JB/T 5895-1991 Guidelines for the use of insulators in polluted areas
Some standard content:
Mechanical Industry Standard of the People's Republic of China
Guidelines for the Use of Insulators in Polluted Areas
This standard refers to IEC Publication 815 (1986) "Guidelines for the Selection of Insulators in Polluted Areas". 1 Subject Content and Scope of Application
JB/T5895-91
This standard applies to the selection of insulators for three-phase AC power systems with a rated voltage of 3 to 500kV. This standard provides some guiding principles for the selection of insulators in polluted areas. The main contents include: the basis for the classification of pollution migration levels, the main parameters for selecting insulators for use in polluted areas, and the influence of insulator shape on electrical performance.
Specific determination of pollution migration levels and external insulation creepage distances should be based on the current regulations for the classification of pollution migration levels. 2 Terminology
The terms and terms used in this standard should comply with the provisions of GB2900.8. 3 Basis for determining the pollution migration level of the operating environment of power equipment Before determining the external insulation creepage distance value and the type of insulator to be selected, the pollution migration level of the insulator operating environment must be determined first. The classification of pollution transfer levels should be "based on the comprehensive consideration of three factors: operating experience, pollution and wetness, and the equivalent salt density of the pollution transfer material on the surface of the external insulation (hereinafter referred to as salt density)." Pollution and wetness are qualitative parameters for the degree of pollution transfer in the operating environment, salt density is a quantitative parameter for the degree of pollution transfer in the operating environment, and operating experience is the result of the comprehensive effect of various actual conditions. The three factors all illustrate the impact of pollution transfer conditions on insulation. When there are differences in the pollution level judgments made by the three factors, the reasons should be analyzed, and operating experience should be used as the main basis for determining the pollution level. The hazards of pollution flashover accidents in important substations and main lines are much greater than those in general power stations and lines. The external insulation of such equipment should be appropriately strengthened. The insulation level of lines in mountainous and dangerous areas with inconvenient transportation, frequent inspections and maintenance should be appropriately strengthened. 3.1 Operating experience
3.1.1 Pollution flashover trip rate is an important parameter indicating the operating status. 3.1.2 The basic measures to prevent pollution flashover should be based on the accurate classification of pollution levels and the selection of corresponding insulation levels, but maintenance and cleaning are still important measures. In order to reduce and prevent pollution flashover accidents, the equipment of the power station in the pollution area should be maintained and cleaned. If the maintenance workload has exceeded the degree required by the regulations (such as the number of cleaning times) to prevent accidents, the pollution level of the area should be adjusted. 3.1.3 For lines and substations where pollution flashover has not occurred, the potential danger of pollution flashover should be considered. For example, if the cleaning is carried out according to the prescribed cleaning times, there will still be frequent spark discharges and local arcs on the insulators under humid climate conditions. These factors that may cause pollution flashover should be considered when classifying pollution levels. 3.2 Pollution and wet characteristics
There are two necessary conditions for pollution flashover on insulators that are affected by the environment; one is that a certain amount of pollution is accumulated on the surface of the insulator; the other is that in humid weather, the pollution absorbs moisture and becomes damp; if either of the two is missing, pollution flashover will not occur. The parameter of "pollution and wetness characteristics" is a qualitative parameter for classifying the pollution level according to the pollution source conditions of the insulator's operating environment and the climatic conditions under which the pollution on the insulator surface is damp. Pollution sources can be generally divided into two categories: one is natural pollution sources, such as salt-reducing areas and coastal areas, and the other is man-made pollution sources, such as industrial pollution, life pollution in densely populated areas, road dust pollution, etc. For areas with obvious pollution sources, the pollution level should be classified according to the nature of the pollution source, the distance from the insulator, the impact range of the pollution source and other factors. For example, for lines crossing dusty roads, the insulation of several towers that can be affected by road dust and automobile exhaust can be appropriately strengthened. For lines in coastal areas, the pollution level can be determined according to the distance from the coast, the terrain, the salinity of seawater, and the degree of influence of seawater and sea fog. Existing operating experience shows that in some areas where there is no obvious pollution source on the surface, such as farmland, hills and mountainous areas, pollution flashover has also occurred. The data obtained by measuring the salt density on the surface of the insulator after the accident showed that the salt density value was very high, and the area was already a pollution transfer area. There are many reasons for pollution in farmland areas. The use of fertilizers may cause pollution to insulators. Farmland near industrial areas or around large cities has generally increased the level of air pollution in the atmospheric environment. Although there is no obvious pollution source in a small area of the area, the pollution in the atmospheric environment will still cause heavy pollution accumulation on the insulators. Therefore, for the classification of pollution transfer levels in areas that have no obvious pollution sources and are traditionally considered to be clean, specific analysis should be made on a case-by-case basis. Under the same pollution conditions, areas with frequent fog, drizzle, ice cover, condensation weather, or close to cooling towers and dam spillways have a higher probability of pollution