Anti pollution flashover of outdoor insulation power station high voltage electric power equipment
Based on the actual operation experience of Dayawan nuclear power station outdoor high voltage equipment as the basis, in accordance with national standards for the surrounding environment pollution level was evaluated. In confirmation of four conditions, the outdoor equipment external insulation creepage distance of basic requirements should be more than 3.5cm/kV, and then re verify whether the equipment external insulation selection to meet the requirements. The distance is less than the required equipment is improved on the part of creepage flashover, the nuclear power plant outdoor power equipment has been greatly improved. Finally, to further improve the anti pollution flashover ability and enhancing equipment maintenance work and puts forward several suggestions.
Key words: outdoor high voltage equipment; external insulation; pollution level; creepage distance; the insulation level of pollution flashover of high voltage electrical equipment insulation coordination is decided by the system. Outdoor electric equipment external insulation level shall meet the corresponding standards at all levels of the insulation level of polluted conditions. Dayawan nuclear power plant since the operation of outdoor high voltage electrical equipment, has repeatedly appeared pollution flashover and creepage phenomenon, therefore, from the perspective of outdoor equipment to prevent pollution flashover, the Dayawan nuclear power plant pollution level classification, external insulation creepage distance requirements, selection of original design, operation and improvement of analysis, research, it is necessary to.
1 outdoor high-voltage electric power equipment and operation of the
HV 1.1 equipment in Dayawan nuclear power plant installed 2 sets of 900MW generator, the generator output voltage 26kV. 1 units of electricity through to 3 400kV capacity of each single phase transformer 375MVA, 2 units of electricity through to 3 500kV capacity of each single phase transformer 375MVA, and then through the closed SF 6 bus duct (GIC) and 400kV/500kV switch station will power from high voltage transmission line to the Hongkong power grid and Guangdong power grid. The 400kV/500kV switch station also has 400kV/500kV connection transformer 2, to adjust the proportion of electricity sent 2 grid. A full set of 400kV/500kV high voltage switch and high voltage bus using SF6 combination electric equipment (GIS). Porcelain insulating equipment 12 (phase) of SF6 gas air tube, 12 (phase) of capacitor voltage transformer (phase) and 24 groups of post insulator. As the Dayawan nuclear power plant 220kV water nuclear line backup power supply, the power on the side of the pole downlead 1 groups (three-phase) pillarInsulator, 1 sets of electrical voltage transformer (three phase) and 1 groups of 220kVSF6 combination electric appliance (GIS) bushing (three).
Since the operation of 1.2 outdoor high-voltage power device 500kV switch station put into operation since 1991, export in 500kV nuclear Hui line once there are insulators due to contamination and creepage phenomenon. Due to design, 500kV nuclear Hui line outlet at the outlet position, trap pillar insulator creepage distance is insufficient, in winter, spring the dry season, the outer surface of the insulator flashover occurs frequently pillar, creepage phenomenon, only in 1993 was more than 3 times (1991 and 1992 also occurred many times). During the operation of nuclear power plants, this issue has worked with manufacturers and design departments had bargaining, but the other party no reply.
From the flashover discharge device, each pollution discharge events, 500kV trap post insulator contaminant discharge of U is the most serious. The main reason is: turbo generator condenser water circuit outlet, because water splash, produce atomized vapor. In the northeast wind blows, salt fog floated down on the wind to 220kV and 500kV post insulator, the formation of salt layer on its surface, and in a strong electric field is formed under the effect of corona discharge or part of insulator surface creepage flashover. Therefore, how to prevent condensation water loop seawater invasion, also is one of effective means to prevent flashover.
In March 16, 1996, 500kV nuclear Hui line traps pillar insulator pollution flashover, the situation is very serious, in order to prevent the short circuit accident may happen, for nuclear emergency Hui line outages in repair, cleaning of all post insulator, returned to power transmission on the line. The same year in May 18th and October 7th, 500kV nuclear Hui wave trap coil support insulator and occurred two times more serious polluted surface flashover phenomena, resulting in many non planned outage repair. Because of the multiple failure repair, not only directly affect the reliable operation of transmission lines and power flow distribution and contamination discharge, the ultimate consequences will directly affect the safe and reliable operation of nuclear power plant. With 500kV external insulation is similar to the equipment operation, 220kV auxiliary power system insulation equipment also occurred several times because of serious contamination discharge of insulators caused by emergency power failure repair events.
