Wind Power and Analysis of Squirrel Cage Induction Generator Based Wind Farm

Contents

ABSTRACT

LIST OF FIGURES

LIST OF TABLES

SYMBOLS

CHAPTER 1
1.1 Introduction to Wind Energy Scenario
1.2 Power Generation in India
1.3 Wind Power in India
1.4 Types of Wind Turbines
1.4.1 Horizontal Axis Wind Turbine
1.4.2 Vertical Axis Wind Turbine
1.5 Types of Wind Turbine Generator
1.5.1 Squirrel Cage Induction Generator
1.5.2 Permanent Magnet Synchronous Generator
1.5.3 Doubly Fed Induction Generator

CHAPTER 2
2.1 Literature Review
2.2 Problem Identification
2.3 Grid Codes
2.4 Objectives

CHAPTER 3
3.1 Modeling of Squirrel Cage Induction Generator

CHAPTER 4
Simulation and Analysis
4.1 Overview of the Wind Farm
4.2 Load Flow Analysis
4.3 Active Power at Various Wind Speeds
4.4 Short Circuit Analysis
4.4.1 3- Phase Short Circuit fault
4.4.2 Single L-G fault
4.5 Real and Reactive Power analysis during Fault Conditions
4.5.1 Real Power Analysis during Single L-G fault
4.5.2 Reactive Power Analysis during Single L-G fault
4.6 Harmonic Analysis
4.6.1 Harmonic Analysis without Harmonic Filter
4.6.2 Harmonic Analysis after Filter Implementation
4.7 Reactive Power Analysis
4.8 A General Comparison of Simulation results obtained between SCIG and DFIG on same Wind Farm

Chapter 5
5.1 Conclusion
5.2 Future Scope

Chapter 6
References
Appendix
Appendix I- Acronyms

ABSTRACT

The rising demand of electricity and the environmental concern in the recent past necessities the need of renewable energy sources. The Renewable energy sources have gained major importance due to the depletion of the conventional fuels in the future. Among the available renewable sources the Wind energy has gained a significant importance due to its high efficiency and pollution free nature. Large Wind Farms have been set up to meet the energy demand globally. The capacity of the Wind Turbine Generator is being increased gradually from a few KW capacities in the beginning rising up to almost 5 MW in the present. More research has to be carried in this field to make it a dominant source for the rising energy demand. Wind energy potential has to be harnessed on a large scale in places which have high wind density.

Before the actual commissioning of the Wind Farm on site, a wide range of analysis has to be carried in terms of simulation. This is done to understand the behavior of the system under various conditions and preventive actions if any are to be taken. The pre analysis gives us an idea of the selection of devices for higher efficiency and system reliability.

This project is a research work carried in ETAP (Electrical Transient Analyzer Program), which is a Power System Simulation tool. The analysis carried out to demonstrate the capabilities of the SCIG (Squirrel Cage Induction Generator) based Wind Farm include Load Flow analysis, to find out the Power transferred to the Grid in normal condition at rated Wind Speed. Active Power Output at various Wind Speeds, which presents the efficiency of the Wind Farm at various range of wind speeds. Short Circuit analysis which is essential to determine the capability of the Wind Farm to recover from any abnormal conditions. Harmonic analysis to determine the Quality of power being delivered and the Harmonic Filter design to mitigate the Harmonic content if any in excess.Reactive Power analysis which is important considering the stability of the system and a suitable Capacitor design for reactive Power compensation.

The WTG (Wind Turbine Generator) considered was a Type 2 Variable speed SCIG of 2.1 MW assigned in ETAP. The Wind Farm consisted of a total of 20 WTG’s with a total capacity of 42 MW. The results obtained were compared with the theoretical values and were found to be the same. The analysis performed presented a clear indication of the future of Wind Energy in SCIG based Wind Farms.

