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PROTECTIVE FUNCTIONS
147
5.3.8 Measurement of main circuit voltages, currents and powers
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Measurement of voltages and currents
Since the voltages and currents on the inverter power supply and output sides include
harmonics, accurate measurement depends on the instruments used and circuits measured.
When instruments for commercial frequency are used for measurement, measure the
following circuits using the instruments given on the next page.
Input
voltage
Input
current
Output
voltage
Output
current
Ar
As
At
Vr
Vs
Vt
W11
W12
W13
Au
Av
Aw
Vu
Vv
Vw
W21
W22
V
R (L
1
)
S (L
2
)
T (L
3
)
U
V
W
Inverter
P (+) N (-)
3-phase
power
To motor
Instrument types
+−
:Moving-iron type
:Electrodynamometer type
:Moving-coil type
:Rectifier type
Three-phase 200V
power input
Typical Measuring Points and Instruments
Note: Use FFT (Fast Fourier Transforms) to measure the output voltage
accurately.
It cannot be measured accurately with a meter or general instrument.