Mitsubishi FR-E520-0.1KN - Leakage Currents and Countermeasures

INSTALLATION AND WIRING
39
2.3.4 Leakage currents and countermeasures
Due to the static capacitance existing in the inverter I/O wiring and motor, leakage
currents flow through them. Since their values depend on the static capacitance, 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 earth leakage
circuit breakers and earth leakage relays unnecessarily.
#
##
#
Countermeasures
!
If 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 leakage circuit breakers designed for harmonics and surges (e.g.
Mitsubishi's Progressive Super Series) in the inverter's own line and other line,
operation can be performed with low noise (with the carrier frequency kept high).
#
##
#
To-ground leakage current
!
Note that a long wiring length will increase leakage currents. Decrease the carrier
frequency of the inverter to reduce leakage currents.
!
Higher motor capacity leads to larger leakage currents.
(
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.
Inverter
Power
s
uppl
y
IM
Thermal relay
Line static capacitances
NFB
Line-to-line leaka
g
e current
p
ath
Motor
#
##
#
Countermeasures
!
Use the electronic overcurrent protection of the inverter.
!
Decrease the carrier frequency. Note that motor noise increases. Selection of
Soft-PWM will make 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.
2