Mitsubishi Electric FR-S520E Series Instruction Manual page 23

(2) Line-to-line leakage currents
Harmonics of
leakage currents
flowing in static
capacities between
the inverter output
cables may operate
the external thermal
relay unnecessarily.
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.)
CAUTION
•Select the MCCB according to the inverter power supply capacity.
•Install one MCCB per inverter.
MCCB
Power
supply
Line-to-Line Leakage Current Path
13
Thermal relay
Inverter
Line static
capacitances
Main circuit terminals
Motor
IM
1