We are facing a line tripping problem in the 132 kV single source transmission line. The fault is temporary. As we restore the line again after 15-20 minutes the fault does not exist and line works well.
As the fault occur protection relay (earth fault and short circuit fault) operate at sending and receiving end. The fault current at the sending end and receiving end are in 5 kilo ampere (kA) range and 100 mili ampere (mA) respectively.
The fault may be LL fault that occur during windy conditions when two line wires touch temporarily. A single line diagram may be required for better analysis.
Dear Rajeev,
Have a look on the attached interesting paper as deals with temporary faults!!
Regards,
Mohamed
Length of line is important, in long line model, the increased leakage current(capacitive) could trip the line after a while.....
The following could be causing the fault:
1. Bird droppings on the insulator causing flash-over - mainly in afternoon/evening - requires cleaning/changing insulator configuration
2. Insulation flash-over due to pollution - mainly in rainy season - insulator cleaning can solve this
3. If there is a numerical relay, you can check details regarding the fault location as seen by the relay. If the location is same every time, line inspection may be carried out.
4. Also, numerical relays provide disturbance records which can be analysed.
Dear Mayank,
Thank you very much for sharing your valuable comment.
In my case the the fault location is changing every time.
In highly windy weather nearby tree branches may touch the lines resulting in LG or LLG faults. Some time unfortunate birds also cause LL faults. You better check the sag of your transmission lines.
It seems that line maintenance is the main issue here. Mayank Nagendran has given logically correct answer to this question.
I would add that such faults occur when the live transmission line is tracking to earth. Examples have been given by Mayank such wind, vegetation touching the live conductor and observe the time of the tripping time. If in the morning then moisture but any time of the day then the other reason.
hi prof. Shaibu,
Thanks ! But the fault time is night 8-10 pm.
What type od relay you use? Numerical ABB, SIEMENS , AREVA ... and have you plots of disturbance recorder and relay tripping diagrams??
It will halp to "see" what type of fault is and where?
Srete
It is important to see the waveform recorders in failure to analyze the characteristics of the fault. In transmission lines to equal or higher levels of 230 kV, the angle between the voltage and current is a good indicator of the fault impedance (type).
Some elements that can cause these types of failures are:
- Approach with other low voltage circuits .
- Approach with vegetation
- Failure arrester
- Contamination in electrical insulators
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