Use Of Ct And Transducer - Mitsubishi Electric FR-A820-00046 Instruction Manual

Measurement of main circuit voltages, currents and powers
7.2.4

Use of CT and transducer

A CT may be used in both the input and output sides of the inverter. Use the one with the largest pos-
sible VA ability because an error will increase if the frequency gets lower.
When using a transducer, use the effective value calculation type which is immune to harmonics.
7.2.5
Measurement of inverter input power factor
Calculate using effective power and apparent power. A power-factor meter cannot indicate an exact
value.
Total power factor of the inverter
7.2.6
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
moving-coil type meter (tester). Although the voltage varies according to the power supply voltage,
approximately 270 V DC to 300 V DC (540 V DC to 600 V DC for the 400 V class) is output when no load
is connected and voltage decreases during driving load operation.
When energy is regenerated from the motor during deceleration, for example, the converter output
voltage rises to nearly 400 V DC to 450 V DC (800 V DC to 900 V DC for the 400 V class) maximum.
7.2.7
Measurement of inverter output frequency
In the initial setting of the FM-type inverter, a pulse train proportional to the output frequency is out-
put across the pulse train output terminals FM and 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 5 V DC is indicated at the maximum frequency.
For detailed specifications of the pulse train output terminal FM, refer to page 5-349.
In the initial setting of the CA-type inverter, a pulse train proportional to the output frequency is out-
put across the analog current output terminals CA and 5 of the inverter. Measure the current using an
ammeter or tester.
For detailed specifications of the analog current output terminal CA, refer to page 5-352.
7 - 18
Precautions for maintenance and inspection
Effective power
=
Apparent power
Three-phase input power found by the 3-wattmeter method
=
3
× V (power supply voltage) × I (input current effective value)  