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8-4
8-3 Measurement of Main Circuit Electrical Quantity
The indicated values depend on the type of meter because the harmonic component is included
in the voltage and current of the main circuit power (input) and the output (motor) side of the
inverter. When measuring with a meter for commercial power frequency use, use the meters
shown in Table 8.3.1.
The power-factor cannot be measured using power-factor meters currently available on the
market, which measure the phase difference between voltage and current. When power-factors
must be measured, measure the power, voltage, and current on the input side and output side,
then calculate the power-factor using the following formula:
Power factor
Power W
3 Voltage V Current A
100−=
××
×
[]
[] []
[%]
Table 8-3-1 Meters for measuring main circuit
Input (power supply) side Output (motor) side DC link circuit
voltage
(P(+) - N(-))
Item
Voltage Current*
Voltage Current
Meter
name
Ammeter
AR,S,T
Voltmeter
V
R,S,T
Powermeter
W
R,S,T
Ammeter
AU,V,W
Voltmeter
V
U,V,W
Powermeter
W
U,V,W
DC voltmeter
V
Meter
type
Moving-iron
type
Rectifier or
moving-iron
type
Digital
power meter
Moving-iron
type
Rectifier type
Digital power
meter
Moving-coil
type
Symbol
Note: When measuring the output voltage using a rectifier type meter, an error may occur.
Use a digital AC power meter to ensure accuracy.
Fig 8-3-1 Connection of the meters