Solution To Emc: Shielding - Delta EB3000 Series User Manual

Appendix A. EMC Standard Installation GuideEB3000
A-4 Solution to EMC: Shielding
A-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.
Figure A-15
A-14
Figure A-16