Others; Leakage Currents And Countermeasures - Mitsubishi Electric FR-V560 Instruction Manual

1.9 Others

1.9.1

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-ground leakage currents
Leakage currents may flow not only into the inverter's own line but also into the other lines through the ground
cable, etc.
These leakage currents may operate ground leakage breakers and ground leakage relays unnecessarily.
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.
• Ground leakage breakers designed for harmonics and surges can be used in the inverter's own line and other
lines to perform operation with the carrier frequency 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 (164.04 feet) or more) for the small-
capacity model (7.5kW (10HP) or less), the external thermal relay is likely to operate unnecessarily because the
ratio of the leakage current to the rated motor current increases.
Line-to-line leakage current data example
Motor capsity Rated Motor
(kW (HP)) Current(A)
2.2 (3) 8.1
Power supply
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.
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.
Installation and selection of no-fuse breaker
Install a no-fuse breaker (NFB) on the power receiving side to protect the wiring of the inverter primary side.
Select the NFB according to the power supply side power factor (which depends on the power supply voltage,
output frequency and load). Especially for a completely electromagnetic NFB, 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 a ground leakage breaker, use the Mitsubishi ground leakage breaker designed for
harmonics and surges.
Leakage Current (mA)
Wiring length Wiring length
50m (164.04 feet) 100m (328.08 feet)
1200
NFB
Thermal relay
Inverter
Line-to-Line Leakage Current Path
19
• Motor SF-JR 4P
• Carrier frequency: 14.5KHz
• Cable :2mm
• Cab tyre cable
1770
Motor
IM
Line static capacitances

Others

2
4-core
1