Polyphase Energy Meter
Two element energy meters:
A two-element energy meter used for measurement of energy in 3-phase, 3- wire circuit.
It consists of two discs mounted on common spindle. The moving system drives a single gear train. Each unit is provided with its own shading ring, shading bands and break magnet for adjustments.
It is essential that the driving torque of two elements be exactly the same for the same power passing through them. This condition is checked by energizing the coils from a single circuit, the two pressure coils being connected in parallel and the circuit coils in series, with one reversed to oppose the other. This arrangement causes the two torques to be in opposition and if the two torques are equal, the disc will not rotate. If there in slights motion, the magnetic shunt is adjusted till the speed of the discs become zero. The lag, light load and unity power factor adjustments are made independently for each element.