Effect of Solar Induced Current on Autotransformer Tertiary Windings

Experimental results are presented showing the effect of solar induced current (SIC) in the series and common windings of an autotransformer on tertiary winding current. The three-phase autotransformer is rated at 18 MVA and 138/69 kV. Current transformers on the tertiary winding phases supply current to several directional relays and an overcurrent relay in the application described. Thus tertiary current fluctuations have the capability of causing transmission line service interruptions.