Since the 500kV switch station operation, repair department always adhere to the implementation of "every stop will sweep" principle, and the regular equipment inspection, found that filthy creepage phenomenon is to strengthen the tracking or apply for power is cleaning and maintenance, thus the pollution flashover accident effectively prevent the occurrence of.
2 nuclear power plants around the environment pollution levels to determine the Dayawan nuclear power plant is located in the east of Shenzhen Dayawan sea, from the sea power equipment 400m. Every year in March to May the weather very damp, maximum humidity up to 100%. June to October is the rainy and typhoon season, November to February second years of drought climate. This region belongs to the serious salt fog invasion area. In order to prevent salt spray atmosphere influence, 400kV/500kV switching station designed for indoor type. According to the early of the region (Longgang area) test results of salt density, salt density greater than 0.1 ~ 0.25mg/cm2. Therefore, as the outdoor equipment external insulation design, manufacturers are three levels of contamination level based selection of creepage distance.
According to the division principles concerning the pollution level (1) in the literature, the surrounding Dayawan nuclear power plant environment and operating experience, the local pollution levels were re evaluation, the evaluation result is local pollution level should be divided according to four. The reason for the four aspects: one is close to the sea, salinity is higher the air and rain; the two is the Longgang area (large area) contamination detection is three, but the nuclear power plant on the equipment safe, reliable operation indicators have higher requirements; three is to show that the historical operation of existing equipment, external insulation equipment due to pollution caused the creepage phenomenon occurred repeatedly, and even have non planned outage cleaning; four is the nuclear power plant outside insulation very little equipment, insulation level increased equipment costs to cost or investment is small, and the pollution flashover accidents would cause a great loss, pollution flashover accident in short is not acceptable the.
The 3 field device creepage distance check
The literature (1) and (2) the provisions of literature, high voltage electric equipment corresponding to the four level in polluted regions external insulation creepage distance should be greater than or equal to 3.1cm/kV, while the original hydropower Ministry issued relevant documents, corresponding to the four level of contamination area of creepage distance shall meet 3.5cm/kV (neutral grounded system) requirements. According to the standard, to the Dayawan nuclear power plant environmental pollution level for the four assessment, and considering the future changes of local pollution level and nuclear power plant equipment itself should have higher reliability (conventional power station safe operation were higher than the general), on the nuclear power plant external insulation creepage distance selection in fact, should have adequate safety margin based on standard, namely the requirements of nuclear power plant equipment external insulation creepage distance shall not be less than 3.1cm/kV, the actual selection should be more than 3.5cm/kV. According to the field device creepage distance measured values (see Table 1), apparently there are multiple equipment external insulation creepage distance is not up to the basic requirements of value. In fact, it is the specific creepage distance is less than 3.1cm/kV equipment under adverse weather conditions is the most serious pollution discharge.
4 improved measures and effect analysis of equipment external insulation electrical strength of the 3 basic factors of voltage, dirty and wet. By improving the equipment external insulation creepage distance, improve the ratio distribution or purge the unclean equipment surface electric field can improve the anti pollution flashover ability of the equipment.
To increase climbing modified in accordance with local pollution level and the actual conditions of the 4.1 part of the equipment, rationally adjust the creepage distance is one of the important measures to prevent the pollution flashover accident. Dayawan nuclear power plant electric porcelain insulation equipment rarely, the whole station post insulators with a total of 24 groups (phase), and less than the post insulator in 3.5cm/kV deficiency group (6 phase), if each group of increasing section insulators, creepage distance can be increased to 3.5cm/kV in the outer insulation. Increased investment costs increased insulator and improve the safety and reliability of the power plant efficiency and future maintenance costs are small compared to the. Therefore, from improving stain resistance of plants, avoid the pollution flashover accident of the general principle of speaking, to improve the insulation creepage distance is one of the effective measures of nuclear power plant has high ability of anti pollution flashover. After the argument, that position, the original equipment design in this way by the basic structure and load-bearing limitations. So, in the adjustment measures should be selected in climbing only increase climbing skirt attached, that is to increase the number of silicon rubber increase climbing skirt to improve equipment external insulation creepage distance in the pillar insulator on the original.
The pressure equalizing device appropriate, can improve the electric equipment electric field distribution along the surface, the insulation is subjected to a uniform voltage stress along the surface of unit length of electric equipment, avoid the corona or creepage. Calculation method of electric field distribution by finite element method, the electric field distribution of the 500kV trap insulators were calculated. In the field of adding pressure after loop distribution calculation, two different equalizing ring diameter and different positions along the pillar comparedInsulatorVoltage distribution, the result is that when the grading ring, the highest electric field intensity on the high-pressure side can be reduced from 345.3kV/m to 240.5kV/m, the maximum electric field strength was 30.4%, the improvement effect is very obvious. In this measure can be implemented in the argument, because of the influence of site equipment the actual layout, the architecture space surrounding equipment, distance constraints, influence each other and electric field and increase the equalizing ring after load intensity on the original post insulators influence, make this approach has been limited.
