Differential Relay Application: The principle of operation depends on a simple circulating current principle where the difference of the currents of the two CTs flows through the relay under normal conditions or even under faults outside the protected section. This is illustrated in Fig. (4.22). The relay R is a simple comparator which compares current […]

Distance Relays Types and their Applications: In applying relays to a transmission system it is necessary to state the relay characteristic in the same terms that the system conditions are stated. This is especially true of Distance Relays Types. If the relay characteristics are thought of in terms of volts and amperes, then the system […]

Directional Overcurrent Relays in Power Systems: Directional Overcurrent Relays in Power Systems – Relay connections must be made so that the currents and voltages applied to the relay during the various fault conditions which may arise on the protected circuit section afford the relay a positive and sufficiently large operating torque. To achieve this for […]

Single Phase Directional Relay: Single Phase Directional Relay – The general Eq. (4.8) suggests that for directional control the individual torques, viz. K |A|2 and K′ |B|2 should be eliminated. Considering a voltage current directional relay the general Eq. (4.8) reduces to The spring constant K” has no function and can be reduced to zero, so The […]

Directional Relays: Selective protection cannot be achieved with time graded overcurrent protection systems in ring or loop systems as well as in radial circuits with two end power supply. A directional feature is incorporated in the Directional Relays as shown in Fig. (4.11). Figure (4.11a) shows how an induction disc type overcurrent relay with split-pole […]

Time Current Relay Application: Time Current Relay Application – Overcurrent and earth fault protective gear can be made discriminative by grading the operating times of successive devices. The pickup currents are adjusted in such a way that the protection nearest the fault operates in a shorter time than the protection in the succeeding section towards […]