Substation lightning protection measures - Solutions - Huaqiang Electronic Network

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Lightning protection measures for substations In the power and power supply systems, various electrical equipment have a certain insulation strength. If it exceeds the extent that the equipment can withstand, the insulation will break down. The voltage that causes the insulation breakdown of electrical equipment is called overvoltage. There are two reasons for causing overvoltage: 1 is the operating overvoltage, also called the internal overvoltage; 2 is the atmospheric overvoltage, also called the external overvoltage. There are many reasons for operating overvoltages, such as arcing the ground, and cutting off the inductor or capacitor will generate an overvoltage. The generation of atmospheric overvoltage is caused by lightning. Therefore, to suppress atmospheric overvoltage, lightning protection measures are very important. 
1 Harm of lightning
The formation of lightning is accompanied by huge currents and extremely high voltages, which cause great destructive power during the discharge process. The hazards of lightning are mainly the following aspects:
1.1 Thermal effects of lightning 
Lightning produces powerful heat that melts the metal, blows the power lines, destroys electrical equipment, and even causes fire and explosion. 
1.2 Mechanical effects of lightning 
The powerful electric power of lightning can destroy the tower and destroy the buildings. People and animals are no longer spared. 
1.3 Lightning flashover discharge
The high voltage generated by lightning can cause the insulator to burn out and the circuit breaker trips, causing the power supply line to lose power. 
2 Introduction to lightning overvoltage
Lightning overvoltage, also known as atmospheric overvoltage, is due to overvoltages in equipment or construction that are subject to direct lightning strikes or lightning induced. Since the energy that causes this overvoltage comes from the outside world, it is inherently an external overvoltage. Lightning shock wave generated by lightning overvoltage, its voltage amplitude. It can be as high as 108V, its current amplitude can be up to several hundred thousand amps, so it is extremely harmful to the power system, and effective measures must be taken to protect it. 
There are three basic forms of lightning overvoltage:
2.1 Lightning overvoltage (direct lightning)
Lightning directly hits electrical equipment, lines or buildings, and a powerful lightning current acts through the object to the earth, creating a higher potential difference on the object, which becomes a direct lightning overvoltage. When the lightning current passes through the object being hit, it will produce a destructive thermal effect and a mechanical effect, accompanied by electromagnetic effects and flashover discharge to nearby objects. 
2.2 Induced overvoltage (inductive lightning)
When the thundercloud is above the overhead line, the thundercloud pilot acts to induce an opposite charge on the overhead line than the pilot channel sign. When the thundercloud discharges, the charge in the pilot channel is quickly neutralized, and the charge on the overhead line is released, forming a free charge flow to both ends of the line, resulting in a high overvoltage (high-voltage lines can reach hundreds of thousands of volts, low-voltage lines can reach Tens of thousands of volts). 
2.3 Lightning wave intrusion
High-potential lightning waves generated by direct lightning strikes or induced lightning strikes, causing harm to the substation or user along the overhead line or metal pipeline. According to statistics, lightning accidents caused by lightning wave intrusion in power supply systems account for more than 50% of the total accidents. Therefore, adequate attention should be paid to its protection issues. 
3 Measures to prevent inductive lightning
The main measure to prevent lightning overvoltage is the parallel arrester. 
3.1 Introduction to the arrester
Electrical equipment in power systems is sometimes subjected to operating overvoltages and lightning overvoltages in addition to normal operating voltages during operation. The value of the overvoltage far exceeds the operating voltage, which shortens the insulation life of the device and even directly destroys it.
The arrester is a protective device specially designed to prevent lightning overvoltage and is connected in parallel with the protected electrical equipment. They are widely used in traction substations, catenary and electric locomotives. 
The insulation level of the electrical equipment in the traction substation is determined by the atmospheric overvoltage, because for a traction power supply system with a maximum voltage rating of 110 kV, the maximum operating overvoltage that may be experienced is often less than the value of the lightning overvoltage. In order to prevent lightning damage, lightning arresters are installed in parallel on the incoming and outgoing sides of the substation to “reduce” and “limit” the lightning waves in the intrusion to a level lower than the residual voltage of each arrester, and to discharge the lightning current. The earth protects the equipment within its protection. These devices also need to have an insulation level that is slightly higher than the residual voltage value so as not to be damaged. 
The role of the arrester is to cut the invading flow wave by parallel discharge gap or non-linear resistance. Reduce the overvoltage value of the protected equipment. The arrester can be used to protect against atmospheric overvoltages and to protect operating overvoltages. 
3.2 Classification of arresters
1 discharge gap and tubular arrester. 2 valve type arrester, including: gap without parallel resistance, such as FS type; gap with parallel resistance, such as FZ, gap with magnetic blowing, such as FCZ, FCD type. 3 gapless zinc oxide arrester. 