flashover. Heavy rain can clean the dirt on the surface of insulators. In seasons with abundant rainfall and frequent rain, the dirt on the insulators can be cleaned well, but sometimes it may cause bridging of the sheds and cause flashover in heavy rain. The data of equivalent salt density measurement on the surface of insulators in most parts of my country over a year show that the amount of dirt on the surface of insulators increases from late autumn to late spring of the following year (approximately October to April of the following year), which is related to the climate conditions in my country where there is little rain and much wind and sand in winter. From April to October, the amount of dirt on the surface of insulators is lower than that in winter and shows a stable trend. The main factor for reducing the amount of dirt on the surface of insulators is the frequent washing with rain in summer. There are great differences in rainfall and seasons in different places. The influence of climate factors should be taken into account when classifying the pollution level. For the pollution level of newly built lines and substations, in addition to determining the pollution level according to the current environmental conditions, the impact of recent changes in environmental pollution should also be taken into account. For the pollution level near the planned projects that can cause environmental pollution, the impact after the completion of the project should be expected. 3.3 Equivalent salt density
Salt density is a parameter that characterizes the degree of pollution transfer of insulators. The equivalent salt density value is the value of sodium oxide that can play the same conductive effect by converting the effect of the conductive component in the pollutant into a sodium oxide value that can play the same conductive effect, regardless of the composition of the pollutant. This value is a quantitative parameter that can make up for the deviation caused by qualitative experience when dividing the pollution level. Generally speaking, the salt density value quotient of the insulator that has pollution flashover in seriously polluted areas. Among the fixed parameters used in China to divide the pollution level, the method of measuring salt density has the longest history of use, the most widespread application, the most accumulated data, and the most summarized experience. The salt density value is easy to measure on site, and the method is simple. It is the main measurement method used by the power operation department. Practice has proved that combining with operating experience, using salt density value to divide the pollution level is currently a more effective method. In the study of the pollution transfer withstand voltage performance of insulators, the salt density value is a parameter that characterizes the degree of pollution of insulators. Experiments show that the pollution transfer withstand voltage value of the insulator decreases with the increase of salt density, and there is a clear correlation between the two in the artificial pollution transfer test. There are many types of pollution sources, the pollution components in different regions are different, and the climatic conditions are also very different. When using salt density values to divide pollution levels, we should combine the local specific conditions to summarize the rules and experience to guide local anti-pollution work. Testing salt density values is a long-term work. Through measurement, we can grasp the degree of pollution migration on the surface of insulators. By comparing the salt density values in different periods, we can understand the changing rules of the amount of pollution migration on the surface of insulators. Salt density value is a statistical parameter. After many years of measurement and obtaining more data, combined with local operating experience, the reliability of using salt density value to divide pollution levels can be improved. Other methods to express pollution migration include conductivity of the pollution layer, leakage current on the surface of the insulator under operating voltage and other parameters. In the field pollution migration measurement, a variety of methods can be used according to the situation to make comparisons and make up for the shortcomings of various methods. 4. Select the main parameters of insulators in pollution migration areas 4.1 Creepage distance
In a certain voltage range, the pollution migration withstand voltage of the insulator string generally increases linearly with the increase of its number of pieces. This is mainly due to the increase of creepage distance and string length, and the pollution migration withstand voltage also increases. When using ordinary insulators in pollution migration areas, in order to achieve the required creepage distance ratio value, the number of insulator strings may increase a lot. Due to the limited insulation space of the pole tower, the amount of increase in the number of pieces is limited, and sometimes it cannot reach the required number of pieces. If the size of the pole tower is increased, a lot of investment will be added. In this case, it is a feasible method to use pollution-resistant insulators or large-diameter insulators (commonly known as large creepage distance insulators). The fundamental difference between the performance of this type of insulator and ordinary insulators is that the pollution withstand voltage performance of the former per unit height is better than that of the latter. Without increasing the length, the pollution migration withstand voltage value of the insulator string is significantly improved. One way to improve the pollution migration withstand voltage performance of pollution-resistant insulators is to increase the creepage distance of single-piece insulators. The height of ordinary insulator XP-70 is 146mm, and the creepage distance is 295mm, while the creepage distance of pollution-resistant insulators can reach 400mm or more at the same height. 4.2 Shelter shape
JB/T589591
The measures to increase the creepage distance of insulators are mainly to improve the shape of the shed, increase the number of sheds, expand the shed extension, and increase the number and height of the ribs. The shape of the shed affects the cleaning effect of wind and rain during the operation of the insulator, the dirt accumulation performance, and the development path of the arc during the flashover process. Therefore, the shape of the shed is a factor that determines the pollution resistance of the insulator. The shape of the insulator working under pollution conditions can be developed in two basic directions.
