Replacing a 1500kVA 3 phase Delta
Replacing a 1500kVA 3 phase Delta
(OP)
An industrial customer is currently fed via a 2000kVA 13860V delta-600 GrdY 347V. The medium term plan is to replace the 13860V system by a 24940GrdY system, and install a new 2500kVA transformer connected GrdY-GrdY
What would be the drawbacks to remove the present transformer (delta primary) and feed him until then, ie a few years, with a 2000kVA 13860V Y - 600 GrdY 347V. (Note the transformer H0 would be insulated and left floating; only X0 would be connected to the ground grid).
Thanks for your help!
What would be the drawbacks to remove the present transformer (delta primary) and feed him until then, ie a few years, with a 2000kVA 13860V Y - 600 GrdY 347V. (Note the transformer H0 would be insulated and left floating; only X0 would be connected to the ground grid).
Thanks for your help!






RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
Presumably, your existing circuit protection on the 600V is based around detecting overcurrent to trip in the event of an earth fault. This won't function any more.
If you want to muddle through a more technical explanation, google "The Whys of Wyes", which is an excellent paper produced by GE on the subject of transformer wye connections, and freely available.
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
Regards
Marmite
RE: Replacing a 1500kVA 3 phase Delta
I also read that leaving the H0 ungrounded, will increase the chances of ferroresonance,(even on a 15kV system), specially because there will be some length of underground cable, and these new Wye padmounted transfomers will be low loss.
For prc..... H0 floating was an early tought. The early thinking was to this would help us to keep the upstream protection as it is currently (ie protecting the existing 13.8kV Delta transformer) until the primary voltage conversion to 25kV in a couple of years. But a floating H0 does not appears to be a good idea in this case!
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta
See attached sketches to (hopefully) explain what happens in each of the two cases - X0 earthed, and X0 unearthed.
RE: Replacing a 1500kVA 3 phase Delta
RE: Replacing a 1500kVA 3 phase Delta