PROTECTIVE FUNCTIONS
39
5.3.7 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 m easurement, measure the following circuits
using the instruments given on the next page.
+-
Ar
As
At
Vr
Vs
Vt
W11
W12
W13
Au
Av
Aw
Vu
Vv
Vw
W12
W22
V
R<L1>
S<L2>
T<L3>
U
V
W
Inverter
P<+>
2
<->N
5
3-phase
power
supply
Instrument
types
Input voltage
Input current
Output voltag
e
Output curren
t
To motor

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 instruments.