MITSUBISHI ELECTRIC FR-S520 - Manual (Page 181)

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(2) Handling of primary side magnetic contactor
When the external terminal is used (terminal STF or STR is used) for operation,
provide a primary side MC to prevent accidents due to an automatic restart at
power restoration after a power failure, such as an instantaneous power failure,
and to ensure safety in maintenance work. Do not use this MC to make frequent
starts and stops. (The switching life of the inverter input circuit is about 100,000
times.)
For parameter unit operation, an automatic restart after power failure is not
made and the MC cannot be used to make a start. Note that the primary side
MC may be used to make a stop but the motor will coast to a stop.
(3) Handling of secondary side magnetic contactor
In principle, do not provide a magnetic contactor between the inverter and motor
and switch it from off to on during operation. If it is switched on during inverter
operation, a large inrush current may flow, stopping the inverter due to overcurrent
shut-off. When an MC is provided for switching to the commercial power supply,
for example, switch it on/off after the inverter and motor have stopped.
(4) Installation of thermal relay
To protect the motor from overheat, the inverter has the protective functions using
electronic overcurrent protection. However, when multiple motors are run by a
single inverter or a multi-pole motor is run (for example), provide a thermal relay
(OCR) between the inverter and motor. In this case, set the electronic overcurrent
protection of the inverter to 0A, and set the thermal relay by adding a line-to-line
leakage current (refer to page 16) to 1.0 times the current value at 50Hz given on
the motor rating plate or 1.1 times the current value at 60Hz
(5) Disuse of power factor improving capacitor (power capacitor)
The power factor improving capacitor and surge suppressor on the inverter output
side may be overheated or damaged by the harmonic contents of the inverter
output. In addition, do not provide a capacitor and surge suppressor since
excessive currents will flow in the inverter to active overcurrent protection. To
improve the power factor, use a power factor improving reactor.
(6) Secondary side measuring instruments
If inverter-to-motor wiring is long, the measuring instruments and CT may
generate heat under the influence of line-to-line leakage currents. To prevent this,
choose the instruments which have allowances for current ratings.
(7) About electromagnetic wave interference
The inputs/outputs of the inverter's main circuit include harmonic content and may
interfere with communications apparatus (AM radios) and sensors used near the
inverter. In this case, installing the FR-BIF radio noise filter (for use on input side
only) or FR-BSF01 or FR-BLF line noise filter reduces interference.