Transient Simulation of Wind Turbine Towers under Lightning Stroke

Abstract

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 coupledπ-type circuit and the multiconductor system is converted into a circuit model. Then, the lightning transient responses can be obtained in different parts on the tower body by solving the circuit equations of the equivalent discretization network. The laboratory measurement is also made by a reduced-scale tower for checking the validity of the proposed algorithm.

Calculation of Lightning Transient Responses on Wind Turbine Towers

“…Since ℎ ≫ 1 and 2 , and 2 is not much larger than 1 , the actual tower body may be simplified as a cylindrical shell, as shown in Figure 1(b). For the purpose of transient calculation, the continuous cylindrical shell can be subdivided into a multiconductor grid constituted by longitudinal and transverse branches [6,7], as shown in Figure 2(a). As the lightning current flowing through the WT tower presents significant harmonic components not exceeding a few MHz, the lightning transient responses should be calculated by the distribution parameter circuit model.…”

“…If the earth is assumed to be perfectly conducting ( = 0), the complex depth is zero according to (2). Substitution of = 0 into (5) or (6) shows that the real part of the impedance is also zero. As a result, the impedance matrix Z is further simplified as…”

“…This process can be illustrated in Figure 5, where the earthing system is simply represented as the earthing resistances ( ). Once the impedance and capacitance parameters are obtained using the formulas given earlier, each coupled branch unit in the multiconductor grid can equivalently be represented by a -circuit consisting of the series impedance and shunt capacitance [6,13]. circuit.…”

“…This indicates that inclusion of the frequency-dependency can give a higher accuracy for the lightning transient calculation. In order to check the validity of the proposed method, the peak potentials at different nodes on the tower body are calculated by the PSCAD/EMTDC software, the time-domain method [6], and the proposed method, respectively. The calculated results are shown in Figure 9.…”

“…The hybrid equation is built in the frequency-domain for the equivalent circuit, and then the discrete Fourier transform with exponential sampling is used to obtain the lightning transient responses in different parts on the tower body. As compared to the traditional time-domain method [6], the proposed method can give due consideration to the frequencydependent characteristic of the branch impedance directly in the frequency-domain and present better applicability to the lightning transient calculation. A numerical example has also been given for checking the validity of the proposed method.…”