Measurement Of Powers - Mitsubishi Electric FR-E700 Instruction Manual

Troubleshooting
7.7.1

Measurement of powers

Use digital power meters (for inverter) or 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 cur-
rent is liable to be imbalanced especially in the input side, it is recommended to use the three-watt-
meter 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.
Fig. 7-8:
FR-E700 SC EC/ENE
Measurement conditions:
Constant-torque (100%) load,
constant-output at 60 Hz or more. 3.7 kW, 4-pole motor,
value indicated in 3-wattmeter method is 100%
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)
Example of measuring inverter input power
Differences when measuring power with different instruments
Meters and measuring methods
Measurement conditions:
Constant-torque (100%) load,
constant-output at 60 Hz or more. 3.7 kW, 4-pole motor,
value indicated in 3-wattmeter method is 100%
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)
Example of measuring inverter input power
I001301E, I001302E,
7 - 31