The specialized production of partial discharge testers for UHV power can help many power workers conduct various power tests more conveniently.
During the operation of power equipment, when partial discharge occurs, various charged particles such as electrons, positive and negative ions, etc., under the excitation of an electric field, generally have energy greater than the bond energy of polymers. These charged particles hitting the interstitial walls of the medium will break the chemical bonds of the insulator. At the same time, the heating of the medium at the partial discharge point will generate extremely high temperatures, which can cause thermal cracking of the insulator or promote oxidative cracking, thereby damaging the molecular structure of the insulator.
High voltage switchgear is a combination of electrical appliances, composed of various materials such as epoxy resin, sulfur hexafluoride, and engineering plastics. There are many reasons for partial discharge, which can be summarized as follows:
① Defects in the manufacturing process of insulation materials.
Due to various factors affecting the insulation structure and process, there may be residual bubbles or impurities in the insulator, and the dielectric constant of gases is often lower than that of liquid or solid materials. Under an alternating electric field, the distribution of electric field strength is inversely proportional to the dielectric constant. So if there are bubbles in the liquid or solid medium, the electric field strength in the bubbles is higher than that in the surrounding medium, but the breakdown field strength is much lower than that in the liquid and solid, so the bubbles will be punctured and discharged first, and the dielectric is still in an insulating state, forming a typical partial discharge; In addition, the presence of impurities can lead to a concentration of the surrounding electric field distribution,
② Uneven distribution of electric field.
Burrs or sharp edges on the surface of conductors can cause electric field concentration and result in partial discharge. During the manufacturing and assembly process of switchgear, metal particles may be introduced. The particles inside the cabinet have a strong ability to accumulate charges, causing distortion and discharge of the electric field in that area; The surface of the switchgear insulator is too dusty or not smooth enough. Partial discharge may also occur due to insufficient creepage distance; Even if the welding seam of the grounding shell is rough, with pores or slag on the surface, the electric field will be unevenly distributed, resulting in partial discharge.
③ The non-uniformity of dielectrics.
With the development of insulation technology, high-voltage metal enclosed switchgear with atmospheric insulation and composite insulation is currently the most widely used product. But it is the use of composite insulation technology that causes differences in the dielectric properties of various parts of the insulation material, and the bubbles and impurities introduced by the manufacturing process of the insulation material itself further lead to uneven dielectric distribution.
Partial discharge is affected by voltage, temperature, humidity, insulation conditions, and external environment.
