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Thoughts on Temporarily Paralleling Two 1600A ACBs with a Bypass Castell Key?

AMK

Hi everyone,

Looking for some insights on a proposed electrical setup and potential risks. We have a single LV switchboard with two 1600 Amp ACBs, each fed by separate transformers but connected to the same HV ring main. Both ACBs are equipped with Castell keys for interlocking. Normally, if one transformer fails, the procedure is to switch off its ACB, remove the Castell key, and close a bus coupler to maintain supply.

We need to perform some HV maintenance, which requires isolating each transformer one at a time. To avoid any supply interruption, there’s a suggestion to use a bypass Castell key to temporarily parallel the two supplies for a few seconds. The idea is to parallel the transformers, then switch off one ACB, keeping the load live throughout.

Has anyone done something similar or seen issues with this approach? Keen to hear your thoughts and experiences!

 Thanks -Andy

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    Another approach might to hire a very large generator, complete with synchronising gear.

    Sequence of events as follows.

     1)load supplied by transformer one.

    2)load supplied by transformer one and* the generator.

    3)Load supplied by generator only.

    4 load supplied by transformer two and* the generator.

    5, load supplied only transformer two. generator shut down.

    *usual precautions required when synchronising.

    Synchronising a generator with the public supply requires permission, which should be relatively easy to obtain, as no back feeding is intended. And if by some mischance back feeding did occur it would only persist for a few seconds.

    Use of the generator synchronised with the mains will increase the fault current, but only slightly. The fault current of a generator is only a few times the load current.

    The generator can be smaller than the normal load, provided that the changeover is done at a time of low load. There is probably an existing generator for critical loads, use this to reduce the load on the temporary generator, and to reduce the consequences if any thing goes wrong.

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  • 0

    Another approach might to hire a very large generator, complete with synchronising gear.

    Sequence of events as follows.

     1)load supplied by transformer one.

    2)load supplied by transformer one and* the generator.

    3)Load supplied by generator only.

    4 load supplied by transformer two and* the generator.

    5, load supplied only transformer two. generator shut down.

    *usual precautions required when synchronising.

    Synchronising a generator with the public supply requires permission, which should be relatively easy to obtain, as no back feeding is intended. And if by some mischance back feeding did occur it would only persist for a few seconds.

    Use of the generator synchronised with the mains will increase the fault current, but only slightly. The fault current of a generator is only a few times the load current.

    The generator can be smaller than the normal load, provided that the changeover is done at a time of low load. There is probably an existing generator for critical loads, use this to reduce the load on the temporary generator, and to reduce the consequences if any thing goes wrong.

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