List OF FIGURES

1.1 World Wide Wind Capacity Till June 2015

1.2 World Installed Wind Capacity Country Wise

1.3 Wind Power Generation in India till January 2016

1.4 Horizontal Axis Wind Turbine

1.5 Vertical Axis Wind Turbine

1.6 Scheme of SCIG System

1.7 Block diagram of SCIG System

1.8 Scheme of PMSG System

1.9 Scheme of DFIG System

1.10 Different parts in the Nacelle

2.1 Voltage Dip Wind Turbine should handle without Disconnection

3.1 Induction Machine Schematic Representation

4.1 Overview of the Wind Farm

4.2 Layout of Network 1

4.3 Layout of Network 2

4.4 Layout of Network 3

4.5 Load Flow Analysis

4.6 Load Flow Analysis at Network 1

4.7 Load Flow Analysis at Network 2

4.8 Load Flow Analysis at Network 3

4.9 Power Curve With respect to the Wind Speed

4.10 Voltage at Bus 1during 3- Phase Short Circuit Fault

4.11 Voltage at Bus 1during Single L-G Fault

4.12 Real Power Analysis during Single L-G fault

4.13 Reactive Power Analysis during Single L-G fault

4.14 %THD in the Wind Farm at various Locations

4.15 %THD at WTG1 in Network 1 without Harmonic Filter

4.16 Harmonic Waveform for Bus 1, Bus 2, Bus 6 without Harmonic Filter

4.17 Harmonic Spectrum at Bus 1, Bus 2, Bu 6 without Harmonic Filter

4.18 %THD at various Locations in Wind Farm after Harmonic Filter implementation

4.19 %THD at WTG 1 after Harmonic Filter implementation

4.20 Harmonic Waveform for Bus 1, Bus 2, Bus 6 after Harmonic Filter Implementation

4.21 Harmonic Spectrum for Bus 1, Bus 2, Bus 6 after Harmonic Filter Implementation

4.22 Reactive Power Analysis without Capacitor bank

4.23 Reactive Power Analysis with Capacitor bank

List OF TABLES

1.1 Electricity Generation from various sources in India

1.2 State Wise Wind Capacity in India

1.3 Indian Wind Power Projects of 75 MW and above

2.1 Voltage Harmonic Limits

2.2 Voltage Withstand limits for Wind Farms

4.1 Specifications of WTG considered

4.2 Power Co-efficient Considered during Modeling

4.3 Load Flow Results

4.4 Power Output of the Wind Farm at various Wind Speeds

4.5 Voltage recovery in 3- Phase Short Circuit fault after fault clearing

4.6 Voltage Recovery in Single L-G fault after fault clearing

4.7 %THD at Various Locations within the Wind Farm

4.8 %THD at Various Location in Wind Farm after Filter Implementation

4.9 Comparison result between the same SCIG and DFIG based Wind Farm

SYMBOLS

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CHAPTER 1

1.1 INTRODUCTION TO WIND ENERGY SCENARIO

The recent past has witnessed a rapid increase in the energy demand globally. Till date the conventional means like The Coal, Diesel, Hydro and Nuclear were being used on a very large scale but today the world necessities the use and potential of the Renewable energy sources like the Geothermal, the Sun, Wind power, Tidal Energy etc. on a whole. As these sources are proven to be cleaner sources having lesser impact on the rising environmental concerns. Out of these sources The Wind energy has proven to be significantly important and gaining more importance considering its capacity in power generation and research done in this sector. The Wind power development has grown considering the rise of Wind Turbines Installations On-Shore and Off-Shore both. The future installation will see a rise in Wind Turbine capacity thus contributing to its power generation. Today the installed wind capacity globally is more than 392,927MW at the end of June 2015 [1]. The major giants in the wind sector include The United Kingdom, Germany, Spain, France, Denmark, and The Netherlands in the continent of Europe. The United States of America, Mexico and Canada in the continent of North America. The Asian giants include China, India, Japan, South Korea and Taiwan. Whereas Morocco, South Africa, Egypt, Tunisia, Ethiopia in the Continent of Africa and Middle East. In the Year of 2014 alone the new installed capacity has been more than 49,832 MW. Amongst all the Renewable Sources, Electricity generation by Wind is the cheapest and the feasible one, so countries are targeting to improve their Wind capacity profile in the coming future. The European countries alone have set a target to satisfy almost their 23% of power requirement by wind energy alone [2].

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Fig. 1.1 World Wide Wind Capacity Till June 2015 [1][2][3]

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Fig. 1.2 World Installed Wind Capacity Country Wise [1]

1.2 POWER GENERATION IN INDIA

As on 31st March 2015 the overall installed capacity of all the Power Plants in India was 267,637 MW [4]. Today India is dependent primarily on Coal for its electricity generation, which generates 61% of the total Generation followed by the Hydro Power and the Renewable energy sources which constitute 15% and 11% respectively. Although the maximum share of energy is met by the Thermal energy, the Coal reserves are limited and will deplete in the near future. So the Government of India is giving emphasis on the Renewable energy sources like the Wind and Solar, which was also strongly presented by India at the Paris Climate Summit held in December 2015. Among these the Wind energy has a vast potential and forms a reliable source for Generation as per its proven Track record. The various sources for Electricity Generation with its installed capacity in India are presented in the Table 1.1 below.

