The following reasons were given: 1. fuses double the amount of space, 2. are subject to damage during normal opening and closing operations of the breaker, which in turn could cause the breaker to trip, 3. the fuses were an unusual request and a potential problem. Can your expert please provide additional details on item 2 concerns. Black & Veatch has specified primary VT fuses on many jobs that use ABB generator breakers. Thank you.
Due to the grounding method of generator star point and delta connection of step-up transformer low voltage-windings, the earth fault current is normally very small. Therefore, fuses with very low melting currents are required to provide protection against all possible faults within a VT. Nevertheless, such elements would have very delicate elements and the possibility of breakage due to mechanical vibration or shock cannot be completely ruled out.
For this reason, fuses having slightly higher melting currents are normally selected in conjunction with ABB GCBs. On the other hand, these fuses might not provide the full range of protection against all types of fault. In any case, this practice is normally accepted considering the relatively low earth fault current. In summary, the use of fuses at the primary side of VTs are not considered as mandatory; however, they are a viable option and could be accommodated upon request based on system data and project requirements assessment.
High Voltage Products
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