Mitsubishi Electric FR-A700 Instruction Manual page 106

Precautions for use of the inverter
● A short circuit or earth fault on the inverter output side may damage the inverter modules.
– Fully check the insulation resistance of the circuit prior to inverter operation since
repeated short circuits caused by peripheral circuit inadequacy or an earth fault caused
by wiring inadequacy or reduced motor insulation resistance may damage the inverter
modules.
– Fully check the to-earth insulation and inter-phase insulation of the inverter output side
before power-on.
Especially for an old motor or use in hostile atmosphere, securely check the motor
insulation resistance etc.
● Do not use the inverter input side magnetic contactor to start/stop the inverter.
Always use the start signal (ON/OFF of STF and STR signals) to start/stop the inverter.
● Across P/+ and PR terminals, connect only an external regenerative brake discharge
resistor. Do not connect a mechanical brake.
● Do not apply a voltage higher than the permissible voltage to the inverter I/O signal circuits.
Contact 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 terminals 10E (10, respectively) -5.
● Provide electrical and mechanical interlocks for MC1 and MC2 which are used for commer-
cial power supply-inverterswitch-over.
When the wiring is incorrect or if there is a commercial power supply-inverter switch-over
circuit as shown below, the inverter will be damaged by leakage current from the power
supply due to arcs generated at the time of switch-over or chattering caused by a sequence
error.
(Commercial operation can not be performed with the vector dedicated motor (SF-V5RU,
SF-THY).)
Power
supply
b
CAUTION:
If the machine must not be restarted when power is restored after a power failure,
provide a magnetic contactor 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.
● 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 bound current, starting current, etc.
Decreasing current may increase the life. However, decreasing current will result in insuffi-
cient torque and the inverter may not start. Therefore, increase the inverter capacity to have
enough allowance for current.
● Make sure that the specifications and rating match the system requirements.
● A motor with encoder is necessary for vector control. In addition, connect the encoder directly
to the backlash-free motor shaft. (An encoder is not necessary for real sensorless vector
control.)
4 - 2
M
3~
Undesirable current
Fig. 4-1:
Mechanical interlocks for MC1 and MC2
Operation
I001042E