Thunder and lightning are common natural phenomena. In recent years The shunt of lightning current will change. From the lightning protection test, some lightning currents show that when the zinc oxide arrester valve is affected with damp or the environmental conditions continue to deteriorate, the breakdown of transmission lines caused by lightning strikes is also increasing, which not only affects the normal operation of equipment, but also greatly affects daily production and life. Lightning stroke has become the main factor affecting the safe and reliable operation of transmission lines.
In order to reduce the lightning strike fault of transmission lines, various comprehensive lightning protection measures have been taken, such as reducing the grounding resistance of towers, improving the insulation level of lines, adopting negative angle protection, and erecting coupling ground wires, which have achieved certain results. But for some lines distributed in high soil resistivity. It is difficult to reduce the grounding resistance of the tower, and there is still no good countermeasure to prevent the line fault caused by shielding lightning.
At present, the line type synthetic insulating zinc oxide arrester has been widely used abroad for lightning protection of transmission lines, and has achieved good results. With the continuous development and progress of our science and technology, our country has also begun to research and develop line arresters. At present, line arresters have been widely used in the power sector. In power distribution lines, the common lightning arresters are: valve type lightning arresters, tube type lightning arresters, zinc oxide lightning arresters, etc. The low-voltage distribution system advocates the selection of low-voltage zinc oxide lightning arresters. The resistance of zinc oxide valve blade is very high under normal operating voltage. Only micro ampere leakage current can be passed. However, when the powerful lightning current is out of date, it shows a very low resistance, which makes it quickly leak to the earth, realizing the purpose of voltage limiting and shunting. The residual voltage on the valve blade almost does not change with the passing current, and it is always maintained at a voltage lower than the impulse test voltage of the protected electrical appliances, so that the insulation of the equipment is protected, and the original insulation state is restored after the lightning flows.
Zinc oxide arrester has excellent nonlinear volt ampere characteristics. The residual voltage changes smoothly with the shock current wave head time, and the steep wave response is good, without gap breakdown characteristics and arc extinction problems. Its resistors can absorb large energy per unit volume and can also be used in parallel, so it is particularly beneficial to protect EHV long-distance transmission systems and large capacity capacitor banks. It is also suitable for the protection of low-voltage distribution network, which is the main protection measure of low-voltage distribution network.
When the difference between the tower top potential Ut and the induced potential U1 on the conductor exceeds 50% of the discharge voltage of the insulator string, flashover will occur from the tower top to the conductor. That is, Ut Ul>U50. If the influence of line power frequency voltage amplitude Um is considered. Then it is Ut Ul+Um>U50. Therefore, the lightning withstand level of the line is related to three important factors, namely the 5 ∞ pier voltage of the line insulator, the lightning current intensity and the impulse grounding resistance of the tower body Generally, 50% of the discharge voltage of the line is constant, and the lightning current intensity is related to the geographical location and atmospheric conditions. When the lightning arrester is not installed, the ground resistance of the tower body is often reduced to improve the lightning withstand level of the transmission line. In mountainous areas, it is very difficult to reduce the ground resistance. This is also the reason why the transmission lines are frequently struck by lightning.
After the installation of lightning arresters, when the transmission line is struck by lightning, the line will spread to the tower. Some of them enter the ground through the tower body. When the lightning current exceeds a certain value, the arrester acts to add shunt. Most of the lightning current flows into the conductor from the arrester and propagates to the adjacent tower. Lightning current flows through the lightning conductor and conductor. Due to the electromagnetic induction between wires, there will be another!} A coupling component is generated between the conductor and the lightning conductor. Because the shunt of the arrester is far greater than the lightning current shunted from the lightning wire, the coupling effect of this shunt will increase the conductor potential, make the potential difference between the conductor and the tower top less than the flashover voltage of the insulator string, and the insulator will not flashover. Therefore, line arrester has good potential clamping effect. This is also the obvious feature of lightning protection of line arrester.
In the past, the lightning protection of transmission lines mainly adopted the method of reducing the tower grounding resistance. It is relatively easy in plain areas. For tower in mountainous areas, long radiation ground wire or deep well drilling with resistance reducing agent are often used at the four tower feet. To increase the contact area between the ground wire and the soil and reduce the resistivity. The grounding resistance will decrease under power frequency condition. However, in the event of lightning stroke, because the grounding wire is too long, there will be a large additional inductance value. The transient component of lightning overvoltage, Ldi/dt, will be added to the tower body potential, which will greatly increase the tower top potential, more likely to cause the tower body and insulator string flashover, which will reduce the lightning withstand level of the line. Because the line arrester has the potential clamping effect, and the requirements for grounding resistance are not too strict, it is easier to achieve lightning protection for lines in mountainous areas, and the lightning withstand level of lines has changed significantly before and after installing the arrester. It is not difficult to find that the lightning protection effect of adding line arrester is very obvious. Before the arrester is used, its relevant technical parameters should be measured to ensure the installation quality of the arrester.
