Descrição: Technical discussion of the Zone System
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Short "Zone blocking" manual for offense in American football
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Why we need to use Check Zone i n Low impedance Busbar protection baskar2k7, Posted on: 2009-12-29 15:55:17
By:
Dear Pearls, Could you explain,Why we need to use check Zone in low impedance busbar protection since we are selecting the Zones via isolator contact. Regards, S.Baskar Mr. Gopala Krishna
By: gkpalepu,
Posted on: 2010-01-05 06:52:45
i am not under standing your Logic Please clarify www.scribd.com/gkpalepu Check zone
By: Pradeep,
Posted on: 2010-01-05 07:25:13
Hi Bhaskar, Check zone does the job of increasing the security of the protection. Traditionally in high impedance differential protection check zone was fed from a seperate CT core from all the feeder circuit connected to the bus (ingnoring the bus coupler/sections). Thus you have only one check zone for a bus bar protection and it would operate for faults in any bus (if you have multiple bus arrangement). With this connection the check zone provides stability against - any CT secondary circuit opening - isolator auxiliary contact / switching relay misbehaviour - any mis operation of main differential relay
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Now with the low impedance differential relay (biased differential relay), use of second CT core for check zone has been dispensed with (infact the earlier schemes such as MBCZ had this option). Thus the check zone effectively took the current input from the same CT core as the main zone. The difference is that while the main zone calculates the differential current for each bus section based on the isolator contact position, the check zone would calculate the overall differential current (all bus sections). Thus the check zone calculation does not require the isolator contact position. So with this kind of arrangement the check zone is primarily to ensure stability for the protection during isolator contact misbehaviour. In some relays the check zone is a simple differential over current function, whereas in some relays you ca n make it also a biased differential element. Hope this gives some idea. Please feel free to ask/discuss further. Cheers Pradeep Mr. Gopala Krishna
By: gkpalepu,
Posted on: 2010-01-12 05:09:38
Hai Pradeep, Thank you for good analysis. Presently Power grid is following Duplicate Busbar Protection (Both 87BB1 & 87BB2) both are same make. The Logic also 1out of 2 logic they are following. what is the problem to adopt different make. Like Distance relays To increase dependability
By: Pradeep,
Posted on: 2010-01-13 02:47:36
Hi Gopalakrishna, The present Power grid (India) philosophy is t o use two complete duplicated busbar protection. It is similar to the two main philosophy used in line protection. This is to increase the dependability for the busbar protection. Each busbar protection will be complete with its own check logic. However in this case main and check will use the same CT core. The decision to use the same type of relay or from different manufacturer is more of a practice. The argument in favor of this is that if there is any hidden problem with one manufacturer problem, then using different manufacturer will he lp. On the other hand there is another argument against it that using different relays means there is more types of relays in the s/s, which increases the spare requirement and competency requirments. Cheers Pradeep
