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Main circuit terminals
(2) Line-to-line leakage currents
Countermeasures
• Use the electronic thermal relay function of the inverter.
• Decrease the carrier frequency. Note that motor noise increases. Selection of
Soft-PWM (Pr. 70) makes it unoffending.
To ensure that the motor is protected against line-to-line leakage currents, it is
recommended to use a temperature sensor to directly detect motor temperature.
Installation and selection of moulded case circuit breaker
Install a moulded case circuit breaker (MCCB) on the power receiving side to
protect the wiring of the inverter primary side. Select the MCCB according to the
power supply side power factor (which depends on the power supply voltage, output
frequency and load). Especially for a completely electromagnetic MCCB, one of a
slightly large capacity must be selected since its operation characteristic varies with
harmonic currents. (Check it in the data of the corresponding breaker.) As an earth
(ground) leakage breaker, use the Mitsubishi earth (ground) leakage breaker
designed for harmonics and surge suppression. (Refer to page 10 for the
recommended models.)
Harmonics of
leakage currents
flowing in static
capacities between
the inverter output
cables may operate
the external thermal
relay unnecessarily.
CAUTION
•Select the MCCB according to the inverter power supply capacity.
•Install one MCCB per inverter.
•The inverter has a protective function based on electronic overcurrent protection
(electronic thermal relay function) to protect the motor from overheating.
However, when running multiple motors with one inverter or operating a multi-
pole motor, provide a thermal relay (OCR) between the inverter and motor. In this
case, set the electronic thermal relay function (electronic overcurrent protection)
of the inverter to 0A. And set the electronic overcurrent relay, add the line-to-line
leakage current to 1.0 times the current value at 50 Hz on the motor rating plate or
to 1.1 times the current value at 60 Hz.
•When the FR-BFP (filter pack) is used, leakage current is 4mA.(8mA for 400V
class.) (equivalent to one-phase of cable for the three-phase three wire
connection)
Line-to-Line Leakage Current Path
Inverter
Power
supply
IM
Thermal relay
Line static
capacitances
MCCB
Motor