a. Insulators with a shape that makes it difficult for surface dirt to accumulate. b. Insulators with a shape that makes it difficult for surface discharge to develop. Increasing the creepage distance is somewhat contradictory to the above two basic directions. Increasing the creepage distance will make the shape of the insulator complicated, and insulators with complex surfaces are prone to dirt accumulation. There is no insulator shape suitable for any pollution condition. The final conclusion of the pollution resistance characteristics of insulators of various shapes can only be obtained after accumulating sufficient operating experience. 4.3 Insulator height
To increase the creepage distance of power station insulators, in addition to measures such as improving the shed shape, sometimes the height of the insulator must be appropriately increased to produce products suitable for operation in heavy pollution areas. It has been found in operation that some products simply increase the number of shed skirts in order to achieve the specified creepage distance, resulting in very small shed skirt intervals and a total insulator height lower than that of ordinary products. Although this type of product meets the creepage distance requirements, its actual performance is very poor and has caused pollution flashover many times during operation.
When selecting pollution-resistant power station insulators, the product quotient cannot be lower than that of ordinary products, because under highly compressed conditions, the electrical performance of the insulator is difficult to meet the operating requirements.
4.4 Method for selecting creepage distance of line insulators In the pollution migration classification standard, the creepage distance value of the external insulation of the line in each pollution zone is specified. The pollution degree of the environment still varies in severity in the same pollution level. The pollution migration withstand voltage value of the insulator decreases with the increase of the surface salt density. When selecting the creepage distance of the line, in the selected pollution level, the lower value in the creepage distance value range can be taken for areas with lighter pollution migration, and the higher value in the creepage distance value range should be taken for areas with heavier pollution migration. Regardless of the specific conditions in the same pollution level, selecting the creepage distance according to the lower value cannot guarantee the safety of the line. 5 Influence of insulator shed shape on electrical performance 5.1 Main shed structure of domestic insulators
5.1.1 Line disc suspension insulator
The shed shape of disc suspension insulator is shown in Figure 1. 91
General shed,
JB/T 5895-91
Figure 1 The shed shape of disc suspension insulator
Double-layer shed,
Needle cover shed,
Large disc diameter shed,
Grass width shed.
Ordinary shed type: This product is the insulator with the largest number of uses and the longest history. It can operate satisfactorily in general areas. When this type of insulator is used in polluted areas, the number of pieces needs to be increased. When the tower size limits the string length, it is necessary to consider using pollution-resistant insulators. b, double-layer shed type; the shed is smooth and has no schooling, which is conducive to wind and rain cleaning, and the dust accumulation rate is low, which is convenient for manual flushing and cleaning. Although the artificial pollution flashover voltage of this type of product is not much higher than that of ordinary products (because the artificial pollution flashover test method cannot reflect the wind and rain self-cleaning performance of this type of product), the actual operation effect is good.
