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hhpp
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Joined: 14-June 09
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17 Jun 2009
Hello everybody, My name is Hector I am nwe here.
I have a serious doubt about relaying, specifically MIFII relay from GE. Could anybody help me to uinderstand this, I will appreciate your help. I have a 6MVA transformer at the main substation, 34.5 KV, Z=7.5% Full load amperes = 100.5A Max fault =1338.8 A Downstreamns: I have a transformer with a breaker in the primary side and a 1200 fuse at secondary Primary protection is as follows: 3MVA, 34.5 KV/3.3KV, z=7.3% transformer Full load amps (pri) = 50.2A Full load ams (sec)= 524.9A Max fault=7189.9A MiFII settings Cts 600:5 200:5 amp tap why are they ussing this tap ? Pickup set at value less than 150% of full load amps at 34.5KV (Why?, where they gets this value?) Therefore pickup set at 30% or 60 Amps primary (why?) Curver = Extremely inverse ( Why) Time dial =9 (why) ANSI curves With this settings what is the exactly time at which the relay will trip during a fault? Downstreams I have a transformer with a breaker in the primary side and another at secondary Primary protection is as follows: 2.5MVA, 3.3 KV/400V, z=5.5% transformer Full load amps (pri) = 437.4A Full load ams (sec)= 3608.4A Max fault=32567.1A MiFII settings Cts 600:5 Pickup set at value less than 150% of full load amps at 3.3KV (Why?) Therefore pickup set at 80% or 480 Amps primary (why?) Curver = Extremely inverse ( Why) Time dial =4 (why) ANSI curves With this settings what is the exactly time at which the relay will trip during a fault? I have the MIFII manual but this is not clear to me. I loocked at this formula: t=m[a+(b/v-c)+(d/(v-c)^2)+(e/(v-c)^3)] where M = time dial setting v=I/Ipickup setting >1.05 what is the value for I? what is the value for Ipickup setting? what this must be geater than 1.05? Well a lot os doubts, i hope you can help me. Thanks a lot. |
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Lo-Fi Version | Time is now: 7th September 2010 - 04:50 PM |
