Motor protection apparatus and method

Claim 1

In a refrigerant compressor of the type having a compression mechanism for receiving a refrigerant gas from a suction line, compressing the refrigerant gas and discharging the compressed refrigerant gas, a motor for operating the compression mechanism and conductor means for applying electrical power to the motor, improved apparatus for protecting the compressor motor comprising in combination: first switch means connected in series with the conductor means, said first switch means being normally in an open position and being movable to a closed position; second switch means connected in series with the first switch means, said second switch means being normally in an open position and being movable to a closed position; first operating means for moving the first switch means to the closed position in response to a pilot signal and for opening the first switch means in the absence of the pilot signal; generating means for generating the pilot signal; third switch means operable in a first state for operatively connecting the generating means to the first operating means and operable in a second state for operatively disconnecting the generating means from the first operating means; second operating means for urging the second switch means toward the closed position and urging the third switch means into the first state in response to the pilot signal and for urging the second switch means toward the open position and urging the third switch means into the second state in the absence of the pilot signal; and third operating means for transmitting the pilot signal to the first and second operating means in response to a demand for operation of the compressor so that the first and second switch means are moved to their closed positions to apply electrical power to the compressor motor, and for preventing the pilot signal from being transmitted to the first and second operating means in the absence of a demand for operation of the compressor so that the first and second switch means are normally both moved to the open position to stop the compressor motor or the first switch means is moved to the open position alone to stop the compressor motor in case the second switch means fails in the closed position.

Claim 11

A method of protecting a motor for driving a refrigerant compressor of the type having a compression mechanism for receiving a refrigerant gas from a suction line, compressing the refrigerant gas and discharging the compressed refrigerant gas by use of a first contactor and a second contactor connected in series between a source of electrical power and the compressor motor, a third switch simultaneously operated with the second contactor, a first operating coil for closing the first contactor in response to a pilot signal and for opening the first contactor in the absence of a pilot signal, a second operating coil for urging the second contactor and the third switch toward their closed positions in response to the pilot signal and for urging the second contactor and the third switch toward their open positions in the absence of the pilot signal, and a generator of the pilot signal, said method comprising the steps of: normally biasing the first and second contactors and the third switch to their open positions; applying the pilot signal to the second operating coil in response to a demand for operation of the compressor so that the second contactor and third switch are moved to their closed positions; applying the pilot signal to the second operating coil through the closed third switch so that the first contactor is moved to the closed position and electrical power is applied to the compressor motor through the closed first and second contactors; blocking the pilot signal from being transmitted to the second operating coil in the absence of a demand for operation of the compressor, so that the second contactor and third switch are biased toward their open positions; and blocking the pilot signal from being transmitted to the first operating coil in the absence of a demand for operation of the compressor, so that the first operating coil opens the first contactor in the event that the second contactor fails in the closed position, whereby the compressor motor is protected from overload conditions.

Claim 12

A method of protecting a motor for driving a refrigerant compressor of the type having a compression mechanism for receiving a refrigerant gas from a suction line, compressing the refrigerant gas and discharging the compressed refrigerant gas by use of a first contactor and a second contactor connected in series between a source of electrical power and the compressor motor, a third switch simultaneously operated with the second contactor, a first operating coil for closing the first contactor in response to a pilot signal and for opening the first contactor in the absence of a pilot signal, a second operating coil for urging the second contactor and the third switch toward their closed positions in response to the pilot signal and for urging the second contactor and the third switch toward their open positions in the absence of the pilot signal, and a generator of the pilot signal, said method comprising the steps of: normally biasing the first and second contactors and the third switch to their open positions; applying the pilot signal to the second operating coil in response to a demand for operation of the compressor so that the second contactor and third switch are moved to their closed positions; applying the pilot signal to the second operating coil through the closed third switch so that the first contactor is moved to the closed position and electrical power is applied to the compressor motor through the closed first and second contactors; blocking the pilot signal from being transmitted to the second operating coil in the absence of a demand for operation of the compressor, so that the second contactor and third switch are biased toward their open positions; and blocking the pilot signal from being transmitted to the first operating coil in the absence of a demand for operation of the compressor, so that the first operating coil opens the first contactor in the event that the second contactor fails in the closed position, whereby the compressor motor is protected from overload conditions.