Hioki PQ3198 - 3-Phase 3-Wire Measurement Methods

A22
、 、
: The vectors of line-to-line voltage
、 、
: The vectors of phase to neutral voltage
、 、
: The vectors of line (phase) current
In 3-wattmeter measurement, 3 line voltages , , and 3 line (phase) currents
、 、
are measured.
Because the actual phase voltage cann
ot be measured for a 3-phase/3-wire line due to the lack of a neu-
tral point, the phase voltage is calculated based on the line voltages.
The 3-phase active power P is calculated as th
e sum of all the phase active power values.
...(1)
In 2-wattmeter measurement, two line-to-line voltages , and two line (phase) currents ,
are mea-
sured.
The 3-phase active power P can be derived from two voltage and current values, as shown below:
(from , )
(from as the precondition of a closed circuit)
...(2)
Appendix 7 3-phase 3-wire Measurement
3-phase/3-wire/3-wattmeter measurement (3P3W3M)
3-phase/3-wire/2-wattmeter measurement (3P3W2M)
Similar circuit of 3-phase 3-wire line
→
I
·
1
→
I
·
2
→
I
·
3
3-phase 3-wire Load
Neutral
point
U
·
1
U
·
2
U
·
3
u
·
1
u
·
2
u
·
3
1
2
3
3-phase 3-wire Source
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
U
·
1
·
U
·
3
–()
3
---------------------=
u
·
2
U
·
2
U
·
1
–()
3
---------------------=
u
·
3
U
·
3
U
·
2
–()
3
---------------------=
P u
·
1
I
·
1
u
·
2
I
·
2
u
·
3
I
·
3
++=
U
·
1
U
·
2
I
·
1
I
·
3
P 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
++ 0=
P u
·
1
I
·
1
u
·
2
I
·
2
u
·
3
I
·
3
++=
HIOKI PQ3198A961-02