Mitsubishi Electric FR-F820-00046, Instruction Manual

Page: 869 / 940

Precautions for maintenance and inspection Measurement of main circuit voltages, currents and powers
FR-F800 7 - 15
7.2.1 Measurement of powers
Use digital power meters (for inverter) for the both of inverter input and output side. Alternatively,
measure using electrodynamic type single-phase wattmeters for the both of inverter input and out-
put side in two-wattmeter or three-wattmeter method. As the current is liable to be imbalanced es-
pecially 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. 7-12: Differences when measuring power with different instruments
Example of measuring inverter input power Example of measuring inverter output power
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 60 Hz or more. 3.7 kW, 4-pole motor,
value indicated in 3-wattmeter method is 100%
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%