Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 62

Let us review a small plant having a 5/7 MVA, ONAN/ONAF, 138 to 4.16 kV transformer. A single incoming transformer would suffice. This plant may have some 4.16 kV and some 480 V loads. The 138 kV primary side may include a 600 A fused load interrupter with arcing horns to allow for switching the magnetizing current of the unloaded transformer. Except for switching the magnetizing current, while the LV side is kept open, the switch is not allowed to be operated. The fuse serves for short‐circuit protection only. The maximum incomer current on the transformer 4.16 kV secondary side is 970 A < 80% of 1200 A frame breaker for continuous rating.

A 1200 A rated breaker would be appropriate for this application. The incomer is fed to a single 4.16 kV switchgear 1200 A bus.