Bell-shaped umbrella type: The ridges under the umbrella of this type of insulator are relatively developed, with a larger protective distance. The deep ridges under the umbrella are more susceptible to moisture, and the deep arc under the umbrella has the effect of inhibiting the development of arcs. It is used in coastal and humid and foggy areas, and can better play the advantages of the umbrella structure. The groove under the umbrella of this umbrella is deep, its self-cleaning property is poor, and manual cleaning is not convenient, but due to its high pollution resistance, it can extend the cleaning cycle. d. Large disk diameter type: The shape is similar to the ordinary type, and the creepage distance is increased due to the increase in disk diameter. The pollution withstand voltage performance of the single-piece large disk diameter insulator is higher than that of the ordinary type but lower than that of the pollution resistant type. Streamline type (grass phase type): The grass-type pollution-resistant insulator has a low pollution accumulation rate during line operation. Good cleaning performance, this type of insulator is used in the upper part and middle of the line insulator string to prevent flashover accidents caused by ice and lightning when the snow melts. This type of insulator can play a special protective role in the insulator application. 5.1.2 Power station post insulator
The shape of the outdoor rod post insulator shed is shown in Figure 2. e
Figure 2 Outdoor rod post insulator shed
Ordinary type, b, c, d-pollution resistant type
JB/T5895-91
a. Ordinary type: Suitable for power stations in areas without obvious atmospheric pollution (see Appendix A). b. Pollution resistant type: The product creepage distance is designed to various values according to the degree of pollution. The main measures to increase the creepage distance are: 1. Improve the shape to increase the number of umbrellas, expand the umbrella extension, deepen the umbrella ridges, increase the number of ridges, etc. In order to improve the pollution resistance performance, the inclination of the umbrella can be adjusted, and the large and small umbrella structures can be adopted. By changing the above adjustment factors, various types of pollution-resistant insulators can be designed. 5.2 The influence of the shape and diameter of the insulator shed on the pollution resistance performance. Several parameters related to the shed shape, diameter and other parameters that affect the pollution resistance performance of the insulator are briefly described as follows. It is recommended to consider these parameters when selecting insulators; the quality of the pollution resistance of the insulator can only be determined through pollution transfer tests and actual operation tests. 5.2.1 Parameters representing the shape of the shed (see Figure 3 and Figure 4) Figure 3 Ordinary umbrella
Figure 4 Large and small umbrellas
5.2.1.1 Minimum distance between umbrellas (c)
The minimum distance between adjacent umbrellas with the same umbrella diameter is the length of the vertical line from the lowest point of the drip edge of the upper umbrella to the surface of the next two umbrellas. This value reflects the discharge bridging of the two adjacent umbrellas under rain conditions; it should generally be greater than 30mm. 5.2.1.2 Ratio of umbrella spacing and umbrella extension (s/p) Umbrella spacing refers to the distance between the same points of two adjacent umbrellas; P umbrella extension
s/p reflects the self-cleaning performance, and this value is generally not less than 0.8, and for non-prism umbrellas, it is generally not less than 0.65. 5.2.1.3 Ratio of local creepage distance to spacing (la/d). L - the height of the creepage distance between any two points; d - the shortest distance along the air between the above two points; as the la/d value increases, the possibility of the creepage distance being short-circuited by air gap discharge increases, and this value should be less than 5 in any part of the insulator. 5.2.1.4 Large and small umbrellas
The difference between the extension of the two umbrellas (P, -P) should be no less than 15mm to avoid bridging between two adjacent umbrellas under rain conditions. 5.2.1.5 Umbrella inclination (a)
This value affects the self-cleaning performance of the insulator, and the minimum inclination should be greater than 5°. 5.2.2 Parameters of the whole insulator
5.2.2.1 Creepage factor CFCF=l./S.
1-total creepage distance of the insulator;
S-arc distance, which refers to the shortest distance between the two electrodes of the insulator along the air discharge. 3. The value is generally recommended:
OF≤3.50
For 1, Class 1 pollution level
For Class N pollution level
The above pollution levels correspond to the pollution migration levels in Appendix B. 93
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5.2.2.2 Profile factor PF (This parameter is not applicable to disc suspension insulators) The profile factor is the ratio of the simplified creepage distance to the actual creepage distance. The simplified creepage distance is: In Figure 3: 2p+s
PF=(2p+s)/l
In Figure 4: 2p+2p:+s
PF=(2pi+2p:+s)/
1 is the actual creepage distance between the two points defining s. For I and I pollution levels; PF>0.8
For I and N pollution levels, PF>0.7
The above pollution levels correspond to the pollution migration levels in Appendix B. 5.2.3 Influence of diameter
As the average diameter (D.) of the post insulator or insulating sleeve increases, the anti-pollution performance will decrease. The recommended diameter coefficient (kp) is as follows: Average diameter D. <300mm
300mm≤D≤500mm
Dm>500mm
The average diameter can be calculated according to formula (1).
