Overload and overcurrent regulation and protection system

Claim 2

In a refrigeration system having an electric motor-driven compressor of the type having controllable mechanical load reducing means, the improvement in a motor overcurrent protection and load regulation system of the type that develops motor current representative signals for the motor, comprising: at least two comparators responsive to different motor current representative signal levels one of which controls the mechanical load reducing means to reduce the mechanical load on the motor for current representative signals representing a low overcurrent situation, and the otHer of which produces an overload signal in response to a current representative signal representing a larger overcurrent situation; a time delay circuit coupled to at least said other comparator and responsive to the overcurrent signal thereof to produce a deenergizing command signal after a time delay period; and means coupled to said time delay circuit and responsive to the deenergizing command signal thereof for deenergizing the electric motor.

Claim 3

An automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, comprising: means for developing a signal that is representative of the current through the coils of the electric motor; means for producing a plurality of reference signals of different preselected values; a plurality of comparators, each coupled to said current representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with a different one of the plurality of reference signals and for producing an overload signal when the current-representative signal exceeds a predetermined relationship with the one reference signal; a timer coupled to at least one of said plurality of comparators for responding to the overload signal thereof, so as to produce deenergizing command signal after a time delay; means coupled to said timer for stopping the flow of electric power to the protected electric motor in response to the deenergizing command signal thereof, and means for changing the mechanical load on the motor, coupled to at least another one of said plurality of comparators for at least preventing increase in the mechanical load on the motor in responsive to the overcurrent and in response to the overload signal thereof.

Claim 4

An automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, comprising: means for developing a signal that is representative of the current through the coils of the electric motor; means for producing a plurality of reference signals of different preselected values; a plurality of comparators, each coupled to said current representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with a different one of the plurality of reference signals and for producing an overload signal when the current-representative signal exceeds a predetermined relationship with the one reference signal; a timer coupled to at least one of said plurality of comparators for responding to the overload signal thereof, so as to produce deenergizing command signal after a time delay; means coupled to said timer for stopping the flow of electric power to the protected electric motor in response to the deenergizing command signal thereof, and means for changing the mechanical load on the motor, coupled to at least another one of said plurality of comparators for at least preventing increase in the mechanical load on the motor in responsive to the overcurrent and in response to the overload signal thereof.

Claim 5

An automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, comprising: means for developing a signal that is representative of the current through the coils of the electric motor; means for producing a first, second, third and a fourth reference signal of different preselected values; a first comparator, coupled to said current representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the first reference signal and for producing a first overload signal when the current-representative signal exceeds a predetermined relationship with the first reference signal; a second comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the second reference signal and for producing a second overload signal when the current-representative signal exceeds a predetermined relationship with the second reference signal; a third comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the third reference signal and for producing a third overload signal when the current-representative signal exceeds a predetermined relationship with the third reference signal; a fourth comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the fourth reference signal and for producing a fourth overload signal when the current-representative signal exceeds a predetermined relationship with the fourth reference signal; a temperature regulator coupled to the first and second comparators which first acts to stop increasing motor current and second acts to reduce motor current in response to, respectively the first and second overload signals; a timer coupled to both said thirD and said fourth comparators for responding to one and to both of the third and the fourth overload signals thereof, so as to produce deenergizing command signal after a time delay; and means coupled to said timer for stopping the flow of electric power to the protected electric motor in response to the deenergizing command signal.

Claim 6

An automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, comprising: means for developing a signal that is representative of the current through the coils of the electric motor; means for producing a first, second, third and a fourth reference signal of different preselected values; a first comparator, coupled to said current representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the first reference signal and for producing a first overload signal when the current-representative signal exceeds a predetermined relationship with the first reference signal; a second comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the second reference signal and for producing a second overload signal when the current-representative signal exceeds a predetermined relationship with the second reference signal; a third comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the third reference signal and for producing a third overload signal when the current-representative signal exceeds a predetermined relationship with the third reference signal; a fourth comparator coupled to said current-representative signal developing means and to said reference signal producing means, for comparing the current-representative signal with the fourth reference signal and for producing a fourth overload signal when the current-representative signal exceeds a predetermined relationship with the fourth reference signal; a temperature regulator coupled to the first and second comparators which first acts to stop increasing motor current and second acts to reduce motor current in response to, respectively the first and second overload signals; a timer coupled to both said thirD and said fourth comparators for responding to one and to both of the third and the fourth overload signals thereof, so as to produce deenergizing command signal after a time delay; and means coupled to said timer for stopping the flow of electric power to the protected electric motor in response to the deenergizing command signal.