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Table. 1.1 Electricity Generation from various sources in India [5]

1.3 WIND POWER IN INDIA

The development of the Wind Power sector in India began from 1986 onwards with Wind Farms set up in Maharashtra, Gujarat and Tamil Nadu in the initial phase. As on 31st Jan 2016 the total installed Capacity of overall Wind Power in India was 25188 MW. Today India ranks fourth with respect to the largest installed Wind Power Capacity in the World. The growth rate in India is increasing at a high rate compared to the Top 3 countries. The Wind network in India is spread mostly across South, West and the Northern part of India, the Eastern part has no Grid connected Wind Power plants till date [1][6].

The reliability, best suited conditions and excellent performance of Wind Turbine Generators has made it a best choice in a place like India. Suzlon an India owned company has emerged at the global level in wind energy sector, which is also the largest manufacturer of Wind Turbines in India. Suzlon has a share of more than 42% in the India market. Today Tamil Nadu state of Southern India has the Largest Wind Capacity of 7455.2 MW as on 31st March 2015 [7]. The representation of the various Indian States with their Wind Capacity Generation is given in the Table 1.2 below

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Table.1.2 State Wise Wind Capacity in India [7]

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Fig. 1.3 Wind Power Generation in India till January 2016

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Table. 1.3 Indian Wind Power Projects of 75 MW and above [8]

1.4 TYPES OF WIND TURBINES

Basically Wind turbines are classified in two main types

A) Horizontal Axis Wind Turbine

B) Vertical Axis Wind Turbine

1.4.1 Horizontal Axis Wind Turbines: -

Horizontal Axis Wind Turbines abbreviated as (HAWT). These form the most common type of wind turbines in practice. The basic description of HAWT is that it has blades which spin on their Horizontal Axis. The HAWT type machines have the rotor shaft and the electrical generator placed on top of the tower and into the direction of the wind. The modern techniques involve the use of wind sensors along with special purpose machines like the servo motors to move the turbine into the direction of the wind. The scheme also involves use of Gear box to adjust the slow rotation of the turbine into Fast and constant speed to drive the Generator.

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Fig. 1.4 Horizontal Axis Wind Turbine

The turbine blades are made strong enough to resist abnormal behavior due to wind speed. The blades are fixed at some distance away ahead of the tower and the blades are also inclined for optimum wind speed. The tower height plays an important role as well ranging till or even more than 90m, this ensures higher wind speeds. The rotor blades are spread till a maximum of 40m both considering the electrical and mechanical aspects. The whole structure is in such a way that it offers less turbulence to wind.

Advantages: -

- The tower height (90m or more) ensures access to large wind speeds thus increasing the electrical power output, in general an increase in 10% Wind speed ensures almost 30% increase in electrical output. - Overall High Efficiency as the blades moves perpendicular to that of the wind.

Dis-advantages: -

- Huge structure hosting the Generator, Gear box, large size blades etc. - They are visible from large distances, they also possess a threat to the birds and opposition by native human beings.

1.4.2 Vertical Axis wind turbine: -

Vertical Axis Wind turbines are abbreviated as (VAWT), they have their rotor shaft arranged in a vertical manner. The features of this type lie in the fact that the Generator and other components can be placed on the ground. This helps reduce the size of the whole structure and also reduce the maintenance issues which had to be solved by climbing on the tower in case of HAWT types. It is always difficult to host the VAWT on the towers so they are always placed near the ground. Moreover, there is drag issues associated when rotating into the wind.

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Fig. 1.5 Vertical Axis Wind Turbine

The Wind power generation depends mostly on the Wind speed, as the VAWT are nearer to the ground, the wind speed is lesser comparatively to an altitude nearer to 90m so the power generation is lesser. This type is also prone to frequent maintenance and lesser useful life.

Advantages: -

- Maintenance is easy as they are mounted nearer to the ground
- Yaw mechanism is not needed
- VAWT’s can start-up at low wind speeds
- This type of structures can be implemented where taller structures are not permitted.

