Power quality indicator

• US 7,085,662 B2
• Filed: 07/30/2004
• Issued: 08/01/2006
• Est. Priority Date: 07/30/2004
• Status: Active Grant

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Inventors: Payack, Walter P. Jr.
• Primary Examiner(s): Tsai, Carol S. W.
• Application Number:
  US10/909,177
• Publication Number:
  US 20060025944A1
• Time in Patent Office: 732 Days
• Field of Search: None
• US Class Current: 702/66
• CPC Class Codes: G01R 23/20 Measurement of non-linear distortion
• CPC Class Codes: G01R 29/04 Measuring form factor, i.e. quotient of root-mean-square value and arithmetic mean of instantaneous value; Measuring peak factor, i.e. quotient of maximum value and root-mean-square value
• CPC Class Codes: H01H 2071/124 with a hybrid structure, the solid state trip device being combined with a thermal or a electromagnetic trip
• CPC Class Codes: H02H 3/04 with warning or supervision in addition to disconnection, e.g. for indicating that protective apparatus has functioned watching of pilot wires H02H1/0084; protection of protective arrangements H02H7/008; indication of the state of electronic switches H03K17/18
• CPC Class Codes: H02H 3/52 responsive to the appearance of harmonics

Abstract

There is provided a method and a power quality indicator coupled to an electrical circuit. The indicator comprises the summing device configured to received a sensed wave form from the electrical circuit, including at least one voltage wave form. A summing device is configured to provide a summed output voltage. A low pass filter (LPF) is electrically coupled to the summing device and configured to receive a summed output voltage from the summing device. The LPF is configured to provide a LPF voltage. A microprocessor is configured to receive the sum upward voltage the LPF voltage, compute an RMS voltage value for each of the summed output voltage, determine the difference of such RMS voltage values and generate a signal representative of the difference of the RMS voltage values, wherein the signal is proportional to the harmonic content in the electrical circuit.

Claims

1. A method for determining harmonic content in an electrical circuit and providing a signal proportional to the degree of harmonic content, the method comprising the steps of:

sensing waveforms with a sensing device in the electrical circuit, including at least one voltage waveform;

summing the waveforms in a summing device;

providing a low pass filter;

providing a microprocessor;

providing output voltage of the summing device to the low pass filter and the microprocessor;

computing the RMS value of each of the output voltage of the low pass filter and output voltage of the summing device in the microprocessor;

determining the difference between the two RMS values; and

generating a signal from the microprocessor representing the determined difference of the two RMS values, wherein the signal is proportional to the degree of harmonic content in the electrical circuit.

2. The method of claim 1, including the step of providing the signal to an indicator.

3. The method of claim 1, including the step of providing the signal to an electrical device.

4. The method of claim 3, wherein the electrical device is a trip mechanism of a circuit breaker.

5. The method of claim 2, wherein the indicator is one of a light and an audio device.

6. The method of claim 4, wherein the low pass filter and microprocessor are housed in an electronic trip unit coupled to the circuit breaker.

7. The method of claim 1, wherein the low pass filter is a fourth order low pass filter.

8. A power quality indicator coupled to an electric circuit to monitor harmonics, the power quality indicator comprising:

a summing device configured to receive a sensed waveform from the electric circuit, including at least one voltage waveform, and configured to provide a summed output voltage;

a low pass filter (LPF) electrically coupled to the summing device and configured to receive the summed output voltage from the summing device, and configured to provide a LPF voltage; and

a microprocessor configured to;

receive the summed output voltage and the LPF voltage,

compute an RMS voltage value for each of the summed output voltage and the LPF voltage,

determine the difference of such RMS voltage values, and

generate a signal representative of the difference of the two RMS voltage values, wherein the signal is proportional to the harmonic content in the electrical circuit.

9. The power quality indicator of claim 8, wherein the signal is provided to an electrical device.

10. The power quality indicator of claim 9, wherein the electrical device is a trip mechanism of a circuit breaker.

11. The power quality indicator of claim 10, wherein the low pass filter and microprocessor are housed in the electronic trip unit coupled to the circuit breaker.

12. The power quality indicator of claim 9, wherein the electrical device is one of a light and an audio device.

13. The power quality indicator of claim 8, wherein the low pass filter is a fourth order low pass filter.

14. A circuit breaker coupled to an electric circuit, the circuit breaker including an operating mechanism coupled to a movable contact, the circuit breaker comprising:

an electronic trip unit (ETU) coupled to the operating mechanism; and

a power quality indicator coupled to the electric circuit, the power quality indicator comprising;

a summing device configured to receive a sensed waveform from the electric circuit, including at least one voltage waveform, and configured to provide a summed output voltage;

a low pass filter (LPF) electrically coupled to the summing device and configured to receive the summed output voltage from the summing device, and configured to provide a LPF voltage; and

a microprocessor configured to;

receive the summed output voltage and the LPF voltage,

compute an RMS voltage value for each of the summed output voltage and the LPF voltage,

determine the difference of such RMS voltage values, and

generate a signal representative of the difference of the two RMS voltage values, wherein the signal is proportional to the harmonic content in the electrical circuit.

15. The circuit breaker of claim 14, wherein the signal is provided to an electrical device.

16. The circuit breaker of claim 15 wherein the electrical device is the ETU of the circuit breaker.

17. The circuit breaker of claim 16, wherein the low pass filter and microprocessor are housed in the electronic trip unit coupled to the circuit breaker.

18. The circuit breaker of claim 15 wherein the electrical device is one of a light and an audio device.

19. The circuit breaker of claim 14, wherein the low pass filter is a fourth order low pass filter.

20. The circuit breaker of claim 14, wherein the circuit breaker is a molded case circuit breaker.

21. A power quality indicator monitoring voltage of an electrical device connected to an power circuit, the power quality indicator comprising:

a board;

an electrical circuit mounted on the board and coupled to the electrical device and the power circuit, the electrical circuit includes a low pass filter (LPF) configured to provide a LPF voltage corresponding to the voltage drop across the LPF directly proportional to the degree of harmonic content sensed by electrical circuit in the power circuit; and

a signal device coupled to the electrical circuit configured to provide one of an audio indication, visual indication, and network instruction, wherein the electrical circuit includes a microprocessor configured to;

receive the summed output voltage and the LPF voltage,

compute an RMS voltage value for each of the summed output voltage and the LPF voltage,

determine the difference of such RMS voltage values,

generate a signal representative of the difference of the two RMS voltage values, wherein the signal is proportional to the harmonic content in the power circuit, and provide the signal to the signal device.

22. The power quality indicator of claim 21, wherein the low pass filter is a fourth order low pass filter.

23. The power quality indicator of claim 21, wherein the electrical circuit includes a summing device configured to receive a sensed waveform from the power circuit including at least one voltage waveform, and configured to provide a summed output voltage to the LPF.

24. The power quality indicator of claim 21, wherein the signal device is mounted in a panel board.