Shanghai Sigriner STEP Electric Co., Ltd.
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A.5.1 Earth leakage current
The earth leakage current will not only flow into the inverter, but also into other equipment through
the ground wire. It may cause misoperation of leakage circuit breakers, relays or other equipment.
The higher the carrier frequency of the inverter and the longer the motor cable, the greater the
leakage current.
Suppression measures: reduce carrier frequency; shorten the motor cable as much as possible; use
leakage circuit breakers specially designed for high harmonic/surge leakage current.
A.5.2 Line-to-line leakage current
The higher harmonics of the leakage current flowing through the capacitor among between cables on
the output side of the inverter may cause the misoperation of external thermal relay. When the
wiring is very long (more than 50 m), the leakage current will increase, which will easily lead to
misoperation of external thermal relay.
Suppression measures: reduce carrier frequency; install an AC output reactor at the output side. It is
recommended to directly monitor the motor temperature with a temperature sensor, or to replace
external thermal relay with the electronic thermal relay with the motor overload protection function
of the inverter itself.
A.6 Radiation emission suppression of the inverter
The inverter is generally installed in a metal control cabinet. The instruments and equipment outside
the metal cabinet are slightly affected by radiation emission of the inverter, and the external
connection cable is the major source of radiation emission. Because all of the power cables, motor
cables, control cables and keyboard cables of the inverter need to be led out of the shielding cabinet,
special measured should be taken at the lead-out position, otherwise the shielding will be invalid.
In Figure A-9, the cable in the shielding cabinet acts as an antenna, and after receiving the noise
radiation in the cabinet, it will propagate the noise to the outside of the shielding cabinet through the
cable and radiate to the space. In Figure A-10, the cable shielding layer is connected to the ground of
the shielding case at the exit, then the noise radiation received by the cable in the cabinet can directly
flow into the ground through the shielding case, thus eliminating the influence on the outside world.
When the shielding layer grounding method shown in Figure A-10 is used, the cable shielding layer
should be connected to ground of the case as close as possible to the outlet, otherwise the cable from
the grounding point to the outlet will still be coupled as an antenna. The distance between the noise
grounding point and the outlet should be less than· 15 cm, and the smaller the distance, the better.
Figure A-9 Radiation Caused by Outgoing Cable of Shielding Cabinet
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