D(1)di
Where: I,-—total creepage distance of the insulator; D(I) is the diameter value at the creepage distance of one end electrode is 1. The average diameter can be simply calculated as follows:
(D, + D)
See Figure 5
(D+D+ 2D,)
See Figure 6
The product of the creepage distance value selected according to the pollution zone level and the corresponding diameter coefficient (K) is used as the creepage distance to be selected considering the influence of diameter. Figure 5 Ordinary umbrella Dm
Effectiveness of creepage distance
Figure 6 Large and small umbrella Dm
The required creepage distance value in each pollution zone specified in the pollution level standard is determined based on the performance of the widely used ordinary insulator with simple appearance. The pollution withstand voltage of the pollution-resistant insulator is higher than that of the ordinary insulator, but the degree of increase in the pollution withstand voltage is not necessarily proportional to the creepage distance. Although the creepage distance of some insulators with poor umbrellas has increased significantly, the pollution resistance performance has not been significantly improved. The creepage distance effectiveness coefficient k can be used to indicate the effectiveness of the creepage distance. This value is determined by the pollution withstand voltage value of the insulator during testing and operation. Taking ordinary suspension insulators and ordinary post insulators as the benchmarks, their k values are taken as 1. The k value of non-ordinary insulators is calculated according to formula (2): 94
Wherein:
JB/T5895-91
U is the pollution withstand voltage of non-ordinary insulators, kV; L is the geometric creepage distance of non-ordinary insulators, mm; U is the pollution withstand voltage of reference insulators, kV; Lo
is the geometric creepage distance of reference insulators, mm. (2)
Tests show that the k value is related to the degree of pollution migration. The heavier the pollution, the lower the k value. Due to the different shapes of insulators, the degree of pollution accumulation in various pollution environments is also different. Therefore, the effective coefficient obtained only based on the artificial uniform pollution migration test is not practical. Only the coefficient determined by the natural pollution migration test is reliable.
JB/T5895-91
Appendix A
Table of natural pollution migration classification standards for external insulation of high-voltage overhead lines and power generation and substation equipment implemented by the Ministry of Energy (reference)
The standards for classification of pollution migration of high-voltage overhead lines are shown in Table A1. Table A1 Standards for Classification of Pollution Mistakes for Commercial Voltage Overhead Lines Pollution Seconds
Pollution Mistake Conditions
Air clean areas and areas more than 50km from the coast Areas with light air pollution: or areas with moderate air pollution: salt-alkali areas, furnace smoke pollution migration areas, areas 10~50km from the coast, dry and foggy (including drizzle) or rainy during the pollution flash season
Air moderately polluted areas: saline-alkali areas, furnace smoke pollution sand areas, areas 3~10km from the sea, during pollution flash season Seasonal humid curtain (including hairy demand) but less amount of both
Severely polluted areas: areas with heavy air pollution, areas 1-3km away from the sea and areas with heavy salt near salt fields
Particularly seriously polluted areas, areas seriously invaded by salt abandonment, areas within 1km from the sea
0~0.03 (strong electrolyte)
0~0.06 (weak electrolyte)
0.03~0.10
0.0 5~0.10
0.10~0.25
Creepage distance
Neutral point
Direct grounding
(1.39~1.74)
[1.45~1.82]
(1.74~2.17)
[1.82~2.27]
(2.17~2.78)
[2.27~2.91]
(2 ,78~3.30)
[2.91~3.45]
Neutral point non
direct grounding
(1.65~2.09)
(2.09~2.61)
(2.61~3.30)
(3.30~3.91)
The salt density of the line and the substation refers to the value measured on the hanging string composed of ordinary suspended insulators (X--4.5). The lines and substations near chemical plants and metallurgical plants can be classified as 2, 3 or 4 levels (2 or 3 for substations) according to the severity of the conductive gas and conductive gold mesh dust emitted by the pollution source. ?
