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6.8 Methods of Measuring the Input/Output Voltages, Current, and Power
This section describes the measuring instruments generally used to measure the input and output voltages, output
current, and output power of the inverter.
R
I
R
S
I
Power supply
S
T
I
T
Measurement item
Measuring point
Input voltage (E
)
Across R-S, S-T, and T-R
IN
(E
), (E
), and (E
R
S
Input current (I
)
Current at R, S, and T
IN
(I
), (I
), and (I
R
S
Input power (W
)
Across R-S, S-T, and T-R
IN
(W
) + (W
11
input power factor
Calculated from the measured input voltage (E
(Pf
)
IN
Output voltage
Across U-V, V-W, and W-U
(E
)
(E
), (E
), and (EW)
OUT
U
V
Output current
Current at U, V, and W
(I
)
(I
), (IV), and (IW)
OUT
U
Output power
Across U-V and V-W
(W
)
(W
) + (W
OUT
01
Output power
Calculated from the measured input
factor (Pf
)
voltage (E
OUT
input power (W
Notes:
1. To measure the output voltage, use an
instrument that reads the effective value of
the fundamental wave. To measure the
current or power, use an instrument that
reads the effective value of full waves.
2. Since the inverter output waveform is
controlled by PWM, it has a large margin of
error, especially at low frequencies. In
many cases, general testers may be
inapplicable for the measurement because
of the adverse effect of noise.
W
I1
E
R
W
I2
E
S
W
I3
E
T
Measuring instrument
Moving-iron voltmeter
)
or
T
rectifier-type voltmeter
Moving-iron ammeter
)
T
Electrodynamometer-type
) + (W
)
wattmeter
12
13
W
IN
＝
√3・E
・I
Pf
IN
IN
IN
Method shown in the figure
below
or
rectifier-type voltmeter
Moving-iron ammeter
Electrodynamometer-type
)
wattmeter
02
), input current (I
), and
OUT
OUT
)
OUT
Diode
600 V, 0.1 A or more
(200 V class model)
1,000 V, 0.1 A or more
(400 V class model)
Effective value of
fundamental wave (V
V
= 1.1 x V
AC
Chapter 6 Maintenance and Inspection
R
U
I
U
I
S
V
V
T
W
I
W
Effective value of full
waves
Effective value of full
waves
Effective value of full
waves
), input current (I
), and input power (W
IN
IN
×100（％）
Effective value of
fundamental wave
Effective value of full
waves
Effective value of full
waves
W
OUT
＝
Pf
OUT
√3・E
・I
OUT
OUT
Method to measure the output voltage
R
U
S
V
T
W
)
AC
DC
6-6
U
W
O1
E
U
V
E
V
W
W
O2
E
W
Remarks
Reference values
200 V class models:
200 to 240 V, 50/60 Hz
400 V class
380 to 480 V, 50/60 Hz
When input currents are
unbalanced
I
= (I
+ I
+ I
)/3
IN
R
S
T
3-wattmeter method
)
IN
2-wattmeter method
(or 3-wattmeter method)
×100（％）
Motor
2W 220ｋ
+
V
DC
－
Moving-coil voltmeter
300 V (200 V class
model)
600 V (400 V class
model)
Motor
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