6–12
Maintenance and Inspection
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
Supply voltage
E
1
Supply current
I
1
Supply power
W
1
Supply power
factor Pf
1
Output voltage
E
0
Output current
I
o
Output power
W
o
Output power
factor Pf
o
Note 1:
Note 2:
Note 3:
Circuit location
of measurement
E
– across L1 and L2
R
E
– across L2 and L3
S
E
– across L3 and L1
T
I
– L1, I
– L2, I
– L3
r
s
t
W
– across L1 and L2
11
W
– across L2 and L3
12
Pf
----------------------------- -
=
1
3 E
E
– across U and V
U
E
– across V and W
V
E
– across W and U
W
I
– U
U
I
– V
V
I
– W
W
W
– across U and V
01
W
– across V and W
02
Calculate the output power factor from the output voltage E,
output current I, and output power W.
Pf
----------------------------- -
=
0
Use a meter indicating a fundamental wave effective value for voltage, and
meters indicating total effective values for current and power.
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.
A general-purpose digital volt meter (DVM) is not usually suitable to measure
a distorted waveform (not pure sinusoid).
Measuring
instrument
Moving-coil
Fundamental
type voltmeter or
wave effective
rectifier type
value
voltmeter
Total effective
value
Total effective
value
W
1
×
100%
×
×
I
1
1
Rectifier type
Total effective
voltmeter
value
Moving-coil
Total effective
ammeter
value
Electronic type
Total effective
wattmeter
value
W
0
×
100%
×
×
3
E
I
0
0
Notes
Reference Value
Commercial
supply voltage
(200V class) 200–
240V, 50/60 Hz
400V class 380–
460V, 50/60 Hz
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