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175
Precautions for Maintenance and Inspection
PROTECTIVE FUNCTIONS
6
Measuring Points and Instruments
Item
Measuring
Point
Measuring
Instrument
Remarks (Reference
Measurement Value)
Power supply
voltage
V1
Across R-S, S-
T and T-R
Moving-iron type AC
voltmeter
Is commercial power supply within
permissible variation of AC
voltage? (refer to page 178)
Power supply side
current
I1
R, S and T line
currents
Moving-iron type AC
ammeter
Power supply side
power
P1
At R, S and T,
and across R-
S, S-T and T-R
Electrodynamic type
single-phase wattmeter
P1 = W11 + W12 + W13
(3-wattmeter method)
Power supply side
power factor
Pf1
Calculate after measuring power supply voltage, power supply side current
and power supply side power.
[For three-phase power supply]
Output side
voltage
V2
Across U-V, V-
W and W-U
Rectifier type AC
voltmeter (Note 1)
(Cannot be measured
by moving-iron type)
Difference between phases is
within ±1% of maximum output
voltage.
Output side
current
I2
U, V and W
line currents
Moving-iron type AC
ammeter (Note 2)
Current should be equal to or less
than rated inverter current.
Difference between phases is 10%
or lower.
Output side power
P2
At U, V and W,
and across U-
V and V-W
Electrodynamic type
single-phase wattmeter
P2=W21+W22
2-wattmeter method
(or 3-wattmeter method)
Output side power
factor
Calculate in similar manner to power supply side power factor.
Converter output Across P-N
Moving-coil type
(such as a meter)
Inverter LED display is lit.
1.35 × V1
Start signal
Select signal
Across STF,
STR, RH, RM,
RL, SQ-SD
Moving-coil type
(Meter, etc. may be
used)
(Internal resistance:
50kΩ or larger)
20 to 30VDC when open.
ON voltage: 1V or less
SD is
common.
CAUTION
1. Use an FFT to measure the output voltage accurately. A tester or general
measuring instrument can not measure accurately.
2. When the carrier frequency exceeds 5kHz, do not use this instrument since
using it may increase eddycurrent losses produced in metal parts inside the
instrument, leading to burnout.
In this case, use an approximate effective value type instrument.
P
f1=
P1
3V1 I1
100%
P
f2=
P2
3V2 I2
100%