| See the figure, below-right; it shows watt measurement
of a three-phase three-wire Wye(Y) connection load. M-System Models
LWT and LTWT Power Transmitter and Model LRP and LTRP Reactive Power
Transmitter use the two-wattmeter method. In this method, the two
current coils are connected to the two wires each of the two wires
of the three-phase three-wire load. The potential coils are connected
between these wires and the rewiring wire. The wattmeter 1 is connected
to the a phase and the c phase; the wattmeter 2 is to the c phase
and the b phase. Each measures the single phase power P1 and P2, respectively.
The sum of the two measured values is equal to the total three-phase
power. |
 |
| A simple method uses only one (1) wattmeter. The
meter is connected to only one phase, a, b or c, as to shown in the
figure, below-left and the three (3) times of the measured value is
equal to the three-phase power, as long as the three-phase are balanced.
If unbalance occurs, the simple method causes a measurement error.
The two-wattmeter method does not even with unbalanced phases. |
|
What
is the two-wattmeter method that is suitable to unbalanced load in measurement
of three-phase power?
The
two-wattmeter method uses two single-phase wattmeters to measure three-phase
power. The sum of the measurement with two single-phase wattmeters becomes
three-phase power in this measuring setup. 