Protective relay device, system and methods for Rogowski coil sensors

• US 7,638,999 B2
• Filed: 04/07/2006
• Issued: 12/29/2009
• Est. Priority Date: 04/07/2006
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Cooper Technologies Company (Eaton Corporation PLC.)
• Inventors: Kojovic, Ljubomir A., Williams, Stephen E.
• Primary Examiner(s): Nguyen; Ha Tran T
• Assistant Examiner(s): Vazquez; Arleen M
• Application Number:
  US11/400,087
• Publication Number:
  US 20070236208A1
• Time in Patent Office: 1,362 Days
• Field of Search: 324/117.H, 324/117.R, 324/126, 324/127, 324/509, 361/42, 361 59- 90, 373/60, 702 57- 59, 702 65- 66, 702/77
• US Class Current: 324/127
• CPC Class Codes: G01R 15/181 using coils without a magnetic core, e.g. Rogowski coils
• CPC Class Codes: H02H 1/0007 concerning the detecting means in general G01R or other subclasses of G01; reed switches H01H71/2445

Abstract

Relay devices, systems and methods for obtaining an accurate representation of a current monitored with a Rogowski coil, without integration of the Rogowski coil output voltage signal in the time domain.

Claims

1. A protective system for a current path in an electrical power system, the system comprising:

a Rogowski coil that generates an output voltage signal corresponding to current flow in the current path;

a microprocessor that receives the output voltage signal in frequency domain and that processes the output voltage signal to obtain a frequency domain representation of the current flow in the current path without integration of the output voltage signal in the time domain; and

a protection device that determines whether a fault condition exists in the electrical power system based on the obtained frequency domain representation of the current flow, the protection device causing the current path to be interrupted when the fault condition is detected.

2. The system of claim 1, wherein the microprocessor processes the voltage output signal according to the following equation to obtain the frequency domain representation of the current flow:

I(jw)=−

(V(jw))/(jwM), where I is current, V is voltage, jw is a Laplace operator, and M is a scalar multiplier.

3. The system of claim 2, wherein computation of the equation includes digitally shifting the phase of the voltage output signal by approximately 90 degrees.

4. The system of claim 1, wherein the protection device comprises a digital relay device.

5. The system of claim 1, wherein the microprocessor is a component of the protection device.

6. The system of claim 1, further comprising a second microprocessor that integrates the voltage output signal to extract power analysis information.

7. The system of claim 1, further comprising a circuit protector operatively connected to the protection device, the protection device causing the circuit protector to open the current path when the fault condition is detected.

8. A protective system for a current path in an electrical system, the system comprising:

a Rogowski coil that generates an output voltage signal proportional to a time derivative of a current flow in the current path;

a microprocessor that receives the output voltage signal and that processes the output voltage signal in the frequency domain to obtain a frequency domain representation of the current flow in the current path without integration of the output voltage signal in the time domain, the processing of the output voltage signal comprising the steps of

modifying at least one frequency component of the output voltage signal by a scalar multiplier, and

digitally shifting the phase of the output voltage signal by approximately 90 degrees; and

a relay device that causes the current path to be interrupted based on the obtained frequency domain representation of the current flow.

9. The system of claim 8, wherein the microprocessor processes the output voltage signal according to the following equation to obtain a frequency domain representation of the current flow:

I(jw)=−

(V(jw))/(jwM), where I is current, V is voltage, jw is a Laplace operator, and M is a scalar multiplier.

10. The system of claim 8, wherein the relay device causes the current path to be interrupted upon detecting detect a fault condition in the current path based on the obtained frequency domain representation of the current flow.

11. The system of claim 8, wherein the microprocessor integrates the voltage output signal to extract power analysis information.

12. The system of claim 8, further comprising a circuit protector operatively connected to the relay device, the relay device causing the circuit protector to open the current path based on the obtained frequency domain representation of the current flow.

13. A protective relay system for managing an electrical system, the system comprising:

a conductor that defines a current path in the electrical system;

a Rogowski coil that receives the conductor and that generates an analog output voltage signal proportional to a time derivative of current flow in the current path; and

a digital relay device that receives the analog output voltage signal, digitizes the signal, and processes the digitized output voltage signal in the frequency domain to obtain a frequency domain representation of the current flow without integration of the output voltage signal in the time domain, the processing of the digitized output voltage signal comprising the steps of

modifying at least one frequency component of the output voltage signal by a scalar multiplier, and

digitally shifting the phase of the output voltage signal by approximately 90 degrees,

wherein the digital relay device causes the current path to be interrupted when a fault condition is detected based on the obtained frequency domain representation of the current flow.

14. The system of claim 13, wherein the digital relay device processes the voltage output signal according to the following equation to obtain the frequency domain representation of the current flow:

I(jw)=−

(V(jw))/(jwM), where I is current, V is voltage, jw is a Laplace operator, and M is a scalar multiplier.

15. The system of claim 13, wherein the digital relay device comprises a microprocessor and a memory, the microprocessor and memory detecting the fault condition based on the obtained frequency domain representation of the current flow.

16. The system of claim 13, further comprising a circuit protector operatively connected to the digital relay device, the digital relay device causing the circuit protector to open the current path based on the obtained frequency domain representation of the current flow.

17. A protective system for an electrical network, comprising:

a Rogowski coil monitoring a current path in an electrical system; and

means for processing an output voltage signal of the Rogowski coil in the frequency domain to obtain a frequency domain representation of a current signal corresponding to a time derivative of current flow in the current path, the means for processing obtaining the frequency domain representation of the current signal by

modifying at least one frequency component of the output voltage signal by a scalar multiplier, and

digitally shifting the phase of the output voltage signal by approximately 90 degrees,

the means for processing obtaining the frequency domain representation of the current signal without integrating the output voltage signal in the time domain.

18. The system of claim 17, wherein the means for processing comprises a digital relay device.

19. The system of claim 17, further comprising means for interrupting the current flow in the current path when the obtained frequency domain representation of the current signal corresponds to a fault condition.

20. The system of claim 17, further comprising means for storing data relating to the obtained frequency domain representation of the current signal over time;

and

means for extracting the stored data and analyzing the data.