Mitsubishi Electric Freqrol-A100 Instruction Manual page 184

Note: 1. The NV should be installed to the primary (power Selection Example
supply) side of the inverter. (for the diagram shown on the left) (mA)
2. Ground fault in the secondary side of the inverter
can be detected at the running frequency of 120Hz
or lower.
3.
In the Y connection neutral point grounded sys-
tem, the sensitivity current is purified against
ground fault in the inverter secondary side.
Hence, the protective ground resistance of the
load equipment should be 10Q or less.
4. When the breaker is grounded on the secondary
side of the inverter, it may be unnecessarily op-
erated by harmonics if the effective value is less
than the rating. In this case, note that the eddy
current and hysteresis loss increase and tem-
perature rises.
* For the leakage current value of the noise filter installed on the inverter input side, contact
the corresponding filter manufacturer.
6.1.4
Power Supply Harmonics
Power supply harmonics may be generated from the converter section of the inverter, affecting the
generator, power capacitor, etc. Power supply harmonics are different in generation source, fre-
quency band and transmission path from noises and leakage currents.
Take the following measures
The difference between harmonics and noise is shown below.
Measures
The harmonic current generated from the inverter to the power supply side differs according to
various conditions such as the control method (PWN, PAM), use of power-factor improvement
reactor, output frequency on load side, and output current size.
Obtaining the output frequency and output current with the conditions of the rated load during the
used max. fre,quency is the most optimum method.
Noise
Harmonics
(several 10kHz to MHz order)
To spaces, distance, laying paths
Occurs randomly, quantitative understanding is
difficult
According to current fluctuation rate (larger with
speed switching)
Item
Frequency
Environment
Quantitative
understanding
Generated amount
Withstand of
effected device
Examples of
measures
~ o t e : The power-factor improvement capacitor and
surge killer on the inverter's output side may
be damaged due to overheating caused by
elements in the harmonics of the inverter out-
put. The overcurrent protection may activate
when an overcurrent flows to the inverter, so
when using the inverter drive, do not insert the
capacitor or surge killer on the inverter's out-
put side. For power-factor improvement, insert
the power-factor improvement reactor on the
inverter's primary side or in the DC current.
Refer to the technical material for datails.
Harmonics
Normally 40 to SO%, 3kHz or less
To wire paths, power impedance
Logical computation is possible
Approx. proportional to load capacity
,
p q ;
,
Power-lactor
improvement
DC reactor
Clarified in standards for each device
Install a reactor (L)
Inverter
Differs according to maker's device specifications
Increase the length (I)
.------
- /
Power-factor Do not insert
~mprovement power-factor
AC reactor improvement
capacitor
Fig.5.2 Inverter power-factor improvement