Introduction to shielding materials

Electromagnetic compatibility (EMC) is a key issue for today’s electronic devices, as they generate electromagnetic radiation and are affected by external interference. To reduce radiation and suppress interference, shielding materials are commonly used for protection, and the following are some of the commonly used shielding materials.

1, Conductor shielding

Role.

  • Can equalize the electric field distribution on the insulation, and reduce the conductor surface due to the conductor effect increasing the maximum field strength.
  • prevent air gap, and improve resistance to partial discharge, and dendritic discharge characteristics.
  • Inhibit dendrite triggering.
  • When the cable temperature suddenly rises (core heating), this layer can be isolated to avoid direct impact on the insulation.

Material.

Semi-conductive material, close to the surface of the conductor, 0.6, 0.8, and 1.0mm thickness of three kinds of thickness. Among them, 0.6, 0.8mm is used for 8.7/10kV, and below, 0.6mm is used for small specification, and 0.8mm is used for large specification. 1.0mm is used for 8.7/10~26/35kV. U less than or equal to 35kV can be used for crosslinked or non-crosslinked semiconductor material. u more than 35kV is used for crosslinked semiconductor material.

Conditions.

Phase voltage greater than 1.8 kV, there should be conductor shielding.

Mode.

The extrusion package is the main conductor nominal cross-section of 500 square millimetres and above using extrusion package + winding package joint shielding.

2, Insulation shielding

Role.

In the high voltage, due to the operation of the cable bending part of the surface by the tension effect of elongation, if this is the existence of localized discharge, it will be due to the surface bending to produce microscopic cracks leading to dendrites triggered or the surface of the localized discharge corrosion caused by the new cracks triggered by the new dendrites. The outer shielding of the cable effectively prevents such conductors from triggering electric dendrites and also prevents the harmful effects of the air gap between the metal shielding and the insulating layer.

Material.

Semi-conductive material, 1.0, 1.2, and 1.5 mm thick, 1.0 mm for 8.7/10 kV and below, 1.2 mm for 35 kV and below, and 1.5 mm for 35 kV and above.

Conditions.

Phase voltage greater than 1.8 kV, with insulation shielding.

Mode.

Phase voltage Voltage less than or equal to 8.7kV, with extruded package or winding, phase voltage greater than 8.7kV with extruded package.

3, Metal shielding

Role.

  • Strengthen and limit the electric field in the insulation, so that the direction of the electric field is along the insulation radius direction.
  • Used in the three-phase four-wire system can be used as a neutral line, bearing the unbalanced current.
  • Copper tape-shielded cable has superior lightning protection characteristics.
  • Prevent cable axial surface discharge.
  • Flows capacitive current under normal conditions and serves as a circuit for short-circuit current in case of short-circuit.

Material.

Annealed soft copper wire, and annealed soft copper tape.

Soft copper tape specifications are generally: 0.10, 12mm two, single-core cable with a nominal thickness of not less than 0.12mm copper tape, multi-core cable with a nominal thickness of not less than 0.10mm copper tape.

Copper wire specifications: phase voltage of 26 kV and the following cable copper wire nominal cross-section S = 16, 25, 35, 50 mm2 four specifications. Phase voltage of 64 kV and above cable shielding nominal cross-section of 95 square millimetres, can be selected according to the short-circuit current capacity.

Conditions.

Phase voltages greater than 1 kV should be metal-shielded.

Mode.

Phase voltage greater than or equal to 21 kV, and the nominal cross-section of 500 square millimetres and above cables, the use of copper wire shielding, the surface of the reverse copper wire, or copper tape tightening. Other cables are made of soft copper tape with heavy reference winding.

Summary

Electromagnetic compatibility is a key issue for modern electronic equipment. Commonly used shielding materials include conductor shielding, insulation shielding, and metal shielding. Engineers should choose the most suitable shielding materials and methods according to the requirements of specific applications when designing electronic equipment to ensure the stability and reliability of the equipment in the electromagnetic environment.