Instruction manual

39
2
INSTALLATION AND WIRING
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 ground
leakage circuit breakers and ground 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 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).
 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.
IM
Power
supply
Thermal relay
Line static capacitances
MCCB
Line-to-line leakage current path
Moto
r
Inverter
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