2. Installation of the frequency converter
a. Separation
Power cables (supplying, motor's) must be separated from signal wires. It is necessary to avoid parallel leading
of power and signal wires in the common wire channels, and especially in group of cables. The crossing of power cables
and signal cables under a right angle is allowed.
b. Equipotential
connections
The frequency converter and the filter should be mounted as close as possible, preferably on a common metal
plate which acts as a ground. For this purpose, for example, the back wall or a mounting plate of a case can be used.
The housing of the frequency converter, the filter and the metal plate shouldn't be coated with any insulation materials. It
is necessary to pay attention to an opportunity of oxidation of a surface that results in deterioration of contact. To limit
the level of asymmetric disturbances, a multipoint connection of the cable shield with ground is preferred.
Additional information about equipotential connections can be found in section 2.1.1.
c.
Shielding
Wires between the mains filter and the frequency converter are not necessary for shielding, if their length doesn't
exceed 300mm. In case the length of conductors exceeds 300mm it is necessary to use the shielded wires. Completely
shielded cable is a cable which fully complies with requirements of interference radiation according to EN 55011 norms.
Such cable should have the screen consisting of spiral metallized aluminium foil and tinned copper plait with a puls-duty
factor of not less than 85%, not separated galvanically.
Connection of the cable ends to ground is obligatory. It is necessary to use grounding of the cable shielding on
whole section of a cable, on both ends. For this purpose a special EMC grommets are used. They provide valid contact
of cable shielding to the case of the equipment. In addition it is necessary to use special cable clips to connect it to back
wall of a case for example. It is necessary to pay attention that the unshielded cables, are as short as possible.
Junctions of the shielding with a ground should be free from insulating coat on a whole section. Be careful not to
damage the shielding. It is not recommended to weave the copper plait in one point (without using EMC grommet) in
order to realize grounding.
In case of need control signal wires should also be shielded using the same principles.
d. F
iltration
The use of the EMC filter limits noises spreading from electric drive system to the mains. The principles of filter
installation are described at the description of equipotential bonding and shielding.
e.
Ferrite rings
Fulfilling the requirements, concerning interference emission in the first
environment and limited distribution, can be realized by using of ferrite rings instead
of additional RFI filter (in converters with rated power 7.5kW and below). It is
necessary to remember the warning placed in section 1.7. “CE marking”.
The ferrite ring should be placed on a supply cable of the frequency
converter, as on the figure 2.4.
f. The list of the equipment reducing EMC problems
The list contains devices that can be added to the drive system to improve
resistance to interference and reduce the emissivity of the drive system installed in
the intended environment of operation:
1) completely shielded cables - we recommend cables TOPFLEX EMV and TOPFLEX EMV 3 PLUS (HELUKABEL),
2) EMC grommets (throttles),
3) ferrite rings,
4) RFI filter (EPCOS, REO, SCHAFFNER),
5) EMC cabinet — optional, not required to comply with the EMC instructions.
Fig. 2.5 - Installation principles reducing EMC problems
Frequency converter MFC710 type with OP-11 control panel. TWERD Power Electronics
17
Fig. 2.4 – Installation of a ferrite
ring
