Delta VFD-ED Series, Руководство пользователя

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Appendix A. EMC Standard Installation Guide | VFD-ED
A-15
Electrical Cabinet Design
In a high frequency electric field, shielding can be achieved by painting a thin layer of conductive metal on the
enclosure or on the internal lining material. However, the coating must be thorough and all parts should be properly
covered without any seams or gaps (just like a Faraday cage). That is only the ideal. Making a seamless shielding
shell is practically impossible since the cage is composed of metal parts. In some conditions, it is necessary to drill
holes in the shielding enclosure for installation of accessories (like optional cards and other devices).
1. If the metallic components are properly welded using sophisticated welding technology to form an electrical
cabinet, deformation during usage is unlikely to occur. But if the electrical cabinet is assembled with screws,
the protective insulating layer under the screw must be properly removed before assembly to achieve the
greatest conductivity and best shielding.
2. Drilling holes for the installation of wires in the electrical cabinet lowers the shielding effectiveness and
increases the chance of electric waves leaking through the openings and emitting interference. We recommend
that the drilled holes are as narrow as possible. When the wiring holes are not used, properly cover the holes
with metal plates or metal covers. The paint or the coating of the metal plate and metal cover should be
thoroughly removed to ensure a metal-to-metal contact or a conductive gasket should be installed.
3. Install industrial conductive gaskets to completely seal the electrical cabinet and the cabinet door without gaps.
If conductive gaskets are too costly, please screw the cabinet door to the electrical cabinet with a short
distance between the screws.
4. Reserve a grounding terminal on the electrical cabinet door. This grounding terminal shall not be painted. If the
paint already exists, please remove the paint before grounding.
Electrical wires and cables
Shielded Twisted Pair (STP) is a type of cable where two insulated copper wires are twisted together with a
metal mesh surrounding the twisted pair that forms the electromagnetic shielding and can also be used for
grounding.
The individual electrical wires and complete cable are surrounded by (synthetic) rubber that provides
insulation and also protects against damage.
There are two types of electrical cables: high voltage and low voltage. The high voltage cable differs from
the low voltage cable in that it has an additional insulation layer called the dielectric insulator within the plastic
sleeve. The dielectric insulator is the most important component in insulation. The low voltage cable is usually only
filled with a soft polymer material for keeping the internal copper wire in place.
The shield has two functions.
1. To shield the electrical wire and cable.
A. Electric currents increase as power flows through the power cable and generate an electrical field. Such
interference can be suppressed inside the cable by shielding the power cables or the electrical wires.
B. To form a protective earthing. When the cable core is damaged, the leakage current will flow via the shield
to ground
2. To protect the cable. A power cable used for the computer control purpose generates only relatively low
amount of current inside the cable. Such power cable will not become the source of interferences but has great
possibility to be interfered by the surrounding electrical devices.
Metallic shield
Centre core
Plastic jacket
Dielectric insulator