Leakage Currents And Countermeasures - Mitsubishi Electric FR-E540 K-EC Series Instruction Manual

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-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
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 durable against 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-earth (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 or more) for the 400V class, the external thermal relay is likely to operate
unnecessarily because the ratio of the leakage current to the rated motor current
increases.
Power
supply
INSTALLATION AND WIRING
NFB
Thermal relay
Inverter
Line static capacitances
Line-to-line leakage current path
37
Motor
IM