto; b. means for connecting said three-phase electrical power source to said first sequence analyzer circuit for measurement of the positive sequence symmetrical component; c. means for connecting said three-phase electrical power source to said second sequence analyzer circuit for measurement of the negative sequence symmetrical component; d. voltage responsive switching means connected to receive the output voltages of said first and second sequence analyzers, said voltage responsive switching means for providing control signals indicative of whether the magnitudes of the positive and negative sequence symmetrical components of said three-phase power source are within predetermined tolerances; e. line switching means for controlling the connection of the motor to the three-phase power source; f. logic means connected to said voltage responsive switching means and to said line switching means, said logIc means for causing said line switching means to disconnect the motor when said control signals indicate an out-of-tolerance condition, and for causing said line switching means to connect the motor to the three-phase power source when said control signals indicate an in tolerance condition; g. residual voltage sensing means connected to the motor and to the logic means for inhibiting the logic means from causing reconnection of the motor to the power source if the residual voltage at the motor exceeds a predetermined value; and h. lockout means connected to said logic means for preventing connection of the motor to the power source when a predetermined number of restart attempts have been made in a given time interval.

Claim 11

A monitoring system according to claim 7 and further including hysteresis means connected to said voltage responsive switching means and operable in response thereto to change the voltage tolerances required for reconnection after a disconnection of the motor has occurred.

Claim 12

A monitoring system according to claim 7 wherein said residual voltage sensing means comprises a relay having a driver connected to a pair of inputs to the motor and having a pair of contacts connected to said logic means.

Claim 13

A monitoring system according to claim 7 wherein said residual voltage sensing means comprises rectification means connected to said motor for providing a DC voltage indicative of the motor voltage and a voltage responsive switch connected to said rectification means and to said logic means.

Claim 14

A monitoring system according to claim 7 wherein said lockout means comprises: a. first time delay means connected to said logic means for delaying the connection of the motor to the power source for a predetermined time period; b. integrating time delay means connected to said logic means for activation when a connection of the motor to the power source is to be made, said integrating delay means having energization and de-energization time constants greater than the energizing and de-energizing time delays of said first time delay means; and c. switching means connected to said logic means and to said integrating time delay means for inhibiting said logic means from causing connection of the load to the power source when said integrating delay means has reached a predetermined level of energization.

Claim 15

A monitoring system according to claim 11 wherein said integrating delay means comprises a thermally insulated time delay relay, and wherein said switching means comprises a stepping relay.

Claim 16

A monitoring system according to claim 11, wherein said integrating delay means comprises a resistance-capacitance charging and discharging circuit, and wherein said switching means comprises a flip-flop circuit.