What is called internal overvoltage

Internal overvoltage is the harmful overvoltage caused by the sudden change of power system state due to operation, accident or improper coordination of grid parameters.
Atmospheric overvoltage is also called external overvoltage, is due to the direct lightning strike caused by direct lightning overvoltage or lightning strike in the vicinity of the equipment, the induction lightning overvoltage produced on the equipment.
Internal overvoltage and atmospheric overvoltage are high, may cause flashover of insulation weak points, cause insulation damage of electrical equipment, or even burn down.

UHV grid insulators can withstand millions of volts and 50 tons of tension

At present, my country’s vertical and horizontal UHV and UHV power grids have become a significant sign of the rapid economic and social development. The densely densely populated towers, wire racks and wire networks are quite spectacular. However, what is not known is that it has achieved a series of electric power. Among the elements of the Great Wall, there is a small thing that is very important and often overlooked. It is an insulator.

A few days ago, the world’s first automated production line of porcelain insulators was officially commissioned in the factory area of Inner Mongolia Jingcheng Insulator Co., Ltd.

“Without insulators, there is no high-voltage power grid.” Zhang Yaochen, the chairman of the company and the leader of Jingcheng porcelain insulator technology research and development, said in an interview with a reporter from Science and Technology Daily: “As a porcelain bottle weighing more than ten kilograms to dozens of kilograms, the appearance of insulators is really poor. It’s eye-catching, but the technology it contains is extremely rich.”

Surge arrester classes

The class of surge arrester to be applied on a system depends upon the importance and value of the protected equipment, the impulse insulation level, and the expected discharge currents the arrester must withstand.

Station class arresters are designed for protection of equipment that may be exposed to significant energy due to line switching surges and at locations where significant fault current is available. They have superior electrical performance because their energy absorption capabilities are greater. Station class arresters are the top choice for protecting valuable equipment where high reliability operation is required.
Intermediate class arresters are designed to provide economic and reliable protection of medium voltage class electrical power equipment. Intermediate arresters are commonly used for the protection of dry-type transformers, for use in switching and sectionalizing equipment and for the protection of URD cables.
Distribution class arresters can be found on smaller liquid-filled and dry-type transformers 1000 kVA and less. These arresters can also be used for application at the terminals of rotating machines below 1000 kVA, if available in the proper voltage rating. The distribution arrester is often used out on exposed lines that are directly connected to rotating machines.
Secondary class arresters are utilized for voltages 999V or less. These are applied in low-voltage distribution systems, electrical appliances, and low-voltage distribution transformer windings.

Some small knowledge of composite insulators

For composite insulators to be more widely used in our country, it is necessary to break through people’s understanding that they are mostly used to prevent pollution flashover, in order to shake the dominance of traditional porcelain and glass insulators. To achieve this goal, we need to pay attention to the following issues and continue to conduct more in-depth research.
Choice of mechanical strength:
The most prominent feature of the composite insulator core rod is high strength and high specific strength. Its tensile strength can reach 7000MPa, and its specific strength is 5 times that of high-quality carbon steel. Some regions and departments have proposed the use of synthetic insulators, whose mechanical strength is higher than that of traditional porcelain and glass insulators. For example, the use of porcelain insulators is 160kN, and the use of synthetic insulators is 210kN. In fact, when the use load is less than 40% of the rated mechanical load, the reliability of operation can be guaranteed. Therefore, synthetic insulators can be selected according to the method of porcelain insulators without increasing the mechanical load value. The measurement of the load deflection of the core rod shows that the composite insulator has good bending resistance, good resistance to galloping and breeze vibration. When used in a tensile tower, it can withstand a certain bending moment. In the long-term operation of products with different end connection structures, how different their mechanical properties will change, it is still necessary to in-depth study.

Separating distance between arrester and transformer in a power station

When the voltage is 400kV or above, the arrester is too large for the transformer box to easily support its volume and weight and must be mounted on a separate base. In addition, such an ‘extended’ distance is required if the transformer must be installed in a place where it is easy to move during maintenance. Access channels designed for this purpose can result in a distance of up to 30m between the arrester and the transformer.

Unfortunately, this magnitude of separation spacing (or protection zone) reduces protection when rapidly rising shock waves invade power stations along overhead transmission lines at close to the speed of light. When the impact hits the arrester, the voltage does decrease, but not to zero, but at best to the discharge voltage of the arrester. The impulse voltage propagates forward through the arrester and is reflected at the transformer. If the separation distance is large enough, the impulse voltage will be doubled. Although in most cases the reflected voltage is only a few percent higher than the impact of the incoming wave, it is this traveling-wave reflection phenomenon and the associated reflection factors that highlight the importance of separation spacing.

Ageing phenomena such as chalking and cracking of hollow core composite insulator housings made from LSR material can greatly impact outdoor performance

Ageing phenomena such as chalking and cracking of hollow core composite insulator housings made from LSR material can greatly impact outdoor performance. In the case of those housings deemed only ‘slightly aged’, repair is both time efficient and economical. Normal outdoor insulation performance can be regained by removing the chalking layer in the silicone rubber housing and spraying RTV coatings onto the aged surface. Mirror glossiness, Shore hardness and hydrophobicity are all parameters that can help evaluate extent of ageing of LSR housings and determine which insulators can be repaired and which have aged beyond repair.

To repair an aged insulator, the first step is to use a grinder to remove the chalking layer and then clean the surface with an air spray gun. The second is to treat the surface with an RTV silicone coating to improve the degraded hydrophobicity.

