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I have a questions about the Phase Differential settings for the GE Multilin SR-489
I have a questions about the Phase Differential settings for the GE Multilin 489
Diff. Trip Min. P.U. is — 0.10 X CT
What are they referring to the CTR 3200/5 or the Generator
Diff. Trip Slope 1— 10%
Diff. Trip Slope 2— 20%Are they referring to Full Load Amps of the Gen
Generator Parameters are
FLA = 3007
2.5 MVA
.8 PF
480 Volt
CTR 3200/5
NCTR 3200/5Thanks for any help
arnie1977
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It should be 0.1 x CT where CT is the maximum secondary current of the CT, typically 5 A in north America. 0.1 x 5A = 0.5 A pick up. Some GE relays will also add the difference between taps of windings as an additional multiplier but generator windings typically have the same CT ratio so that factor will not apply.
It is important that you perform the pickup test using three phase balanced currents because a single phase test may add correction factors such as 1.73, 1.5, 1.414 depending on the relay.
Dear Chris,
My comment is a year on the road, but still…
The 0.1PU should be a guiding number referring to actual currents. CTs are sometimes set higher then the Gen I-nominal (FLA), so, the 0.1 PU starts to loose relevancy for the specific Gen, and therefor, not adequately protecting it.
N.B. in case the zone of protection includes a Transformer, the CTs will have different ratios, and compensations will be done in the relay setting file and not externally (as per GE guide).
Kind regards,
Eric Stark
RNItechnology
Sr. Eng. Trainer & Consultant
Protection & Control Engineering
T: 1-416-546-546-1
[email protected]
http://www.RNItechnology.com
LinkedIn profile @: ca.linkedin.com/pub/eric-stark/2b/143/b7