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Power Generation by Vertical Axis Wind Turbine with Maglev Technology

Waquar Ahmad Ansari1, Avinash Chandra Tripathi2, Prince Kumar3, Ajay Singh4, Pintu Kannaujiya5

1-5, Student, Mechanical Engineering, Buddha Institute of Technology,

Gorakhpur, Uttar Pradesh, India

[email protected]

Abstract – Our paper “Wind Turbine with Maglev Technology” is review on vertical axis wind turbine (VAWT) is introduced by magnetic levitation technology to most effective the performance. This system utilize the nature of permanent magnet as a replacement for ball bearings to levitate the turbine component and thus minimize energy losses like friction losses etc while rotating, which is the more important problem that faced by conventional wind turbine. The Maglev Wind Turbine is expected to carry wind power technology to the next generation. Furthermore, this system can be suited in rural and urban areas of low wind speed regions but mostly in urban areas. The choice of magnet materials in the designing of maglev wind turbine system will be depend upon the turbine size and weight. A model of maglev wind turbine is built to check the several tests such as the starting wind speed, rotational speed at constant wind speed, and time taken to stop rotation completely. The results obtained will be compared with the model of conventional vertical axis wind turbine. Power will then be generated with the help of an axial flux generator, which includes the use of permanent magnets and a set of coils.

Keywords – Magnetic Levitation, Vertical Axis Wind Turbine, Permanent magnet flux generator.

I. INTRODUCTION

At this time, we will ultimately need to search for renewable or virtually non ending energy for the human development to continue. Renewable energy is generally electricity provided from sources, such as wind power, solar power, geothermal energy, hydropower and various forms of biomass energy. These sources have been devised renewable due to their continuous restore and able to use over and over again.

The popularity of renewable energy has experienced a significant upsurge in recent times due to the exhaustion of conventional power production method and become greater realization of its unfavorable effects on the atmosphere. The exploration of renewable energy is the only approach to become smaller our dependence on fossil fuels. Among the renewable energy sources Wind Energy is one of the fastest growing energy sources that is growing at the rate of 32% annually. [1]

Wind energy was first harvested centuries ago, when early wind mills were used to power millstones, pumps, and forges. More recently, the wind is harnessed by using a special collector, called wind turbine to generate a clean and safe source of electricity. Various designs have been proposed in order to generate a high efficient wind turbine which will be able to generate maximum electric power. They may vary either in the design of shape of the turbine blades, the axis of rotation, and other useful modification.

The wind speeds in most of Asian zone is much lower than 7 m/s, especially in the cities, but the mechanical frictional resistance of existing wind turbines is too big, usually it can't start up when the wind speed is not big enough. This project introduces structure and principle of the proposed magnetic levitation wind turbine for better utilization of wind energy. Maglev Wind turbine has the features of no mechanical contact, no friction etc. minimizing the damping in the magnetic levitation wind turbine, which enables the wind turbine start up with low speed wind and work with breeze. The Maglev wind turbine, which was first unveiled at the Wind Power Asia Exhibition in Beijing, is expected take wind power technology to the next level with magnetic levitation [2].

The aim of this major qualifying project is to design and integrate an advance technique, Magnetic Levitation (Maglev) into turbine system in order to increase the efficiency. If the efficiency of a wind turbine is increased, then more power can be generated thus decreasing the need for expensive power generators that cause pollution. Since one of the main complaints about wind turbines is the sound they produce, this is a huge advantage over other turbine designs.

This technology focuses on the utilization of wind energy as a renewable source. The aim of this major qualifying project is to study and implement a magnetically levitated vertical axis wind turbine system that has the ability to operate in both high and low wind speed conditions. Our choice for this model is to showcase its efficiency in varying wind conditions as compared to the traditional horizontal axis wind turbine and contribute to its steady increasing popularity for the purpose of mass utilization in the near future as a reliable source of power generation.

II. ABOUT MAGNETIC LEVITATION TECHNOLOGY

Magnetic levitation (maglev) is a method in which an object is suspended with no support other than magnetic fields. The magnetic force produced is used to counteract the effects of the gravitational force and lift up the object.

