Why REF is provided in the LV side of SUT and UT?

Why REF is provided in the LV side of SUT and UT? 
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1 Answer

Answer :

The LV sides of the two transformers are earthed through the resistance. This will limit the flow of current in case of LV earth fault. Hence the differential protection may not act for a LV earth fault. Hence ref protection is provided. 
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