Wiring
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together, especially when installed the EMC filter. Otherwise the distributed capacitances
of its input and output power cable can be coupling each other to make the EMC filter out
of function.
4.7.3.3 Ground
Inverter must be ground safely when in operation. Grounding enjoys priority in all EMC
methods because it does not only ensure the safety of equipment and persons, but also is
the simplest, most effective and lowest cost solution for EMC problems.
Grounding has three categories: special pole grounding, common pole grounding and
series-wound grounding. Different control system should use special pole grounding, and
different devices in the same control system should use common pole grounding, and
different devices connected by same power cable should use series-wound grounding.
4.7.3.4 Leakage Current
Leakage current includes line-to-line leakage current and over-ground leakage current.
Its value depends on distributed capacitances and carrier frequency of inverter. The
over-ground leakage current, which is the current passing through the common ground
wire, can not only flow into inverter system but also other devices. It also can make
leakage current circuit breaker, relay or other devices malfunction. The value of
line-to-line leakage current, which means the leakage current passing through distributed
capacitors of input output wire, depends on the carrier frequency of inverter, the length
and section areas of motor cables. The higher carrier frequency of inverter, the longer of
the motor cable and/or the bigger cable section area, the larger leakage current will
occur.
Countermeasure:
Decreasing the carrier frequency can effectively decrease the leakage current. In the
case of motor cable is relatively long (longer than 50m), it is necessary to install AC
reactor or sinusoidal wave filter at the output side, and when it is even longer, it is
necessary to install one reactor at every certain distance.
4.7.3.5 EMC Filter
EMC filter has a great effect of electromagnetic decoupling, so it is preferred for customer
to install it.
For inverter, noise filter has following categories:
z Noise filter installed at the input side of inverter;
z Install noise isolation for other equipment by means of isolation transformer or
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