Introduction to Protective Relays

Introduction to Protective Relays:

Basic Ideas of Protection Relay : Basic Ideas of Protection Relay should ensure the availability of electrical energy without interruption to every load connected to the system. When the electric power supply is extended to remote villages the power system would consist of several thousand kilometres of distribution lines. The high voltage transmission lines carrying bulk power could extend over several hundred kilometres. Since all these lines are generally overhead line:, and are exposed, there are many chances of their breakdown due to …


Basic Principle of Operation of Protective System : Basic Principle of Operation of Protective System – Each relay in a protection scheme performs a certain function and responds in a given manner to a certain type of change in the circuit quantities. For example one type of relay may operate when the current increases above a certain magnitude, while another may compare current and voltage and operate when the ratio V/1 is less than a given value. The first relay is known …


Essential Qualities of Protection Systems : Every Protection Systems which isolates a faulty element is required to satisfy four basic requirements: reliability; selectivity; fastness of operation; and discrimination. Without reliability and selectivity the protection would be rendered largely ineffective and could even become a liability. Reliability: Reliability is a qualitative term. Quantitatively it can be expressed as a probability of failure. Failure is not confined to protective gear but may also be due to breaker defects. Therefore every component and circuit involved in fault clearance …


Fault Meaning : Fault Meaning and Statistics – It is useful to have some idea of the frequency of the incidence of faults on the different items of equipment in a power system. This information is of help in considering the problems of design and application of protection. Table 1.1 gives an idea of how faults are distributed in the various sections of a power system. It is of interest to note that faults on overhead lines account for nearly half of the …


Zone Protection : The Zone Protection is that part of a power system guarded by a certain protection and usually contains one or at the most two elements of the power system. The zones are arranged to overlap so that no part of the system remains unprotected. Figure (1.1) shows a typical arrangement of overlapping Zone Protection. When it becomes desirable for economic or space saving reasons to overlap on one side of a breaker blind spots occur as shown in Fig. (1.2). It can …