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PROTECTIVE FUNCTIONS
182
5.3.9 Measurement of main circuit voltages, currents and power
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.
+-
Ar
As
At
Vr
Vs
Vt
W
11
W
12
W
13
Au
Av
Aw
Vu
Vv
Vw
W
21
W
22
V
R
〈
L
1
〉
S
〈
L
2
〉
T
〈
L
3
〉
U
V
W
Inverter
P
〈
+
〉〈
–
〉
N
3-phase
power
supply
Instrument
t
yp
es
Input voltage
Input current
Output voltage
Output current
To motor
:Moving-iron type
:Moving-coil type
:Electrodynamometer type
:Rectifier type
Typical Measuring Points and Instruments
Note: Use an FFT to measure the output voltage accurately. Accurate measurement cannot be made if you
use a tester or general measuring instrument.
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