Transformer Grounding and Winding Configurations
At most medium-voltage industrial facilities, the main incoming transformer that provides the tie to the utility system is generally configured to be a delta primary, wye grounded secondary transformer. The secondary wye winding is generally grounded through a grounding resistor at industrial facilities.
Typically, these resistors reduce ground current to between 50 and 400 A and are dependent on client preference and system-charging currents.
There are three major reasons for the use of a secondary grounding resistor to reduce industrial system ground current: