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7. PRECAUTIONS FOR MAINTENANCE AND INSPECTION
7.2 Measurement of main circuit voltages, currents, and powers
7.2.1
Measurement of powers
Use a digital power meter (for inverter) for the input side of the converter unit.
7.2.2
Measurement of voltages
Use a digital power meter (for inverter) for the input side of the converter unit.
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. Hence, it is recommended to monitor values on the operation panel. Install the operation panel of the inverter on the
converter unit.
7.2.4
Example of measuring converter unit input power
factor
Calculate the factor from the effective power and the 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 can be measured with a voltmeter (such as a digital multimeter) between terminals P and
N. The voltage varies according to the power supply voltage. Approximately 540 to 600 VDC 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 VDC maximum.
7.2.6
Insulation resistance test using megger
• For the converter unit, conduct the insulation resistance test on the main circuit only as follows and do not perform the test
on the control circuit. (Use a 500 VDC megger.)
NOTE
• Before performing the insulation resistance test on the external circuit, disconnect the cables from all terminals of the converter
unit so that the test voltage is not applied to the converter unit.
• For the continuity test of the control circuit, use a tester for high resistance range and do not use the megger or buzzer.
Total power factor of the inverter =
Effective power
Apparent power
=
Three-phase input power found by the 3-wattmeter method
3×V (power supply voltage) × I (input current effective value)
√
Converter
Earth (ground) terminal
500VDC
megger
Power
supply
P/+
N/-
R/L1
S/L2
T/L3
