Protective digital relay device

• US 7,902,813 B2
• Filed: 09/24/2009
• Issued: 03/08/2011
• 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:
  US12/566,279
• Publication Number:
  US 20100020457A1
• Time in Patent Office: 530 Days
• Field of Search: 324/117.R, 324/117.H, 324126-127, 324/509, 361/42, 361 62- 63
• 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 digital relay device comprising:

a non-transitory computer readable medium having instructions encoded thereon; and

a processor configured to execute the instructions to;

receive an output voltage signal from a Rogowski coil, the output voltage signal corresponding to current flowing in a current path in an electrical power system,

process the output voltage signal in the frequency domain to obtain a frequency domain representation of the current flow,

determine whether a fault condition exists in the electrical power system based on the obtained frequency domain representation of the current, and

cause a protection device associated with the digital relay device to interrupt the current path when the processor determines that the fault condition exists.

2. The digital relay device of claim 1, wherein the processor obtains the frequency domain representation of the current flow without integration of the output voltage signal in the time domain.

3. The digital relay device of claim 1, wherein the processor 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.

4. The digital relay device of claim 3, wherein computation of the equation includes digitally shifting the phase of the voltage output signal by approximately 90 degrees.

5. The digital relay device of claim 1, wherein the output voltage of the Rogowski coil is an analog signal, and

wherein the digital relay device further comprises an analog-to-digital converter configured to digitize the output voltage signal.

6. A digital relay device comprising:

a non-transitory computer readable medium having instructions encoded thereon; and

a processor configured to execute the instructions to;

receive an output voltage signal from a Rogowski coil, the output voltage signal corresponding to current flowing in a current path in an electrical power system,

process the output voltage signal in the frequency domain to obtain a frequency domain representation of the current flow, 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,

determine whether a fault condition exists in the electrical power system based on the obtained frequency domain representation of the current, and

cause a protection device associated with the digital relay device to interrupt the current path when the processor determines that the fault condition exists.

7. The digital relay device of claim 6, wherein the processor obtains the frequency domain representation of the current flow without integration of the output voltage signal in the time domain.

8. The digital relay device of claim 6, wherein the processor 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.

9. The digital relay device of claim 6, wherein the output voltage of the Rogowski coil is an analog signal, and

wherein the digital relay device further comprises an analog-to-digital converter configured to digitize the output voltage signal.

10. A digital relay device comprising:

a non-transitory computer readable medium having instructions encoded thereon; and

a processor configured to execute the instructions to;

receive an output voltage signal from a Rogowski coil, the output voltage signal corresponding to current flowing in a current path in an electrical power system,

process the output voltage signal in the frequency domain to obtain a frequency domain representation of the current flow, the processing including use of the following equation;

I(jw)=−

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

determine whether a fault condition exists in the electrical power system based on the obtained frequency domain representation of the current, and

cause a protection device associated with the digital relay device to interrupt the current path when the processor determines that the fault condition exists.

11. The digital relay device of claim 10, wherein the processor obtains the frequency domain representation of the current flow without integration of the output voltage signal in the time domain.

12. The digital relay device of claim 10, wherein computation of the equation includes digitally shifting the phase of the voltage output signal by approximately 90 degrees.

13. The digital relay device of claim 10, wherein the output voltage of the Rogowski coil is an analog signal, and

wherein the digital relay device further comprises an analog-to-digital converter configured to digitize the output voltage signal.