Three-Phase Power Measurement with One Wattmeter
Three-phase power measurement with one wattmeter can only be applied when the three-phase load in balance (symmetrical). Three-phase load is said to be balanced when the current flowing in each phase the same, thus the power carried by each of the same phase. So that the total power is three times the power of each phase. Suppose wattmeter in Figure 7.8 shows the value of 1500 watts (1.5 kW), the three-phase power is 3 x 1.5 kW = 4.5 kW.
Figure 7.8 Three-Phase Power Measurement with One Wattmeter
Three-Phase Power Measurement with Three Wattmeter
Figure 7.9 Three-Phase Power Measurement with Three Wattmeter
Measurement of three-phase power with three wattmeter only applies when a three-phase load in a state of unbalanced (asymmetric). Three-phase load is said to be unbalanced when the current flowing in each phase is not the same, thus the power carried by each phase is not the same. So that the total power is the sum of the power of each phase. Suppose first wattmeter in Figure 5.40 shows the value of 1500 watts (1.5 kW), the second wattmeter menunukkan value of 2 kW and third wattmeter shows the value of 1.2 kW, the three-phase power is 3.7 kW.
Figure 7.10 Three-Phase Power Measurement with Two Wattmeter
Three-phase power measurement with two wattmeter only applies when a three-phase load in a state of unbalanced (asymmetric). But because of economical reasons then the measurement is not symmetrical three-phase power can be done by using two wattmeter. In this way the two wattmeter neutral channel is not used. Furthermore, three-phase active power value is obtained by summing the appointment of the two wattmeter.
Another advantage of three-phase power measurement with two wattmeter is, with the appointment of the two wattmeter can be used also to determine the apparent power and reactive power and the phase angle of the slide at once, as follows: Suppose the first wattmeter at 7:10 picture showed a value of 2.5 kW, wattmeter both showed a value of 2 kW, then the three-phase active power
P = 2.8 kW + 1.7 kW = 4.5 kW.
three-phase reactive power
Q = 3 x (W1 – W2) = 1.9 KVAR
Three-phase apparent power
S = P + j JQ = 4.5 + 1.9 = 4.9 kVA
Angle = arc tg. (P / S) = arc. tg. (4.5 / 4.9) = 47.30.