Effectiveness and Influencing Factors of Insulator Creepage Distance

Effectiveness of creepage distance

The pollution resistance characteristics of different suspension insulators are not linearly related to the creepage distance. For insulators with poor umbrella type, the creepage distance is increased, but the pollution withstand voltage is not significantly improved, and some are reduced. Because the creepage distance is relatively large, the local creepage distance is easily short-circuited by the air gap discharge under the conditions of pollution and moisture.

Pollution characteristics and self-cleaning

The fouling characteristics and self-cleaning properties of the insulator are related to the distance between the two co-located umbrellas at the same location and the ratio of the extension of the two adjacent umbrellas, and the shape of the umbrella skirt such as the inclination angle of the umbrella. Investigate the pollution characteristics and self-cleaning properties of different types of insulators, especially DC insulators. In addition to the above factors, the fouling characteristics of the operating insulator are also closely related to the surface condition of the insulator and the natural environment. The following issues should be studied:

1) Comparison of the equivalent salt-attached density when the on-site AC insulator is uncharged or charged and the DC charged insulator;

2) Analyze the chemical composition of natural contaminants;

3) Simulate natural fouling characteristics in the laboratory.

Suspension Insulators

Pollution pressure characteristics

In addition to the creepage distance effective coefficient k, dirt accumulation characteristics and self-cleaning characteristics, the dirt pressure resistance characteristics should also be related to the shape parameters of the umbrella skirt. The determination of the artificial pollution withstand voltage shall be carried out under the following test conditions:

1) An equal amount of pollution on the upper and lower surface area (mainly AC);

2) Unequal pollution of upper and lower surface area (mainly DC);

3) Consider the pollution accumulation characteristics of various types of insulators, and set the salt density and gray density of various high-voltage insulators according to the test results of on-site trial hanging and rapid pollution accumulation method.

Arc resistance

Insulator strings for power transmission lines in my country are not equipped with arcing angles. Therefore, the arc resistance of the insulator must be considered when selecting the insulator, so as to avoid the unsuccessful failure of the insulator string and reclosing.

Deterioration

The high annual deterioration rate of porcelain insulators and the high self-detonation rate of glass insulators severely inhibit the use of insulators of two different materials. An investigation should be made into the causes and annual deterioration rate of deteriorated insulators.

1. Causes of degraded insulators

Suspension type composite insulators have the deterioration of the surface of the insulator caused by the leakage current caused by pollution and wetting conditions and the deterioration caused by lightning strikes and arcs, as well as the deterioration caused by long-term mechanical loads or temperature changes. The more important cause of degradation is due to the inherent causes of the insulator manufacturing, such as siphon absorption, different thermal expansion coefficients of insulator parts, defects in the insulator, electrical corrosion of metal accessories and self-explosive.

2. The hazards of degradation

The degraded insulator loses its insulation strength or mechanical strength at a lighter level, and at the same time causes string drop.

Countermeasure

1) Control the expansion coefficient of cement;

2) Do internal water pressure test, thermal shock and power frequency spark test to remove the unqualified products with some micro defects in the insulator;

3) Strengthen the detection of degraded insulators.

Insulator selection

When choosing different types and types of insulators on AC and DC high-voltage transmission lines, the following points should be fully considered:

1) Comprehensive consideration of transmission line cost, maintenance costs and accident losses, and strive to achieve the purpose of safe, economic and high-quality power supply;

2) The arrangement of insulator strings composed of different types of insulators should meet the insulation design requirements for AC and DC transmission lines at different voltage levels;

3) The mechanical strength of the insulator should be compatible with the design and operation requirements of transmission lines with different voltage levels;

4) Has the ability to withstand arcs suitable for the system fault current;

5) Excellent pollution resistance;

6) Low annual deterioration rate.

7) Less maintenance;

8) According to the operating conditions and usage environment, its characteristics are relatively good or bad, so choose to use it.

In conclusion

a. In the AC and DC insulators currently produced and put into operation, the design values of porcelain and glass suspension insulators are high, which can ensure high reliability, and the main mechanical characteristics are small in dispersion, ≥160kN porcelain insulator machinery The margin of the tensile load is greater than that of glass insulators, but the residual mechanical properties of glass insulators are greater than that of porcelain insulators. As the mass of the insulator increases, the margin of its mechanical strength decreases, and the dispersion is greater, reflecting the greater the difficulty of manufacturing.

b. In recent years, the product quality of AC and DC suspension porcelain and glass insulators has been greatly improved, and its steep wave shock resistance and power frequency arc resistance have been improved.

c. At the same time as structural height and operating conditions, the dry and wet industrial frequency flashover voltage of organic composite insulators is significantly lower than that of suspended porcelain glass insulation.

d. The power frequency arc resistance characteristics of organic composite insulators still need to be studied.

e. When choosing different types and types of insulators on the AC and DC high-voltage transmission lines, the performance requirements of the operating conditions and the use environment should be compared to the advantages and disadvantages, and the choice should be used.

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