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E6581381
A-18
1
(2)Affects of leakage current across lines
Power
supply
Inverter
Thermal relays
CT
A
M
Leakage current path across wires
(1) Thermal relays
The high frequency component of current leaking into electrostatic capacity between inverter out-
put wires will increase the effective current values and make externally connected thermal relays
operate improperly. If the wires are more than 50 meters long, it will be easy for the external
thermal relay to operate improperly with models having motors of low rated current (several
A(ampere) or less), especially the 400V class low capacity (5.5kW or less) models, because the
leak current will increase in proportion to the motor rating.
Remedies:
1.Use the electronic thermal built into the inverter. ⇒ See section 5.12.
The setting of the electronic thermal is done using parameter
QNO, VJT.
2.Reduce the inverter's PWM carrier frequency. However, that will increase the motor's magnetic
noise.
The setting of PWM carrier frequency is done with the parameter
H. ⇒ See section 6.11.
3.This can be improved by installing 0.1µ~0.5µF - 1000V film capacitor to the input/output terminals of
each phase in the thermal relay.
U/T1
V/T2
W/T3
IM
Thermal rela
y
s