Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Electrical and Computer Engineering

Supervisor

Prof. Tarlochan Singh Sidhu

Abstract

This research work is mainly concerned about dealing with temporary short circuit faults in power system transmission lines. In fact, there are two types of electrical faults in power systems, namely temporary and permanent. When a fault is permanent, the only way to clear it is to de-energize the transmission line by opening the associated circuit breakers. However, in many cases the fault is not solid and is caused by objects such as flying birds or broken branches of trees. For these cases, electrical arc plays a major role. For such fault cases, it is also possible to de-energize the faulted phase, temporarily, and re-energize it after a short delay by reclosing the opened circuit breakers. This operation is called single-phase reclosing. There is a chance that the fault becomes clear by natural extinction of the arc after the faulted phase isolation in case the fault is temporary.

There are two considerable challenges regarding traditional single-phase reclosing in transmission lines. The first challenge is the determination of the fault type, i.e., permanent or temporary, as there is no guarantee that the fault is temporary. This is crucially important as reclosing-on-fault, i.e., reclosing the opened breakers while the fault still stands, is harmful for both power system stability and power system equipment. The second challenge which is regarding temporary faults only, is that there is still no guarantee that the arc is extinguished by the moment of reclosing. In such cases, reclosing leads in re-striking of arc and therefore, an unsuccessful reclosing.

This research work is conducted in two phases. At the first phase, two adaptive methods are developed to improve the traditional reclosing method upon the two challenges mentioned in the second paragraph. The developed methods are capable of recognition of the fault type in a reasonable amount of time after single-phase isolation of the line. Therefore, the protection system will be able to block the reclosing function in case the fault is recognized as permanent and to issue three-phase-trip signal as the next action. For temporary faults, re-energizing of the isolated phase by reclosing the opened breakers is the next action which has to be performed after the arc extinction. The developed methods also have the capability of detection of the arc extinction and therefore, a better performance for temporary fault cases is guaranteed. This is the second feature required for an adaptive reclosing method.

The second phase of the research project is to estimate the arc extinction time well in advance in case the fault is temporary. The idea is that three-phase tripping could be the right action if the arc extinction time is too long as working under unbalanced conditions for an unnecessarily long time duration is harmful for the power system.

Both of the proposed adaptive single-phase reclosing methods in this research work employ local voltage information. Therefore, communication facilities are not needed for implementation of the proposed methods. It is shown in the thesis that the proposed methods are able to quickly detect the fault type and also the arc extinction if the fault is temporary. Also, the two proposed arc extinction time prediction methods are capable of prediction of the arc extinction time well in advance and with acceptable precision.

All four proposed methods are effective for various system configurations including ideally-transposed, untransposed and partially-transposed transmission lines and also for transmission lines with different compensation conditions including with and without shunt reactor. Superior performance of the proposed methods have been verified using 550 case studies simulated in PSCAD and Matlab, and also a field recorded temporary fault case associated with a 765 kV transmission line. The 550 simulated case studies include 100 ideally-transposed, 240 untransposed and 210 partially-transposed line cases. The performances of the two proposed reclosing methods are also compared with two of the existing adaptive reclosing methods where considerable improvements are observed.

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