Method of detecting ground faults in a network for distribution of electric power and a device for carrying out the method

• US 4,529,929 A
• Filed: 10/29/1982
• Issued: 07/16/1985
• Est. Priority Date: 11/02/1981
• Status: Expired due to Fees

• Current Assignee: ASEA AB Vasteras Sweden
• Original Assignee: Asea Aktiebolag (ABB Limited)
• Inventors: Berggren, Jan
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/437,634
• Time in Patent Office: 991 Days
• Field of Search: 324/51, 324/52, 324/54
• US Class Current: 324/509
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: G01R 31/086 in power transmission or distribution networks, i.e. with interconnected conductors
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105
• CPC Class Codes: H02H 7/26 Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured locating faults in cables G01R31/08
• CPC Class Codes: Y04S 10/52 Outage or fault management, e.g. fault detection or location

Abstract

A method and a device for detecting ground faults in a network for distribution of electric power from a power station from which a number of lines, included in the network, emanate and where the ground fault current I_J of each line is measured. According to this method, that line is selected (10) which shows the greatest active ground fault current I_JR (8), alternatively the greatest ground fault current I_J, or the greatest change in the ground fault current ΔI_J. Thereafter, the measured ground fault current, or the change thereof, in the selected line is compared (12) with at least one predetermined reference value (11). A fault indication is obtained (13) at a level exceeding the reference value.

Claims

1. Device for detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate and where the active ground fault current I_JR of each line is measured, comprising means for selecting the line having the greatest active ground fault current I_JR, means for comparing the measured active ground fault current in the selected line with at least one predetermined reference value, and means for producing a fault-indicating output signal with said measured active ground fault current exceeding the reference value.

2. Device according to claim 1 further comprising an interface unit for receiving the measured active ground fault current I_JR of each respective line, and means for synchronously controlling said interface unit and said means for selecting, and said means for producing having one output for each line, which outputs are fault-indicating signals.

3. Device according to claim 2 wherein said means for synchronously controlling includes a measuring unit for comparing the neutral point voltage U₀ with a predetermined value and to produce an output signal when the rate of change of the neutral point voltage changes signs.

4. Device according to claim 2 wherein said means for synchronously controlling includes means for generating clock signals for synchronous control of said interface unit and said means for selecting.

5. Method of detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate by measuring the ground fault current I_J for each line,

selecting the line having the greatest ground fault current I_J, comparing the measured ground fault current in the selected line with at least one predetermined reference value, and deriving a fault indication at a level exceeding the reference value.

6. Method according to claim 5 including continuously forming the difference between the measured value on one measuring occasion and the measured value on a corresponding measuring occasion during the preceding cycle.

7. Method according to claim 5, wherein the ground fault current I_J is measured instantaneously on a plurality of measuring occasions during each cycle of the power frequency, and adding a specified number of the measured values for each line in synchronism to form a measure of the amount of said ground fault current I_J.

8. Method according to claim 7 including continuously forming the difference between the measured value on one measuring occasion and the measured value on a corresponding measuring occasion during the preceding cycle.

15. Device according to claim 7, further comprising an interface unit for receiving the ground fault current I_J of each respective line, and means for synchronously controlling said interface unit and said means for selecting, and said means for producing having one output for each line, which outputs are fault-indicating output signals.

16. Device according to claim 15 wherein said means for synchronously controlling includes means for generating clock signals for synchronous control of said interface unit and said means for selecting.

17. Device according to claim 15, further comprising a measuring unit for comparing the neutral point voltage U₀ with a predetermined value and to produce an output signal when said neutral point voltage U₀ is >

than said predetermined value.

18. Device according to claim 15 wherein said measuring unit for ground fault current I_J is arranged to measure both the change in the ground fault current Δ

I_J and the absolute value of the ground fault current or its active component, and, at a value exceeding a predetermined reference value, to deliver a fault-indicating output signal.

19. Device according to claim 17 wherein said measuring unit for ground fault current I_J is arranged to measure both the change in the ground fault current Δ

I_J and the absolute value of the ground fault current or its active component, and, at a value exceeding a predetermined reference value, to deliver a fault-indicating output signal.

9. Device for detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate and where the ground fault current I_J of each line is measured, comprising means for selecting the line having the greatest change Δ

I_J in ground fault current, means for comparing the change in ground fault current Δ

I_J in the selected line with at least one predetermined reference value, and means for producing a fault-indicating output signal with said measured change in the ground fault current exceeding said reference value.

10. Device according to claim 9 further comprising an interface unit for receiving the measured ground fault current I_J of each respective line, and means for synchronously controlling said interface unit and said means for selecting, and said means for producing having one output for each respective line, which outputs are fault-indicating signals.

11. Device according to claim 10 further comprising a measuring unit for comparing the neutral point voltage U₀ with a predetermined value and to produce an output signal when the rate of change of the neutral point voltage changes signs.

12. Device according to claim 10 wherein said means for synchronously controlling includes means for generating clock signals for synchronous control of said interface unit and said means for selecting.

13. Device for detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate and where the ground fault current I_J of each line is measured, comprising means for selecting the line having the greatest ground fault current I_J, means for comparing the measured ground fault current in the selected line with at least one predetermined reference value, and means for producing a fault-indicating output signal with said measured ground fault current exceeding the reference value.

14. Device according to claim 13 wherein said measuring unit for ground fault current I_J is arranged to measure both the change in the ground fault current Δ

I_J and the absolute value of the ground fault current or its active component, and, at a value exceeding a predetermined reference value, to deliver a fault-indicating output signal.

20. Method of detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate by measuring the ground fault current I_J for each line,

selecting the line having the greatest change Δ

I_J in the ground fault current I_J,

comparing the change Δ

I_J in measured ground fault current in the selected line with at least one predetermined reference value, and

deriving a fault indication at a level exceeding the reference value.

21. Method according to claim 20 including continuously forming the difference between the measured value on one measuring occasion and the measured value on a corresponding measuring occasion during the preceding cycle.

23. Method according to claim 21, including further determining when the rate of change of the neutral point voltage changes signs and wherein the ground fault current I_JR is measured instantaneously when the rate of change of the neutral point voltage changes signs, and adding the measured values for each line so that the sum becomes a measure of the amount of the active component of the ground fault current.

24. Method according to claim 23 including forming the sum of the amounts of the individual differences, obtained for each measuring occasion, in ground fault current I_J during two cycles of power frequency, and generating the change in ground fault current Δ

I_J.

25. Method according to claim 23 including initiating the measuring of the ground fault current I_JR and measuring for as long as the measured neutral point voltage U₀ of the network attains a certain predetermined value.

22. Method of detecting ground faults in networks for distribution of electric power from a power station from which a number of lines, included in the network, emanate by measuring the active ground fault current I_JR for each line,

selecting the line having the greatest active ground fault current I_JR,

comparing the measured active ground fault current in the selected line with at least one predetermined reference value, and

deriving a fault indication at a level exceeding the reference value.

26. Method according to claim 22 including continuously forming the difference between the measured value on one measuring occasion and the measured value on a corresponding measuring occasion during the preceding cycle.