By analyzing the various reform program has run the antifouling performance comparison and analysis of the equipment and technology demonstration, in the increase climbing skirt, the antifouling coatings, cleaning and water washing three project were discussed one by one, the additional creepage distance technology is the best method. The implementation of the transformation is to install anti fouling thermal shrinkage increase climbing skirt in the post insulator, thereby enlarging the insulator of creepage distance and limit the leakage current, so as to improve the level of support insulator anti flashover (after transformation can improve the flashover voltage of more than 50%).
The modification of the 500kV kernel Hui wave trap coil support insulator and 220kV equipment was completed in 1997 December. 500kV nuclear Hui line traps pillar insulator after transformation, each pillar insulator actual installed 4 increase climbing skirt, each column insulator is installed 12 increase climbing skirt. The equipment after the transformation of creepage distance is increased from 3.08cm/kV to 3.56cm/kV. 220kV equipment after the transformation of the creepage distance has increased to more than 3.50cm/kV. Field installation of petticoat main features are: creepage distance increases; the strong hydrophobicity; self-cleaning ability; arc road twists and turns, the pollution flashover voltage increased; the service life is long, up to 15 years; the maintenance cycle is long, generally 3 to 5 years without cleaning filth.
Transformation effect analysis: the 500kV nuclear Hui line traps post insulator and 220kV water nuclear line outdoor high-voltage equipment to increase climbing after the transformation, after nearly 4 years of operation, equipment, pollution resistant performance is good, the corona discharge noise equipment is obviously reduced, not happen again because of pollution discharge caused by power failure maintenance events. This transformation is very effective.
4.2 regular cleaning of no rain season in every winter drought of equipment, porcelain skirt lack of self-cleaning ability, encountered heavy fog and other adverse climate, pollution serious porcelain easy flashover. Therefore, after a long time in cleaning pollution is one of the important means to improve the capability of anti pollution equipment. The maintenance program of Dayawan nuclear power station provides outdoor equipment annual cleaning work, namely in the equipment planned annual overhaul, the outdoor equipment according to the procedure for inspection and cleaning, and equipment to ensure the capability of anti pollution. As antifouling work equipment, even to have to increase climbing transformation equipment, also according to the procedures for inspection and cleaning.
5 conclusion a) according to the Dayawan nuclear power plant geographical environment, climatic conditions, pollution humidity, running status of equipment and equipment for the importance of requirements, in accordance with the provisions of national standards, the Dayawan nuclear power plant pollution level classification environment shall be determined according to the four level to. Device specific creepage distance should be greater than 3.5cm/kV.
B) to improve the post insulator nuclear power plant of creepage distance, is feasible in conditions and technology. Indicates that the transformation effect part of equipment, increase equipment creepage distance to improve equipment anti pollution flashover ability is very effective.
C) in maintenance equipment, must comply with the "every stop will sweep" principle. After the transformation of the equipment "general 3 ~ 5 years without cleaning" this statement is in fact is not reliable. Therefore, every year the annual overhaul equipment must be cleaned, namely should guarantee should be cleaned at least once a year. Manual cleaning to work out corresponding measures in technology, in order to ensure the cleaning quality and personnel, equipment safety.
D) contamination flashover discharge is not only related with the pillar insulator structure modeling, and correlated with the deposition quantity. Accurate detection of ESDD on the equipment surface pollution substances, is an important reference for the outdoor insulation flashover characteristics of master device filthy. Although the environmental pollution level delineated around Dayawan nuclear power plant is four level, however, still should be regularly on the surrounding environment pollution degree of Dayawan were detected, so that the anti fouling work do know the score.
E) other measures feasible: the generator condenser water circuit outlet and drainage with cover, the water by the culvert discharge, prevent the formation of salt fog; the use of silicone rubber high voltage insulation paint, in the post insulator surface using RTV silicone rubber coating technology, can improve equipment anti creepage and anti the flashover performance. These two methods are non increasing creepage distance method to power ratio.
F) after the transformation of the petticoat with life requirements, therefore, should do this kind of equipment tracking and supervision. The performance degradation or life is about to expire, measures should be taken to replace.