Choice of Methods of Measuring Three-Phase Power

Author: E.E. Kimberly

In any three-phase, three-wire circuit, either the three-wattmeter method or the two-wattmeter method may be used, regardless of the degree of load unbalance. If the system has a fourth wire leading to the neutral point of the generator, the system is a four-wire system. Single-phase loads may be connected at random between the neutral wire and the other wires of the line. Three wattmeters connected as in Fig. 9-12 are required to measure the power in a four-wire system. The number of wattmeters required to measure the power in a system is always one less than the number of wires in the system.

Fig. 9-12, Arrangement of Meters in Four-Wire System