This paper proposes a fault current limiter (FCL) of resonant type. The FCL consists of a capacitor and a reactor. The inductive reactance of the reactor is controlled by a spark gap. The operating principle of the FCL is based on producing a large current-limiting impedance in the fault system network. The current-limiting effect of the FCL is examined by experiment and Alternate Transients Program simulation, which shows that such a limiting device can reduce the fault currents significantly during short-circuit faults.

Purpose – The purpose of this paper is to propose an efficient algorithm for computing the transient responses on wind turbine (WT) towers struck by lightning. Design/methodology/approach – The tower is modeled as an electric network and a set of formulas are given for calculating the related electrical parameters. The parameters of grounding rods are also proposed. Based on the numerical representation of the transient characteristics of inductive elements, the electric network is converted into an equivalent circuit. The transient responses are obtained from the equivalent circuit by using circuit analysis method. Findings – The calculated results are in good agreement with results computed by a hybrid method in frequency and time domain, which demonstrating the validity of the proposed method. Originality/value – The transient responses on WT towers struck by lightning are computed using the numerical calculation method directly in time domain and electric field, electromagnetic field and induced potentials will be computed from the responses directly, which can provide guidelines for lightning protection design.

An efficient method is proposed for predicting the attenuation and distortion of the damped oscillation surges traveling on single-phase overhead lines under the influence of corona and frequency dependence of line parameters. The Finite Difference Time Domain (FDTD) algorithm is employed in the transient computation. The Suliciu's corona model is extended to simulate the charge-voltage curves with minor loops under the damped oscillation surges. The corona effect is considered by adding a corona current term in the telegraphers' equations. The frequency dependence effect is also taken into account by using the vector fitting and recursive convolution in time domain. The computed voltage waveforms are compared with the measured ones to examine the validity of the proposed method. The computed results show that the minor loops have a greater effect on the attenuation and distortion for the damped oscillation surges under negative polarity.

A circuit model is proposed in this paper for calculating the transient potential rise on the wind turbine struck by lightning. The model integrates the blade, sliding contact site, and tower and grounding system of the wind turbine into an equivalent circuit. The lightning current path from the attachment point to the ground can be fully described by the equivalent circuit. The transient potential responses are obtained in the different positions on the wind turbine by solving the circuit equations. In order to check the validity of the model, the laboratory measurement is made with a reduced-scale wind turbine. The measured potential waveform is compared with the calculated one and a better agreement is shown between them. The practical applicability of the model is also examined by a numerical example of a 2 MW Chinese-built wind turbine.

The impact of converter control strategies on the drive train of wind turbines during voltage dips is investigated in this paper using a full electromechanical model. Aerodynamics and tower vibration are taken into consideration by means of a simulation program, named FAST. Detailed gearbox and electrical subsystems are represented in MATLAB. The dynamic response of electromagnetic torque and its impact on the mechanical variables are the concern in this paper and the response of electrical variables is less discussed. From the mechanical aspects, the effect of rising power recovery speed and unsymmetrical voltage dips are analyzed on the basis of the dynamic response of the high-speed shaft (HSS). A comparison of the impact on the drive train is made for two converter control strategies during small voltage dips. Through the analysis of torque, speed and tower vibration, the results indicate that both power recovery speed and the sudden torque sag have a significant impact on drive trains, and the effects depend on the different control strategies. Moreover, resonance might be excited on the drive train by an unbalanced voltage.