Basic principle of lightning protection for high-voltage transmission line tower arrester:
When lightning strikes the tower, part of the lightning current flows to the adjacent tower through the lightning line, and the other part of the lightning current flows into the land through the high-voltage transmission line tower. The grounding resistance of the high-voltage transmission line tower is a transient resistance, similar to the impact grounding resistance.
When lightning strikes the tower, part of the lightning current flows to the adjacent tower through the lightning line, and the other part of the lightning current flows into the land through the high-voltage transmission line tower. The grounding resistance of the high-voltage transmission line tower is a transient resistance, similar to the impact grounding resistance.
Under the action of lightning rod, the capacitance on the top of high-voltage transmission line tower increases rapidly, and the potential value is.
ut=iRd+Ldi/dt(1)
I - lightning current in the formula;
Contact point - ground resistance:
Ldi/dt - transient component.
If the difference between the tower top potential superconductivity and the conductor induced potential superconductivity of the high-voltage transmission line tower exceeds 50% of the discharge voltage of the insulator string, the flashover from the tower top to the conductor will occur. If the power frequency voltage amplitude of the line is considered as Um, then Ut Ul>U50. Ut-Ul+Um>U50。 Therefore, the lightning endurance of the line is related to three important factors, namely, the 5 ∞ pier voltage of the line insulator, the lightning current intensity and the impact resistance of the tower body to the ground. In this way, 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 method of reducing the tower grounding resistance is often used to improve the lightning withstand level of transmission lines. In mountainous areas, it is very difficult to reduce the grounding resistance. That is why the transmission lines are repeatedly struck by lightning.
After the lightning arrester is installed, when the line is struck by lightning, the line messenger will approach the tower. Some of them enter the ground through the high-voltage transmission line tower. When the lightning current exceeds a certain value, the action of the arrester will add shunt. Most lightning currents flow from the lightning arrester into the conductor and then spread to the tower. Lightning current is generated when passing through lightning conductor and conductor. Because of the electromagnetic induction between wires, connectors are composed of conductors and lightning conductors. Since the shunt line of the arrester is much larger than the shunt lightning current of the lightning conductor, the coupling effect of this shunt line will increase the potential of the conductor, so that the potential difference between the conductor and the tower top is less than the flashover voltage of the insulator string, and the insulator will not flashover. Thus, the line lightning arrester has good clamping potential. It is also a remarkable feature of line lightning protection device.
In the past, lightning protection of transmission lines was mainly realized by reducing the grounding resistance of high-voltage transmission tower. For tower in mountain area, it is easy to install it in plain area. Generally, long radial ground wire or deep well resistance reducer are installed at four tower feet. Increase the contact area between ground wire and soil, and reduce the resistivity; The grounding resistance will decrease to a certain extent under the operating frequency. However, when struck by lightning, 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 body potential. It is easy to cause flashover between the tower body and insulator strings, which will reduce the lightning resistance of the line. As the line arrester has the potential clamping effect, the requirement for grounding resistance is not high. On the line in mountainous areas, the lightning withstand grade of the line has changed significantly after the installation of the arrester.
HENGFENGYOU ELECTRIC GROUP, is an electrical enterprise with transmission and distribution industry as its main business, integrating product research and development, manufacturing and trade. Designated suppliers for the world's top 500 enterprises .Its main products include power transformers, medium and low voltage switchgear, distribution panel ,circuit breakers, transmission tower ,Cable and other power distribution equipment , HENGFENGYOU ELECTRIC GROUP has been working hard to provide the best transmission, distribution solutions for users all over the world. www.transmission-tower.com ; sales@hengfengyou.com ； WhatsApp：+86158 5325 2696（Jack）