Instruction manual

Measurement of main circuit
voltages, currents and powers
101
PRECAUTIONS FOR MAINTENANCE AND INSPECTION
7
7.4 Measurement of main circuit voltages, currents and powers
7.4.1 Insulation resistance test using megger
1) Before performing the insulation resistance test on the external circuit, disconnect the cables from all terminals
of the inverter so that the test voltage is not applied to the inverter.
2) For the continuity test of the control circuit, use a tester (high resistance range) and do not use the megger or buzzer.
3) For the inverter, conduct the insulation resistance test on the main circuit only as shown below and do not
perform the test on the control circuit. (Use a 500VDC megger.)
7.4.2 Pressure test
Do not conduct a pressure test. Deterioration may occur.
z Measurement of voltages and currents
Since the voltages and currents on the inverter power supply and output sides include harmonics, measurement
data depends on the instruments used and circuits measured.
When instruments for commercial frequency are used for measurement, measure the following circuits with the
instruments given on the next page.
Examples of Measuring Points and Instruments
CAUTION
Use an FFT to measure the output voltage accurately.
A tester or general measuring instrument cannot measure accurately.
R
S
T
U
V
W
IM
Power
supply
500VDC
megger
Inverter
Earth (ground) terminal
Motor
Earth (Ground) terminal
+-
Ar
As
At
Vr
Vs
Vt
W11
W12
W13
Au
Av
Aw
Vu
Vv
Vw
W21
W22
V
U
V
W
Input voltage
Input current
Output current
Three-phase
power supply
Inverter
To motor
Instrument
types
: Moving-iron type
: Moving-coil type
: Rectifier type
Output voltage
: Electrodynamometer type
R
S
T
P
N