Explanation of Common Terms of High Voltage: Gas Discharge, Electrical Insulation

Partial discharge
Terminological Interpretation: Partial discharge refers to the discharge occurring between the electrodes but not through the electrodes. It is a phenomenon of repeated breakdown and extinction under the action of high electric field strength due to the weakness in the insulation of the equipment or the defects in the production process.
It is shown by the breakdown of gases in insulation, the partial breakdown of solid or liquid medium in a small range, or the partial discharge caused by the concentration of electric field at the edge and sharp corner of metal surface, etc. The energy is very small, and does not affect the insulation strength of electrical equipment in a short time.
Examples of research:
A. If partial discharge occurs continuously in the insulation of electrical equipment, weak discharge will produce cumulative effect, which will deteriorate the performance of insulation nodes and expand the local defects, resulting in the decrease and destruction of the electrical strength of the main insulation of the equipment.
B. In order to eliminate this latent fault phenomenon, many methods for on-line detection of partial discharge are derived from some electrical impulse, ultrasonic, electromagnetic radiation signals accompanied by partial discharge.
C. Partial discharge characteristic is also an important index to measure the quality of power transformer insulation system.


Corona discharge
Terminological Interpretation: Corona discharge refers to the partial self-sustaining discharge of a gas medium in an inhomogeneous electric field. It is the most common form of gas discharge.
When the radius of curvature of the electrode is very small or the distance between the electrodes is very long, the local electric field intensity exceeds the ionization field strength of the gas when the voltage reaches a certain level due to the non-uniform electric field, and the gas is ionized and stimulated, thus corona discharge occurs.
Its performance is accompanied by a "hissing" sound, sometimes with a weak glow.
Examples of research:
A. Corona discharge can be used for electrostatic precipitation, sewage treatment, air purification, etc.
B. Corona discharge occurs on the conductors of HV and EHV transmission lines in power systems, which can cause corona power loss, radio interference, television interference and noise interference.
C. For high voltage electrical equipment, corona discharge will gradually destroy the insulation performance of the equipment.


Non-uniform electric field
Terminological Interpretation: Non-uniform electric field is an electric field in which the magnitude and direction of electric field intensity varies with space coordinates.
The degree of electric field inhomogeneity is characterized by the ratio of maximum field strength to average field strength: f < 2 is a slightly inhomogeneous electric field (which can not maintain stable corona discharge), 2 < f < 4 is an inhomogeneous electric field, and F > 4 is a very inhomogeneous electric field (which can maintain stable corona discharge). </f<4 is an inhomogeneous electric field, f>
Examples of research:
A. The degree of non-uniform electric field will affect the dielectric insulation strength. Under the same other conditions, the more inhomogeneous the electric field, the lower the breakdown voltage of the dielectric, the lower the insulation strength. Therefore, when analyzing the breakdown of insulation structure, not only the insulation distance, but also the influence of electric field non-uniformity should be considered.
B. At the tip or edge of the electrode, because of its small radius of curvature, high surface charge density, dense power lines and high electric field intensity, it is easy to produce extremely uneven electric field. Therefore, it is necessary to improve the shape of the electrode in engineering to avoid too small radius of curvature or sharp angle on the surface of the electrode.
C. Extremely uneven electric fields are often encountered in high-voltage power equipment, such as the electric field around the high-voltage overhead transmission line, the electric field at the outlet of the high-voltage AC motor rod, and the electric field near the lead of the power transformer.