This is mainly to consider the selectivity of the relay حفاظت action. The high-ولتاژ side quick-break حفاظت is mainly to protect the serious external fault of the transformer. The short-جریان current value of the range does not change much and is basically equal, which will expand the range of the high-ولتاژ side quick-break protection to the low-voltage outgoing line, thus losing selectivity. The protection is more reliable after the loss of selectivity, but it brings inconvenience to permission. For example, many industries now have a 10KV general power distribution room (10KV busbar + outgoing circuit breaker), and each workshop has a low-voltage power distribution room (ring network cabinet + Transformer), if the circuit breaker does not escape the maximum short-circuit current on the low-voltage side of the transformer, it will cause the low-voltage main switch, (ring main unit load switch fuse), and the high-voltage circuit breaker will operate, which will cause inconvenience to the operation.