VM1000 Series
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2.3.4 Leakage Current and Handling
There are two forms of leakage current while using VFD: one is earth leakage current,the other
is leakage current between cable and cable.
(1)Factors that influenced earth leakage current and solutions
There exists distributed capacitance between wire and earth.The bigger the distributed
capacitance, the larger the leakage current.It can decrease the carrier frequency in order to
decrease leakage current. However, to decrease carrier frequency will increase motor noise.
Please note that the installation of the reactor is also an effective way to solve the leakage
current.
Leakage current increases with the loop current. When motor power is high, the corresponding
leakage current is high.
(2)The factors that caused leakage current between cable and cable and solutions
There exists distributed capacitance in VFD output circuits. It is likely to cause resonance and
bring about leakage current if the current in the circuits contains higher harmonics. If thermal
relay is put into use at this time, it will cause malfunction.
Solutions: decrease carrier frequency or install output reactor. When using VFD, it is suggested
to use its electronic overload protection, and do not install a thermal relay before the motor.
Precautions of installing EMC input filter at power input side
①Notes：Strictly comply with the ratings when using the EMC filter. The EMC filter is
category I electric apparatus, and therefore, the metal housing ground of the filter should be in
good contact with the metal ground of the installation cabinet on a large area, and requires good
conductive continuity. Otherwise, it will result in electric shock or poor EMC effect.
②As result of EMC test, it founds that the ground of the EMC filter and the PE conductor of
the AC drive must be tied to the same common ground. Otherwise, the EMC effect will be
affected seriously.
③The EMC filter should be installed as closely as possible to the power input side of the AC
drive.
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