Electrical Engineering ⇒ Topic : One-Wattmeter Method - Balanced Load

One-Wattmeter Method Balanced Load

If the 3-phase load (Y or A) is balanced, then one wattmeter is sufficient to measure the power drawn by the load. There are two methods in which one wattmeter may be applied.

(1) Artificial-star method. In this method, two impedances each equal in value (magnitude and phase) to the impedance of the potential coil of the wattmeter are so connected that these two impedances and the potential coil form a Y-connected load as shown in Fig. (a). The wattmeter will read the phase power andl the total power will be three times the wattmeter reading

                                                        (a)                                                                            (b)

                                                                                      figure

(2) Double-reading method. In this method, two readings of the two-wattmeter method are taken with a single wattmeter as shown in Fig. (b). The current coil of the wattmeter is connected in any one line and the pressure coil is connected alternately between this and the other two lines. The algebraic sum of the two readings gives the total power drawn by the balanced 3-phase load.