An electrical current transformer for installation upon a power distribution line including a generally annular, split core and a secondary winding. The secondary winding includes a first winding portion, wound with a first winding polarity about the split core, and a second winding portion, wound with a second, opposite winding polarity about the split core, and a tap. The transformer further includes first and second rectifiers, electrically connecting a tap output to terminals of the first and second winding portion opposite the tap, respectively, and a tap control for controlling the tap output, where the tap is both electrically connectable to the output to provide an additive connection and electrically isolatable from the output to cause a subtractive connection. The tap control controls the tap output in response to a condition sensed in the powered circuit. Self-cancellation may be achieved by using windings having an equal number of turns.