Answer The current coils is connected in series with the line, and the voltage coil is connected across the line, both coils are wound on a metal frame of special design provided two magnetic circuit. A light aluminium disk is suspended in the air gap of the current to flow in the disk. The reaction of the voltage coil creates a torque [motor action] on the disk, causing it to rotate. The developed torque is proportional to the field strength of the voltage coil and the eddy current.