The two wattmeter method is used to measure active power on a three phase, three wire system. If the phase voltage is unbalanced, then the power reading is

A $$3$$ - $$\phi $$ load operates with balanced voltages applied to its terminals, and draws balanced currents. The potential coil of a moving coil wattmeter is connected from $$R$$ to $$Y$$ terminals of the load. The current coil of the meter is connected in series with phase $$B.$$ by appropriate derivation, show that the quantity indicated by this wattmeter is proportional to the reactive power drawn by the load

Instrument transformers are known to introduce magnitude and phase errors in measurements. These are primarily due to

The compensating winding in a dc machine