Mitsubishi Electric 800 Series Instruction Manual page 82

Checkpoint
The voltage applied to the inverter I/O
signal circuits is within the specifications.
When using the electronic bypass
operation, electrical and mechanical
interlocks are provided between the
electronic bypass contactors MC1 and
MC2.
A countermeasure is provided for power
restoration after a power failure.
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.
Countermeasure
Application of a voltage higher than the permissible voltage to the inverter
I/O signal circuits or opposite polarity may damage the I/O devices.
Especially check the wiring to prevent the speed setting potentiometer
from being connected incorrectly to short circuit the terminals 10E and 5.
When using a switching circuit as shown below, chattering due to mis-
configured sequence or arc generated at switching may allow undesirable
current to flow in and damage the inverter. Mis-wiring may also damage
the inverter.
(The commercial power supply operation is not available with PM
motors.)
Power
R/L1 U
supply
S/L2 V
T/L3 W
Inverter
If switching to the commercial power supply operation while a failure such
as an output short circuit has occurred between the magnetic contactor
MC2 and the motor, the damage may further spread. If a failure has
occurred between the MC2 and the motor, a protection circuit such as
using the OH signal input must be provided.
If the machine must not be restarted when power is restored after a power
failure, provide an MC in the inverter's input side and also make up a
sequence which will not switch ON the start signal. If the start signal (start
switch) remains ON after a power failure, the inverter will automatically
restart as soon as the power is restored.
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.
If using an MC for emergency stop during operation, select an MC
regarding the inverter input side current as JEM 1038-AC-3 class rated
current.
Switch the magnetic contactor between the inverter and motor only when
both the inverter and motor are at a stop.
When a failure occurs between the MC2 and motor, make sure to provide
a protection circuit, such as using the OH signal input.
In an application, such as fan and blower, where the motor is driven by
the load, a low-voltage manual contactor must be connected at 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 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 signal cables as far away as possible from power cables (inverter
I/O cables).
• Use shielded cables.
• Install a ferrite core on the signal cable.
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.
MC1
Interlock
M
MC2
Undesirable current
3. PRECAUTIONS FOR USE OF THE INVERTER
3.6 Checklist before starting operation
Refer to Check
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