# Do circuit reclosers of substations respond to any fault on the low voltage side of distribution transformer?

As I don't have any practical experience in power distribution networks, I'm pretty confused about a few things. Typically a lot of transformers are connected to an 11KV distribution line ( 11KV feeder.)

For an 11KV/440V three-phase transformer, if any fault (L-L / L-G / L-L-L-G) occurs on the low voltage side, the fuses of the transformer will trip.

Is there any possibility that the ACR (or OCR for old substations) will trip and will shut down the whole 11KV line?

If a fault occurs on one transformer's low voltage side, will the other transformer on the same 11KV line be affected?

If a fault occurs on one transformer's low voltage side, will the other transformer on the same 11KV line be affected?

Short answer: it shouldn't be affected.

Longer answer: The 11 kV feed to a whole bunch of 11 kV / 440 volt transformers has to provide power simultaneously to all of them. In other words, the 11 kV feed is capable of $$\N\cdot P\$$ where P is the power per transformer and N is the number of transformers. And to use your scenario: -

an 11KV distribution line ( 11KV feeder.)

It will have massive power capacity compared to each individual transformer that connects to it. Hence, it's unlikely that any problematic event on the secondary side of one transformer is going to spoil the whole picture for other transformers.

In other words, the reclosers on the distribution side are rated much in excess of what can occur as a fault on the secondary side of one transformer. But, your question says this: -

Is there any possibility that the ACR (or OCR for old substations) will trip

And so I cannot categorically state that this won't happen in some obscure circumstances.

It is unlikely that the substation circuit breaker or recloser will trip due to a fault in the LV of a transformer. The current of this short circuit will be limited by the impedance of the distribution transformer and, therefore, the short current seen by the substation will be small (compared to the load of all transformers on that feeder) and will not trip the protection.

During a LV fault of one distribution transformer, the others can, and probably will, experience a voltage sag (voltage sag). Of course, this depends on the topology of the distribution network, the cables used and the position of the transformer that has the short in the LV.

Generally, the recloser that protects the transformers is configured according to the actuation curve of the fuses that are used in that network. This is a 'protection coordination' theme.