Measurement Of Converter Output Voltage (Across Terminals P/+ - N/-); Measurement Of Inverter Output Frequency; Insulation Resistance Test Using Megger; Pressure Test - Mitsubishi Electric FR-A720-0.4K Instruction Manual

Measurement of main circuit voltages,
currents and powers
6.2.6

Measurement of converter output voltage (across terminals P/+ - N/-)

The output voltage of the converter is developed across terminals P/+ - N/- and can be measured with a moving-coil
type meter (tester). Although the voltage varies according to the power supply voltage, approximately 270V to 300V
(approximately 540V to 600V for the 400V class) is output when no load is connected and voltage decreases when
a load is connected.
When regenerative energy is returned from the motor during deceleration, for example, the converter output voltage
rises to nearly 400V to 450V (800V to 900V for the 400V class) maximum.
6.2.7

Measurement of inverter output frequency

A pulse train proportional to the output frequency is output across the frequency meter signal output terminal FM-
SD of the inverter. This pulse train output can be counted by a frequency counter, or a meter (moving-coil type
voltmeter) can be used to read the mean value of the pulse train output voltage. When a meter is used to measure
the output frequency, approximately 5VDC is indicated at the maximum frequency.
For detailed specifications of the frequency meter signal output terminal FM, refer to page 252.
6.2.8

Insulation resistance test using megger

For the inverter, conduct the insulation resistance test on the main circuit only as shown below and do not perform
the test on the control circuit. (Use a 500VDC megger.)
CAUTION
• Before performing the insulation resistance test on the external circuit, disconnect the cables from all terminals of the
inverter so that the test voltage is not applied to the inverter.
• For the continuity test of the control circuit, use a tester (high resistance range) and do not use the megger or buzzer.
6.2.9

Pressure test

Do not conduct a pressure test. Deterioration may occur.
418
R/L1
Power
Inverter
S/L2
supply
T/L3
500VDC
megger
Earth (ground)
Motor
U
IM
V
W