Dis-advantages: -

- Frequent maintenance has to be done
- Subjected to low wind speeds

1.5 TYPES OF WIND TURBINE GENERATORS

There has been a vast research made in the field of Wind Turbine Generators in the past 20 to 25 years. The main types of Wind Generators presently in use are

A) Squirrel Cage Induction Generator

B) Permanent Magnet Synchronous Generator

C) Doubly Fed Induction Generator

1.5.1 SQUIRREL CAGE INDUCTION GENERATOR: -

The conversion of Electrical energy into its Mechanical form usually occurs in the moving part of the Electrical Machine. In case of the DC Machine electrical power is conveyed directly to the armature. In case of AC machines electric power is transferred inductively in the same way like a Transformer. Here the power is transferred inductively hence such machines are called as Induction Type Machines. Here the Primary (Stator) is stationary and the Secondary (Rotor) is free to rotate [9].

The main Advantages of this type of Generator involve: -

- It’s simple and ultimate rugged construction
- Minimum Maintenance
- Low Cost and reliability
- Good power factor and higher efficiency in normal running conditions

Dis-advantages: -

- Draws Reactive Power from the Grid

Squirrel Cage Induction rotor

Today in the industry most of the Machines which are used are Induction type, Induction Machines contribute to almost 90% of the machines in the industry only because of its features. Cylindrical laminated core constitutes the rotor with parallel slots for the rotor conductors made up byAluminum, Copper bars, or particular Alloys. The bars are arranged in the slots and bolted to the end rings giving it a Squirrel Cage construction. The bars of rotor are permanently short circuit and hence it is practically not a general consideration to add external resistance if required for the starting purpose. Here the rotor slots are given a slight skew to reduce the magnetic locking and magnetic hum [9].

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Fig. 1.6 Scheme of a SCIG system

The figure above shows the general scheme of the Squirrel Cage Induction Type Generator, the system consists of a Wind Turbine being coupled to the Generator through a gear box system. The stator terminals are connected to the grid with the help of Converters, The Coupling Inductors are also provided to filter the high frequency ripples present due to frequent switching, a control strategy depending upon its best suitability is selected for its active and reactive power flow control [10].

WORKING: -

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Fig. 1.7 Block diagram of a SCIG system

The figure above shows the schematic arrangement of the SCIG system, the blades are connected to the SCIG through a gearbox. The system consists of Pitch Control system, Wind Turbine and a Reactive Power Compensation. The total system is arranged in the 3 stages for transferring the energy generated to the Grid. The 1st stage is of the Wind Farm which usually handles the Low Voltage side. The 2nd stage as presented in the figure is of the distribution which handles the voltage of medium range. The 3rd stage is of the Grid Transmission which is associated with high Voltage . The distribution Voltage is represented by . The Transformers are used generally to take care of the network between the above stages. The Nominal Power is considered as Active power reference to control the Pitch angle. Resembles the Line to Line Voltage of the distribution and is the phase current. These parameters are monitored for Reactive Power compensation. This technique is possible in SCIG due to its rugged construction and high efficiency. As the Wind Speed varies so is the Active Power output, after the desired Wind speed the Pitch angle is regulated at a very slow rate owing to the large blade sizes and inertia [11].

1.5.2 PERMANENT MAGNENT SYNCHRONOUS GENERATOR: -

This configuration responds to a variable speed topology. Where the Wind turbine with Permanent Magnet Synchronous Generator is connected to the grid, and consists of a power converter which is represented in the Fig 1.8 below. It consists of blades, A Synchronous Generator, Full power converter, Transformer and a dc capacitor. It employs two power converters to convey the power generated to grid, the wind generators and the grid can be totally isolated hence the system could function under varying frequency and thus remain unaffected. As it employs a grid side and a stator side converter. The optimal power to be drawn out from the generator under varying range of wind speed is done by the Stator Side Converter. The converter at the Grid side is used generally to keep up the Voltage at the dc link, to control the sending of active power to the grid and control of the reactive power flow [12].

