General Inverter Electrical Measurements

The following table specifies how to measure key system electrical parameters. The
diagrams on the next page show inverter-motor systems and the location of
measurement points for these parameters.
Parameter Circuit location of
measurement
Measuring
instrument Notes Reference Value
Supply voltage
E1
ER – across L1 and L2
ES – across L2 and L3
ET – across L3 and L1
Fundamental
wave effective
value
Commercial supply
voltage
200V class:
200–240V, 50/60 Hz
400V class:
380–460V, 50/60 Hz
Supply current
I1
Ir – L1
Is – L2
It – L3
Total effective
value
Supply power
W1
W11 – across L1 and L2
W12 – across L2 and L3
Moving-coil type
voltmeter or
rectifier type
voltmeter
Total effective
value
Supply power
factor Pf1%100
311
1
1u
uu
IE
W
Pf
Output voltage
EO
EU – across U and V
EV – across V and W
EW – across W and U
Rectifier type
voltmeter
Total effective
value
Output current
IO
IU – U
IV – V
IW – W
Moving-coil type
ammeter
Total effective
value
Output power
WO
WO1 – across U and V
WO2 – across V and W
Electronic type
wattmeter
Total effective
value
Output power
factor PfO
Calculate the output power factor from the output voltage E,
output current I, and output power W.
%100
3
1u
uu
OO
OIE
W
Pf
Note1:Use a meter indicating a fundamental wave effective value for voltage, and meters
indicating total effective values for current and power.
Note2:The inverter output has a distorted waveform, and low frequencies may cause
erroneous readings. However, the measuring instruments and methods listed above
provide comparably accurate results.
Note3:A general-purpose digital volt meter (DVM) is not usually suitable to measure a
distorted waveform (not pure sinusoid).

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Troubleshooting and
Maintenance
6 12
Troubleshooting and
Maintenance