Based on the practical experience of outdoor high voltage equipment of Dayawan nuclear power station, the environmental pollution zone of the station is evaluated according to the national standard. Under the condition of the confirmation for the four stage, the basic requirements of the outdoor equipment external insulation and the distance to the distance should be greater than 3.5cm/kV. The anti pollution flashover of outdoor power equipment in nuclear power station has been greatly improved by the transformation of the equipment which is less than the requirement. At last, some suggestions are put forward to improve the ability of anti pollution flashover and strengthen the maintenance of equipment.
Key words: outdoor high voltage equipment; external insulation; pollution grade; climbing distance; the insulation level of the pollution flashover voltage electrical equipment is determined by the insulation coordination of the equipment in the system. Outdoor electric porcelain equipment external insulation level shall meet the corresponding standards at all levels of the insulation level of polluted conditions. Daya Bay nuclear power station outdoor high-voltage electrical equipment since the operation, has repeatedly appeared pollution climb flash phenomena. Therefore, from preventing outdoor equipment pollution flashover point, of Daya Bay nuclear power plant pollution level classification, insulation creepage ratio from the selection requirements, design, operation condition and situation etc. carries on the analysis, the research is very necessary.
1 outdoor high voltage power equipment and its operation
1.1 equipment Dayawan nuclear power station installed capacity of 2 900MW high voltage generator, the output voltage of the generator is 26kV. Power unit 1 through 3 sets of capacity for the 375MVA single-phase step-up transformer 400kV, No. 2 unit of electricity by 3 sets of capacity for 375MVA single-phase step-up transformer of 500kV, and then through the closed SF 6 bus duct (GIC) and 400kV/500kV switch station power by high voltage transmission lines sent to Hong Kong in Guangdong Power Grid and. In the 400kV/500kV switch station also has a 400kV/500kV connection transformer 2, in order to adjust the power transmission ratio of the 2 power grid. Full set of 400kV/500kV high voltage switch and high voltage bus are using SF6 combination of electrical equipment (GIS). Porcelain insulation equipment for 12 (phase) of SF6 gas to air bushing, 12 (phase) of capacitor voltage transformer and 24 groups (phase) pillar insulator. As a standby power supply to the Daya Bay nuclear power plant 220kV water nuclear line, its nuclear power on the side of the tower lead line with group 1 (three-phase) pillar insulator, group 1 electric voltage transformer (three phase) and group 1 kV SF 6 combination electric appliance (GIS) into the bushing (three phase).
1.2 outdoor high-voltage power equipment operation since 1991 500kV switch station put into operation since, in 500 kV nuclear Hui line export once there is a pillar insulator due to pollution and creepage phenomenon. Due to the design, 500kV nuclear Hui line outlet is the outlet position, wave drag strut insulator creepage distance is insufficient, in the winter and spring drought, frequent pillar insulator surface flashover and creepage phenomenon, 1993 only reached 3 times (1991 and 1992 also has happened many times. Nuclear power plants in the early operation, this issue has been with the manufacturers and the design department had to negotiate, but the other did not reply.
From the point of view of pollution flashover equipment, the U phase pollution discharge is the most serious in the 500kV phase of the insulator of the. The main reason is that: when the steam turbine generator condensate water circuit is discharged, the water splashing and the atomization water vapor are generated. When the wind blows in the northeast, the salt fog falls to the 220kV and 500kV post insulators, forming the salt pollution layer on the surface, and the corona discharge or partial insulator surface flashover under the action of strong electric field. Therefore, it is an effective way to prevent the pollution flashover of insulators to prevent the water from the outlet of the condensate water.
On March 16, 1996, 500kV nuclear Hui line resistance filter pillar insulator pollution flashover, the situation is very serious, in order to prevent the short circuit accidents may occur and emergency applications nuclear Hui line outage maintenance, after cleaning of all post insulators, was restored to the line of power transmission. In May 18th and October 7th of the same year, the 500kV nuclear power line barrier insulator and the two more serious surface flashover discharge phenomenon, resulting in a number of non planned outage maintenance. As a result of repeated outage maintenance, not only directly affect the reliable operation of power transmission lines and power flow distribution, and the final consequences of pollution discharge will be a direct impact on the safe and reliable operation of nuclear power plants. Similar to the operation of the 500kV external insulation equipment, the external insulation equipment of 220kV auxiliary power supply system also occurred many times because of the serious pollution discharge of the post insulator, which led to the emergency maintenance.
500kV switch station operation since, maintenance department has always insisted execution every stop must sweep the principle, and the equipment, regular inspection, found that filthy creepage phenomenon in a timely manner to strengthen tracking or outage application for cleaning and maintenance, and effectively prevent the pollution flashover accident from happening.
