Hitachi SJ700-4000HFU2

Chapter 6 Maintenance and Inspection
6-6
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.
IR
IS
IT
ER
ET
ES
WI2
WI3
WI1
R
T
S
U
V
W
IU
IV
IW
EU
EW
EV
WO2
WO1
W
V
U
R
S
T
Power supply
Inverter
Motor
Measurement item
Measuring point
Measuring instrument
Remarks
Reference values
Input voltage (E
IN
)
Across R-S, S-T, and T-R
(E
R
), (E
S
), and (E
T
)
Moving-iron voltmeter
or
rectifier-type voltmeter
Effective value of full
waves
200 V class models:
200 to 240 V, 50/60 Hz
400 V class
380 to 480 V, 50/60 Hz
Input current (I
IN
)
Current at R, S, and T
(I
R
), (I
S
), and (I
T
)
Moving-iron ammeter
Effective value of full
waves
When input currents are
unbalanced
I
IN
= (I
R
+ I
S
+ I
T
)/3
Input power (W
IN
)
Across R-S, S-T, and T-R
(W
11
) + (W
12
) + (W
13
)
Electrodynamometer-type
wattmeter
Effective value of full
waves
3-wattmeter method
input power factor
(Pf
IN
)
Calculated from the measured input voltage (E
IN
), input current (I
IN
), and input power (W
IN
)
Output voltage
(E
OUT
)
Across U-V, V-W, and W-U
(E
U
), (E
V
), and (EW)
Method shown in the figure
below
or
rectifier-type voltmeter
Effective value of
fundamental wave
Output current
(I
OUT
)
Current at U, V, and W
(I
U
), (IV), and (IW)
Moving-iron ammeter
Effective value of full
waves
Output power
(W
OUT
)
Across U-V and V-W
(W
01
) + (W
02
)
Electrodynamometer-type
wattmeter
Effective value of full
waves
2-wattmeter method
(or 3-wattmeter method)
Output power
factor (Pf
OUT
)
Calculated from the measured input
voltage (E
OUT
), input current (I
OUT
), and
input power (W
OUT
)
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.
Method to measure the output voltage
R
T
S
Inverter
U
V
W
Motor
+
－
VDC
2W 220ｋ
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
AC
)
V
AC
= 1.1 x V
DC
Moving-coil voltmeter
300 V (200 V class
model)
600 V (400 V class
model)
PfIN＝
WIN
√3・EIN・IIN
×100（％）
PfOUT＝
WOUT
√3・EOUT・IOUT
×100（％）