8-4 Maintenance and Inspection
8
8-3 Measurement of Current and
Voltage in Main Circuit
Because the voltage and current of the power
supply (input) of the main circuit of the inverter
and the output (motor) include harmonic
components, the indicated value varies
according to the type of the meter. Use meters
indicated in Table 8-3-1 when measuring with
meters for commercial frequencies.
Marketed power factor meters measuring phase
difference between the voltage and current
cannot measure the power factor. To obtain the
power factor, measure the power, voltage and
In case of Single-phase
Table 8-3-1 Meters for measurement of main circuit
Fig 8-3-1 Connection of measuring instruments
In case of Three-phase
Input (power supply) side Output (motor) side Link voltage
(P(+)-N(-))
Voltage Current Voltage Current
Ammeter Voltmeter Wattmeter Ammeter Voltmeter Wattmeter DC voltmeter
A
R
,
S
,
T
V
R
,
S
,
T
W
R
,
S
,
T
A
U
,
V
,
W
V
U
,
V
,
W
W
U
,
V
,
W
V
Moving iron Rectifier or Digital Moving iron Rectifier Digital Moving coil
type moving iron power type type power type
type meter meter
current on each of the input and output sides
and calculate in the following formula.
Item
Name of
meter
Type of
meter
Symbol of
meter
Note) When the output voltage is measured by a
rectifier type, an error may be included. To increase
the accuracy, use a digital AC power meter.
A
U
A
V
A
W
WU
W
W
V
U
V
V
V
W
A
W
V
Power
Supply
L1/L
L2/N
V
+-
P(+) N(-)
U
V
W
M
Motor
VXSM***-1 VXSM***-3
A
U
A
V
A
W
WU
W
W
V
U
V
V
V
W
A
R
A
S
A
T
WR
W
T
V
R
V
S
V
T
Power
Supply
L1/R
L3/T
L2/S
V
+-
P(+) N(-)
U
V
W
M
Motor
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