A simulation algorithm is proposed in this paper for lightning transient analysis of the wind turbine (WT) towers. In the proposed algorithm, the tower body is first subdivided into a discrete multiconductor system. A set of formulas are given to calculate the electrical parameters of the branches in the multiconductor system. By means of the electrical parameters, each branch unit in the multiconductor system is replaced as a coupled
Global warming effect accelerates the utilization of wind energy. As a clean energy source, wind energy can be used to generate electric power without emission of carbon dioxide into the atmospheric environment. In consequence of the rapid growth in the utilization of wind energy for electric power supply, wind turbines (WTs) have increased constantly in size and rated power during recent decades. WTs are particularly vulnerable to lightning strokes due to their great height, distinctive shape, and rather exposed position. The lightning stroke effect on WTs has become a major concern as the number of the installed WTs continues to increase. Therefore, lightning protection of WTs is crucially important for the operational reliability of large wind power generation systems. The lightning protection design needs to obtain the lightning transient responses on WT towers since the tower body is the main conducting path of lightning current. The simulation algorithms were presented in the literature [
After a WT is struck by lightning, lightning current usually passes from the blade root to the tower and then dissipates in the ground through the earth-termination system. Since most manufactures have used many kinds of brushes and sliding contact systems to divert the lightning current from the main shaft, only a much smaller part of lightning current flows through the gearbox and the generator. For the WT structure, the tower is the longest conducting path of lightning current. When the tower conducts lightning current, serious transient potential rise appears on the tower body and may result in flashback to the electrical and electronic components installed inside the tower. Much attention to the potential rise has been paid in the lightning protection design of WTs. For the sake of the transient analysis of the potential distribution on the tower, the blade and the conducting path in the nacelle are left out of consideration. Instead, lightning current is injected into the tower body from its top, as shown in Figure
WT tower.
Multiconductor system.
The inductance parameters can be determined by Neumann’s integral method [
Branches in the multiconductor system.
The dot products of the vector differential segments become
The integral
Coplanar branch pairs, (a) longitudinal pair, and (b) transverse pair.
For the two coplanar transverse branches (
The noncoplanar branch pairs are shown in Figure
Noncoplanar branch pairs, (a) longitudinal pair, and (b) transverse pair.
On the basis of the formulas given previously, the self and mutual inductances can be calculated for a branch unit with
The branch resistance per unit length is approximately calculated by [
The mutual potential coefficient between the branches
By means of the electrical parameters obtained previously, a branch unit with
Coupled
If the blade and the conducting path in the nacelle are taken into account, the former can be converted into a series circuit unit consisting of a few
An experimental setup was built in the laboratory space, as shown in Figure
Experimental setup.
The potential measurement wire is grounded, that is, connected to the steel plate, at a point 9 m apart from the tower. Five resistances of 5
Measured and simulated waveforms: (a) injected current waveform and (b) potential waveform at the top of the tower.
This example takes into account an actual WT with a rated power of 2.5 MW. The dimensions of the WT tower are
Transient potential waveforms: (a) potential waveforms at the top of the tower and (b) potential waveforms at the bottom of the tower.
Peak potential distribution along the height of the tower.
In an actual wind farm, individual WT earth-termination systems are usually connected by the metallic armor of the power cable running between the WTs. An interconnected grounding system consisting of 5 WTs and a substation is shown in Figure
Layout of the interconnected grounding system.
Earth potential distribution in the interconnected grounding system.
In view of the results obtained above, the efficient protective measures against the transient potential rise on the tower body and the transferred overvoltage in the interconnected grounding system need to be taken for the multimegawatt WTs [
The lightning transient analysis has been carried out in this paper for the WT towers. The subdividing treatment of the large-sized continuous conducting shell allows a WT tower to be converted into a discrete multiconductor system. For calculating the electrical parameters of the branches in the multiconductor system, a set of analytical formulas have been given. These formulas have the capability of considering the electromagnetic coupling between the branches in different space positions. By means of the electrical parameters, the branch units are represented by the coupled
This work was financially supported by the National Natural Science Foundation of China under Award no. 509770926 and the Fundamental Research Funds for the Central Universities under Award no. 2012JBZ006. The author expresses his thanks to the foundation committees.