Instruction Manual of
-S3 Inverter for Elevator
A.5 Leakage Current and Countermeasures
Figure A.8 shows that the leakage current will flow through the line capacitor and motor
capacitor on the input and output sides of the Inverter, including the leakage current to
earth and the leakage current between lines. The leakage current is determined by the
carrier frequency and the capacitance.
Figure A8 Leakage current path
A.5.1 Leakage current to earth
Leakage current to earth may not only enter the inverter, but also other equipment through
the grounding conductor, causing wrong actions of leakage circuit-breaker, relay or other
equipment. The leakage current goes higher with higher carrier frequency and longer
motor cable.
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Countermeasures: lower the carrier frequency; shorten the motor cable as much as
possible; use a leakage circuit-breaker specifically designed for high harmonic/surge
applications.
A.5.2 Leakage current between lines
External thermal relays may take wrong actions due to the high harmonic of the leakage
current cross the distributed capacitors on the output side of the inverter. Especially for
inverters with capacity lower than 7.5kW, higher leakage current with a long conductor
(above 50 m) may trigger wrong actions of external thermal relays.
Countermeasures: lower the carrier frequency; install an AC reactor on the output side;
use a thermal sensor to directly monitor the motor temperature; use the electronic thermal
relay for motor over-load protection of the inverter itself instead of an external relay.
A.6 Restraint of Radiation from Inverter
The control cabinet containing the inverter is generally made of metal, thus reducing the
radiation from the inverter to the instruments and equipment outside the cabinet. The
connecting cable is the major radiation source. Since the cables for inverter power supply,
motor, control circuit and keyboard shall be led out of the shielded cabinet, special