ELECTRICAL NETWORK FAULT LOCATION BY DISTRIBUTED VOLTAGE MEASUREMENTS

• US 20100102824A1
• Filed: 04/16/2008
• Published: 04/29/2010
• Est. Priority Date: 04/18/2007
• Status: Active Grant

• Current Assignee: Hydro-Quebec (Province of Québec)
• Original Assignee: Hydro-Quebec (Province of Québec)
• Inventors: Zavoda, Francisc, Pater, Ryszard, Germain, Mario, Tremblay, Mario
• Granted Patent: US 8,269,503 B2
• Time in Patent Office: Days
• US Class Current: 324/522
• CPC Class Codes: G01R 31/088 Aspects of digital computing
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass

Abstract

A method of locating a fault on an electrical network energized by a source uses a form of triangulation of voltage measurements at least three different locations on the network, with at least one of the locations situated upstream from the fault with respect to the source. Voltage phasors corresponding to the voltages measured during the fault are time synchronized. Conductors of the network involved in the fault are determined as a function of characteristics of the voltage phasors and a fault current causing a voltage drop at one of the locations with respect to an initial voltage value is evaluated. A position of the fault is evaluated at a point of the network where a ratio between a difference of the voltages measured at two of the locations and an impedance between one of the two locations and the point is equal to the fault current.

Claims

1. A method for locating a fault on an electrical network energized by a source, comprising the steps of:

measuring voltages at least three different measurement locations on the electrical network, at least one of the measurement locations being situated between the source and the fault;

determining voltage phasors corresponding to the voltages measured during the fault, the voltage phasors being time synchronized;

determining conductors of the electrical network involved in the fault as a function of characteristics of the voltage phasors corresponding to the voltages measured during the fault at one of the measurement locations;

evaluating a fault current causing a voltage drop at least one of the measurement locations with respect to an initial voltage value at said at least one of the measurement locations; and

evaluating a position of the fault on the electrical network corresponding to a point of the electrical network where a ratio between;

i) a difference of the voltages measured during the fault at two of the measurement locations, and

ii) an impedance between one of the two measurement locations and said point of the electrical network, depending on the conductors involved in the fault,

is equal to the fault current.

2. The method according to claim 1, further comprising the step of detecting voltage drops at the measurement locations, the voltages being measured when the voltage drops are detected.

3. The method according to claim 1, wherein one of the measurement locations is situated on the electrical network so as to provide voltage measurements the most equivalent to the voltage of the source with respect to the voltage measurements coming from the other measurement locations.

4. The method according to claim 1, wherein one of the measurement locations is situated on the electrical network so as to provide voltage measurements equivalent to the voltage on a line section of the electrical network situated past the fault.

5. The method according to claim 1, wherein the voltages measured at least one of the measurement locations are taken on secondaries of transformers of the electrical network.

6. The method according to claim 1, wherein:

the fault current evaluated is function of the voltage phasors during the fault at two of the measurement locations upstream from the fault, and an impedance between the two measurement locations; and

the position of the fault is function of an intersection between an axis coinciding with a voltage drop phasor defined by the voltage phasors during the fault at the two measurement locations upstream from the fault, and a reference axis coinciding with a phasor corresponding to the fault current.

7. The method according to claim 1, wherein the voltage phasors during the fault are synchronized as a function of voltage phasors corresponding to the voltages measured before the fault and corresponding voltage phasors simulated according to a model representing the electrical network and including impedance and load estimations according to a flowing path of the fault current on the electrical network.

8. The method according to claim 7, wherein the step of determining the voltage phasors during the fault comprises the sub-steps of:

determining voltage level and phase angle adjustment factors between the voltage phasors corresponding to the voltages measured during the fault and the corresponding simulated voltage phasors;

applying the adjustment factors to the voltage phasors corresponding to the voltages measured during the fault; and

synchronizing the voltage phasors to which the adjustment factors have been applied.

9. The method according to claim 8, further comprising the step of:

verifying that the voltage measurements come from a same perturbation as a function of at least one criterion comprising a duration of the fault, a phase angle of the voltage phasors at the beginning of the fault, a fault type, and a waveform during the fault.

10. The method according to claim 1, further comprising the step of:

correcting the voltage phasors during the fault according to characteristics of the electrical network applicable at the evaluated position of the fault on the electrical network to compensate effects caused by load currents during the fault.

11. The method according to claim 10, wherein the step of correcting the voltage phasors during the fault comprises the sub-steps of:

determining voltage level and phase angle adjustment factors corresponding to the effects caused by the load currents during the fault; and

applying the voltage level and phase angle adjustment factors to the voltage phasors during the fault.

12. The method according to claim 11, wherein the adjustment factors are determined by comparing voltage phasors simulated according to a model of the electrical network while respectively including and excluding the load currents.

13. The method according to claim 10, further comprising the step of:

re-evaluating the fault current and the position of the fault depending on whether the electrical network comprises branches between the source and the position of the fault initially evaluated, the position of the fault and the characteristics of the electrical network used for correcting the fault voltage phasors being modified as a function of the re-evaluated fault current and position of the fault.

14. The method according to claim 1, further comprising, prior to the step of determining the voltage phasors during the fault, the step of:

ordering the voltage measurements according to a succession of the measurement locations along a flow path of the fault current on the electrical network beginning from the source, as a function of ratios between voltage phasors moduli corresponding to the voltages measured before and during the fault.

15. The method according to claim 14, further comprising the step of:

forming trios from different combinations of the voltage phasors corresponding to the voltages measured during the fault, the step of evaluating the position of the fault on the electrical network being carried out for all the trios.

16. The method according to claim 15, wherein the step of evaluating the position of the fault comprises the step of selecting one of the trios providing a best location precision among all the trios, the position of the fault being evaluated according to the voltage measurements at the measurement locations associated to the selected trio.

17. The method according to claim 1, wherein the measured voltages come from wave quality measuring devices disposed on the electrical network, capable of detecting voltage drops and recording and communicating voltage measurements.

18. The method according to claim 1, wherein:

the electrical network comprises different branches; and

the at least three measurement locations comprise measurement locations situated on at least some of the branches of the electrical network, the method further comprising the steps of;

analyzing the voltage measurements so as to locate one of the measurement locations situated downstream from the fault; and

identifying at least one of the branches of the electrical network leading to the measurement location located downstream from the fault, the position of the fault on the electrical line being evaluated as a function of the at least one of the branches identified.

19. The method according to claim 1, further comprising the step of:

re-evaluating the fault current and the position of the fault depending on whether the electrical network comprises branches between the source and the position of the fault initially evaluated, as a function of predetermined characteristics related to the branches involved between the source and the position of the fault initially evaluated.

20. The method according to claim 19, wherein the predetermined characteristics related to the branches involved comprise distances of the branches with respect to the source and impedances of equipments situated at the branches.

21. The method according to claim 1, further comprising the steps of:

determining a fault voltage at the position of the fault as a function of the evaluated fault current and characteristics of the electrical network between the source and the position of the fault; and

providing an indication of the fault voltage determined at the position of the fault.