Delta VFD-ED Series, User Manual

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Appendix A. EMC Standard Installation Guide | VFD-ED
A-13
Solution to EMI: Shielding
4.1 What is Shielding?
Electrostatic shielding
is used to isolate equipment so that it will not create electromagnetic field interference
or be influenced by an external electromagnetic field. A conductive material is used for electrostatic shielding to
achieve this isolation.
A
Faraday cage
can be made from a mesh of metal or a conductive material.
One characteristic of metal is that it is highly conductive and not electrostatic, which offers shielding and prevents
interference by external electrical fields. Metal with its high conductivity protects the internal devices from high
voltages—no voltage will enter the cage even when the cage is experiencing a high current. In addition,
electromagnetic fields can also pass through the Faraday cage without causing any disturbance.
Electromagnetic shielding is applied to some electrical devices and measurement equipment for the purpose of
blocking interference. Examples of shielding include:

earth high-voltage indoor equipment using a metal frame or a high-density metal mesh

shielding a power transformer is achieved by wrapping a metal sheet between the primary and secondary
windings or by adding an enamel wire to the winding wire which is then earthed.

a shielding coating, which is made of metal mesh or conductive fibers to provide effective protection for the
workers who work in a high-voltage environment.
In the picture below, the radio appears to be not fully covered by metal but if the conductivity of the metal is
high, radio waves are completely blocked and the radio will not receive any signal.
Mobile phone connections are also established through the transmission of radio waves. This is why the
mobile phone reception is often cut off when we walk into an elevator. The metal walls of the elevator create the
same shielding effect just as if we had entered a metal cage. Another example is a microwave oven. The
microwave door may seem transparent in visible light, but the density of the metal mesh in the microwave door
blocks the electromagnetic waves. A higher density of the metal mesh offers better shielding.