Mitsubishi Electric 800 Series Instruction Manual page 90

Checkpoint
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.
When using vector control, the
encoder is properly installed.
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.
Countermeasure
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 vector control
dedicated motors (SF-V5RU, SF-THY) nor with PM motors.)
Power
R/L1
supply
S/L2
T/L3
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.
The encoder must be directly connected to a motor shaft without any backlash.
(Real sensorless vector control, PM sensorless vector control do not require an
encoder.)
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 motor driving, select an MC
regarding the inverter input side current as JEM1038-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 (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.
PRECAUTIONS FOR USE OF THE INVERTER
Checklist before starting operation
MC1
Interlock
U
IM
V
MC2
W
Undesirable current
Refer Check
to by
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