Claim 7

The automatic safety system for the protection of an electric motor by stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 3 wherein; said system is for the protection of a motor of the polyphase type having at least two different phased AC power inputs; and said current-representative signal developing means produces a signal representative of the maximum current drawn by any one of the different phased AC power inputs of the motor whereby the flow of electric power to the motor may be reduced and stopped when overcurrent overloading occurs in only one phase of the power input as well as when overcurrent overloading occurs in more than one phase of the power input.

Claim 8

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 4, wherein: said current-representative signal developing means developes a DC voltage signal as the current-representative signal whose amplitude varies as a function of the maximum current drawn by any one of the different phased AC power inputs of the motor; said reference signal producing means produces DC voltage signals as the first, second, third and fourth reference signals, which signals have different relative preselected amplitudes; and said first, said second, said third and said fourth comparators respectively produce their respective overload signals in response to the amplitude of the current-representative signal reaching a predetermined level in relation to, respectively, the amplitude of the first, the second, the third and the fourth reference signals.

Claim 9

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 5, where: said system further includes an overload indicator circuit having an input coupled to said third comparator and means for giving a sensory indication operatively controlled by the presence or absence of the third overload signal.

Claim 10

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 6, wherein: said sensory indication means of said indicator circuit is a lamp and said overload indicator circuit further includes a switching device operated in response to the third overload signal in circuit with said lamp and an electric power input in circuit connection with said lamp and said switching device.

Claim 11

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 7, wherein: said first comparator is a Schmitt Trigger circuit having a first and second input connected respectively to said current-representative signal developing means and to said reference signal producing means for respectively communicating the current-representative signal and the first reference signal thereto and an output upon which it produces the first overload signal in the form of a shift in voltage amplitude from one value to another when the amplitude of the current-representative signal reaches and surpasses the amplitude of the first representative signal; said second comparator is a Schmitt Trigger circuit having a first and second input connected respectively to said current-representative signal Developing means and to said reference signal producing means for respectively communicating the current-representative signal and the second reference signal thereto and an output upon which it produces the second overload signal in the form of a shift in voltage amplitude from one value to another when the amplitude of the current-representative signal reaches and surpasses the amplitude of the second representative signal; said third comparator is a Schmitt Trigger circuit having a first and second input connected respectively to said current-representative signal developing means and to said reference signal producing means for respectively communicating the current-representative signal and the third reference signal thereto and an output upon which it produces the third overload signal in the form of a shift in voltage amplitude from one value to another when the amplitude of the current-representative signal reaches and surpasses the amplitude of the third representative signal; said fourth comparator is a Schmitt Trigger circuit having a first and second input connected respectively to said current-representative signal developing means and to said reference signal producing means for respectively communicating the current-representative signal and the fourth reference signal thereto and an output upon which it produces the fourth overload signal in the form of a shift in voltage amplitude from one value to another when the amplitude of the current-representative signal reaches and surpasses the amplitude of the fourth representative signal;

Claim 12

The automatic safety system for the protection of an electric motor by reducing or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 8, wherein: said first, said second, said third and said fourth comparator Schmitt Trigger circuits each include an Operational Amplifier with a first and a second primary input terminal and an output terminal which is respectively the same as the output of the Schmitt Trigger circuits; the current-representative signal is coupled to second primary input of the Operational Amplifier of said first, said second, said third and said fourth comparators, the first, the second, the third and the fourth reference signals are coupled respectively to the second primary input terminals of the Operational Amplifier of said first, second, third and fourth comparators; and said timer comprises a resistance-capacitive circuit determined by the presence or absence of said third and said fourth overload signals.

Claim 13

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 5, wherein: said current-representative signal producing means includes: at least two coils, each of which is in transformer relationship with one of the AC power input line of said motor; means for rectifying coupled to each of said coils for developing a signal whose value is proportional to the maximum instantaneous current drawn by any one of said coils; and a peak detector circuit coupled to said rectifying means for developing as the current-representative signal a DC voltage whose level is proportional to the peak reoccurring value of the instantaneous maximum current signal.

