Mitsubishi Electric FR-F800, Instruction Manual

Page: 777 / 834

Precautions for maintenance and inspection Measurement of main circuit voltages, currents and powers
FR-F800 7 - 17
7.2.3 Measurement of currents
Use moving-iron type meters on both the input and output sides of the inverter.
However, if the carrier frequency exceeds 5 kHz, do not use that meter since an overcurrent losses pro-
duced in the internal metal parts of the meter will increase and the meter may burn out. In this case,
use an approximate-effective value type.
Since current on the inverter input side tends to be unbalanced, measurement of three phases is rec-
ommended. Correct value cannot be obtained by measuring only one or two phases. On the other
hand, the unbalanced ratio of each phase of the output side current should be within 10%.
When a clamp ammeter is used, always use an effective value detection type. A mean value detection
type produces a large error and may indicate an extremely smaller value than the actual value.
The value monitored on the operation panel is accurate if the output frequency varies, and it is rec-
ommended to monitor values (provide analog output) using the operation panel.
Examples of measured value differences produced by different measuring meters are shown below.
I001303E, I001304E
Fig. 7-13: Differences when measuring currents with different instruments
Measurement conditions
Indicated value of the moving-iron type
ammeter is 100%.
Measurement conditions
Indicated value of the moving-iron type ammeter
is 100%.
Example of measuring inverter input current Example of measuring inverter output current
Moving-
iron type
Clip AC power meter
Clamp-on
wattmeter current
measurement
Clamp meter
Moving-iron
type
Clamp-on
wattmeter current
measurement
Clamp meter
Clip AC power meter