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An investigation into a new approach to UHS protection of EHV transmission lines based on detection of fault generated noise

Agrawal, P. (1989). An investigation into a new approach to UHS protection of EHV transmission lines based on detection of fault generated noise. (Unpublished Doctoral thesis, City, University of London)


This thesis describes a new approach to UHS protection of HV transmission line using high frequency components of fault generated noise. The approach is based on a scheme of the non-unit type which has features of unit type of protection. Advantages of unit-type protection are very well known for providing discrimination between internal and external faults. Such a scheme makes use of a stack-tuner circuit of the HV system which has a conventional coupling capacitor of the voltage transformer. The stack-tuner is tuned to a certain frequency bandwidth which does not interfere with the frequency of carrier communication if used, and the output is processed for comparison with a threshold voltage and the resulting signal being fed to a decision logic. A high speed directional detector has been used for discrimination against external faults. A signal from this directional detector can also be fed to the decision logic. The final operation of tripping depends on the output signal of the decision logic. For testing the scheme, a 100 km long 400 kV transmission line has been digitally simulated with sources of 5 GVA and 20 GVA for high frequency applications, typically 300 kHz. In order to cancel out the effect of noise due to other sources like communication etc., the tuner output of each phase has been summed in Aerial mode-2 form (1, -2, 1) and tests have been carried out for cases with and without bus bar capacitance.

Further effects of an electric arc on the newly developed scheme have been discussed as most faults involve arcing or some other kind of discharge. In the present scheme, a significant high frequency component of the arc voltage has been noticed which can affect the performance of the scheme. When carrying out simulation tests, a remarkable feature of the arc repeating every half cycle has been noticed. Another revolutionary feature of the arc model has been noticed; a significant response which repeats every half cycle, even for zero voltage fault inception. It has thereby been found that the scheme can operate at least in principle, for zero-voltage point - on-wave faults. This represents a significant improvement over schemes based on travelling wave phenomena which have been considered a failure for faults at zero degree fault inception angle. This has been a difficult task to simulate the system due to limited memory of the computer Gould 9095 available at the City University, London. For this purpose, program has been optimised for two power cycles of observation time for tuner frequency of 100 kHz.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering > Electrical & Electronic Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Agrawal thesis 1989 PDF-A.pdf]
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