Claim 14

In a refrigeration system of the type employing a polyphase electric motor as its prime mover and a centrifugal compressor of the type having adjustable means for mechanical load reduction, the improvement in an overcurrent protection system comprising: current signal means for sampling the current drawn by each phase of the electric motor and for developing therefrom a current representative signal; control means for controlling the mechanical load reduction means of the compressor, coupled to said current signal means for reducing the mechanical load of said compressOr when the current representative signal exceeds a certain value; reference signal means for generating a first, a second, a third and a fourth reference signal; first, second, third, and fourth comparator means, each actively coupled to said current signal means and said reference signal means, for comparing the current-representative signal with, respectively, the first, second, third and fourth reference signal and for generating, respectively, a first, second, third and fourth overload signal when the current-representative signal exceeds a certain relationship with respectively the first, second, third and fourth reference signal; load reducing means coupled to said first and second comparator for reducing the mechanical load of the motor in response to either or both of the first and second overload signals, actively coupled to said current signal means and said reference signal means, for comparing the current-representative signal with said second reference signal and for generating a second overload signal when the current-representative signal exceeds a reference signal; timing means, actively coupled to said third and fourth comparator means, for generating a deenergizing signal in response to the continued time sustained or frequent reoccurrence of one or both of the third and fourth overload signals; and current stopping means, responsive to said timing means, for stopping the flow of electric current to the motor; whereby said motor is protected from excessive overload conditions.

Claim 15

In a refrigeration system of the type employing a polyphase electric motor as its prime mover and a centrifugal compressor of the type having adjustable means for mechanical load reduction, the improvement in an overcurrent protection system comprising: current signal means for sampling the current drawn by each phase of the electric motor and for developing therefrom a current representative signal; control means for controlling the mechanical load reduction means of the compressor, coupled to said current signal means for reducing the mechanical load of said compressOr when the current representative signal exceeds a certain value; reference signal means for generating a first, a second, a third and a fourth reference signal; first, second, third, and fourth comparator means, each actively coupled to said current signal means and said reference signal means, for comparing the current-representative signal with, respectively, the first, second, third and fourth reference signal and for generating, respectively, a first, second, third and fourth overload signal when the current-representative signal exceeds a certain relationship with respectively the first, second, third and fourth reference signal; load reducing means coupled to said first and second comparator for reducing the mechanical load of the motor in response to either or both of the first and second overload signals, actively coupled to said current signal means and said reference signal means, for comparing the current-representative signal with said second reference signal and for generating a second overload signal when the current-representative signal exceeds a reference signal; timing means, actively coupled to said third and fourth comparator means, for generating a deenergizing signal in response to the continued time sustained or frequent reoccurrence of one or both of the third and fourth overload signals; and current stopping means, responsive to said timing means, for stopping the flow of electric current to the motor; whereby said motor is protected from excessive overload conditions.

Claim 16

The improvement in a refrigeration system as defined in claim 11, of the type in which the compressor of said system is of the centrifugal type and includes prerotation vanes as the means for mechanical load reduction, which is further particularized by having: said current signal means includes a plurality of current transformers, each of which is coupled to one phase of the electric motor, and a rectifying circuit connected to said plurality of transformers for developing a DC signal proportional to the maximum current present in any phase; said prerotation vanes are operated during no overload signal situations in accordance with sensed temperature functions, which functioning is overridden when an overload signal is received; said reference signal source is a voltage divider circuit; said first comparator means, said second comparator means, said third comparator means and said fourth comparator means are each made up of an Operational Amplifier circuit connected to form a Schmitt Trigger comparator circuit; said timing means includes a capacitor, a resistive charging path for said capacitor whose effective resistance is controlled by the third and fourth comparator means, and a command signal triggering device coupled to the said capacitor to activate the deenergizing signal when the voltage level across said capacitor reaches a predetermined triggering level; and said current stopping means includes a thyristor device responsive to the deenergizing signal to interrupt the current to the electric motor.

Claim 17

The automatic safety system for the protection of an electric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads as defined in claim 2, wherein: said plurality of comparators 52, 54, 56 and 58 are each solid state circuits having substantially matching characteristics, with one another; a single calibration control 40 is provided for adjusting the relative value between the current representative signal and the plurality of reference signals, whereby said safety system may be calibrated during setup and afterward, by a single step operation of adjusting the calibration control to set the magnitude of overcurrent at which each of the comparators will produce an overcurrent signal and also to thereby adjust the sensitivity of the system.

Claim 18

The automatic safety system for the protection of an elecTric motor by reducing the load thereon or stopping the flow of electric power thereto in response to certain sensed overloads, as defined in claim 6, wherein: said sensory indication means of said indicator circuit is a light emitter and said overload indicator circuit further includes a switching device operated in response to the third overload signal in circuit with said light emitter and an electric power input in circuit connection with said light emitter and said switching device.