Nine questions and nine answers to basic knowledge of insulators

1. How is the structure of the insulator? What is its function?

answer:

An insulator (commonly known as a porcelain bottle) is composed of a porcelain part and a hardware part, and the middle part is glued with cement adhesive. The porcelain part is to ensure that the insulator has good electrical insulation strength, and the metal parts are used to fix the insulator.

The role of the insulator has two aspects: one is to firmly support and fix the current -carrying conductor, and the other is to form a good insulation between the current-carrying conductor and the ground.

It should have sufficient dielectric strength and mechanical strength, and at the same time have sufficient resistance to the erosion of chemical impurities, and can adapt to changes in the surrounding atmospheric conditions, such as the influence of temperature and humidity changes on itself. The insulators used in substations and overhead lines include pin insulators, post insulators, porcelain cross-arm insulators and high-voltage wall bushings.

2. What is the creepage distance ? What is the leakage distance ?

answer:

Both creepage distance and leakage distance are specific parameters of external insulation. The discharge distance along the outer insulating surface is the leakage distance of electricity, also known as creepage distance, or creepage distance for short.

Leakage distance multiplied by the effective coefficient and then divided by the line voltage is the leakage distance , that is, λ=KL/U where: λ is the leakage distance ; K is the effective coefficient; L is the leakage distance; U is the line voltage.

3. What is creeping discharge?

answer:

many suspension and pin insulators, transformer bushings and wall bushings in the power system, and many of them are in the air. When the voltage of these devices reaches a certain value, the air on the surface of these porcelain devices will discharge . It is called discharge along the surface of solid medium, or surface discharge for short.

When the surface discharge penetrates between the two electrodes, a surface flashover is formed. The creeping discharge voltage is lower than that in the air . The surface discharge voltage is related to the uniformity of the electric field, the surface state of the solid medium and the meteorological conditions.

4. What is flashover? What is the cause of pollution flashover?

answer:

When the gas or liquid dielectric around the solid insulation is broken down, the phenomenon of discharge along the surface of the solid insulation is called flashover.

There are a lot of industrial pollution particles on the surface of porcelain insulators in dirty areas. When these pollution particles are wet, they will form a conductive liquid film on the porcelain surface, which will significantly reduce the withstand voltage of porcelain insulation, and the flashover voltage will become very low. This is The reason why porcelain insulation is extremely easy to flashover under dirty and wet conditions. Pollution and damp are the necessary conditions for pollution flashover, and porcelain insulation will not cause flashover if it is only dirty but not wet .

5. How to prevent pollution flashover of insulators in substations?

answer:

(1) Add basic insulation. For example, increase the number of insulators, increase the distance of discharge along the surface, and meet the leakage ratio specified by the pollution classification.

(2) Strengthen cleaning. Porcelain insulation in dirty areas must be cleaned regularly to keep the surface of the porcelain insulation clean and prevent pollution flashover. Charged water flushing is an effective means.

(3) Adopt dust-proof paint. When the effective leakage ratio of ceramic insulation in dirty areas cannot meet the requirements, and the cleaning workload needs to be reduced, methods such as coating silicone oil and ozokerite are often used to increase the pollution flashover voltage and prevent pollution flashover accidents.

(4) Semiconductor sleeve insulators and silicone rubber insulators are used.

6. Why is the surface of the porcelain insulator corrugated?

answer:

distance within the same effective height, and each of them can play the role of blocking the arc.

(2) In case of rainy days, it can block the water flow, and the sewage cannot flow directly from the upper part of the porcelain bottle to the lower part, so as to avoid becoming flying and causing confusion .

(3) When the dust falls on the corrugated porcelain insulator, the distribution is uneven, so the resistance strength of the porcelain bottle is guaranteed to a certain extent.

7. Under what circumstances are porcelain insulators easily damaged?

answer:

(1) The installation and use of porcelain insulators are unreasonable, such as the mechanical load exceeds the regulations, the voltage level does not meet the requirements, and the installation location is improper.

(2) Due to sudden cold and hot weather and external damage caused by hail.

(3) Flashover caused by thunderstorm and fog due to pollution of porcelain insulators.

(4) Short circuit of electrical equipment, damage to porcelain insulators caused by excessive electrical and mechanical stress.

8. What are the consequences of cracks in insulator castings and glued parts?

answer :

in the iron valve flange and the glued layer, the sealing performance of the electrical appliances will be reduced, which may cause moisture ingress, water ingress and internal insulation damage to the oil-filled equipment. In severe cases, it may cause equipment explosion accidents. Cracks in the cast iron flange of the isolating switch or the busbar support insulator may cause the support to separate from the insulator , resulting in equipment operation failure, and may cause the insulator to collapse or fall, resulting in a short circuit accident.

9. Why is there one more piece of tension insulator string than the general line?

answer:

Operation experience proves that tension insulator strings are prone to deterioration due to heavy mechanical load, and the chances of zero-value insulator strings appearing are more than those of hanging strings, so the number of reserved insulators should be more than that of straight strings .

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