What is the 'little bowl' on the wire?
These "small bowls" are scientifically called insulators, because in the past, most of them were made of ceramics, so many power workers also like to call them porcelain bottles. Don't underestimate these 'little bowls', they are very important components of transmission lines, directly related to the stability and safe operation of the power grid.
What is the insulators?
Insulators are composed of insulating material and metal fittings, and are generally bonded together with adhesive in the middle. The insulation material part can ensure good electrical
insulation strength of the insulator, while the hardware part is used to fix the insulator.
There are many types of insulators.
According to the installation method, it can be mainly divided into suspension insulators and post insulators.
△ Suspension insulators are widely used for insulation and mechanical fixation of flexible busbars in high-voltage overhead transmission lines, power stations, and substations. Suspension insulators can be divided into disc-shaped suspension insulators and rod-shaped suspension insulators.
Pillar insulators are mainly used for insulation and mechanical fixation of busbars and electrical equipment in power stations and substations. Post insulators are often used as components of electrical equipment such as isolating switches and circuit breakers.
According to the insulation material used, it can be divided into ceramic insulators, glass insulators, and composite insulators (also known as composite insulators). Glass insulators and porcelain insulators are mainly disc-shaped, while composite insulators are mainly long rod-shaped. So, the "little bowl" is most likely a glass insulatoror porcelain insulator.
What is the advantage of porcelain insulators?
The insulation part of porcelain insulator is made of electrical ceramics, which has good chemical stability and thermal stability, strong anti-aging ability, good electrical and mechanical properties, and flexible assembly. However, if there is a defect, it is not easy to be found.
What is the advantage of glass insulators?
The insulation part of glass insulators is made of tempered glass, which has high mechanical strength, is not prone to cracking on the surface, and has a slow aging rate.
What is the advantage of composite insulators?
Composite insulators are small in size, light in weight, high in tensile strength and excellent in pollution flashover resistance, but their anti-aging ability is inferior to porcelain and glass insulators.
In addition, there are pollution resistant insulators specifically designed for heavily polluted areas (what does pollution mean? Let's reveal later!), as well as DC insulators used in DC transmission lines.
What is the function of 'small bowl bowl'?
What is the function of insulators?
The transmission lines we usually see are supported and connected by iron towers and poles. A friend once asked, reinforced concrete poles and metal towers are both conductors, and wires with higher voltage levels are generally "bare wires" without insulation. Will there be no leakage when connected to them?
In fact, if you observe carefully, you will find that the wires are not directly connected to the poles and towers, but to the insulators.
From the above figure, it can be seen that the wire is fixed on the insulator, the insulator is fixed on the cross arm (i.e. the iron frame), and the cross arm is fixed on the pole or iron tower.
So, the function of insulators is:
✔ To withstand the tension and pressure generated by the wire, fix the wire to the tower.
✔ Establish good insulation between current carrying conductors (such as wires) and the earth.
On transmission lines with higher voltage levels, insulators are generally not "single soldier combat", but are connected in series. We call this type of "group combat" insulator string. The higher the voltage level of the transmission line, the longer the insulator string is generally.
Let us insert a small scene:
One day, you and your girlfriend (boyfriend) were walking on the road when suddenly an iron tower and power transmission line appeared in front of them. My girlfriend (boyfriend) majoring in electrical engineering has decided to test you: "What voltage level is this transmission line
At this point, you only need to find the "small bowl" on the transmission line and count the number of "small bowls" to roughly determine the voltage level of the line.
Generally speaking——
There are about three "small bowls" of 35 kV power lines,
There are about 7 "small bowls" of 110 kV lines,
There are about 14 "small bowls" of 220 kV power lines,
There are about 19 "small bowls" of 330 kV lines,
About 28 "small bowls" of 500 kV lines,
About 36 "small bowls" of 750 kV lines,
There are about 58 "small bowls" of 1000 kV lineyous.
Of course, this is only a rough judgment, and often specific issues need to be analyzed, such as high-altitude, heavily polluted areas or important power towers, where insulators need to be added.
This is an insulator string with a high voltage of 1000 kilovolts. After careful counting, there are about 50-60 "small bowls", there are so many!
Why are insulators made in this way?
Here we need to first explain a professional term closely related to insulators - pollution flashover.
The agricultural dust pollution, salt alkali pollution, coastal seawater (fog) pollution, bird droppings pollution and other pollutants attached to the surface of electrical equipment insulators will form a conductive film under humid conditions, reducing the insulation performance of the insulators. This may result in leakage current flowing through the surface of the insulator and strong discharge phenomena under the action of the electric field. This phenomenon is called pollution flashover.
Insulator pollution flashover test. (From China Electric Power Research Institute)
There are many measures to prevent pollution flashover. The traditional method is to clean the power grid during maintenance in spring and autumn, and to use coatings such as silicone oil and silicone grease. Reasonably adjusting the creepage distance of insulators is also a method.
Here, please provide the second professional term - creepage distance. Creepage distance is the shortest path measured along the surface of an insulator between two conductive components or between a conductive component and the protective interface of the equipment. The minimum creepage distance requirement for insulators in transmission lines is related to the voltage between the conductive components at both ends of the insulator, the insulation material, and the pollution situation in the surrounding environment. Generally, the longer the creepage distance, the less likely it is for pollution flashover to occur.
The creepage distance can be seen as the shortest distance that an ant must travel from one charged body to another.
Designing insulators in the shape of curved, layered 'small bowls' or' plates', as well as increasing the number of insulators, can increase the creepage distance and prevent transmission lines from experiencing 'pollution flashover'. In addition, during rain, this shaped insulator can prevent sewage from flowing directly from its upper part to its lower part, forming a water column and causing a grounding short circuit. After the dust falls onto this shaped insulator, it will be unevenly distributed, which to some extent ensures its compressive strength.
Preventing pollution flashover is a very important task in the operation and maintenance of transmission lines. During the spring and autumn inspections of the power grid, grid employees will climb up high poles and towers to clean and wipe insulators!
Seeing this, do you realize that these 'little bowls' are quite important?Since it's so important, don't call it 'little bowl bowl bowl'. Read out its scientific name loudly with her: Jue Yuan Zi! Insulator