EMC Guide MD320/MD320N User Manual
158
The surrounding equipment is separately earthed, which can avoid the interference 3)
caused by the leakage current of the inverter’s earth wire when common earth mode is
adopted.
7.3.5 Leakage current and handling
There are two forms of leakage current when using the inverter. One is leakage current to the
earth, and the other is leakage current between the cables.
Factors inuencing the leakage current to the earth and the solutions: 1)
There are distributed capacitance between the lead cables and the earth. The larger the
distributed capacitance is, the larger the leakage current will be. The distributed capacitance
can be reduced by effectively reducing the distance between the inverter and the motor. The
higher the carrier frequency is, the larger the leakage current will be. The leakage current can
be reduced by reducing the carrier frequency. However, reducing the carrier frequency may
result in addition of motor noise. Note that additional installation of reactor is also an effective
method to remove the leakage current.
The leakage current may increase following the addition of circuit current. Therefore, when the
motor power is high, the corresponding leakage current will be high too.
Factors of producing leakage current between the cables and solutions: 2)
There is distributed capacitance between the output cables of the inverter. If the current passing
the lines has higher harmonic, it may cause resonance and thus result in leakage current. If
thermal relay is used, it may generate error action.
The solution is to reduce the carrier frequency or install output reactor. It is recommended that
thermal relay not be installed before the motor when using the inverter, and that electronic over
current protection function of the inverter be used instead.
7.3.6 Precautions for Installing EMC input îš¿lter at the input end of power supply
When using the inverter, please follow its rated values strictly. Since the îš¿lter belongs to 1)
Classiîš¿cation I electric appliances, the metal enclosure of the îš¿lter shall be large and the
metal ground of the installing cabinet shall be well earthed and have good conduction
continuity. Otherwise there may be danger of electric shock and the EMC effect may be
greatly affected.
Through the EMC test, it is found that the îš¿lter ground must be connected with the PE end 2)
of the inverter at the same public earth. Otherwise the EMC effect may be greatly affected.
The îš¿lter shall be installed at a place close to the input end of the power supply as much 3)
as possible.
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