As far as RTV coated insulators are concerned, removing the original coating is inefficient and hence the better choice is to recoat new RTV coatings directly over the original layer. Weather, surface condition and application methods all influence adhesion between the new and the original coating. Tests have shown that adhesion of RTV coatings is best when applied at ambient temperatures from 5°C to 45°C. High relative humidity will not affect adhesion whereas extremely low humidity can lead to coupling failure. Dust and moisture have a great negative impact on adhesion and therefore must be thoroughly eliminated. Spraying is believed to be the best method to apply RTV coatings and ideal air pressure, spraying distance and time are 0.6 MPa, 20 cm and 5 s respectively.

Questions and Answers on Construction Technology of Overhead Transmission Lines

1. What is the main task of line lightning protection and grounding?

(1) Prevent lightning from destroying the wires and causing major accidents.

(2) Prevent the high voltage formed by lightning from destroying the line insulation and causing a counterattack.

2. The raw materials and equipment used in the transmission line project should meet those requirements?

The raw materials and equipment used in the transmission line project should meet the following requirements:

1) There should be a certificate of factory quality inspection for the batch of products;

2) There should be various quality inspection materials that meet the current national standards;

3) For sand, stone and other raw materials without quality inspection data, samples should be sampled and inspected by qualified inspection units, and they can be used only after they are qualified;

4) When there is doubt about the result of product inspection, it should be tested and passed the technical appraisal of the professional department to prove that its quality meets the design requirements and relevant standards before it can be used.

3. What are the raw materials and equipment that must be re-inspected?

(1) The storage period exceeds the prescribed period;

(2) Possibility of deterioration due to poor storage;

(3) The samples are not taken according to the standard or the samples are not representative.

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Contact: Alice

Pin remover for R pin insulator insulation rod completes the live removal of the blank

In the construction of overhead power transmission lines, a large number of insulators must be used to support live wires, so as to maintain insulation between the wires, between the wires and the tower, and the ground. After the commonly used suspension insulators are connected, they must be locked by inserting a locking pin to ensure that the insulators will not fall off the string during operation. With the development of power transmission technology, the letter R-shaped locking pin with a more stable operating state is widely used in the connection of overhead transmission line insulators, but this also causes the old-fashioned pin remover to be unable to remove this type of lock smoothly. pin.

Under the traditional operation method, if you want to deal with the defect of the R pin insulator, you need to climb to the defect part of the insulator to be treated by the live operator under the condition of ensuring a safe distance, and pull out the pin with pliers and hooks. Carry out related operations; if the safety distance is not enough, you still need to apply for a power outage of the line to complete the defect elimination. The work time can be as little as one or two hours, and as long as at least one day. When the newly developed tool is used, the hook of the pin remover is hooked to the round hole of the head of the R-pin, the top of the slide is against the bowl of the insulator, and the screw on the head of the rod is rotated by rotating the insulating rod, thereby moving The nut, the nut drives the steel wire and pulls the hook head to pull the R-shaped locking pin in the slideway, and the locking pin can be pulled out in about 20 minutes. The development of this tool greatly saves manpower and time, and at the same time makes the operation safer and more reliable. At present, this new tool has been piloted in the company’s transmission and transportation inspection center.

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Biological growths have been observed mostly in hot and humid environments but also in temperate and cold environments

The nature of polymeric housings of composite insulators is that premature ageing can become a problem if these insulators are incorrectly specified or not properly designed and manufactured. Similarly, composite insulators can be attacked by biological growths such as algae and fungi and in manners from minor to severe. Theoretically, this can influence pollution performance (in the short run) as well as ageing characteristics (in the long run). Another concern is whether the housing material can be consumed as a food source by a biological growth. It could also be that fungi penetrate into the insulator, even without consuming the base material.

Biological growths have been observed mostly in hot and humid environments but also in temperate and cold environments. These have been found on line insulators, cable terminations, bushings, arresters, breakers and even RTV-coated porcelain station posts. Colonization by biological growths is not inherent only to composite insulators and has also been observed on glass and porcelain insulators. There are also indications that different types of biological growths can be observed on different silicone rubber materials, e.g. HTV versus LSR.

CIGRE TB 455 provides the following statement: “According to present knowledge, a biological growth is located only on the surface of the silicone rubber and in the worst cases reduces the hydrophobicity on the part of the insulator (usually the shaded part). The risk for flashover due to the biological growth is rather low because in order to lead to flashover, the resistance of the pollution layer should be relatively low. However, biological growth normally occurs in relatively clean areas leading to a situation where either insulator will be hydrophilic, but clean, i.e. with high resistance, or it will be contaminated but free of biological growth and therefore be hydrophobic (due to recovery of hydrophobicity) with high resistance.”

Hydrophobic charged detection device for composite insulators-characteristics and methods


■ Adopt water spray classification method (HC classification method)

■ Online detection, no need to power off

■ The device is compact, easy to carry, and convenient for field operations

■ Combination of experience and scientific judgment

■ Simple operation and accurate judgment

■ High electrical safety performance

Detection method:

It adopts a combined detection method on the tower and on the ground.

The staff went up to the tower and sprayed quantitative water mist on 1 to 3 umbrella skirts near the grounding side, and at the same time used a digital camera to take images of the composite insulator umbrella group after spraying water.

After returning to the ground, input the captured digital image into a portable microcomputer, and analyze the hydrophobicity of the composite insulator using hydrophobicity analysis software.

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Contact: Alice