Zogzog
Primary injection would require removal of this fixed mounted breaker and taking it to the shop. The plant would be down for a long day. Do you have a drg that shows the polarity orientation of the neutral CT for the Digitrip 520 unit? Thanks
Many thanks Waross. Icannot install a seperate CT as the main 3000A breaker is equipped with its own CT for ground sensing. I beleive it is the zero-sequence type. By code we cannot set it to more than 1200A and 0.5 secs. Is this delay not sufficient for the magnetizing current to decay?
Zogzog
It does have a Digitrip unit. Can this be tested and repaired at the site, or does the entire breaker have to go to the shop? Also is it possible to swap just the trip unit with another tested, or new, unit in the field?
The 59N relay is used primarily on ungrounded systems. You need to install 3 PT's connected in grounded wye:broken delta configuration with a loading resistor across the broken delta to avoid ferroresonance. You could use the scheme on a high resistance grounded system, but the settings on the...
Raghun. I am talking about the 480V side
We were able to energize the xformer with the 3000A main breaker GF set at 1200A with a delay of 0.5 secs, and the 2000A xformer feeder breaker set at 1000A with a delay of 0.4 secs. Interestingly when we lowered the 3000A main breaker GF delay to 0.4...
Many thanks to all who have responded. I will clarify some points raised:
The 2000A breaker is rated for 100% of its rating continously. There is no instantaneous setting on it.
The Ho/Xo terminal on the transformer may either be grounded at the xformer, or a cable run from it to the swbd...
Perhaps I should have explained the circit a bit better. The 480V switchboard has a 3000A main fed from a 13.8KV/480V utility transformer. This main has LSIG trips. The G trip is set at 1200A with a delay of 0.3 secs. We used a 2000A breaker on the bus to connect to the new 1500KVA transformer...
Before you parallel two sources you need to confirm the following:
1 The 2 sources MUST be in phase a.k.a. in synchronisim
2 You will substaintially increase the amount of fault current. You must make sure your switchgear can handle it
3 If the 2 services are fed from transformers then the...
When we energize a 1500KVA, 480V, Wye/Wye transformer the upstream breaker trips on ground fault. The ground fault is set at 800A, 0.15 secs. Could it be because of the unbalance between phases on the magnetizing current plus the presence of third harmonic current, a typical compoment of the...
