Pump and electric motor protector

• US 4,841,404 A
• Filed: 10/07/1987
• Issued: 06/20/1989
• Est. Priority Date: 10/07/1987
• Status: Expired due to Fees

• Current Assignee: Dayton Scientific, Inc.
• Original Assignee: Spring Valley Associates, Inc.
• Inventors: Marshall, William W., Springer, Lamar D.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/106,048
• Time in Patent Office: 622 Days
• Field of Search: 361/33, 361/23, 361/20, 361/31, 361/79, 361/85, 361/86, 361/87, 361/88, 361/92, 318/455, 417/18, 417/45
• US Class Current: 361/30
• CPC Class Codes: F04D 15/0236 Lack of liquid level being detected by analysing the parameters of the electric drive, e.g. current or power consumption
• CPC Class Codes: H02H 1/04 Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks
• CPC Class Codes: H02H 3/12 responsive to underload or no-load for motors H02H7/0827
• CPC Class Codes: H02H 3/382 involving phase comparison between current and voltage or between values derived from current and voltage
• CPC Class Codes: H02H 7/0827 responsive to underload or no-load, e.g. pump-off control circuits for pump motors

Abstract

An electrical circuit for providing electrical energy to an electric motor which operates a liquid pump. The motor and the pump are adapted to be submerged in the liquid which is pumped by the pump. The circuit disclosed herein senses the phase angle between the current and the voltage applied to the electric motor. When the phase angle indicates that the motor is operating without a load, the circuit deenergizes the electric motor. Thus, the motor and the liquid pump are protected against damage. Recognizing that harmonics may exist in the current flow through the motor, the circuit provides for obtaining a filtered signal proportional to the fundamental frequency of the current flowing through the motor. Thus, an accurate measurement of the loading of a motor is obtained. The circuitry of this invention also provides an accurate method of compensation for applied line voltage variations, so that a change in the applied line voltage does not produce a false indication that the motor loading has changed.

Claims

1. An electric circuit for energization of an electric motor and for protection of a fluid pump operated by an electric motor which is joined to a source of alternating current electrical energy and in which the alternating current which flows through the electric motor may include harmonic frequencies and in which the source of the alternating current voltage has a fundamental frequency which may vary in amplitude, comprising:

a plurality of electric conductors for attachment to a source of alternating current electrical energy,

switch means for connecting the electric conductors to the electric motor,

phase angle sensing means for sensing the phase angle between the voltage applied to the electric conductors and the current flowing in the electric conductors, the phase angle sensing means including first signal means, the first signal means providing a signal waveform which represents the voltage applied to the electrical conductors, the phase angle sensing means also including second signal means, the second signal means providing a signal waveform representing the current flow through the electric conductors, the phase angle sensing means also including means for attenuating harmonic frequencies in the signal provided by the second sensing means to provide accurate measurement of the voltage and current waveforms in the signals,

means joining the phase angle sensing means to the electric conductors,

actuator means for operation of the switch means to disconnect the electric conductors from the electric motor,

voltage level sensing means,

voltage compensation means connected to one of the electric conductors and to the voltage level sensing means, the voltage compensation means including means compensating for variations in the phase angle between the applied voltage to the electric conductors and the alternating current flow through the electric conductors with variations in amplitude of the applied voltage, the voltage compensation means thus providing a voltage signal to the voltage level sensing means which compensates for variations in the amplitude of the alternating current voltage,

and means joining the voltage level sensing means to the actuator means and to the phase detector means, whereby the phase detector means and the voltage compensation means provide voltage signals to the voltage level sensing means in accordance with the phase angle for energization of the actuator means by the voltage level sensing means,

whereby the voltage level sensing means energizes the actuator means in response to a predetermined shift in said phase angle in response to a combination of the voltage signals applied to the voltage sensing means by the phase detector means and by the voltage compensation means.

2. The method of protecting a liquid pump which is operated by an electric motor to which alternating current electrical energy having a fundamental frequency is applied through a plurality of electric conductor members, and a switch operable to connect and to disconnect the electric motor with respect to the electric conductor members comprising:

providing a first voltage signal, the first voltage signal being related to the current flow through the electric conductor members and through the electric motor,

attenuating harmonic frequencies which may exist in the first voltage signal as a result of current flow through the electric motor and providing a modified first voltage signal,

providing a second voltage signal, the second voltage signal being related to the voltage of the alternating current electrical energy which is applied to the electric conductor members,

sensing the phase angle between the modified first voltage signal and the second voltage signal and obtaining a phase angle voltage signal proportional to the phase angle,

generating a third voltage signal in accordance with the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, modifying the third voltage signal to obtain a fourth voltage signal which compensates for changes in phase angle which occur as a result of variations in the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, comparing the phase angle voltage signal to the fourth voltage signal, and operating the switch when the difference between the phase angle voltage signal and the fourth voltage signal exceeds a predetermined magnitude.

