Leakage Currents And Countermeasures - Mitsubishi FR-E 500 Instruction Manual

2.3.3 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 harmonic and surge
suppression (e.g. Mitsubishi's Progressive Super Series) in the inverter's own line
and other line, operation can be performed with the carrier frequency kept high
(with low noise).
" " " " 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. The leakage currents of
the 400V class are higher than those of the 200V class.
( 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.
When the wiring length is long (50m (164.04 feet) or more) for the 400V class models,
the external thermal relay is likely to operate unnecessarily because the ratio of the
leakage current to the rated motor current increases.
Power
supply
NFB
Thermal relay
Inverter
Line static capacitances
Line-to-line leakage current path
39
INSTALLATION AND WIRING
Motor
IM
2