GB2500589A

GB2500589A - Pre-assembled wind turbine for offshore applications

Info

Publication number: GB2500589A
Application number: GB1205202.3A
Authority: GB
Inventors: Kamran Khalid Ghouri
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-03-24
Filing date: 2012-03-24
Publication date: 2013-10-02
Also published as: GB201205202D0

Abstract

A fully assembled wind turbine for offshore applications, where the wind turbine is fully assembled and then transported via a ship to the required location to be connected to the system. Preferably, the wind turbine can be installed on any platform or foundation, such as a floating bed, and the wind turbine may comprise counter or contra rotating dual rotors to reduce the gyroscopic effects. The blades may comprise carbon fibre and be reinforced with Kevlar and there may only be 2 blades on each rotor. Preferably the tips of the blades have a built I weak point to allow the tip to bend completely backwards above a speed of 4 m/s to reduce wake related effects. The front hub may move horizontally towards or away from the rear hub to increase or decrease slip stream effect.

Description

Dual twin bladed direct drive multistage axial generator Wind Turbine designed by Kamran Khalid Ghouri April2008 Scope This offshore wind turbine design covers multiple novel technologies to resolve offshore barge or floating bed mounted wind turbine design issues to ensure operational stability when mounted on a barge/floating bed 200miles from the coast, high efficiency, high output low operational maintenance and high reliability at the lowest possible cost.

Abstract A Carbon fibre designed twin dual blade either counter rotating or synchronous rotating wind energy generating turbine designed for offshore use were the use of counter rotating carbon fibre blades is in order to reduce the gyroscopic effect at the base thus allowing for the use of floating beds and or foundations of a lighter structure than currently possible using prior art. The use of cabon fibre for the blades allows for incremental fibrous movement within the blade structure to automatically adjust for prevailing offshore wind conditions unlike prior offshore wind turbine art.

Technical Field

001 The general field of the invention is for Offshore Wind Turbine electricity generation.

Background

002 There have and are still major challenges in using technology for Wind Turbines which in most cases have been designed for onshore use offshore. Specifically that the majority of previously proposed solutions require the dismantling of the turbine or are supplied pre-dismantled to be shipped to the offshore Wind Farm location on special ships carrying the sub-components of the Wind Turbine such as the tower, nacelle, hub and separate blades which are then assembled using multiple cranes and separate barges or on the same ship. This process is long winded, tedious, prone to ElSE issues, cost prohibitive and is resource and time consuming. The invention allows multiple fully assembled wind turbines to be transported on ordinary ships, barges or surface vessels of loading capability to carry the fully assembled wind turbines to the offshore installation site thus eliminating the need to assemble the components offshore, the need for specialist resources, cranes, multiple ships or tugs or barges and the costs and time wasted in such an exercise that is unique to the prior art. The invention as we will hereafter explain addresses these major offshore installation challenges.

003 The use of 3 bladed turbines further adds to the complexity of transportation and offshore assembly in that it limits the size of the ship in what it can carry due to the size of the blades but also because each blade then has to be lifted individually and located onto the hub offshore which with the high wind and prevailing tide conditions can be awkward. The 3 bladed rotor cannot be easily pre-assembled and transported onto ships in a fully assembled condition because of the large surface area that the 3 blades consume. The invention as we will explain hereafter will address this problem.

004 The use of standard onshore designed blade materials using either glass fibre resin, or glass fibre and a mixture of polycarbonate or even carbon fibre for the spars as the prevalent material technology used today for blade construction has several limiting factors such as strength, high level of distortion during operation that is often uncontrolled, high harmonics, inefficient aerodynamics due to thicker cross sections, turbulence creating effects, increase in wake effects, higher inertia and thus performance losses, excessive weight thus affecting bearing and or transmission drive train life. The invention as we will explain hereafter will address this problem.

Current technology relies on using larger numbers of turbines to extract the energy to deliver electrical power. This in itself may prove cost effective and profitable for the Wind Turbine supplier but is not cost effective or profitable for the end user of electricity who not only has to foot the bill for subsidizing wind turbines in higher tax's but also paying higher electricity bills. The invention as we will explain hereafter will address this problem by extracting more power per installation than is currently possible.

