Posted by Winnie Melda on October 9th, 2018
The article provides a systematic and comprehensive analysis of the voltage and currents that get used in operating distance relays so as to determine their suitability and the outcomes that get expected. System relays are crucial in protecting transmission systems against short circuits and ground faults. Regardless of the kind or system conditions, the system relays divide all the faults on the transmission line it protects into two divisions that are 1) faults that occur between the relaying station and the next sectionalizing point on the line, and 2) all other faults. It is crucial that the classification of the faults gets done instantaneously so that the section in trouble gets isolated immediately, hence minimizing the damage at the point of the failures and the shock to the remainder of the system. It permits the operation nearer the stability limit. The various quantities used for classification are voltages, currents, the phase relations between them, and time.
The nearer method for the protection of single lines, exclusive of pilot-wire or superposed high-frequency methodologies gets obtained by the use of distance relays, while, for parallel lines, a closer approach gets obtained using balanced-current relays. It is, however, necessary to place additional protection for single-line operation and cater for the possibility of simultaneous faults on both lines, for which distance relays are appropriate. When distance relays, get made sufficiently accurate and rapid, the balanced current relays get dispensed with or provided for backup protection only. Distance relays are divided into two types namely impedance relays and reactance relays. Various modified types of relays have also got developed, for the purpose of reducing the threat of unwanted relay operation during load swings or other system disturbances, while retaining the relay ability to operate faults in the protected zone with fault resistance. The characteristics of these modified types of relays are modifications of, or combinations of, the characteristics of impedance or reactance relays.
A single set of relays is not desirable for use in the protection against all kinds of faults. One set of relays gets required to protect against faults that involve two or more conductors, while another set of relays is required for the protection against faults between a conductor and ground. A single set of distance relays can also get used to protect against faults using a set of transfer relays connected in a particular way for faults involving two or more conductors, and in a different way for faults involving one conductor and ground.
In previous studies, the quantities upon which distance relays depend on for their operation have got determined for each possible type of fault taking place at a single location. It has been demonstrated that the quantities obtained using the earlier distance relay connections for both line and ground faults do not provide the closest methodology to the desired outcome, a constant indication of each type of defect at a given location.
For protection against line and ground faults, distance relaying is appropriate for general application to either single- or multiple circuit lines. The only limitation to the use of distance relaying is the variations in the balance-point locations introduced by the impacts of fault resistance. The first or second balance is the limiting factor. The analysis in this article concludes that the earlier conventional approaches of distance relaying can be affected by errors other than those as a result of fault impedance. These errors can, however, get eliminated by the use of delta relaying or by the use of current or voltage compensation, thus concluding that distance relaying is a suitable approach for ground fault protection.
Like it? Share it!
About the AuthorWinnie Melda
Joined: December 7th, 2017
Articles Posted: 364
More by this author