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Fig. 1.8 Scheme of a PMSG system

The main Advantages of this type of generator involve: -

- Overall High efficiency
- Compatible with frequency range of 50- 60 Hz
- Low initial cost

Dis-advantages: -

- High cost of Power Converters
- Losses in Power Converters

1.5.3 DOUBLY FED INDUCTION GENERATOR: -

This type of a Machine has gained a larger importance in the recent past. The Doubly Fed Induction Generator (DFIG) is a Machine who’s both the Rotor and the Stator are being connected to the Grid. It is also capable of providing the reactive power to the grid which is its outstanding feature in the power flow. It consists of back to back connected converter, where the stator windings are connected to the grid and the rotor windings are connected to the back- to- back connected Voltage Source Converters. The other side of the converter is connected to the grid. The amount of the reactive and the active power flow control is achieved by controlling the power electronic circuitry connected to the rotor. The cost of the Converters is still a concern to the power engineers but still this is a much more efficient technology [13].

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Fig. 1.9 Scheme of a DFIG system

The main Advantages of this type of Generator involve: -

- Capable of giving Reactive Power to the Grid
- Highly efficient topology

Dis-advantages: -

- Gear box requires frequent maintenance
- High cost of Power Converter Devices
- Power Quality Issues
- Proper Starting Mechanism to be employed for Synchronism
- Low- Voltage ride through capability during grid disturbances.

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Fig. 1.10 Different Parts in the Nacelle

Retrieved from, “Wind Power in Power Systems” byThomas Ackermann, John Wiley and Sons Ltd, where,

1–oil cooling system, 2 –generator cooling system, 3 –Transformer unit, 4 –ultrasonic wind sensors, 5 –Top controller with converter, 6 –service crane, 7 –Generator unit, 8-composite disc coupling, 9 –yaw gears, 10 –gearbox system, 11 –parking brake system, 12 –Machine Foundation, 13–blade bearing, 14–blade hub, 15 –blade, 16 –pitch cylinder, 17 –hub controller.

CHAPTER 2

2.1 LITERATURE REVIEW: -

In the paper “Control and Dynamic Analysis of Grid connected variable speed SCIG based wind energy conversion system”by Manaullah, Arvind Kumar Sharma, Hemant Ahuja, G. Bhuvaneswari , at the 2012 Fourth International Conference on Computational Intelligence and Communication Networks [10]. The author presents a dynamic analysis of a grid connected variable speed SCIG based wind energy conversion system. It is mentioned that the features of the SCIG that is the construction, efficiency, ruggedness, operation under varying wind speeds makes it an outstanding machine for wind power generation. Here a simulation study is done to demonstrate the single line to ground fault, the effects of grid disturbances and varying wind speed on SCIG’s performance is done. Here the entire study is carried in MATLAB/ Simpower and the effects during and after the grid faults is also studied. Results obtained show a graphical representation of wind speed, generator speed, active power, reactive power, voltage at PCC, DC link voltage, Current (per unit). The author also presents the Power Quality issues related to the SCIG machines with frequency oscillations at the DC link Voltage and non-sinusoidal current Waveforms.

In the paper “The Impact of SCIG Wind Farm Connecting into a Distribution System” by Ching-Yin Lee, Li-Chieh Chen, Shao-Hong Tsai, Wen-Tsan Liu and Yuan- Kang Wu in 2009 at IEEE Conference [12]. The author presents the impact of connecting a 120 MW wind farm to the Transmission utility. The author represents the use of FACT devices like the SVC (Static VAR Compensator) and the STATCOM (Static Compensator) for Stability of the system. STATCOM is used to provide the integration of a large wind farm into weak power system. The graphical representation of real power, reactive power with respective to time is shown. Along with the Voltage at POI and Voltage (per unit) with respect to time and the rated power, pitch angle and rotor speed, the same graphs are compared with using SVC and STATCOM. The author also proposes the use of Fixed Capacitors for the reactive Power Compensation. The Comparative study carried amongst STATCOM, SVC and Fixed Capacitors presents a better stability result obtained by use of STATCOM compared to the other fixed devices.

In the paper“Performance Comparison of DFIG and SCIG based Wind Energy Conversion Systems” by Manaullah, Arvind Kumar Sharma, Hemant Ahuja, Arika Singh at the 2014 International Conference on Innovative Applications of Computational Intelligence on Power, Energy and Controls with their impact on Humanity (CIPECH) [14]. The author gives the comparison in terms of performance of the two machines the DFIG and the SCIG. Here the system model is developed in MATLAB/ Simpower and comparison is made of active power with respect to the wind speeds and the superiority of the SCIG is found at low and medium wind speeds. Similarly, the author discusses the power quality issues related to the DFIG. Also it is found that the %THD of the DFIG system is more compared to SCIG at various wind speeds. The author proposes the use of the SCIG machines compared to the DFIG machines considering the Quality of Power delivered and High Power Output at Medium Wind Speeds which contributes to its High efficiency. Overall the paper presents a complete performance comparison of WECS based on DFIG and SCIG for large Power ratings.