For power plants with cooling towers, their pollution transfer level can be determined to be 2 or 3 according to the dust removal efficiency of the power plant smoke and whether the cooling tower is equipped with a dehumidifier. The nearby lines are also determined to be 2, 3 or 4 according to the above conditions. The line and substation distance calculation takes the system rated line voltage. The numbers in parentheses (
) represent the distance calculated for voltage levels of 220kV and below using the highest line voltage of the system. The numbers in the square brackets [
] represent the creepage distance for 330kV and 500kV voltage levels calculated based on the highest line voltage of the system. This table is quoted from the document of the former Ministry of Water Resources and Electric Power, (83) Water Resources and Electric Power Technology No. 23 "Notice on Issuing the "Standard for Classification of Pollution Transfer for External Insulation of Insulators for High Voltage Overhead Lines and Power Generation and Substations"
JB/T5895-91
A2 The standards for classification of pollution transfer for power plants and substations are shown in Table A2 Table A2 The standards for classification of pollution transfer for power plants and substations Pollution transfer
Pollution and humidity to be determined
Pollution transfer conditions
mg/emt
Creepage distance
Neutral point
Grounding
Areas with no obvious air pollution or areas with light air pollution. During the pollution flashover season, when it is dry and less fog (including drizzle) or when there is more fog
moderately polluted areas; along the tourist areas and near the salt fields, during the pollution flashover season, when there is more fog (including drizzle) and less fog
areas with severe air pollution; areas with severe salt fog Note: See Notes ① to ? in Table A1.
0~0.03(strong electrolyte)
0~0.06(weak electrolyte)
Neutral point non
directly grounded
Pollution transfer level classification see Table B1
Pollution transfer level
JB/T589591
Appendix B
IEC815 pollution transfer level classification table
(reference)
Table B1 Pollution transfer level classification table
Type environment examples
Areas with low density of houses without industry and heating equipment Areas with low density of industry or houses but frequent wind and (or) rain 1-light
1-medium
N very heavy
Agricultural areas\
All these areas should be at least 10km to 20km away from the sea and cannot be directly affected by sea breeze\ =Areas with industrial areas and (or) buildings with heating equipment that do not produce particularly polluting ash; Areas with a high density of buildings and (or) industries but with frequent winds and (or) rain; Areas exposed to sea breezes but not too close to the coast (at least a few kilometers away); Areas with a high density of industries and suburbs of large cities with a high density of heating equipment that can produce pollution; Areas close to the sea or areas that are exposed to fairly strong sea breezes in any case; Areas exposed to conductive dust and industrial ash that can produce particularly thick conductive deposits; Areas that are relatively close to the coast and exposed to sea condensation or are exposed to very strong polluting sea breezes; Areas that are relatively long-term without rain; Desert areas that are exposed to strong winds with sand and salt and often have condensation. Note: 1) Spraying fertilizers or burning residues can lead to a higher pollution level due to the wind dispersal effect. 2) The distance from the coast depends on the topography of the coastal area and the conditions of extremely strong winds. B2
The relationship between pollution migration level and minimum nominal creepage distance is shown in Table B2Table B2bzxZ.net
1-hydroxy
1-medium
1-heavy
N-very heavy
Relationship between pollution migration level and minimum nominal creepage distanceMinimum nominal creepage distance\
mm/kvm
In areas with very light pollution migration, a nominal creepage distance lower than 16mm/kV can be used based on operating experience. 12mm/kV appears to be the lower limit. Note·?