2 nuclear power plants around the level of environmental pollution to determine the level of Dayawan nuclear power station is located in the eastern part of Dayawan Shenzhen sea, power plant equipment from the sea less than 400m. Every year from March to May, the weather is very humid, the maximum humidity can reach 100%. June to October for the rainy and typhoon season, November to second years in February climate drought. This area belongs to the area of severe salt fog. In order to prevent salt fog in the atmosphere, 400kV/500kV switching station design for indoor type. According to the early test results of salt density in the region (Longgang region), the salt density is greater than 0.1 ~ 0.25mg/cm2. Therefore, as outdoor equipment outside the insulation design, manufacturers are based on the three level of pollution level to choose from the distance.
In accordance with the literature [1] about the contamination grades according to the principle of, for environmental and operating experience around Daya Bay nuclear power station, to local pollution levels were re assessment, the assessment result is local pollution level should according to four types. Cost of external insulation lead to pollution history of three level although the reason for the four aspects: one is close to the sea, air and rainwater in salt is higher; the second is the Longgang area (area) contamination detection, but the nuclear power plant equipment safe and reliable operation of indicators have higher requirements; the third is the existing equipment operation show that the external insulation equipment for creepage phenomenon occurred many times and even resort to non planned outage cleaning; fourth, nuclear power plant equipment is seldom, improve equipment insulation level of cost or investment with minimal impact, and pollution flashover accident will cause great losses, the station pollution flashover short-circuit accident is not acceptable.
3 check the electric distance of the field equipment
Stipulated in the literature [1] and [2], corresponding to the four pollution area of high-voltage electric power equipment external insulation creepage distance should be according to is greater than or equal to 3.1cm/kV, and original hydro issued by the Ministry of the provisions of the relevant documents, corresponding to the four pollution area of creepage distance should meet the requirements of 3.5cm/kV (neutral point directly connected to the system). In accordance with the above criteria, in Daya Bay Nuclear Power Station surrounding environment pollution level for four level assessment, and considering the changes in the future in this region and the pollution level and nuclear power plant equipment itself should have more high reliability (the safe and reliable operation of the index to be higher than conventional power plants), of nuclear power plant insulation creepage distance selection, in fact, should have proper safety margin in the standard based on and the requirements of nuclear power plant equipment, insulation creepage distance shall not be less than 3.1cm/kV and practical choice is greater than the 3.5cm/kV. According to the measured value of the field equipment (see Table 1), it is obvious that the external insulation of the equipment can not reach the basic requirements. In fact, it is the equipment which is less than 3.1cm/kV, the most serious pollution discharge in the harsh weather conditions.
4 improvement measures and effect analysis of the 3 basic factors that affect the electrical strength of the external insulation of the equipment are voltage, contamination and moisture. By increasing the distance of the external insulation of the equipment, improving the electric field distribution or the surface contamination of the equipment, the purpose of improving the anti pollution flashover ability of the equipment can be achieved.
4.1 to increase the transformation of some equipment in accordance with the level of pollution in the region and the actual conditions, a reasonable adjustment of the ratio of the distance is an important measure to prevent pollution flashover accident. Daya Bay nuclear power station insulator insulation equipment rarely, the whole station post insulators a total of 24 groups (phase), and less than 3.5cm/kV pillar of insulator insufficient 6 groups (phase), if each group to appropriately increase the section insulator, external insulation creepage distance can be increased to 3.5cm/kV to. Increasing the cost of the investment and the benefit of the safety and reliability of the power station and the maintenance cost in the future are very small. Therefore, in order to improve the anti pollution capacity of power station and avoid the total principle of pollution flashover accident, it is one of the effective measures to ensure the high anti pollution flashover ability of the nuclear power station. After the argument, it is believed that this method is limited by the original equipment design position, the foundation structure and the bearing and so on. Therefore, in the adjustment measures should be used only to choose to increase the additional skirt, that is, in the original post insulators to increase the number of silicone rubber to increase the skirt to improve the equipment's external insulation to climb the distance.
The appropriate pressure equalizing device, electric porcelain equipment to improve the surface electric field distribution along and make electric porcelain equipment along the surface per unit length of insulation is subjected to uniform voltage stress and avoid corona or creepage. The electric field distribution of the 500kV insulator was calculated by the finite element method. In the calculation of electric field distribution to install, compared the two different equalizing ring diameter and different positions along the pillar insulator voltage distribution situation, the result is when the pressure ring and on the high-pressure side of the maximum electric field strength can be by 345.3kV/m drop 240.5kV/m and maximum electric field strength decreased by 30.4%, the improvement effect is very obvious. In this implementation argument, due to the influence from the scene of the actual equipment layout, namely peripheral equipment, the structure of the spatial distance constraints, alternating electric field interaction and increase equalizing ring after loading strength of the original pillar insulator effect, make this approach has been limited.
