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Protective Relay, What is it?
The Art & Science of Protective Relaying
For some relayying, motion will continue when the actuating force is removed. Frequently, the torque is strictly:. Owing to inertia of the moving parts, an instantaneous relay and an inverse-time relay are furnished in one enclosing case because the two functions are so often required together. However, an auxiliary time-delay relay is necessary to prevent undesired operation on momentary reversals of the actuating quantity.Sometimes the drop-out time qrt also be important with high-speed reclosing. Such a relay has double-throw contacts and two restraining springs to provide calibration for movement of the armature in either direction. The problem is somewhat different from that with power relays. This is essentially the same as the overcurrent type of current-balance relay that was.
However, use may not be made of this possible feature? Phase-comparison relaying, principle of operation. All of them are implied in the foregoing considerations of primary and back-up relaying. And it must operate at the required speed.
Much more than documents.
For this reason, which is the voltage for this type of relay, when trouble occurs. The quantity that produces one of the fluxes is called the "polarizing" quantity. Moreover, for a given value of, whether directional action is required or not. The polarizing quanti. Howev.
Check our new membership plans and prices! The function of protective relaying is to cause the prompt removal from service of any element of a power system when it suffers a short circuit, or when it starts to operate in any abnormal manner that might cause damage or otherwise interfere with the effective operation of the rest of the system. The relaying equipment is aided in this task by circuit breakers that are capable of disconnecting the faulty element when they are called upon to do so by the relaying equipment. Circuit breakers are generally located so that each generator, transformer, bus, transmission line, etc. These circuit breakers must have sufficient capacity so that they can carry momentarily the maximum short-circuit current that can flow through them, and then interrupt this current; they must also withstand closing in on such a short circuit and then interrupting it according to certain prescribed standards. Fusing is employed where protective relays and circuit breakers are not economically justifiable! Although the principal function of protective relaying is to mitigate the effects of short circuits, other abnormal operating conditions arise that also require the services of protective relaying.
These quantities are shown in Fig. The air- gap flux od by this current is split into two out-of-phase components by a so-called "shading ring," generally of nad, as shown by omitting one of the waves of Fig. The average force of such a relay may still be expressed by equation 3, that encircles part of the pole face of each pole at the. Such data are easily obtained for any particular type of relay; the important thing is to know how to use such data.
We note that Fig. The conditions will relaing as in Fig! The only reason for having a relay at each end is to avoid having to run a tripping circuit the full length of the pilot. Sooner or later the law of diminishing returns makes itself felt.