In particularly severe pollution migration, a nominal creepage distance of 31mm/kV may not be sufficient. Based on operating experience and/or laboratory test results, higher creepage distance values can be used, but in some cases, it may be more practical to consider full washing or oiling. The specified creepage distance tolerances (see IEC Publication 273 "Dimensions of indoor and outdoor support and support insulation components for systems with rated voltages above 1000 V", IEC Publication 305 "Characteristics of disc insulator strings", IEC Publication 433 "Characteristics of long standard insulator components" and IEC Publication 720 "Characteristics of line post insulators") are also applicable. The ratio of the creepage distance measured between phase and earth to the relative phase effective value of the highest voltage of the equipment (see IEC Publication 71-1). 2) JB/T5895-91 Appendix C (Supplement) C1 defines the pollution migration level and selects insulation level C1.1In recent years, the pollution transfer situation in many areas has become serious. In addition to the influence of natural pollution sources, the development of small and medium-sized enterprises in towns and villages, the sharp increase in transportation, and the worsening air pollution around large cities and industrial areas will lead to more pollution on the surface of insulators. Pollution flashover accidents often occur in winter and spring. During this period, many areas have a dry climate and little rainfall. The northern region is windy and sandy, and the surface of insulators is seriously polluted. During this period, if the weather changes suddenly, there will be continuous foggy days, and there will often be drizzle, rime, sleet, and driving frost weather. Under these weather conditions, it is easy to cause pollution flashover accidents. C1.2The survey shows that a considerable number of 110kV and above voltage level lines and substations have external insulation creepage distances that are lower than the basic requirements of the actual pollution transfer level in the area where the equipment is located. Many pollution flashover accidents occur in suburban farmland and hilly areas. These areas are generally configured with creepage distances according to level 0 or level 1 pollution areas. Due to the change in pollution transfer conditions, the salt density values measured at the fault point after the pollution flashover have mostly exceeded 0.1mg/cm. This shows that the insulation level of some lines and power stations is lower than the insulation level required by the actual pollution migration degree, which is the main cause of pollution flashover.
C1.3 The configuration of the external insulation distance should meet the requirements of the pollution migration level in the area, and should consider the situation of environmental pollution, leaving an appropriate margin. Important lines, plants, and stations (main outgoing lines of the main power plant, important interconnecting lines of the power grid, and hub substations) can appropriately increase the external insulation distance.
C2 Control pollution sources and strengthen cleaning
C2.1 Attention should be paid to the pollution discharge of newly built large and medium-sized enterprises near the power grid, and requirements for reducing pollution should be put forward. Small enterprises and workshops that discharge pollution should be stopped in time.
C2.2 The number of pollution flashovers in the bad vertical insulator string is much greater than that of the tension string and the V-type string. This is mainly because the self-cleaning performance of the tension string and the V-type string is better than that of the suspension string, and the pollution accumulation is lighter in the same operating environment. The number of double suspension insulator strings used in the line is far less than that of single suspension insulator strings, but many pollution flashover accidents occur on double suspension insulator strings. When selecting the double suspension insulator string structure, attention should be paid to the influence of the suspension method on the pollution resistance performance of the insulator string. C2.3 Further work should be carried out to measure salt density and strengthen the quantitative measurement of the pollution level of the operating environment. Salt density value is one of the basic data in the three factors for dividing the pollution level, and salt density measurement work should be carried out in accordance with relevant standards. Localities should draw the pollution level distribution map of the local area based on operating experience, pollution and humidity, and salt density value, and submit it to the relevant departments for review and approval. The approved pollution level distribution map will serve as one of the basis for determining the pollution level and insulation level. C2.4 Strengthening the cleaning of external insulation of power equipment is an important means to prevent external insulation pollution flashover. Insulator cleaning should be guided by salt density monitoring, and combined with operating experience, cleaning cycles should be arranged to improve the actual pollution flashover resistance of external insulation. In principle, 110-500kV transmission and transformation equipment should be cleaned once a year. Localities can determine according to specific circumstances. In areas with serious pollution migration, when the creepage distance cannot meet the requirements, the use of anti-fouling paint is an effective means. C3 Strengthen the quality management of insulators
In line pollution flashover accidents, there have been many line drop accidents caused by the explosion of insulator steel caps and the falling off of ball heads. Analysis shows that most accidents are caused by the appearance of zero-value insulators in the string, which reduces the external insulation creepage distance and promotes the occurrence of pollution flashover. The short-circuit current passes through the insulator head, causing the head to heat up and the steel cap to explode.
In order to reduce such accidents, manufacturers should strengthen management, improve the quality of insulators, and reduce the deterioration rate. Infrastructure units should inspect the insulators used in the project in accordance with regulations and not use insulators with quality problems in the project. The operating department should regularly test zero-value insulators and promptly replace insulators of poor quality. The insulator quality inspection unit should monitor and track the quality of the products of the electric porcelain factory, and regularly feedback the quality inspection results to the power supply, design, and manufacturing departments.
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