3.3 Structural Analysis
The valve type arrester consists of a spark gap and a valve type resistor disk. The valve type resistance plate of the valve type arrester is a non-linear resistor, and its resistance value is very large at the power frequency voltage, and its resistance value is very low under the impact high voltage. Under normal conditions, the spark gap has a high dielectric strength, the power frequency AC voltage can not penetrate it, no current flows through the valve type resistor plate; when the lightning strikes, the spark gap is quickly penetrated, and the impact voltage acts. Under the valve disc resistance has a very low resistance value, the lightning current flows into the ground through the valve type resistance plate; when the lightning current passes, the valve type resistance returns to the high impedance property because the power frequency current is small. The volt-second characteristic and the volt-ampere characteristic are two basic characteristics of the valve type arrester. The magnetic blow valve type arrester uses a magnetic field to drive current to improve the arc extinguishing performance. 
The basic structure of the zinc oxide surge arrester is a valve piece. The valve piece is mainly composed of zinc oxide, and a small amount of metal oxide additives such as Bi2O3, Co2O3, MnO2, and Sb2O3 are added. This valve plate has excellent non-linearity and a large flow capacity. The zinc oxide valve plate is insulated at the operating voltage, and the current passing through is small, and the current increases as the valve plate withstands the voltage. 
The angular gap arrester protects the tear flow from the earth by the angular air gap discharge. During the discharge, the arc in the two gaps is elongated by the action of the electric power, and is cooled and extinguished by the surrounding air medium when the alternating zero crossing occurs. 
Tube-type arrester When the line is struck by lightning or induced, the atmospheric over-voltage causes the external and internal clearance of the tube-type arrester to break down, and a powerful lightning current flows through the grounding device into the ground. At the same time, due to the strong arc in the internal gap of the arrester, the material of the inner wall of the tube is burned. A large amount of arc extinguishing gas is generated to be ejected from the nozzle, and the arc is extinguished when the current crosses zero. 
3.4 Model
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3.5 Selection of arrester
Selection of arrester on 110kV side: Select Y10W5-100/295 zinc oxide arrester, the parameters are: system nominal voltage is 11 0kV, rated voltage is 100kV, continuous running voltage is 73kV, 8/20us lightning impulse residual voltage (peak) is not greater than The nominal discharge current is 295kV at 10kA (Note: source of information; manufacturer: Pingdingshan Tianying Group Co., Ltd.; price: 0.95 million / Taiwan). 
Selection of arrester on 27.5kV side: Select Y10W5-40/142 zinc oxide arrester. The parameters are: system nominal voltage is 2 7.5kV, rated voltage is 42kV, continuous running voltage is 30kV, 8/20us lightning impulse residual voltage is not greater than the standard It is said to be 140kV when the discharge current is 10kA (Note: source of information; manufacturer: Pingdingshan Tianying Group Co., Ltd.; price: 0.75 million / Taiwan). 
4 Measures to prevent direct lightning strikes
An effective measure to prevent direct lightning strikes is to direct the lightning discharge to the earth and protect the electrical equipment from damage. In transmission lines, lightning protection lines are generally used to prevent direct lightning strikes and to reduce induced lightning. In the substation equipment area, lightning rods are generally installed to prevent direct lightning strikes. 
4.1 The role of the lightning rod.

There are two main functions of the lightning rod: 1 When the cloud block is close to the lightning rod, the lightning rod can be charged by the static electricity, and can be placed in the air and neutralized in the cloud at any time, thereby violent discharge to mitigate multiple discharges and reduce lightning strikes. . 2 As a discharge path, electricity flows from the lightning rod wire into the earth. Without destroying equipment or buildings. 
4.2 How the lightning rod works 
The lightning rod is made according to the principle of tip discharge. When the conductor is charged, the electric field near the tip is particularly strong, causing the nearby gas to ionize and cause discharge. The lightning rod needle is pointed. The lightning rod tip always accumulates the most charge during electrostatic induction. Lightning protection forms a capacitor for the charged cloud layer. Because of its sharpness, the capacitor plate area is small, the capacitance is small, and the charge it holds is small. And it accumulates most of the charge, so the air between the lightning rods in the clouds easily breaks down into conductors, bringing lightning into the earth. This protects the equipment or building. 
4.3 Protection range of lightning rods
The protection range of the lightning rod is related to the number of pins used and the height of the installation. In general, the higher the number of stitches, the higher the range of protection. 
The protection range of a single lightning rod is usually calculated by the following method:
The protection radius of the lightning rod on the ground is: 
——Protection radius (m)
——Lightning rod height (m)
The protection radius of the lightning rod on the height level of the protected object is: 
——The radius of protection of the lightning rod on the horizontal plane (m)
——the height of the protected object (m)
——High impact coefficient ≤30m=1
5 Conclusion 
The main role of the substation is to change the voltage, as well as the task of concentrating and distributing the flow of electrical energy and adjusting the voltage. Therefore, the substation is an important part of the power system, and it is an important protection part of lightning protection. Do a good job of lightning protection of substations, ensure the normal operation of substations, reduce the scope and time of power outages, and bring many conveniences to social production and people's lives.