By placing two magnets on top of each other with like polarities facing each others, the magnetic repulsion will be strong necessary to keep both magnets at a distance away from each others. The force produced as results of this repulsion can be used for suspension purposes and is strong enough to balance the weight of an object depending on the threshold of the magnets.

There are a lot of advantages for utilizing magnetic levitation that is to minimize friction, make force measurement, design, and entertaining devices. Recently, this advance technology is applied into transportation system in which non contacting vehicle travel safely at very high speed while lift, guided, and propelled above a guide way by magnetic fields. The concept of magnetically levitated vehicle stimulates the development of useful application in various fields such as the power generation.[3]

Fig. 1 Magnetic levitation concept

A body will be under Magnetic levitation when it floats due to that special repelling (or attracting) quality of the magnet, when the force created by the electromagnetic repulsion (or attraction) is strong enough to balance the weight of the object.

There are two techniques of magnetic levitation:

Attractive or Electromagnetic Suspension

Repulsive or Electrodynamics  Suspension  

In “attractive” levitation, a ferromagnetic body is attracted to a source of magnetic flux, as a piece of steel is attracted to a permanent magnet. Levitation forces can be created with a DC magnetic field created by DC currents, superconducting coils or permanent magnets.

This type of levitation is unstable without feedback control but numerous analog and digital control techniques are available. A full -scale electromagnetic suspension (EMS) Maglev system using copper coils for generation of magnetic is currently being tested in Germany. The projected revenue-producing train service would begin in 2005 from Berlin to Hamburg.

 Fig. 1.1: Attractive or Electromagnetic Suspension

In “repulsive” levitation or electrodynamics or “EDS” levitation, eddy currents are generated in a conducting body when the body is subjected to a time-varying magnetic flux. The interaction of the eddy currents with the magnetic flux generates forces levitates the body. In EDS Maglev, the changing magnetic flux is produced by a superconducting magnet on the moving train.  This changing magnetic flux   generates circulating currents in stationary conducting loops (or sheets) over which the train levitates. The interaction of the induced currents with the magnetic field creates the forces. Another way to test magnetic levitation principles is a stationary coil carrying a time-varying current, levitated above a conducting sheet. A coil may be levitated in a stable, but under damped equilibrium without feedback control.

Fig.1.2: Repulsive or Electrodynamics Suspension

Magnetic levitation has numerous practical applications in research and in industry where friction must be reduced or eliminated. Some of the more promising applications are transportation (low and high speed Maglev transportation System), low friction bearings for gyroscopes and flywheel energy storage. Many future applications have been proposed, using Maglev Technology such as levitation melting of conductive metals. [4]

III. MAGNETIC LEVITATION WIND TURBINE

The vertically oriented blades of the wind turbine are suspended in the air above the base of the machine by using permanent magnet which produces magnetic force to lift up the turbine. This system does not require the electricity to operate because no electromagnets are involved. Since the turbine blades are lift by magnetic force produce by the permanent magnet, there is no need of ball bearing to retain the blades.

Fig. 2 Free body diagram of magnetically levitated turbine

This allows the friction between the blades and ball bearing can be decrease significantly and thus, minimizes the energy loss. This also helps decrease maintenance costs and increases the life span of the generator.

IV. IMPORTANCE OF MEGLEV TECHNOLOGY

As a efficient upgrade this project prefers an advanced technique, Magnetic levitation for Wind Energy Power Generation. Maglev wind turbines have several advantages over conventional wind turbines. They are able to use winds with starting speeds as low as 4.5 meters per second (m/s). Also they can operate in winds exceeding 40 m/s. It would also increase power generation capacity by 20% over conventional wind turbines and decrease operational costs by 50%. This make the efficiency of the system become higher than the conventional wind turbine The maglev wind turbines will be operational for about 100 years.

Unlike the traditional horizontal axis wind turbine, this design is levitated via maglev (magnetic levitation) vertically on a rotor shaft. This maglev technology serves as an efficient replacement for ball bearings used on the conventional wind turbine and is implemented with permanent magnets. This levitation will be used between the rotating shaft of the turbine blades and the base of the whole wind turbine system.

