Investigating transient electromagnetic states in wind turbines

Master thesis in electrical engineering (power orientation)

Abstract

Investigation of transient electromagnetic states in wind turbines

With development Increasing the number of wind turbines, increasing its efficiency has become more critical. One of the factors for measuring wind turbine efficiency is its performance in transient state problems. The phenomena that lead to the creation of electromagnetic transients on the wind farm are divided into two categories: lightning and switching, each of which is divided into two sub-categories: intra-system studies and inter-grid studies. In the lightning section, issues such as the impact of converters on lightning, the role of the ground system in overvoltages, the effect of turbine height on overvoltages, the effect of the presence of each arrester on reducing overvoltages, the effect of farm design (the presence or absence of step-up transformers) on overvoltages, lightning striking the transmission line connected to the farm and its effect on the turbines, and lightning striking the turbine nacelle have been discussed.

In the switching section, the main switching factors are investigated in two areas: switching on the DFIG system and switching on the network. Among the switching factors on the DFIG system, we can mention synchronizing the turbines with the grid, de-energizing the turbines, connecting the capacitor banks, and causing unwanted errors on the converters. In the field of switching on the network, only disconnection and connection of lines are mentioned.

To achieve these goals, this thesis is compiled in five chapters. In the first chapter, a brief introduction to wind turbines is given, including the introduction of various types of turbine divisions and also the introduction of the components of a turbine. The possible transient states in a DFIG are included in the second chapter, which includes the lightning and switching domains. The third chapter deals with the modeling of wind turbine with DFIG generator. The simulation results obtained by the model presented in the third chapter are included in the fourth chapter, and finally, the conclusions and suggestions for future studies are described in the fifth chapter.

Introduction

What is now threatening mankind as one of the biggest global problems, the lack of energy and air pollution due to the use of fuel are fossils. To solve this big problem, researchers and scientists have started studying and researching the use of renewable and clean energy for a long time. From the recent past, solutions to produce energy from natural sources have been studied and elements such as the sun, water, wind and ocean waves have been taken into consideration, and scientists are trying to solve the energy problem by using these natural elements, which will result in reducing air pollution and a healthy environment. The use of boats and sailing ships and wind and water mills, the extensive use of solar energy for heating purposes and burning wood and the like to produce heat, the installation of natural wind deflectors for cooling residential areas and many other cases are among the clear examples of human use of natural energy sources.

With the passage of time and due to the development of societies and the increasing complexity of industry and technology, the human need for energy sources intensified and the discovery and extensive exploitation of fossil resources forced In today's world, the explosion of population and the improvement of the standard of living and well-being of humans, which has intensified the need for energy resources, on the one hand, and the ever-increasing damages and threats that the indiscriminate use of fossil energies has brought to nature and the environment, on the other hand, have made it impossible to continue this process. Therefore, by looking again at the sun, wind and other pure natural resources, mankind has tried to reduce its dependence on fossil resources as much as possible. One of the cheapest and most accessible of them is wind energy [1]. Examining the amount of use of this energy in recent years is a good indication of its importance and position in energy supply in the world.

Advantages of using wind energy

Wind energy, like other renewable energy sources, has high characteristics and advantages.

Advantages of using wind energy

Wind energy, like other renewable energy sources, has high characteristics and advantages compared to other energy sources, the most important of which are:

No need for wind turbines for fuel, which as a result reduces the amount of fossil fuel consumption.

Wind energy being free

The ability to supply a part of electricity energy demands

Lower current costs and wind energy investment costs in the long term

Diversifying energy sources and creating a sustainable energy system

High maneuverability to operate in any capacity and size (from several Watts to several megawatts)

Not needing a lot of land for installation

No environmental pollution compared to fossil fuels

1-2- Wind turbines

A wind turbine is a device that has a number of blades that have the ability to receive energy from the wind and convert it into mechanical energy. This mechanical energy is transferred to an electric machine and electric energy is produced. 1-2-1 Introduction of wind turbine components: A wind turbine generally consists of parts such as rotor, gear box, low speed axis, high speed axis, generator, rotor system support tower, brake mechanisms and turbine deflection mechanisms, vane, anemometer and The body of the turbine is composed of

rotor

The rotor of a turbine is composed of blades, a hub and its components. The rotor is connected to the low speed axis through its hub and transfers its rotational energy to the low speed axis. Rotors are made on two types with horizontal axis (HAWT) [1] and with vertical axis (VAWT) [2] and their blades can be made of fiberglass reinforced with polyester or laminated wood or steel. Blades made of reinforced fiberglass are light and put less stress on the bearings and hub. Blades made with multi-layered wood have very good resistance to fatigue and steel blades are used due to simple manufacturing technology, high strength and low manufacturing cost. The diameter of the blades of the turbines can be made from several meters to several tens of meters, and the power that can be produced in a wind turbine is proportional to the circular surface that results from the rotation of the rotor blades around the rotor axis, and for this reason, according to the environmental and wind conditions in each region and the amount of power required, the blades of the turbine rotor are made in different sizes.

high and low speed axes

The low speed axis is connected to the rotor blades on one side and to the gearbox on the other side, and its rotation speed is equal to the speed of the rotor blades, and the task of this axis is to transfer the rotational energy produced by the wind to the gearbox. to the axis of the generator.

Gear box

The speed of rotation of the rotor in wind turbines is low and according to the condition and type of turbine, it will be around 30 to 40 revolutions per minute, while to produce energy in the frequency range of 60 Hz, according to the number of poles of the generator, a speed between 1200 and 1800 revolutions is needed. It is per minute that in order to create such a speed, we need a power transmission mechanism that converts low speed and high torque on the low speed axis to high speed and low torque on the high speed axis. This mechanism is called a gearbox. In the gearbox of wind turbines, the speed increase rate is fixed and the gears in it will only increase the rotation speed of the low speed axis to a specific ratio, which is usually about one to fifty, which makes the rotation speed of the high speed axis fifty times the rotation speed of the low speed axis.