A
2
An artificial circuit of a three-phase 3-wire line
: The vectors of line-to-line voltage
: The vectors of phase to neutral voltage
: The vectors of line (phase) current
3-phase/3-wire/3-wattmeter measurement (3P3W3M)
In 3-wattmeter measurement, three phase voltages (
) and three line
(phase) currents (
) are measured. Because the lack of a neutral point in 3-
phase, 3-wire lines makes it impossible to measure actual phase voltages, phase
voltages are measured from a virtual neutral point.
The 3-phase active power P is calculated as the sum of all the phase active power
values.
P
= +
+
(1)
3-phase/3-wire/2-wattmeter measurement (3P3W2M)
In 2-wattmeter measurement, two line-to-line voltages (
) and three line
(phase) currents (
) are measured. The 3-phase active power P can be derived
from two voltage and current values, as shown below:
P =
+
(
=
-
,
=
-
)
=
(
-
)
+ (
-
)
=
+
(- - ) +
(because + + =0 due to precondition of a closed circuit)
=
+
+
(2)
Since equations (1) and (2) agree, it is possible to prove that 2-wattmeter measure-
ment can be used to measure the power of a 3-phase, 3-wire line. Since the only
special conditions are that the target be a closed circuit without leakage current, it is
possible to calculate 3-phase power without regard to the balance or unbalance
state of the electric circuit.
Appendix2 Three-phase 3-wire Measurement
Three-phase 3-wire
Power-supply side
Three-phase
3-wire Load side
I
1
1
U
1
U
3
u
1
Neutral
point
u
3
u
2
U
2
I
3
I
2
2
3
U
1
,
U
2
,
U
3
u
1
,
u
2
,
u
3
I
1
,
I
2
,
I
3
u
1
,
u
2
,
u
3
I
1
,
I
2
,
I
3
u
1
I
1
u
2
I
2
u
3
I
3
U
1
,
U
2
I
1
,
I
3
U
1
I
1
U
2
I
3
U
1
u
1
u
2
U
2
u
3
u
2
u
1
u
2
I
1
u
3
u
2
I
3
u
1
I
1
u
2
I
1
I
3
u
3
I
3
I
1
I
2
I
3
u
1
I
1
u
2
I
2
u
3
I
3
Summary of Contents for PW3360-20
Page 2: ......
Page 66: ...3 8 Verifying Correct Wiring Wiring Check 58 ...
Page 104: ...7 2 Settings That Can Be Added to Quick Set Settings 96 ...
Page 120: ...8 8 Formatting the SD Memory Card or Internal Memory 112 ...
Page 166: ...11 4 Outputting a Pulse Signal 158 ...
Page 210: ...13 4 Disposing of the Instrument 202 ...
Page 218: ...A8 ...
Page 222: ...Index Index 4 ...
Page 223: ......
Page 224: ......