The turbine uses permanent type of frequently earth magnets (neodymium), not electromagnets and therefore, it does not require electricity to run. This friction between the turbine blades and the base can be reduced significantly and thus produces maximum power output.

V. CALCULATION OF POWER

Power Available In the Wind: -

The power (P) contained in the wind comes from its kinetic energy per unit of time, which can be calculated from the mass flow rate and the wind velocity.

K.E.=1/2 mv^2 (1)

Where, K.E = kinetic energy, m = mass, v  = velocity,

Mass flow rate comes from air density multiplied by volume of air flowing per second

dm/dt=ρAV (2)

Where, ρ = air density, A = swept area, V = wind velocity

Kinetic energy per unit of time is given by :

P=1/2  dm/dt V^3=1/2 ρAV^3 (3)

Thus it can be seen that power in the wind is most strongly influenced by wind velocity because it is proportional to the cube of wind velocity.[5]

To convert the energy to kilowatts, a non-dimensional proportionality constant k is introduced where,

k = 2.14 × 10-3 (4)

Therefore

Power in KW (P) = 2.14 ρAV3 × 10-3 (5)

Where

Air Density (ρ) = 1.2 kg/m3

Area (A) = area swept by the blades of the turbine

Velocity (V) = wind speed

Magnetic Force Calculation:-

Pull force of a single magnet:-

The strength of a given magnet is sometimes given in terms of its pull force— its ability to move (push/ pull) other objects. The pull force exerted by either an electromagnet or a permanent magnet at the "air gap" (i.e., the point in space where the magnet ends) is given by the Maxwell equation:

F=AB^2/(2μ_0 )   (6)

Where

F is force (SI unit: Newton)

A is the cross section of the area of the pole in meters2

B is the magnetic induction exerted by the magnet

μ0 is the permeability of space, which equals 4π×10−7 Tm/A

Therefore, if a magnet is acting vertically, it can lift a mass m in kilograms given by the equation:

m=(AB^2)/(2μ_0 g_n )   (7)

Where gn = gravitational acceleration

Force between two magnetic poles:-

The force between two magnetic poles is given by:                                                                                        

F= (μq_(m_1 ) q_(m_2 ))/(4πr^2 ) (8)

Where

F    is force (SI unit: Newton)

qm1 and qm2    are the magnitudes of magnetic poles (SI unit: ampere-meter)

μ    is the permeability of the intervening medium (SI unit: tesla meter per ampere, Henry per meter or Newton per ampere squared)

r   is the separation (SI unit: meter).

The pole description is useful to the engineers designing real-world magnets, but real magnets have a pole distribution more complex than a single north and south. Therefore, implementation of the pole idea is not simple. In some cases, one of the more complex formulae given below will be more useful.

Force between two nearby magnetized surfaces of area A:

The mechanical force between two nearby magnetized surfaces can be calculated with the following equation. The equation is valid only for cases in which the effect of fringing is negligible and the volume of the air gap is much smaller than that of the magnetized material:

F=(μ_0 H^2 A)/2=(B^2 A)/(2μ_0 ) (9)

Where:

A is the area of each surface, in m2

H is their magnetizing field, in A/m

μ0 is the permeability of space, which equals 4π×10−7 Tm/A

B is the flux density, in T.

Force between two bar magnets:-

The force between two identical rectangular bar magnets

B_x=B_r/π (tan^(-1)'⁡'〖'AB/(2X√(4X^2 '〖'+A'〗'^2+B^2 ))  -tan^(-1)'⁡'〖'AB/(2(L+X) √(4(L+X)^2+A^2+B^2 ))'〗' '〗' )   (11)

     The force between two identical cylindrical bar magnets

placed end to end is given by:

F=[(B_0^2 A^2 (L^2+R^2 ))/(πμ_0 L^2 )][1/x^2 +1/(x+2L)^2 -2/(x+L)^2 ]    (12)

Where:

B0 is the magnetic flux density very close to each pole, in T,

A is the area of each pole, in m2,

L is the length of each magnet, in m,

R is the radius of each magnet, in m, and

x is the separation between the two magnets, in m.

      B_0=μ_0/2 M              (13)

Relates the flux density at the pole to the magnetization of the magnet.