3. The method of claim 2 in which the modifying of the third voltage signal to obtain the fourth voltage signal includes modifying the voltage signal in accordance with m(VLine)-k, in which VLine is the potential applied to the electric conductor members, and in which m is a constant slope and in which k is a fixed voltage.

4. A protective circuit for a liquid pump which is operated by an electric motor, which is energized by electric circuit means to which alternating current electrical energy is applied, including switch means for connection of the electric motor to the electric circuit means for energization of the electric motor, the alternating current electrical energy being of the type having a given fundamental frequency which may vary in amplitude, the protective circuit also being of the type which includes phase angle detector means which senses the phase angle between the voltage of the alternating current electrical energy applied to the electric circuit means and the alternating current flow in the electric circuit means, the phase detector means providing an output voltage related to the phase angle between the voltage of the alternating current electrical energy and the alternating current flowing in the electric circuit means, voltage level detector means, means joining the voltage level detector means to the phase detector means for providing a signal from the phase angle detector means to the voltage level detector means in accordance with the phase angle sensed by the phase angle detector means, the voltage level detector means having an output terminal, wherein the voltage level detector means provides a signal at the output terminal thereof during the time that phase angle exceeds a predetermined magnitude, and connection means joining the output terminal of the voltage level detector means to the switch means for operation of the switch means for deenergization of the electric motor, the improvement comprising:

attenuation means for attenuating harmonic frequencies in the alternating current electrical energy flowing through the electric motor, the attenuation means including filter means and amplifier means, means joining the attentuation means to the phase angle detector means,

voltage compensation means connected to the electric circuit means, the voltage compensation means including means compensating for variations in phase angle between the voltage of the alternating current electrical energy and the current flow through the electric circuit means as the phase angle changes as a function of the amplitude of the applied voltage, and connection means connecting the voltage compensation means to the voltage level detector means for introducing a signal to the voltage level detector means which compensates for variations in the amplitude of the voltage of the source of the alternating current electrical energy.

5. The method of protecting a liquid pump which is operated by an electric motor to which alternating current electrical energy having a fundamental frequency is applied through a plurality of electric conductor members, and a switch operable to connect and to disconnect the electric motor with respect to the electric conductor members comprising:

providing a first voltage signal, the first voltage signal being related to the current flow through the electric conductor members and through the electric motor,

attentuating harmonic frequencies which exist in the first voltage signal,

providing a second voltage signal, the second voltage signal being related to the voltage of the alternating current electrical energy which is applied to the electric conductor members,

sensing the phase angle between the first voltage signal and the second voltage signal and obtaining a phase angle voltage signal proportional to the phase angle,

generating a third voltage signal in accordance with the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, modifying the third voltage signal to obtain a fourth voltage signal which compensates for changes in phase angle which occur as a result of variations in the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, comparing the phase angle voltage signal to the fourth voltage signal, and operating the switch when the difference between the phase angle voltage signal and the fourth voltage signal exceeds a predetermined magnitude.

6. A protective circuit for an alternating current electric motor to which electric energy is applied through a plurality of electric conductor members, and in which the amplitude of the applied voltage may vary comprising:

first signal means, the first signal means presenting a signal representing the voltage applied to the conductor members,

second signal means, the second signal means presenting a signal representing the current flow through the conductor members,

attenuation means attenuating the harmonic frequencies which exist in the second signal means,

phase detector means measuring the phase angle between the signal of the first signal means and the signal of the second signal means and providing a voltage signal in accordance with the signals of the first signal means and the second signal means,

voltage comparator means, means connecting the voltage comparator means to the phase detector means, whereby the phase detector means provides a voltage signal to the voltage comparator means,

voltage compensation means connected to one of the electric conductor members and compensating for variations in the amplitude of the voltage applied to the conductor members, and means connecting the voltage comparator means to the voltage compensation means for providing a compensated voltage signal to the voltage comparator means, the voltage compensation means including third signal means providing a voltage signal proportional to the voltage of said one of the conductor members and amplifier means which includes means for amplifying the voltage signal of the third signal means in accordance with m VL-k, in which m is a fixed value and in which k is an adjustable value and in which VL is the average RMS value of the applied voltage,

connector means connecting the switch means to the voltage comparator means and to the conductor members for operation of the switch means by the voltage comparator means for deenergization of the electric motor in accordance with voltage signals applied to the voltage comparator means by the phase detector means and by the voltage compensation means.

