Basic Static Relays in Protective System

Basic Static Relays in Protective System:

Basic Elements of Static Relay : The basic elements of a static relay are namely, Input Element: Mixing circuits are needed to sum the input signals in a convenient form. Semiconductor circuits are suited to the use of summing junctions, well-known in the analog computing field. Use of operational amplifier as a summer or mixer has already been discussed in an earlier chapter. These input signals are derived from CTs and PTs. Measuring Element: This is the most important element as far as Basic Static Relays in Protective System operation is concerned since this sends the deciding signal to the output circuit for operation or nonoperation of …


Differential Protection Relay in Power System : A Differential Protection Relay in Power System scheme compares quantities derived from the input and output currents of the protected circuit in such a manner that, for all healthy system and through fault conditions, the quantities balance and the protection is inoperative, while for internal fault conditions the balance is disturbed and the protection operates. For small lengths of the order of 25 km, pilot wires are used for transmission of information from one end to the other so that the relays can effect a continuous comparison of quantities derived at the two ends. However, for …


Overcurrent Protection Relay in Power System : The technique of Overcurrent Protection Relay in Power System is still widely used as a means of detecting faults on distribution system and on transmission lines fed from one end. In the case of lines fed from both the ends it is used along, with directional relays. Overcurrent Protection Relay are also used in conjunction with distance relays to provide backup protection. Fault current level detectors are termed overcurrent relays; in their static form they are more complicated as compared to their electromagnetic counterpart. The static form offers the following advantages over the electromagnetic form: Low burden on …


Static Distance Protection Relay : Static Distance Protection Relay are characterized by having two input quantities respectively proportional to the voltage and current at a particular point in the power system, referred to as the relaying point. The ideal forms of such relays have characteristics which are not dependent on the actual values of voltage and current, but only on their ratio and the phase angle between them. The basic measurement of impedance is done in comparators of the type already discussed which pass on the signal to tripping circuit through suitable timing unit. Typical Distance Relay Characteristics: A schematic block diagram showing the …