What protective equipment to put on the low side of the transformer?

Good afternoon, Dmitry. Circuit breakers, fuses installed immediately after the low-voltage output of the transformer cut off the short circuit on the busbars - they save the transformer. Circuit breakers, fuses installed on the outgoing feeders, disconnect these connections when they are overloaded or “save” the substation equipment in case of short circuit on the outgoing cables.

When choosing automatic machines, fuses for outgoing connections, one should not pay attention to the composition of power consumers. Here, the main factor is the rated current of the outgoing cable supplying electricity to the consumer. Guided by the rated current of the cable, overhead line, choose the machine, the fuse of the nearest upper rating. Let's say the cable In is 500 amperes, pick up the machine with the closest rated current.

If the connection feeds single high-voltage power consumers - for example, a pump that selects 70% of the cable rating, consider the permissible overloads. The rating of the machine will have to be increased. Here the issue is solved by calculation. Similarly with a fuse.

I advise giving preference to circuit breakers. They guarantee the best selectivity - the 8A machine will always work faster than the 6A machine. Fuses are harder: they have to jump over a step. That is, insert 31A will burn faster than insert 50A, and an insert with an intermediate value of 40A may get ahead of 31A.