Forums » Electrical Engineering


    • 1 posts
    September 11, 2019 8:19 AM PDT


    I work on transformer which is rated 630kVA and 400kVA load is connected. There is a back up transformer 400kVA. Can I connect this as a backup. But I heard a transformer should be loaded maximum 80%?

    This post was edited by Domenic Melvin at September 11, 2019 8:21 AM PDT
    • 29 posts
    September 11, 2019 12:15 PM PDT

    You could connect the spare 400kVA transformer as a backup, but as a minimum would need to review the transformer protection that should have been designed for a 630kVA unit to make sure it adequately protects the smaller 400kVA unit.  Transformers can be operated at 100% rated current. Depending on your local codes, you may need to derate the ampacity of your primary and secondary feeders and associated switchgear.  If your load increases over 400kVA then you will be drawing more than the transformer's rated current which will result in accelerated thermal degradation that will shorten the life span of the transformer.  Every hour operating your transformer at 10 degrees C over rated temperature takes one year off its designed lifespan.

    • 33 posts
    September 11, 2019 11:01 PM PDT

    if the power factor is a unity, yes you can.

    • 72 posts
    September 13, 2019 12:34 PM PDT

    you can load 400kVA transfomer to be loaded 24/7h at 400kVA.