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1.6 Others
1.6.1 Leakage currents and countermeasures
Leakage currents flow through static capacitances existing in the inverter I/O wiring and motor. Since their values
depend on the static capacitances, carrier frequency, etc., take the following measures.
(1) To-earth (ground) leakage currents
Leakage currents may flow not only into the inverter's own line but also into the other lines through the earth
(ground) cable, etc.
These leakage currents may operate earth (ground) leakage breakers and earth (ground) leakage relays
unnecessarily.
z Countermeasures
• When the carrier frequency setting is high, decrease the carrier frequency (Pr. 72) of the inverter.
Note that motor noise increases. Selection of Soft-PWM (Pr. 240) will make it unoffending.
• By using earth (ground) leakage circuit breakers designed for harmonic and surge suppression in the inverter's
own line and other line, operation can be performed with the carrier frequency kept high (with low noise).
(2) Line-to-line leakage currents
Harmonics of leakage currents flowing in static capacitances between the inverter output cables may operate the
external thermal relay unnecessarily. When the wiring length is long (50m or more) for the 400V class small-
capacity model (7.5kW or less), the external thermal relay is likely to operate unnecessarily because the ratio of the
leakage current to the rated motor current increases.
z Line-to-line leakage current data example (200V class)
*The leakage currents of the 400V class are about twice larger.
z Measures
• Use the electronic thermal relay function (Pr. 9) of the inverter.
• Decrease the carrier frequency. Note that motor noise increases. Selection of Soft-PWM (Pr. 240) will make it
unoffending.
For other than the dedicated motor (SF-V5RU), using a temperature sensor to directly detect the motor
temperature is recommended to ensure that the motor is protected against line-to-line leakage currents.
z 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 surges.
Motor Capacity
(kW)
Rated Motor
Current(A)
Leakage Current (mA)
Wiring length 50m Wiring length100m
1.5 9.0 370 560
2.2 13.0 400 590
• Motor SF-V5RU 4P
• Carrier frequency: 13.5KHz
• Cable :2mm
2
4-core
• Cab tyre cable
Inverter
Power supply
IM
Thermal relay
Line static capacitances
MCCB
Line-to-Line Leakage Current Path
Motor