Protection selection for power transformers

① Transformer primary current = S / (1.732 * 10), secondary current = S / (1.732 * 0.4).

② Transformer primary fuse selection = 1.5 to 2 times the transformer's primary rated current (for transformers above 100KVA).

③ Transformer secondary switch selection = transformer's secondary rated current.

④ Transformers of 800KVA and above should, in addition to installing gas relays and protection circuits, have appropriate overcurrent and instantaneous overcurrent protection in the system circuit; setting values ​​and periodic verification.