This panel provides the medium voltage side protection of a distribution transformer. The load break switch takes the transformer in and out of service, while the medium voltage fuse on the transformer side of the switch performs the protection duty.
The fuse interrupts the circuit by melting on transformer short circuit and on overload. A striker arrangement that detects fuse operation also trips the load break switch, ensuring that all three phases are interrupted together — leaving a transformer on a single phase is hazardous.
Initial investment cost is markedly lower than a circuit breaker solution. The limits are the breaking capacity of the fuse and the transformer rating; at higher ratings a circuit breaker transformer protection panel is used instead.
An earthing switch is fitted on the transformer side; before maintenance the transformer connection is earthed through it.