In the paper “Dynamic simulations of Wind Generators connected to distribution systems” by Wellington Santos MOTA and Luciano Sales BARROS at the 18thInternational conference on Electricity distribution [15], the author has produced a methodology applied to a distribution system, where two type of generators were considered SCIG and the DFIG and the simulation curves were obtained with respect to wind speed, for both high wind speed and also for low wind speed simulation. Along with this the Single L-G fault simulation was done and results were presented. It was also demonstrated that pitch control mechanism was implemented during high wind speeds for safety precaution and limit the active power in its permissible limits. The 3-Phase to ground fault Simulation at a particular Bus in the system presents a Voltage variation in both the SCIG and DFIG machine. The active power output at High Wind speeds, which is 8% more than the average wind speed, presents an increased Power Output. Similarly, the simulation carried under Low Wind speed which is 13% less than average Wind speed presents a decreased Power Output.

In the paper “Comparison of Power Quality in Different Grid-Integrated Wind Turbines” by M.Q. Duong, K.H. Le, F. Grimaccia, S. Leva, M. Mussetta, and R.E. Zich at the 16th International Conference on Harmonics and Quality of Power (ICHQP), 2014 IEEE [16], the author has done a study of the impact of the connection of the Synchronous and Induction Generator to the distribution networks. It was found that the SCIG was used by less wind farms because of its lack of potential of controlling reactive power. This problem could be overcome by DFIG but it has its limitations in terms of power quality, cost and its frequency prone to system faults. However, PMSG was preferred for efficiency, robustness, and reliability along with SCIG for its cost, reliability and efficiency. The active power, reactive power, terminal voltage and rotor speed was demonstrated with respect to time in the graphical form. The comparison gives the superiority of each of these generators.

In the paper “Impact of SCIG and DFIG Type Wind Turbine on the Stability of Distribution Networks: static and dynamic Aspects” by N. K. Roy, H. R. Pota,M. J. Hossain, D. Cornforth , at the 11th International Conference on Environmental and Electrical Engineering (EEEIC), IEEE 2012 [17], the author presents the impact of SCIG and the DFIG type wind turbine in distribution network under static and dynamic condition. It was found that SCIG has certain disturbances due to its inability to supply the reactive power. Hence it was recommended that certain stability devices were to be used with SCIG. It was found that although DFIG was superior to Voltage stability but still it had significant power loss. This also suffered from peak overshoots and under shoots this causes serious problem to the distribution utility. Thus this analysis is vital in determining the stability of distribution networks.

2.2 PROBLEM IDENTIFICATION: -

The major problems identified are:-

- Power quality issues (frequency and voltage) with variable nature of the wind.
- Sensitivity to Faults
- Recovery from low Voltage after a Fault
- Harmonic issues related to Wind Farms
- Reactive Power in the System

2.3 GRID CODES: -

Grid Codes are general standards or protocols followed by various generation, transmission and distribution parties associated with the electrical sector. Proper implementation of Grid code implies safe, secure, efficient, economic operation and proper functioning of the electric system. Grid codes generally specify the behavior of the system in normal operating condition and during disturbances. The parameters which are governed generally include response to system faults, power factor limits, and Voltage variation limits, Harmonic Indices, frequency changes on the grid and interruptions during operations. Grid codes are governed by certain legal and technical considerations. Each sector can be assigned a unique standard to be followed in the grid codes which is formed by the Central governing authority [18].

The main purpose of forming the grid codes is governing the rising concern about Power Quality. The importance of Power quality and reliability of supply has led to awareness and successful implementation of these Grid Codes.

The General Grid Code Requirements include-

1) The Wind Turbine should be connected to the Grid for a specific time period during fault condition.

2) The Wind farms should maintain a certain power factor limit as determined

3) Reactive power Compensation should be of prime importance

4) The frequency limits are to be maintained.

5) The System should operate in the desired permissible Voltage limits.

6) The Harmonics associated with Power Quality are of prime concern and desired steps are to be taken.

7) Under/ over voltage protection

8) Under/ over frequency protection [18]

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Table.2.2 Voltage Withstand limits for Wind Farms

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