Yoh Yasuda

Surge Analysis on Wind Farm When Winter Lightning Strikes

The rapid expansion of wind power generation has brought problems involving lightning strikes to the fore. Many such incidents have damaged not only the wind turbine that was actually struck but also other turbines that were not, a phenomenon that has yet to be fully explained. In this paper, the authors present a case study using a wind farm model with multiple wind turbines connected to a power system. The aim is to clarify the influence of the grounding system on surge propagation from a wind turbine that has been struck to others which have not, during a winter lightning strike. Sensitivity analyses show that the surge propagated to nearby wind turbines can sometimes become large, depending on the conditions of the grounding system, and result in the burnout of surge arresters in turbines that have not been struck, especially during winter lightning strikes.

Electronic Chaos in Silicon Thyristor

Deterministic chaos was observed in the ac response of the Si thyristor in relation to its S-shaped negative differential conductivity. Period-doubling and period-adding chaotic sequences appeared in the same device corresponding to the change of operating parameters. A simple device/circuit model reproduced experimental Lorenz plots qualitatively.

Causes of wind turbine blade damages due to lightning and future research target to get better protection measures

In this paper, the authors summarized the results of the previous research activities and assess the possible causes of wind turbine blade damages. Moreover, the authors propose future research projects which are thought to be necessary for better protection measures for blades of a wind turbine.

Equivalent equation of earth resistance for ring electrode of wind turbine

Earth resistance is a one of the most important issues for wind turbine lightning protection. Although various equations have been proposed to simulate earth resistance, it is still difficult to accurately estimate an actual wind turbine earth impedance because of its complex shape combined with a concrete foundation, auxiliary vertical and ring electrodes. This report clarified how the shape and size of the foundation and the auxiliary electrodes affects to the earth resistance using FDTD (Finite Difference Time Domain) calculation. An equivalent equation to practically simulate wind turbine earthing can be proposed with some correction parameters and improved conventional equations.

Classification of wind turbine blade incidents regarding lightning risk management

The authors already proposed a classification of incidents in wind turbine blades with four-level categories and corresponding countermeasures depending upon the incident levels. In this report, we try to verify the proposed classification after the resent incidents of turbine blades due to lightning that occurred in Japan. Though some of the resent incidents do not look like catastrophic nor serious, social influence was not ignored because of the turbines were installed nearby residential area in the local communities. These incidents suggested us importance of consideration on the risk management regarding social acceptance. This report will discuss the newly proposed classification of turbine blade incidents considering with risk management methodology and social acceptance.

Clarification of the mechanism of wind turbine blade damage taking lightning characteristics into consideration and relevant research project

We investigated various types of damages on a wind turbine blades and estimated the possible causes of them. The cause of catastrophic damages such as explosion or falling down is different from that of less serious damages such as a surface tearing. It may be necessary to protect wind turbine blades by means of special measure against severe lightning for example lightning in winter. Also we should clarify the validity of long gap discharge test in the laboratory as the simulation of actual lightning. It leads to establishing appropriate test methods.

Surge analysis on dispersed generation with voltage-source inverter interconnecting to power system

Dispersed generation or decentralized power systems, represented by wind turbines, photovoltaics, fuel cells and so on, is expected to become more important in the future distribution system as well as FACTS (flexible AC transmission systems) technology. However, it seems that there are few investigations on insulation scheme, grounding design and other transient analyses for such new apparatus. While control method and stability analysis for various types of inverters linked to power system have been relatively discussed, those behavior under surge invasion from power line are not clarified yet. This paper discusses surge analysis on an ideal dispersed generation system interconnecting to power system via an inverter. The present model is regarded as a simplified model for wind farm generation interconnecting to transmission line. In the dispersed generation model, a three-phase voltage-source inverter with PWM signal generation circuits and ideal GTO switches was modeled using TACS cards in EMTP simulation. Moreover, the case studies of single line-to-ground fault at the certain point on the line far from the dispersed generation source were simulated, which fault is one of the simplest cases for EMTP (electro-magnetic transients program) simulation and one of the most typical accidents for the actual application. In this paper, focusing to the transient behavior of the interconnecting inverter, surge analysis on the power system with dispersed generation is described.

Lightning Surge Analysis of a Wind Farm

The rapid expansion of wind power generation has brought problems involving lightning strikes to the fore. Many such incidents have damaged not only the wind turbine that was actually struck but also other turbines that were not, a phenomenon that is yet to be fully explained. In this chapter, the author presents a case study using a wind farm model with multiple wind turbines connected to a power system. The aim is to clarify the influence of the earthing system on surge propagation from a wind turbine that has been struck to others which have not, during a winter lightning strike. When one of the wind turbines in a wind farm is struck by lightning, the phenomenon of surge invasion to the collection system is categorised as “back-flow surge”. It has been reported that this back-flow surge sometimes burns out surge protection devices (SPDs) or breaks low-voltage circuits even far from the point where the lightning struck. In practice, many such incidents that have occurred not only involved the wind turbine that was actually struck but also other affected wind turbines that had not been struck. This chapter will analyse incidents of burnout to SPDs resulting from winter lightning at wind farms using ARENE and PSCAD/EMTDC. Calculations were performed to clarify the mechanism of how the back-flow surge propagates to other turbines from the directly struck wind turbine. The calculations also clarified that burnout incidents could easily occur even in a turbine that had not been struck by the lightning. It also became evident that burnout incidents can be reduced when interconnecting earthing wires are installed between wind turbines.