Me ke shi ake kare da Lines ko Feeder Protection?

Me kadan Lines ko Feeder Protection?

Ta'rifin Da Kyauwar Hanyar Zafi

Da kyauwar hanyar zafi shi ne wani set of tattalin da ake amfani da su don gano da isoli faults a cikin hanyoyi na zafi, tare da masu zafi da ya ba da hukuma da kuma hada yadda ake bukata.

Time Graded Over Current Protection

Wannan zai iya tabbatar da ita a matsayin over-current protection of electrical power transmission line. Ba ni bayyana different schemes of time graded over current protection.

Da Kyauwar Radial Feeder

A cikin radial feeder, zafi ya ci gaba daya kawai, wanda ya shiga daga mai muhimmanci zuwa take. Wannan irin feeders za su iya da kyauwa da kasuwanci ta haka tare da amfani da definite time relays ko inverse time relays.

Da Kyauwar Hanyar Definite Time Relay

Tattalin da kyauwa haka shi ne mafi yawan sauƙi. A nan total line ya jagoranci sabon sections kuma kowane section an samun da definite time relay. An samun relay da ya fiye waɗanda ke fadada hanyar da tsawon lokaci da ɗaya, sannan tsawon lokaci na relay ɗuka suna zama da ƙarin, zuwa mai muhimmanci.

Misali, idan akwai mai muhimmanci a point A, a dukunan da aka ƙarfe

A point D an samun circuit breaker CB-3 da tsawon lokacin relay operation 0.5 sec. Sannan a point C an samun wasu circuit breaker CB-2 da tsawon lokacin relay operation 1 sec. Circuit breaker CB-1 an samun a point B wanda ya fiye waɗanda ke mai muhimmanci. A point B, an samun relay da tsawon lokacin operation 1.5 sec.

Daga baya, idan fault yake faru a point F. Saboda wannan fault, faulty current ya ƙoƙari ɗaya ɗaya a cikin all the current transformers or CTs connected in the line. Amma saboda tsawon lokacin operation of relay a point D shi ne ɗaya, CB-3, wanda ake ƙara da shi ya zama zuba ɗaya don isoli faulty zone daga ɓangaren hanyar.

Idan abin da yake da ɗaya, CB-3 ba zuba ɗaya, sannan next higher timed relay zai yi ƙiyasin don ƙara da associated CB to trip. A nan, CB-2 zai zuba. Idan CB-2 ba zuba ɗaya, sannan next circuit breaker, ya ƙara da CB-1 zai zuba don isoli major portion of the line.

Fadada Definite Time Line Protection

Fadin da ƙanan tattalin da kyauwa haka shi ne sauƙi. Fadin da ƙarin ƙanan shi ne, a lokacin fault, only nearest CB towards the source from fault point zai yi ƙiyasa don isoli specific position of the line.

Nau'in Definite Time Line Protection

Na biyu a hanyar, relay close to the source na ƙarin lokaci, wanda yana nufin cewa faults near the source za su iya zama da ƙarin lokaci don isoli, wato zai iya haifar da buƙatun da ya ƙara.

Over Current Line Protection by Inverse Relay

Nau'in da a lura a matsayin definite time over current protection of transmission line, zai iya ƙoƙari da amfani da inverse time relays. A inverse relay, tsawon lokacin operation yana nuna inversely proportional to fault current.

A dukunan da aka ƙarfe, overall time setting of relay at point D shi ne ɗaya, sannan tsawon lokacin setting ya ƙara da ƙarin for the relays associated with the points towards the point A.

Idan fault yake faru a point F, CB-3 a point D zai zuba ɗaya. Idan CB-3 ba zuba ɗaya, CB-2 zai yi ƙiyasa saboda overall time setting is higher in that relay at point C.

Kafin nau'i mai yawa faru a point A, relay closest to the source zai zuba ƙarin saboda tsawon lokacin operation yana nuna inversely proportional to the fault current.

Over Current Protection of Parallel Feeders

Don inganta hukumar da system, yana buƙata a kan load daga mai muhimmanci da biyu da sauran feeders a parallel. Idan fault yake faru a kan feeders, only that faulty feeder zai isoli daga system don inganta continuity of supply daga mai muhimmanci zuwa load. Wannan buƙatar zai ƙara da da kyauwan parallel feeders ƙarin da simple non direction over current protection of line as in the case of radial feeders. Da kyauwan parallel feeder requires to use directional relays and to grade the time setting of relay for selective tripping.

Akawo biyu na feeders ana ƙoƙari a parallel daga mai muhimmanci zuwa load. Dukkan feeders na biyu na non-directional over current relay a source end. Wannan relays da suka zama inverse time relay. Kuma dukkan feeders na biyu na directional relay or reverse power relay a their load end. Reverse power relays used here should be instantaneous type. Wannan yana nufin cewa wannan relays zai yi ƙiyasa ɗaya idan flow of power in the feeder is reversed. Normal direction of power shi ne daga mai muhimmanci zuwa load.

Daga baya, idan fault yake faru a point F, faɗa fault current shi ne I f.

Fault haka zai samun biyu parallel paths daga mai muhimmanci, one through circuit breaker A only and other via CB-B, feeder-2, CB-Q, load bus and CB-P. Wannan yana nuna a dukunan da aka ƙarfe, where IA and IB are current of fault shared by feeder-1 and feeder-2 respectively.

According to Kirchoff’s current law, I A + IB = If.

Daga baya, IA yana ƙoƙari through CB-A, IB yana ƙoƙari through CB-P. Saboda direction of flow of CB-P is reversed, it will trip instantly. But CB-Q will not trip as flow of current (power) in this circuit breaker is not reversed. As soon as CB-P is tripped, the fault current IB stops flowing through feeder and hence there is no question of further operating of inverse time over current relay. IA still continues to flow even CB-P is tripped. Then because of over current IA, CB-A will trip. In this way the faulty feeder is isolated from system.

Differential Pilot Wire Protection

Wannan shi ne differential protection scheme applied to feeders. Several differential schemes are applied for protection of line but Mess Price Voltage balance system and Translay Scheme are most popularly used.

Merz Price Balance System

Principle of work of Merz Price Balance system yana nuna sauƙi. A tattalin da kyauwan hanyar, identical CT is connected to each of the both ends of the line. Polarity of the CTs is same. The secondary of these current transformer and operating coil of two instantaneous relays are formed a closed loop as shown in the figure below. In the loop pilot wire is used to connect both CT secondary and both relay coil as shown.

Daga baya, from the figure it is quite clear that when the system is under normal condition, there would not be any current flowing through the loop as the secondary current of one CT will cancel out secondary current of other CT.

Daga baya, if any fault occurs in the portion of the line between these two CTs, the secondary current of one CT will no longer equal and opposite of secondary current of other CT. Hence there would be a resultant circulating current in the loop.

Due to this circulating current, the coil of both relays will close the trip circuit of associate circuit breaker. Hence, the faulty line will be isolated from both ends.