Archive for the ‘Academic’ Category

Sodar: Operation and Limitations (1/2)

February 18, 2012

On last post I explained briefly some features related to this Remote Sensing (RS) apparatus, but I consider that it should be explained further. Therefore, I am going to detail other considerations related to Sodar’s technology through two posts based on the academic paper of S. Bradley, I. Antoniou et al. (2005). By now, physical principles and uncertainties will be described. Next post will focus on its calibration methods.

Sodar is a Remote Sensing apparatus that measures 3D wind speeds at high altitudes. By emitting vertical sound beams of sound, it is possible to interpreter the backscattering frequencies due to the Doppler Effect and thus, wind components can be decoded (See Fig. 1). Usually, three or five beams are necessary to obtain reliable raw data measurements. Each of them is usually tilted 15-20º (ϕ) to the vertical (See Fig. 2). Though the emitted signal produces a continuous backscattering echo after crossing the infinite turbulent layers in the atmosphere, the echo generated at the studied altitude (Z) can be recognized according to the following formula. This means that among the continuous echo signal received, the specific signal generated at the Scattering Volume at Z height is generated at t (time) moment. The same principle is used by pulsed lidars.

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New reports

February 15, 2011

Since the beginning of this program, we made many reports and assignments. I don’t want to upload all of them, but I would like to share the articles that I personally wrote:

Improvements in the transmission grid network for a succesful wind power integration: In this report I analyzed how the wind power development can be improved in Europe. j

Spatial planning in the region of Galicia. This region in Spain has a lot of installed wind power capacity. Why?

Spanish Wind Power Policy: A brief and simple diagram.

Leassons learned at Gotland University

February 15, 2011

From the last time I posted, we have learnt many things about the wind power industry. Here is a short summary of what we studied on this Master:

  • Principles of wind turbines: Components of wind turbines and the differences between synchronous and asynchronous generators must be known to understood the basic principles.
  • Climatology and Boundary Layer Theory: Kinetic energy from wind moves the blades, and thus electrical energy can be produced.
  • Aerodynamics: The shape and chord of blades are optimized by using formulas. Lectures provided by some accademics of Risoe and Uppsala universities were useful to understand these phisical principles.
  • Measurements Methods: Linear, non linear, CFD (Computational Fluids Dynamics) are useful to predict the wind resources at a determinated place by using MCP (measurement correlate and predict) techniques. Hence, software such as WindPro or WinSim are useful tools.
  • Wind Power potentials: Places located in cold climates or offshore wind farms have high potential in future but there are some considerations they must be valorated.
  • Grid Network: Before starting a new wind power project four words must be considered: Wind, wind, wind and infrastructure/grid network. Hence, it is important to know the point of common coupling (PCC) to connect the wind farm to the grid network.
  • Logistic: The other leg of the four words is obvious; roads, docks, and so on.
  • Public acepttance and environmental impact: Visual impact, flicker shadows, noises, consequences to the wildlife are other important aspects.
  • Policy and Legal Planning: Incentives and subsidiaries from administrations, legal frameworks… These frameworks can explain why some countries as Germany has such installed wind power capacity.

First reports.

September 16, 2010

Master is running fast. After the Power Point presentations which were useful to know the rest of students and analyze the energetic situation in our countries, now it is time to write the reports. I must recognize writing technical reports in English is more demanding as I had expected.

However, I am proud of my work with the few time we had to write them. Here are posted:

Spain: Energy Situation: Briefly report about the Energetic situation in Spain with personal comments.

Spain: Wind Power Situation: Wind Power policies, forecasts, present situation, so on.

Power Quality Standards.

July 13, 2010

Voltage provided by Wind turbines must comply some requirements specified in the IEC 61400-21 standard. Here we are some power quality parameters that power energy from wind turbines must be under control:

Rated Data

  • Rated Power (Pn) (or Active Power): Maximum continuous electric output power for a wind turbine under operating conditions.
  • Rated Reactive Power (Q­­­­­n): Reactive power under rated power, nominal voltage and frequency.
  • Rate Apparent Power (Sn): Apparent power from the wind turbine while operating at rated power and nominal voltage and frequency.
  • Rated Current (In): Current from the wind turbine while operating at rated power and nominal voltage a frequency.

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Brake Systems in Wind Turbines

July 12, 2010


According to quality parameters, DS472 (Danish Standard) and GL rules, wind turbines must have two independent braking systems. However, the IEC 61400-1 requirement does not specify what kind of two braking systems must have, but requires the protection system to remain effective even after the failure of any non-safe-life protection system component.

Usually, it makes sense to supply both aerodynamic and mechanical braking. Aerodynamic brake is more benign than mechanical braking, so it is always used in normal shut-downs. On the other side, although a braking system must be used during shut-downs, sometimes technicians allow rotor free turns (idle) within low winds. This strategy reduces the frequency of imposition of braking loads on the gear train.

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Power Electronic Concepts in Wind Turbines.

July 10, 2010

In recently years, we have lived big discoveries on the Power Electronic field that unveil new opportunities to improve the performance in the electric circuits and therefore, in Wind Power industry. Power Electronic can be defined as the brand of the electrical engineering which studies the control and conversion of electric power. Therefore, the power conversion systems can be classified according to the type of the imput and output power:

Here we are the basic components in the Wind Power industry.

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Generators in Wind Turbines.

July 9, 2010

Basically, any type of three-phase generator could work in a wind turbine but they must fulfill some requirements. We have just classified them according to their generator type and the coming prototypes that nowadays we are studying. This post, as the last one, is a summary from the book Wind Power in Power Systems (Chapter 4) by Thomas Ackermann. However, for any further information, this link can be interesting.

Asynchronous (Induction) Generator.

It is the most numerous in wind turbines. Advantages: Robustness, mechanical simplicity, low price. Disadvantages: It has to receive an exciting current from another source and consumes reactive power (so, reactive power is supplied by the grid or by a power electronic system).

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Types of Commercial Wind Turbines.

July 8, 2010


We already saw the different wind turbines we can find nowadays, from the HAWT to VAWT. However, the most commercial at this moment are the High Tip Speed Ratio HAWT. In this post, we are going to describe the different models of wind turbines and what kind of technology they use to convert the mechanical energy to electric energy.

If we pay attention at the above table, we can see there are two wind turbines models according to their Speed Control and Power Control. Thereby, we can find four models: Type A, Type B, Type C, and Type D (see the below diagram). There are three variants for the Type A (A1,A2 and A3). Although it would be possible to manufacture the same variations for the B, C and D Types, it would be not worthy (from the commercial point of view) because these models lack the capability for a fast reduction of power (see the grey-colored boxes in the first diagram). Let´s start describing the possibilities to control the power the aerodynamic forces on the turbine rotor.

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What’s inside a wind turbine?

July 7, 2010

This video posted on Youtube.com has sparked my attention. Firstly, because there are not so many videos like this that explains the main parts of a wind turbine, and second because it is worthy and is well-structured. The video is made by UVSAR, a British company which provides technical services for all those involve in work at height.

The video shows us the layout of two typical wind turbine generators, from the transformer at the floor level, ladders (or elevators), to the electrical cables attached to the walls of the tower.

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