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7.5 Measurement of Electrical Amounts in Main Circuit
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Chap
7
7.5 Measurement of Electrical Amounts in Main Circuit
Because the voltage and current of the power supply (input, primary circuit) of the main circuit of the inverter and
those of the motor (output, secondary circuit) contain harmonic components, the readings may vary with the type of
the meter. Use meters indicated in Table 7.5-1 when measuring main circuit.
The power factor cannot be measured by a commercially available power-factor meter that measures the phase
difference between the voltage and current. To obtain the power factor, measure the power, voltage and current on
each of the input and output sides and use the following formula.
■
Three-phase input
% 100 ×
(A) Current × (V) Voltage × 3
(W) power Electric
= factor Power
Table 7.5-1 Meters for Measurement of Main Circuit
Item
Input (primary) side Output (secondary) side
DC link bus
voltage
(P(+)-N(-))
W
av
efor
m
Voltage Current Voltage Current
Nam
e
of
m
eter
Ammeter
AR, AS, AT
Voltmeter
VR, VS, VT
Wattmeter
WR, WT
Ammeter
AU, AV, AW
Voltmeter
VU, VV, VW
Wattmeter
WU, WW
DC voltmeter V
Ty
pe of
m
eter
Moving iron
type
Rectifier or
moving iron
type
Digital
AC power
meter
Digital AC
power meter
Digital AC
power meter
Digital AC
power meter Moving coil type
S
ym
bol
of m
eter
   
It is not recommended that meters other than a digital AC power meter be used for measuring the output
voltage or output current since they may cause larger measurement errors or, in the worst case, they may
be damaged.
Figure 7.5-1 Connection of Meters