Through to various transformation strategies of anti pollution equipment performance comparative analysis and technical argumentation, to use increases the creepage skirt, using method of antifouling paints, cleaning and water washing three schemes are discussed one by one, it is considered that the additional creepage distance technique is the best method. Implementation of the reform is on the pillar insulator installation of antifouling heat shrinkable increase climbing skirt. In order to enlarge the insulator of creepage distance and limit the leakage current, so as to improve the pillar insulator antifouling lightning level (after transformation can enhance the pollution flashover voltage of more than 50%).
On the site of the 500kV nuclear line barrier insulator and 220kV equipment, completed in December 1997. After the modification of the 500kV core benefit line barrier insulator, the actual installation of the 4 pieces of post insulators in each section of the umbrella skirt, a total of 12 increase in the installation of the post insulator. After the transformation of the equipment, the power up ratio of the equipment is increased from 3.08cm/kV to 3.56cm/kV. 220kV equipment after the transformation of the power up to 3.50cm/kV than the distance has been increased to more than. On-site installation of creepage skirt main features: the specific creepage distance increased; hydrophobicity; self clean ability is strong; arc road twists and turns, pollution flashover voltage is increased; use long life, up to 15 years; long maintenance cycle, generally 3 ~ 5 years without cleaning the filth.
Transformation effect analysis of 500kV nuclear Hui line resistance filter pillar insulator and 220kV water nuclear line outdoor high-voltage equipment of creepage transformation, after nearly four years of operation and tolerance filthy performance good, equipment corona discharge noise is decreased obviously did not occur again and for pollution discharge and guide outage maintenance events. This shows that the transformation is very effective.
4.2 the regular cleaning in every winter drought, no rain season, petticoat porcelain lack of self-cleaning ability, encountered fog and other adverse weather, severe contamination of insulator easy flashover. Therefore, in after a long time of timely cleaning pollution is one of the important means to improve the capacity of anti pollution equipment. Daya Bay nuclear power plant maintenance program provides annual outdoor equipment cleaning work, namely in equipment plan and annual maintenance outage, for outdoor equipment according to the procedures for inspection and cleaning, to ensure the equipment anti fouling ability. In order to do a good job of anti fouling of the equipment, even if the device has been carried out to climb the transformation of the equipment, the same procedures should be carried out to check and clean.
Conclusion 5 a) according to the Daya Bay nuclear power station of geographical environment, climatic conditions, contamination and humidity characteristics, equipment operating conditions and equipment importance of requirements, in accordance with the provisions of national standards, the Daya Bay Nuclear Power Station surrounding environment pollution level classification should be determined according to the four stages. Equipment should be selected than the distance than 3.5cm/kV.
B) to improve the power of the nuclear power plant post insulators to climb the distance, in terms of conditions and technology are feasible. The modification effect of some equipment shows that the increase of the equipment's creeping distance is very effective to improve the anti pollution flashover ability of equipment.
C) maintenance work in the field of equipment, must comply with "every stop will sweep" principle. After the transformation of the equipment under normal circumstances 5 to 3 years without cleaning, this statement is currently in practice is not reliable. As a result, the annual equipment outage overhaul must be cleaned, that should be guaranteed to be cleaned at least once a year. Manual cleaning must be developed in the technical measures to ensure the quality and safety of personnel and equipment.
D) pollution flashover discharge is not only related to the structure of the post insulator, but also related to the quantity of pollution. The accurate detection of the equivalent salt density of the equipment in the outer surface of the area is an important reference for the control of pollution flashover discharge characteristics of outdoor insulation equipment. Although the Daya Bay Nuclear Power Station surrounding environment pollution level designated for the four level, however, still should regularly of Daya Bay, the surrounding environment pollution degree was detected. To make the anti contamination work, accomplish know fairly well.
E) other feasible antifouling flash measures are: generator condensation water loop discharge outlet and drainage installing cover plate, the seawater by the underdrain discharge, prevent the formation of salt fog; using silicone rubber high voltage insulation paint, in pillar insulator with RTV silicone rubber coating technology, improve equipment of anti climb electricity and anti flashover performance. These two methods belong to the non - increase of the distance of the method.
F) after the transformation of the increase in the life of the skirt is required, therefore, should do a good job in the tracking and supervision of the equipment. It is found that the performance degradation or life expectancy is about to expire, and the measures should be taken to replace it.