006 Current prevailing technology in use for offshore further add complexity in the design of foundations that are often almost 30% of the cost of offshore wind turbine installation costs. This is because the various solutions either consume a lot of concrete or steel and still have to overcome high gyroscopic forces and wave induced loads that have to be offset by expensive foundations. The invention as we will explain hereafter will address this problem.

007 Current prevailing technology in use today for offshore wind turbines also create large wake related problems that ultimately reduce the efficiency of the Wind Turbines immediately behind the front turbines thus reducing the efficiency of the whole wind farm. Current prior art tries to resolve this issue by either using a bigger surface area to space the Turbines apart or use complex formations that again involve extending the installation envelope of the Wind Farm. These current solutions to address wake effects result in additional costs because either the spacing is more than previously contemplated or that the cables connecting the turbines to the grid have to be extended in length thus increasing distribution losses.

Or the effect is that not so ideal wind conditions are encountered as the scope of the location of the turbines thus increases perhaps beyond the effective wind yield envelope of the original area. The invention as we will explain hereafter will address this problem.

008 Other prior solutions documented also mention the use of counter rotating rotors opposite each other such as U5 2007/0029801, US 2011/0038728, US 2011/0038726, US 2010/0111697 however none of these solutions propose to improve the efficiency of the rear rotor to offset shrouding from the tower or offset limited overall efficiency according to the Betz limit. Furthermore the prior art not ideal to resolve the offshore conditions that are unique (high wind speeds, higher shear loads, simultaneous wake effects etc) and none of them propose the use in an offshore environment such as on hollow concrete floating beds which this invention is designed for although alternative use is mentioned, the unique offshore environment is not. This is like proposing the use of a car designed for the Earth to be used for the moon that experiences different and a harsher operating environmental conditions than the Earth in exactly the same way that Offshore Wind Turbines experience compared to onshore. It is these harsher conditions that this invention addresses using a combination of self adjusting materials for the blades, dual front and rear rotors, aerodynamic features for both the rotors and the nacelle.

The rear rotor works in the slip stream of the front rotor but were the rear blades are trailing or offset to the front blades by 9odegree so that the front rotor has a reduced effect to restricting air flow to the rear rotor is not mentioned in any prior art or invention. Furthermore the design of the nacelle is critical to helping to create the slip stream effect this is also unique to this invention. The invention as we will explain hereafter will highlight the uniqueness of the invention to address these many unique offshore wind related problems not addressed so far until now.

009 Other prior art have mentioned the use of Winglets US 2007/0029801 but not in the context of increasing slip stream effects to the rear rotor. Furthermore the design of the prior art for winglets would probably be unsuitable for offshore use and the invention explains an alternative design were the additional small blade structure is built into the end of the large blade on one single surface using weakened fibrous carbon structures that move into position automatically as the vortex forces increases moving into the correct position to simultaneously increase slip stream effects to the rear rotor. This in contrast to the prior art using fixed winglet forms which also cross over both the leading and trailing edges as shown in the prior art mentioned. The effect of the built in twisting of the blade fibre and its benefits are explained unique to this invention and not explained elsewhere. Additional small blade aerodynamic surfaces can either increase vortex forces or decrease them and this invention shows how the use of a uniquely designed small surface aerodynamic aerofoil to the larger blade can help reduce wake effects not addressed by previous Wind Turbine art.

None of the prior art suggest the use of carbon fibre material for the blade in order to address unique high wind shear loads experienced in offshore wind turbines as well as create built in weak zones in the blade to allow pre-determined controllable blade twisting deformations to increase aerodynamic yield, increase or decrease blade stall angles or increase slip stream effects or reduce wake effects. These features built into the blade fibre material are unique to this offshore wind turbine design in that the unique construction material has the capacity to allow such pre-determined controlled load variations to take place. The invention as we will explain hereafter will address this problem and explain the additional benefits of the use of carbon fibre in the construction of the blade, the nose and Nacelle for the purpose of improving the electrical yield and performance close to the Betz maximum possible efficiency for Wind Turbines.

011 The design also incorporates an outer Bernouli Nacelle to increase laminar flow to the rear rotor without shrouding either the front or rear rotor but guiding front low pressure air over to the rear rotor to further increase slip stream effects using Bernouli principles. These additional features unique to this design will be explained hereafter.

012 The design uses either multiple direct drive generators or a single multi stage multiple vertical rotor and stator disc system to substantially increase power produced in a compact housing. This design is new and not proposed for Wind Power until now.

