Fault direction calculation during current transformer saturation

Patent metadata

Field	Value
Publication number	US-11474139-B2
Application number	US-201916376635-A
Country	US
Kind code	B2
Filing date	Apr 5, 2019
Priority date	Apr 5, 2019
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

Improvements in the functioning of a line-mounted device to calculate a direction to a fault during current transformer (CT) saturation are disclosed herein. The line-mounted device may determine a load direction using voltage and current zero-crossings and a power system frequency before the fault condition. The line-mounted device may determine a fault direction in relation to the direction to the load after calculating and removing direct current (DC) components of a sampled current signal using valid sample pairs obtained during unsaturated regions of peaks of the sampled current signal. The line-mounted device may indicate the direction to the fault. A system of line-mounted devices may be used to determine a faulted section of a power system using indications of fault direction.

First claim

What is claimed is:

1. A line-mounted device for an electric power delivery system, configured to determine a direction to a fault under conditions of a saturated current transformer (CT), comprising:
a current transformer in electrical communication with a conductor of the electric power delivery system, comprising a core and a winding including secondary leads;
sensor circuitry in electrical communication with the secondary leads, configured to:
calculate a frequency of a current signal on the electric power delivery system using zero-crossings a secondary current signal from the secondary leads;
record zero-crossings of a voltage signal;
compare a current magnitude of the secondary current signal against a predetermined fault current threshold;
when the current magnitude exceeds the predetermined fault current threshold, signal a controller of a fault condition;

the controller in communication with the sensor circuitry, comprising:
a processor;
a non-transitory computer-readable storage in communication with the processor, comprising instructions that when operated cause the processor to:
record samples of the secondary current signal from the sensor circuitry to form a sampled secondary signal;
calculate a load direction using the zero crossings of the secondary current signal and the zero crossings of the voltage signal;
calculate a DC component of the sampled current secondary signal;
remove the DC component from the sampled current secondary signal;
calculate a direction to the fault in relation to the load direction using the sampled current secondary signal with the DC component removed; and
indicate the direction to the fault.

2. The line-mounted device of claim 1 , further comprising communication circuitry in communication with the processor for transmitting the calculated fault direction to a consuming device.

3. The line-mounted device of claim 1 , wherein the non-transitory computer-readable storage medium comprises further instructions that cause the processor to:
determine first and second peaks of the secondary current signal;
calculate a first unsaturated region of the first peak of the secondary signal and a second unsaturated region of the second peak of the secondary current signal;
determine valid pairs of samples from the sampled current secondary signal within the first and second unsaturated regions; and
calculate the DC component of the sampled current secondary signal from the valid pairs of samples.

4. The line-mounted device of claim 3 , wherein each of the valid pairs includes a first sample in the first unsaturated region and a second sample in the second unsaturated region.

5. The line-mounted device of claim 1 , wherein the secondary current signal is distorted due to saturation of the CT.

6. The line-mounted device of claim 1 , wherein the direction of the load is calculated by
calculating a difference between a zero-crossing time of the voltage signal and a zero-crossing time of the secondary current signal; and,
comparing the difference with calculated thresholds.

7. The line-mounted device of claim 6 , wherein the calculated thresholds are functions of the calculated power system frequency.

8. The line-mounted device of claim 6 , wherein the zero-crossing time of the voltage signal comprises the latest zero-crossing time of the voltage signal before the controller is signaled of the fault condition, and the zero-crossing time of the secondary current signal comprises the latest zero-crossing time of the secondary current signal before the controller is signaled of the fault condition.

9. A method of improving functioning of a line-mounted device in determining fault direction in presence of current transformer (CT) saturation, comprising the steps of:
before detection of a fault, the line-mounted device receiving a secondary current signal using the CT in electrical communication with an electric power delivery system, receiving voltage signals from the electric power delivery system, determining zero crossings of the secondary current signal and zero crossings of the voltage signals, time stamping and recording the current and voltage zero crossings, and comparing a magnitude of the secondary current signal with a predetermined fault current threshold;
calculate a power system frequency using the zero crossings;
calculate a load direction using the time stamps of the zero crossings of the secondary current signal and the voltage signal;
upon the magnitude of the secondary current signal exceeding the predetermined fault current threshold, the line-mounted device:
sampling the secondary current signal to form a sampled secondary current signal;
calculating a DC component of the sampled secondary current signal from the sampled secondary current samples;
removing the DC component of the sampled secondary current signal; and
calculating a direction to the fault in relation to the load direction from the sampled secondary current signal with the DC component removed; and

indicating the fault direction.

10. The method of claim 9 , further comprising the steps of:
determining first and second peaks of the secondary current signal using the sampled secondary current signal;
calculating a first unsaturated region of the first peak of the secondary signal and a second unsaturated region of the second peak of the secondary current signal;
determining valid pairs of samples from the sampled secondary current signal within the first and second unsaturated regions; and
the calculation of the DC component is from the valid pairs of samples.

11. The method of claim 9 , wherein calculating the load direction comprises:
calculating a difference between a zero crossing time of the voltage signal and a zero crossing time of the secondary current signal; and
comparing the difference with calculated thresholds.

12. The method of claim 11 , wherein the calculated thresholds are functions of the calculated power system frequency.

13. The method of claim 11 , wherein the zero-crossing time of the voltage signal comprises the latest zero-crossing time of the voltage signal before the controller is signaled of the fault condition, and the zero-crossing time of the secondary current signal comprises the latest zero-crossing time of the secondary current signal before the controller is signaled of the fault condition.

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Hao Kei

Classifications

• G01R31/085 Primary

  in power transmission or distribution lines, e.g. overhead · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• G01R31/088

  Aspects of digital computing · CPC title