Note that all these formulations are based on Gilbert's model, which is usable in relatively great distances. In other models (e.g., Ampere’s model), a more complicated formulation is used that sometimes cannot be solved analytically. In these cases, numerical methods must be used.

Force between two cylindrical magnets:-

For two cylindrical magnets with radius R and height t, with their magnetic dipole aligned, the force can be well approximated (even at distances of the order of) by,

F(x)=(πμ_0)/4 M^2 R^4 '⌈'1/x^2 +1/(x+2t)^2 -2/(x+t)^2 '⌉'        (14)

Where M is the magnetization of the magnets and x is the gap between the magnets. In disagreement to the statement in the previous section, a measurement of the magnetic flux density very close to the magnet B0 is related to M by the formula, [6]

B_0=μ_0 M (15)

The effective magnetic dipole can be written as

m=MV (16)

Where, V is the volume of the magnet. For a cylinder, this is

V=πR^2 t (17)

When t << x, the point dipole approximation is obtained,

F(x)=(3πμ_0)/2 M^2 R^4 t^2  1/x^4 =(3μ_0)/2π M^2 V^2  1/x^4 ='〖'3μ'〗'_0/2π m_1 m_2  1/x^4              (15)

VI. TEST RESULTS

Table.1 Starting wind speed of wind turbine model

Wind Turbine Model Starting Wind Speed Average Speed(m/s)

Maglev 2.3 2.0 2.6 2.30

Conventional 4.2 4.6 4.8 4.53

Table. 2 The rotational speed of wind turbine model at constant wind speed

Wind Turbine Model Rotational Speed (rpm) Average

(rpm)

Maglev 52 50 51 53 52 51.60

Conventional 27 28 25 26 29 27.0

Table. 3 The time taken by wind turbine model to stop rotation

Wind Turbine Model Time Taken (s) Average(s)

Maglev 12 14 13 13

Conventional 1.5 1.6 1.7 1.6

VII. CONCLUSION

Over all, the magnetically levitated vertical axis wind turbine was a success. The rotors that were designed harnessed enough air to rotate the stator at low and high wind speeds while keeping the center of mass closer to the base yielding stability. The wind turbine rotors and stator levitated properly using permanent magnets which allowed for a smooth rotation with negligible friction. The Vertical Axis Wind Turbine (VAWT) with magnetic levitation performed better than the conventional wind turbine.

Tests results VAWT model has lower starting wind speed compare to conventional one. The rotational speed of maglev VAWT is higher. The time taken for the maglev wind turbine to stop rotating is longer than that of conventional. Therefore, the Maglev wind turbine is more suitable for power generation application. The home for the magnetically levitated vertical axis wind turbine would be in residential areas. Here it can be mounted to a roof and be very efficient and able to extract free clean energy thus experiencing a reduction in their utility cost and also contribute to the “Green Energy” awareness that is increasingly gaining popularity.

The use of magnetic bearing in Wind Turbine is effective, efficient and environment friendly. It increases the performance of wind turbine drastically. Today when the conventional fuel are decreasing day by day, this technology provides a perennial source of energy and that too with much greater efficiency than before. Hence this technology should be developed further for the benefit of mankind.

References

[1] Wind Power Generation in Germany

The Journal of Tran disciplinary Environmental Studies vol. 10, no. 1, 2011.

[2] MAGLEV Data sheets - NUENERGY TECHNOLOGIES

Gonen, Turan. Electric Power Distribution System Engineering. Boca Raton: CRC P,2008.

 [3] "What is Magnetic Levitation?" The Tech FAQ. 29 Apr. 2009

<http://www.techfaq.com/magnetic-levitation.shtml>.

[4] Maglev Wind Turbine Technologies

RFI - Vertical Axis Wind Turbine 200 Mega Watt Off Shore Wind Farm.

[5] Giancoli, Douglas C. Physics for scientists & engineers with modern physics.

Upper Saddle River, N.J: Prentice Hall, 2000.

[6] “Magnet Design”. 2000 Magnet Sales & Manufacturing Company, Inc.

<http://www.magnetsales.com/Design/DesignG.htm>.

[7] Putnam, Palmer Cosslett. Putnam's Power from the wind. New York: Van Nostrand

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