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Composite insulator is a new insulator composed of at least two kinds of insulation materials and metal accessories.

Pollution flashover of insulators seriously affects the safe operation of power system. This paper analyzes the principle and influence factors of outdoor insulator pollution flashover, and puts forward the improvement method for field insulator flashover in substation.
 
According to statistics, the fog flashover trouble for power line trouble 21%. The pollution flashover incidents often constitute a large area blackout, maintenance and rehabilitation for a long time, so tough. According to statistics, the pollution flashover trouble which electricity loss is 9.3 times of lightning trouble
 
 
The principle of 1 pollution flashover
 
Insulator is used to support and fix the bus and electric conductor and meet the interval and the insulation between the electric conductor or conductor and the earth, is the main insulation of various power transmission and transformation equipment.
 
In the operation of the power grid in the field of insulator, influence by sulfur dioxide, nitrogen oxides and particles of dust and other atmospheric environment, the appearance of a layer of accumulated filth. In the case of dry climate, with the appearance of these insulators dirt maintained high insulation level, the discharge voltage and boring situation to clean. However, when there is fog, dew, and other rainy humid climate, the appearance of insulator filth to absorb water, the electrolyte is dissolved, ionizing polluted layer, resulting in the pollution layer conductivity added. At this time, the leakage current will add the appearance of insulator. The effects of the shape and structure of insulator and insulator scale surface dirt layer spread unevenly and wetting degree is not the same as other factors, the current density in various parts of the insulation surface is not the same, which results in large current density parts constitute the dry zone, such as bar type column insulator skirt and mandrel junction.
 
With the appearance of the insulator to form dry voltage spread more evenly, boring with high voltage at. When the electric field intensity is large, the glow discharge will occur, and then some arc will occur. At this time, the appearance of a contaminated discharge model, the equivalent of a series of external arc resistance. At this point some arc may subside, there may be carried out. When part of the arc continues to occur and develop, to reach and beyond the critical state, the arc runs through the north and south poles, ending flashover.
 
The insulator flashover principle: appearance of dirt, dirt layer wet and dry layer structure, part of arc, arc through.
 
2 elements pollution flashover effect
 
Dirty appearance surface discharge process, pollution layer leakage current size factor plays a dominant effect, and the size and the pollution layer conductivity, the current atmospheric humidity, the appearance of the shape and medium electrode interval.
 
Insulator appearance accumulation filth is varied, the flashover voltage of the most obvious is the decline in dust contains many soluble salts or acids and alkalis. This pollution is usually by chemical, exercise and other companies exhaust gas or sea salt mist beads gathered in the insulator appearance. Wet dirt layer contained in the soluble salts and acid-base components dissolved in water, so that the appearance of conductance increased, leakage current is added, the flashover voltage decreased greatly. Our main influencing factors of Chenjiagang substation post insulator pollution flashover phenomenon appeared is industrial accumulation in salt and pH of insulator surface.
 
Atmospheric humidity flashover incidents are attack in the fog, dew, snow and rain and high humidity climate. Because of this condition, dust and water soluble salts dissolved, the pollution layer into the semiconductor layer, greatly increase the leakage current, the flashover voltage decreased. But the heavy rain, the appearance of integrated insulator contamination, especially water soluble conductive material is easily washed away by the rain, appearance still has a high resistance, so in the thunderstorm season, the insulation level of regional insulation does not fall foul.
 
In the same pollution and damp conditions, medium appearance, between North and south poles along the surface of the shortest interval that creepage distance is impact resistance of the pollution layer, so it is an important factor affecting the flashover voltage.
 
Creepage distance is added, the pollution flashover voltage is added (creepage distance between the measured appearance, insulation along the two conductive parts in use is not the same, because the insulating material around the conductor electrode, the insulating material charged scene, this area is charged the radius of creepage distance). This is because the creepage distance, to constitute part of flashover, the arc length must be large, to make a long arc not subsided, requires high voltage leakage current and large.
 
As pollution and damp conditions, although the creepage distance, but the appearance of the large diameter of the insulator resistance is small, so the pollution flashover voltage will be lower. For insulators with large diameter, such as porcelain insulator, the flashover voltage should be decreased with the increase of insulator diameter.
 
The improvement measures 3 field insulator flashover.
 
Regular cleaning insulator. In the year before the flashover trouble prone season, it is necessary to conduct a clean throughout the insulator. In dirty critical areas, appropriate cleaning times should be added.
Add creepage distance, the insulation level of progress. Such as adding contaminated area of insulator pieces, or choose dust insulator. Operating experience shows that in the heavily polluted areas, the use of dust insulators, antifouling effect is better.
 
On insulator coated with a layer of hydrophobic dustproof coating, the dust is not easy to form a series of pollution layer. In the humid climate, the appearance of condensed water dripping is not easy to form a series of water film, so the appearance of resistance, leakage current, discharge is not easy to carry out, will not decrease the flashover voltage. Commonly used coating with organic silicone oil, organic silicone, ceresin, progress of insulator.