Mitsubishi Electric 800 Series Installation Manualline page 40

PRECAUTIONS FOR USE OF THE INVERTER
Checkpoint
A magnetic contactor (MC) is
installed on the inverter's input
side.
The magnetic contactor on the
inverter's output side is properly
handled.
When using a PM motor, a low-
voltage manual contactor is
installed on the inverter's output
side.
An EMI countermeasure is
provided for the frequency setting
signals.
A countermeasure is provided for
an overload operation.
The specifications and rating
match the system requirements.
Countermeasures are taken
against electrical corrosion on the
motor bearing.
*1
Recommended common mode choke: FT-3KM F series FINEMET® common mode choke cores manufactured by Hitachi Metals, Ltd.
FINEMET is a registered trademark of Hitachi Metals, Ltd.
34
Countermeasure
On the inverter's input side, connect an MC for the following purposes:
To disconnect the inverter from the power supply at activation of a protective function or at
malfunctioning of the driving system (emergency stop, etc.).
To prevent any accident due to an automatic restart at power restoration after an inverter stop made
by a power failure.
To separate the inverter from the power supply to ensure safe maintenance and inspection work.
To use an MC to perform an emergency stop during operation, select the MC conforming to JEM
1038-AC-3 rated current for the inverter rated input current.
Switch the magnetic contactor between the inverter and motor only when both the inverter and
motor are at a stop.
A PM motor is a synchronous motor with high-performance magnets embedded inside. High-voltage
is generated at the motor terminals while the motor is running even after the inverter power is turned
OFF. In an application, such as fan and blower, where the motor is driven by the load, a low-voltage
manual contactor must be connected on the inverter's output side, and wiring and inspection must
be performed while the contactor is open. Otherwise you may get an electric shock.
If electromagnetic noise generated from the inverter causes the frequency setting signal to fluctuate
and the motor rotation speed to be unstable when changing the motor speed with analog signals,
the following countermeasures are effective:
Do not run the signal cables and power cables (inverter I/O cables) in parallel with each other and
do not bundle them.
Run the signal cables as far away as possible from the power cables (inverter I/O cables).
Use shielded cables.
Install a data line filter to signal cable (example: ZCAT3035-1330 by TDK).
When performing frequent starts/stops by the inverter, rise/fall in the temperature of the transistor
element of the inverter will repeat due to a repeated flow of large current, shortening the life from
thermal fatigue. Since thermal fatigue is related to the amount of current, the life can be increased
by reducing current at locked condition, starting current, etc. Reducing current may extend the
service life but may also cause torque shortage, which leads to a start failure. Adding a margin to the
current can eliminate such a condition. For an induction motor, use an inverter of a higher capacity
(up to two ranks). For a PM motor, use an inverter and PM motor of higher capacities.
Make sure that the specifications and rating match the system requirements.
When a motor is driven by the inverter, axial voltage is generated on the motor shaft, which may
cause electrical corrosion of the bearing in rare cases depending on the wiring, load, operating
conditions of the motor or specific inverter settings (high carrier frequency). Contact your sales
representative to take appropriate countermeasures for the motor. The following shows examples of
countermeasures for the inverter.
Decrease the carrier frequency.
Provide a common mode choke
*1
on the output side of the inverter.