Measurement of main circuit voltages, currents and powers
162
PRECAUTIONS FOR MAINTENANCE AND INSPECTION
7.2.1
Measurement of powers
Use a digital power meter (for inverter) for the input side of converter unit.
7.2.2
Measurement of voltages
Converter unit input side
Use a digital power meter (for inverter) for the input side voltage.
7.2.3
Measurement of currents
Use a digital power meter (for inverter) for the input side of the converter unit.
Since the converter unit input current tends to be unbalanced, measurement of three phases is recommended. The correct
value cannot be obtained by measuring only one or two phases.
The converter unit input current can be monitored on the operation panel. The value displayed on the operation panel is
accurate even if the output frequency varies. Hence, it is recommended to monitor values on the operation panel.
7.2.4
Example of measuring converter unit input
power factor
Calculate using effective power and apparent power. A power-factor meter cannot indicate an exact value.
7.2.5
Measurement of converter output voltage
(across terminals P and N)
The output voltage of the converter is output across terminals P and N, and can be measured with a voltmeter such as a
digital multimeter. Although the voltage varies according to the power supply voltage, approximately 540 to 600 V is output
when no load is applied. The voltage decreases when a load is applied.
When energy is regenerated from the motor during deceleration, for example, the converter output voltage rises to nearly 800
to 900 V maximum.
Total power factor of the converter unit
=
Effective power
Apparent power
=
Three-phase input power found by the 3-wattmeter method
V (power supply voltage)
I (input current effective value)
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