Mitsubishi Electric FR-A700 EC, Instruction Manual

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Meters and measuring methods Troubleshooting
7 - 32
7.7.1 Measurement of powers
Using an electro-dynamometer type meter, measure the power in both the input and output
sides of the inverter using the two- or three-wattmeter method. As the current is liable to be im-
balanced especially in the input side, it is recommended to use the three-wattmeter method.
Examples of measured value differences produced by different measuring meters are shown
below.
An error will be produced by difference between measuring instruments, e.g. power calculation
type and two- or three-wattmeter type three-phase wattmeter. When a CT is used in the current
measuring side or when the meter contains a PT on the voltage measurement side, an error will
also be produced due to the frequency characteristics of the CT and PT.
I001301E, I001302E,
Fig. 7-8: Differences when measuring power with different instruments
3-wattmeter method (Electro-dynamometer type)
2-wattmeter method (Electro-dynamometer type)
Clip AC power meter
(For balanced 3-phase load)
Clamp-on wattmeter
(Hall device power arithmetic type)
3-wattmeter method (Electro-dynamometer type)
2-wattmeter method (Electro-dynamometer type)
Clip AC power meter
(For balanced 3-phase load)
Clamp-on wattmeter
(Hall device power arithmetic type)
Measurement conditions:
Constant-torque (100%) load,
constant-output at 60Hz or more. 3.7kW, 4-pole motor,
value indicated in 3-wattmeter method is 100%
Measurement conditions:
Constant-torque (100%) load,
constant-output at 60Hz or more. 3.7kW, 4-pole motor,
value indicated in 3-wattmeter method is 100%
Example of measuring inverter input power Example of measuring inverter output power