Mitsubishi Electric 800 Series Assembly & Installation Manuallines page 26

PRECAUTIONS FOR USE OF THE INVERTER
When using the electronic bypass operation, electrical and
mechanical interlocks are provided between the electronic
bypass contactors MC1 and MC2.
When using a switching circuit as shown on the right,
chattering due to misconfigured sequence or arc generated at
switching may allow undesirable current to flow in and
damage the inverter. Mis-wiring may also damage the
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 a magnetic contactor (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.
Vector control is available with an encoder-equipped motor. And such an encoder must be directly connected to a motor shaft
without any backlash. (Real sensorless vector control does not require an encoder.)
Inverter input side magnetic contactor (MC)
On the inverter input side, connect an MC for the following purposes. (Refer to the FR-A870 Instruction Manual (Hardware).)
– To disconnect the inverter from the power supply when a fault occurs or when the drive is not functioning (e.g. emergency
stop operation).
– To prevent any accident due to an automatic restart at restoration of power 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 JEM1038-AC-3
class rated current.
Handling of inverter output side magnetic contactor
Switch the magnetic contactor between the inverter and motor only when both the inverter and motor are at a stop. When the
magnetic contactor is turned ON while the inverter is operating, overcurrent protection of the inverter and such will activate.
When MC is provided for switching to the commercial power supply, for example, switch it ON/OFF after the inverter and motor
have stopped.
Countermeasures against inverter-generated EMI
When the motor speed is unstable, due to change in the frequency setting signal caused by electromagnetic noises from the
inverter, take the following measures when applying the motor speed by the analog signal:
– 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 as signal cables.
– Install a ferrite core on the signal cable (Example: ZCAT3035-1330 by TDK).
Instructions for overload operation
When performing operation of frequent start/stop of the inverter, increase/decrease in the temperature of the transistor
element of the inverter may repeat due to a continuous 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. Decreasing current may increase the life. However, decreasing current will result in insufficient torque and the
inverter may not start. Adding a margin to the current can eliminate such a condition. Use an inverter of a higher capacity (up to
2 ranks).
Make sure that the specifications and rating match the system requirements.
20
R/L1 U
Power supply
S/L2 V
T/L3 W
Inverter
MC1
Interlock
IM
MC2
Undesirable current