Regarding power system loop-closing and path reversal
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Please note carefully: I am not asking about paralleling transformers, but about low-voltage ring connection! ! Our factory’s 0.4KV low-voltage distribution room is powered by two power sources; in other words, there are two identical transformers (10KV/0.4KV) within the low-voltage distribution room, each of which supplies one of the busbars, namely busbar 1 or busbar 2. The high-voltage sides of these transformers draw power from the 1st and 2nd power sources in the 10KV high-voltage distribution room. Under normal operating conditions, the 1st and 2nd power sources in the high-voltage distribution room operate separately, and the low-voltage sides of the two transformers also operate separately. When it is necessary to clean or test a certain 10KV busbar without shutting down the low-voltage supply, it is required to perform a low-voltage side interconnection operation. I would like to ask what precautions should be taken during such an operation, and what conditions are necessary? This is the rule in my factory: when it is necessary to close the circuits on busbars 1 and 2 on the low-voltage side of the transformer, the 10KV busbars 1 and 2 must be closed first. And when it is time to close the circuits on those 10KV busbars, the 110KV substation in our factory must close its circuits first before such operation can take place. In other words, to perform circuit closing on the low-voltage side, the circuits at the higher voltage level must be closed first. What is the basis for this rule? Are there any relevant standards or documents? What range should the circulating current after circuit closing be considered normal within? Thank you all
When there is a difference in voltage between the two high-voltage power supplies, the high-voltage current flows through one transformer to the low-voltage side, and then returns from the low-voltage side to the high-voltage side of the other transformer; this is known as \"circulating current\". When the circulating current is severe, it can cause the transformer to overload or the switch to trip.
Such regulations take into account the issue of circulating currents; there is a concern that excessive closing current on the low-voltage side could cause the low-voltage circuit breaker to trip. Therefore, this order is appropriate – the closing current should not trigger the operation of the switch. Of course, it is best to keep the parameters of the two power supplies as similar as possible.