7. A protective circuit for a fluid pump which is operated by an alternating current electric motor to which electric energy is applied through a plurality of electric conductor members, and in which the amplitude of the applied voltage may vary, the protective circuit being of the type provided with first signal means, the first signal means presenting a signal representing the voltage applied to the conductor members, second signal means, the second signal means presenting a signal representing the current flow through the conductor members, phase detector means, the phase detector means being joined to the first signal means and to the second signal means, the phase detector means sensing the phase angle between the signal of first signal means and the signal of the second signal means, voltage comparator means, means connecting the voltage comparator means to the phase detector means, whereby the phase detector means provides a voltage signal to the voltage comparator means, switch means, connector means connecting the switch means to the voltage comparator means and to the conductor members for deenergization of the electric motor,

the improvement comprising voltage compensation means compensating for variations in the amplitude of the voltage applied to the electric conductor members, the voltage compensation means including voltage sensing means connected to one of the electric conductors and providing a voltage signal proportional to the amplitude of the applied voltage, the voltage sensing means including means compensating for variations in phase angle between the applied voltage to the electric conductors and the current flow through the electric conductors as a function of the amplitude of the applied voltage, amplifier means connected to the voltage sensing means, the amplifier means including an output terminal, and means connecting the output terminal of the amplifier means to the voltage comparator means, whereby the amplifier means provides a voltage signal to the voltage comparator means, the voltage comparator means comparing the voltage signal received from the phase detector means and the voltage signal received from the amplifier means and operating the switch means when the difference between the voltage signals is of a predetermined magnitude, the improvement also including attentuation means, means connecting the attenuation means to the second signal means and attenuating the harmonics in the voltage wave form developed in the current flow through the conductor members.

8. A protective circuit for a fluid pump which is operated by an alternating current electric motor to which electric energy is applied through a plurality of electric conductor members, and in which the amplitude of the applied voltage may vary, the protective circuit being of the type provided with first signal means, the first signal means presenting a signal representing the voltage applied to the conductor members, second signal means, the second signal means presenting a signal representing the current flow through the conductor members, phase detector means, the phase detector means being joined to the first signal means and to the second signal means, the phase detector means sensing the phase angle between the signal of first signal means and the signal of the second signal means, voltage comparator means, means connecting the voltage comparator means to the phase detector means, whereby the phase detector means provides a voltage signal to the voltage comparator means, switch means, connector means connecting the switch means to the voltage comparator means and to the conductor members for deenergization of the electric motor in accordance with a predetermined phase angle sensed by the phase detector means,

the improvement comprising voltage compensation means compensating for variations in the amplitude of the voltage applied to the electric conductor members, the voltage compensation means including voltage sensing means connected to one of the electric conductors and providing a voltage signal proportional to the applied voltage, modification means modifying the voltage signal in accordance with m(V Line)-k, in which V Line is the potential applied to the electric conductor members and m is a constant slope and in which k is a fixed voltage, the voltage sensing means including means compensating for variations in phase angle between the applied voltage to the electric conductors and the current flow through the electric conductors as a function of the amplitude of the applied voltage, the voltage sensing means including an output terminal, and means connecting the output terminal of the voltage sensing means to the voltage comparator means, whereby the voltage sensing means provides a voltage signal to the voltage comparator means, the voltage sensing means thus providing a voltage signal which compensates for variations in the amplitude of the applied voltage, the voltage comparator means comparing the voltage signal received from the phase detector means and the voltage signal received from the voltage sensing means and operating the switch means when the difference between the voltage signals is of a predetermined magnitude.

9. The method of protecting a liquid pump which is operated by an electric motor to which alternating current electrical energy having a fundamental frequency is applied through a plurality of electric conductor members, and a switch operable to connect and to disconnect the electric motor with respect to the electric conductor members comprising:

providing a first voltage signal, the first voltage signal being related to the current flow through the electric conductor members and through the electric motor,

attenuating harmonic frequencies which exist in the first voltage signal,

providing a second voltage signal, the second voltage signal being related to the voltage of the alternating current electrical energy which is applied to the electric conductor members,

sensing the phase angle between the first voltage signal and the second voltage signal and obtaining a phase angle voltage signal proportional to the phase angle, and operating the switch when the phase angle voltage signal exceeds a predetermined magnitude.

10. A protective circuit for a fluid pump which is operated by an alternating current electric motor to which electric energy is applied through a plurality of electric conductor members, and in which the amplitude of the applied voltage may vary comprising:

first signal means, the first signal means presenting a signal representing the voltage applied to the conductor members,

second signal means, the second signal means presenting a signal representing the current flow through the conductor members,

phase detector means measuring the phase angle between the signal of first signal means and the signal of the second signal means,

voltage comparator means, means connecting the voltage comparator means to the phase detector means,

switch means,

connector means including operator means connected to the switch means and to the voltage comparator means for deenergization of the electric motor in accordance with a predetermined phase angle sensed by the phase detector means, voltage compensation means connected to one of the electric conductor members and compensating for variations in voltage applied to the electric conductor members, and means connecting the voltage comparator means to the voltage compensation means,

the voltage compensation means including voltage divider means connected to one of the electric conductors, a first resistor and a capacitor connected to the voltage divider means, and an operational amplifier having a first input terminal and a second input terminal, the first input terminal being connected to the first resistor, a second resistor connected to the first resistor and to the first input terminal of the operational amplifier, the operational amplifier having an output terminal, a third resistor connected to the output terminal of the operational amplifier and to the second input terminal of the operational amplifier, a potentiometer, a fourth resistor connected between the second input terminal of the operational amplifier and the potentiometer, and means connecting the output terminal of the operational amplifier to the voltage comparator means.