Porcelain insulators are referred to as insulators, formerly known as obstacles or electron barriers. Porcelain or stoneware ceramic material used to support and insulate conductors. It normally used with power fittings. According to the usage, it divides into lines, power station electrical appliances, telecommunications and special insulators; according to the structural shape, it divides into needle type, butterfly type, disc type, rod type, cross arm and casing; according to the use occasion, it divides into indoor and outdoor; according to the voltage level, it divides into low voltage (below 10kV), high voltage (above 10kV) and ultra-high voltage (above 500kV). The main indicators measured are its electrical properties, mechanical properties, thermal properties and antifouling capabilities. They are mainly used for overhead power transmission and distribution lines, substation busbars and the insulation and support of live bodies in various electrical equipment.
The effective insulating part of the porcelain insulator is the inorganic material alumina ceramics. This inorganic material has good chemical stability and very good anti-aging ability, but the service life of the porcelain insulator depends on the insulating body, and its life span is 25 years - 50 years . However, what are the common fault types of porcelain insulators in live operation? How to prevent and avoid such failures?
1. The electrical performance faults of porcelain insulators mainly include breakdown and flashover: the breakdown fault occurs inside the insulator, the porcelain insulator discharges through the porcelain body between the cap and pin, and there may be no traces on the surface of the insulator, but the insulator overall insulation performance were completely lost; flashover occurs on the surface of the porcelain insulator, and burn marks can be seen. Under normal circumstances, the insulation performance will not be completely reduced, and the operation can still continue. The insulation breakdown at the end of the porcelain piece is also manifested as surface burns or cracks in the porcelain disc. According to the insulation coordination of the insulator performance, the power frequency breakdown voltage of the insulator should be 1.5 times the rated power frequency dry flashover voltage. When its operating power frequency breakdown voltage is lower than the dry flashover voltage, the insulator is an unqualified insulator, also called Zero value insulator. Under normal circumstances, the zero-value insulator may have large cracks, air gaps and air gap channels at the ends of the porcelain parts. When there is no large current passing through the air gap channels, in the dry state, the insulator still has insulating ability. It can withstand the operating voltage, but there is already a defect of insulation drop, which brings hidden dangers to safe operation. Therefore, the insulator zero value detector series products should be used to regularly conduct live detection on the running porcelain insulator to prevent zero value.
2. Cracks on the surface of porcelain insulators: There are cracks on the surface of porcelain insulators, insulating sleeves and epoxy resin products, both in terms of mechanical properties and electrical properties, there are potential safety hazards and operational defects, and they need to be replaced as soon as possible. Although local skirt defects or flange defects may not necessarily cause failure, the overall insulation performance of the insulator has deteriorated and needs to be replaced as soon as possible. Therefore, it is recommended to use the HB-TX2 insulator flaw detector to regularly conduct live flaw detection on porcelain insulators to detect various damages in time.
3. Oil leakage of porcelain bushing: the porcelain insulating bushing with insulating oil inside may cause damage to the end of the bushing due to external force during maintenance and transportation. After a period of operation, mechanical stress and electric power are added. It may deform the connection part, resulting in a decrease in the sealing ability. The sealing material of the porcelain sleeve is made of mailing materials such as cyanide-butylene copolymer cork and synthetic rubber. It is inevitable that with the prolongation of operating time, the sealing performance of the material will deteriorate and oil leakage will occur. There are also cracks in the porcelain casing, excessive tension and compression, and bending loads that cause the porcelain casing to dislocate, and the sealing material is exposed to the air and loses its sealing effect which causing oil leakage.
4. Corona discharge on the protruding part of the fittings of the porcelain sleeve terminal: the corona phenomenon is a discharge phenomenon caused by the uneven intensity of the electric field, which makes the charged particles in the air rhyme to the electric field in two levels. The insulating surface of the insulator with serious contamination will form a conductive film on the surface of the insulator as the contamination layer on the surface is dampened, the electrical strength of the insulator will drop, and a leakage current will begin to appear. In order to avoid this kind of corona discharge phenomenon affecting the operation safety, the insulators can be cleaned in time; on the other hand, the insulator pollution level can be checked regularly by using the insulator salt density and dust density tester.