CIRCUIT ARRANGEMENT FOR RECOGNITION OF A DEFECT CAUSED BY PHASE BREAKDOWN OR GROUND SHORT IN THE CURRENT SUPPLY OF A THREE-PHASE MOTOR

• US 3,824,430 A
• Filed: 05/16/1973
• Issued: 07/16/1974
• Est. Priority Date: 08/23/1972
• Status: Expired due to Term

• Current Assignee: Michael Hentschel
• Original Assignee: Michael Hentschel
• Inventors: Hentschel, Michael
• Primary Examiner(s): Hix, L. T.
• Application Number:
  US05/360,946
• Time in Patent Office: 426 Days
• Field of Search: 317/13R,33R
• US Class Current: 361/23
• CPC Class Codes: H02H 3/13 for multiphase applications, e.g. phase interruption
• CPC Class Codes: H02H 3/34 of a three-phase system

Abstract

A circuit arrangement for recognition of a defect from detection alternating voltages proportional to current values at the outer conductors of a three-phase motor and which defects are brought about by phase breakout or ground short in the current supply of the three-phase motor, wherein there are provided a time divisonmultiplex device and thereafter a rectifier circuit arrangement for generating a time division-multiplex signal from the detection alternating voltages by means of cyclically successive samples of uniform duration and forming from the positive or negative parts of the time division-multiplex signal through smoothing a measurement voltage, the amplitude of which is approximately equal to the arithmetic mean value of the rectified multiplex signal. There is further provided a differentiator for differentiating the time division-multiplex signal for the recognition of a phase breakdown, a first comparator for comparing the voltage pulse of the differentiator possessing the maximum amplitude value with a percentual part of the measurement voltage, and wherein the percentual part of the measurement voltage is selected such that the phase breakdown comparator with undisturbed current supply of the motor does not respond and upon the occurrence of a phase breakdown delivers a phase breakdownindicating signal. For the recognition of a ground short from the time division-multiplex signal there is provided a low pass filter arrangement for deriving peak values of signal components occurring with the frequency of the detection alternating voltages, and a second comparator for comparing the peak values with another percentual part of the measurement voltage, wherein this another percentual part is chosen such that the ground short-comparator during undisturbed current supply of the motor does not respond and upon occurrence of a ground short delivers a ground short-indicating signal.

Claims

1. A circuit arrangement for the recognition of a defect from detection alternating voltages proportional to the current values at outer conductors of a three-phase motor and which defects are brought about by phase breakout or ground short, in the current supply of the three-phase motor, the combination comprising a time division-multiplex device and a rectifier circuit arrangement connected in circuit after the time divisionmultiplex device for generating a time division-multiplex signal from the detection alternating voltages by cyclic successive samples of uniform duration and forming from the positive or negative parts of the time division-multiplex signal through smoothing a measurement voltage, the amplitude of which is approximately equal to the arithmetic mean value of the rectified multiplex signal, a differentiator for differentiating the time division-multiplex signal for the recognition of a phase breakdown, a phase breakdown comparator for comparing the voltage pulse of the differentiator possessing maximum amplitude value with a percentual part of the measurement voltage, wherein the percentual part of the measurement voltage is selected such that the phase breakdown comparator with undisturbed current supply of the motor does not respond and upon the occurrence of a phase breakdown delivers a phase breakdown-indicating signal, and that for the recognition of a ground short from the time divisionmultiplex signal there is provided a low pass filter arrangement for deriving peak values for signal components occuring with the frequency of the detection alternating voltages, and a ground short comprator for comparing the peak values with another percentual part of the measurement voltage, wherein this another percentual part of the measurement voltage is chosen such that ground short comparator during indisturbed current supply of the motor does not respond and upon occurrence of a ground short delivers a ground short-indicating signal.

2. The circuit arrangement as defined in claim 1, wherein an amplifier having an adjustable gain for standarizing the output signal is connected in circuit between the output of the time division-multiplex device and the rectifier circuit.

3. The circuit arrangement as defined in claim 2, wherein the amplifier comprises an operational amplifier having a first input and a second input, said first input being connected with the output of the time division-multiplex device and its second input being connected with a voltage divider for adjusting the gain of the operational amplifier, and wherein the resistance relationship of the voltage divider branch determined by the tap for the operational amplifier input determines the gain.

4. The circuit arrangement as defined in claim 1, wherein the ground short comparator contains an operational amplifier having a first input, a second input and an output, said first input being connected with the low pass filter and said second input having applied thereto the corresponding percentual part of the measurement voltage, and said output being connected with the control input of an electronic switch which responds upon occurrence of a ground short signal at the output of the ground short comparator.

5. The circuit arrangement as defined in claim 4, wherein the electronic switch comprises a field-effect transistor.

6. The circuit arrangement as defined in claim 1, wherein the phase breakdown comparator contains an operational amplifier having a first input, a second input and an output, said first input being connected with the differentiator, and the second input having applied thereto the correspoNding percentual part of the measurement voltage, and said output being connected with the control input of an electronic switch which responds upon occurrence of a phase breakdown signal at the output of the phase breakdown comparator.

7. The circuit arrangement as defined in claim 6, wherein the electronic switch comprises a field-effect transistor.

8. The circuit arrangement as defined in claim 1, wherein the rectifier circuit contains a precision rectifier means having an output connected to a voltage divider and for smoothing the output voltage is coupled with at least one capacitor, and wherein the part of the measurement voltage for the ground short and/or phase breakdown comparator is tapped off this voltage divider.

9. The circuit arrangement as defined in claim 4, wherein the phase breakdown comparator contains an operational amplifier having a first input, a second input and an output, said first input being connected with the differentiator, and the second input having applied thereto the corresponding percentual part of the measurement voltage, and said output being connected with the control input of an electronic switch which responds upon occurrence of a phase breakdown signal at the output oc the phase breakdown comparator, each comparator containing a field-effect transistor constituting the corresponding electronic switch, and wherein a respective resistor of a voltage divider determining the gain of the amplifier is connected with the field-effect transistor of the ground short comparator and with the field-effect transistor of the phase breakdown comparator and bridges each such field effect transistor, and the gain of the amplifier upon occurrence of a ground circuit and a phase breakdown through blocking of the corresponding field-effect transistor by the output signal of the corresponding operational amplifier switches the corresponding comparator to a different value, and at the outputs of the operational amplifiers of the ground short- and phase breakdown-comparators there is connected a defect indicator circuit having a signalling device.