Inverter Output Voltage Measurement Techniques; Voltage Measurement With Load; Voltage Measurement Without Load - Hitachi L300P Series Instruction Manual

6–16
Maintenance and Inspection
L1
L2
L3
Inverter Output
Voltage Measure-
ment Techniques
L1/R
L2/S
L3/T
V class
200V class
400V class
The figure below shows measurement locations for voltage, current, and power measurements
listed in the table on the previous page. The voltage to be measured is the fundamental wave
effective voltage. The power to be measured is the total effective power.
Three-phase measurement diagram
I
1
E W
1 01
I
2
E W
1 02
I
3
E
1
Taking voltage measurements around drives equipment requires the right equipment and a safe
approach. You are working with high voltages and high-frequency switching waveforms that
are not pure sinusoids. Digital voltmeters will not usually produce reliable readings for these
waveforms. And, it is usually risky to connect high voltage signals to oscilloscopes. The
inverter output semiconductors have some leakage, and no-load measurements produce
misleading results. So, we highly recommend using the following circuits to measure voltage
for performing the equipment inspections.

Voltage measurement with load

U/T1
V/T2
Inverter
W/T3
220kΩ
2W
Diode bridge
600V 0.01A min.
1000V 0.1 A min.
HIGH VOLTAGE: Be careful not to touch wiring or connector terminals when working with
the inverters and taking measurements. Be sure to place the measurement circuitry above in an
insulated housing before using them.
Inverter
I
R U
1
I
S V
1
T W I
1

Voltage measurement without load

L1/R
L2/S
L3/T
+ –
Voltmeter V class
300V range 200V class
600V range 400V class
T1
E W
U-V 01
T2
Motor
E W
U-V 02
T3
E
U-V
U/T1
V/T2
Inverter
W/T3
5kΩ
30W
220kΩ
2W
+
Diode bridge Voltmeter
600V 0.01A min. 300V range
1000V 0.1 A min. 600V range
–