Hioki PQ3198, Инструкция по эксплуатации

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A
23
App
e
ndix
Since equations (1) and (2) agree, it is possible to prove that 2-wattmeter measurement can
be used to measure the power of a 3-phase, 3-wire line. The circuit allowing 3-phase power
measurements with this method is a only closed circuit without leakage current. Since there are no
special conditions other than the above, it is possible to calculate 3-phase power regardless of the
balanced or unbalanced state of the electric circuit.
Additionally, since the sum of the voltage and current vectors always equals 0 under these
conditions, the instrument internally calculates the third voltage
and current values as follows:
However, because the three phases are calculated from two power values in 2-wattmeter measurement,
it is not possible to check the power balance between respective phases. If you wish to check the power
balance for individual phases, use 3-wattmeter (3P3W3M) measurement.
In 3P3W2M measurement, the instrument inputs the 3-phase line’s T-phase current as each current’s I2
parameter. For display purposes, a current value of Phase T in the 3-phase line is displayed as the cur-
rent I2;
and a calculated value of Phase S in the 3-phase line, as the current I3.
U
·
3
I
·
2
U
·
3
U
·
2
U
·
1
– =
I
·
2
I
·
1
– I
·
3
– =
Item 3P3W2M
Relative
merits
3P3W3M
Voltage
U1
=
,
U2
,
U3
,
Current
I1
= I2
I3
Active power
P1
Since the three phases are
calculated from 2-wattme-
ter,it is not possible to check
the active power balance for
individual phases.
<
It is possible to check the
active power balance for
individual phases.
P2
P3 -
P
See equation (2).
=
Apparent
power
S1
Since calculations are
based on the line-to-line
voltage and phase (line) cur-
rent,apparent power values
are not generated for indi-
vidual phases.
<
Since calculations are
based on the phase voltage
and phase (line) current, it is
possible to check the appar-
ent power for individual
phases.
S2
S3
S =
U
·
1
U
·
1
u
·
1
U
·
1
U
·
3
–
( )
3
------------------------ =
U
·
2
U
·
2
u
·
2
U
·
2
U
·
1
–
( )
3
------------------------ =
U
·
3
U
·
2
U
·
1
– =
U
·
3
u
·
3
U
·
3
U
·
2
– ( )
3
------------------------ =
I
·
1
I
·
1
I
·
3
I
·
2
I
·
2
I –
·
1
I
·
3
– = I
·
3
U
·
1
I
·
1
u
·
1
I
·
1
U
·
2
I
·
3
u
·
2
I
·
2
u
·
3
I
·
3
U
·
1
I
·
1
U
·
2
I
·
3
+ u
·
1
I
·
1
u
·
2
I
·
2
u
·
3
I
·
3
+ + =
u
·
1
I
·
1
u
·
2
I
·
2
u
·
3
I
·
3
+ +
U
·
1
I
·
1
u
·
1
I
·
1
U
·
2
I
·
3
u
·
2
I
·
2
U
·
3
I
·
2
u
·
3
I
·
3
3
3
-------
U
·
1
I
·
1
U
·
2
I
·
3
U
·
3
I
·
2
+ +
( )
3
3
-------
U
·
1
I
·
1
U
·
2
I
·
2
U
·
3
I
·
3
+ +
( )
HIOKI PQ3198A961-03