Detailed description of invention

013 Novel Installation The twin dual blade design for offshore can be assembled in the harbor and placed each one fully assembled onto a ship which can then carry as many fully assembled wind turbines as its size can permit.

Because there are only two blades either end of the nacelle the blades can be orientated in the same direction as the tower thus allowing the turbine to be loaded fully assembled which is not possible using the 3 bladed design. The fully assembled turbines can then be assembled offshore onto either prefabricated monopole, multipile, floating bed, or other locating points, surfaces or retention features.

014 The wind turbine is located on special flexible transport fixtures that allow the entire wind turbine to be transported and lifted without removal of the transport fixtures which are built into the tower, Nacelle and blades. The fixtures within the nacelle also lock the generator and drive train mechanically so that there is no unsafe movement that would cause damage to the drive train and generator during lifting and transportation. The base fixture of the tower is located such that when the nacelle is lifted the base rotates into the floor of the ship thus allowing the whole structure to rotate into the vertical position easing the vertical hoop stress loads to a ensure that the tower does not buckle at the base and also allowing a single crane to lift the entire structure onto the foundation.

The ability to transport both front and rear blades fully attached to the hub onto the nacelle on a fully assembled wind turbine structure further reduces installation complications and waiting for low wind conditions in which to install the blades as this is now made redundant by the fact that the entire Wind Turbine is fully assembled on installation to the foundation and only the time to install onto the foundation and connecting the electrical ancillaries and commissioning is required.

016 The cost of installation and time of installation to the time the wind turbine is generating useful power is dramatically reduced by having a full pre-assembled wind turbine -this cost can be up to 25% of offshore

wind turbine costs based on prior art.

017 Blade Design The blades are made from preformed carbon fibre with Kevlar reinforcement that can be processed and produced using automated assembly processes negating costly lay up manual processes Fig 4.

018 The wind turbine incorporates two front blades and two rear blades each with preformed and pre-stressed carbon fibre skins that allows for variation in the loading of the fibres thus allowing controlled deformations such as twisting and curling to take place in order to adjust to the prevailing environmental loading conditions. The use of carbon fibre to automatically adjust to aerodynamic needs and the inherent strength found using this material allowing for thinner and lighter blade configurations than current prior art creates considerable flexibility to run the turbine at wind velocities beyond 28m/s which is the cut off

point for most prior art offshore wind turbines.

019 The carbon fibre Kevlar reinforced blade design incorporates torsional adjustment flexibility along the trailing edge of the blade to further enhance energy generating performance at both high and low wind speeds. At high wind speeds the trailing edge of the blade bends curling the surface to allow reduced drag resistance however at lower wind speeds the trailing edge remains in position to capture as much wind as possible this allows for more alternate shapes and forms of the blade so as to increase the wind capture capability at the root of the blade previously not feasible due to the very large thickness at the root of the blade using glass fibre pre-preg material.

The root of the twin dual rotor wind turbine blade is 20% less than for a lOOm length blade than would be possible using predominant prior art material this allows for a lighter, stronger and more aerodynamic configuration especially at the root of the blade to allow greater air pressure to be created and thus lift than using current prior art materials or blade forms.

021 The special shape and form of blade is possible by using various carbon material fibre strengths orientated such that the fibres of the carbon fibre blade material either result in increased strength or greater flexibility to twist without inducing unwanted shear and strain loads. This is achieved throughout the entire length of the blade so that the leading edges have built in movement of the fibres so as to either incrementally increase lift or decrease lift this is also the case for the trailing edges optimizing flow and stall angles simultaneously reducing turbulence and vortex related wake generating conditions.

022 The tips of the blade have additional built in weak points allowing the tip to bend completely backwards above speeds of 4m/s in order to reduce wake related effects. The adjustment is further increased by further twisting in the vertical plane of the net aerofoil to reduce the size of the vortex and increase the front slip stream effect to the rear rotor.

023 The front blades can either counter rotate to the rear blades to reduce moments to allow stable operation on floating barges that would otherwise make the barge unstable 200 miles out in the sea from the coast, or the blades can rotate in the same direction to the front blades if gyroscopic forces do not need to be reduced such as on a onshore application or a standard foundation such as a monopole but not restricted to such a foundation.

024 The effect of counter rotation is electronically controlled to ensure that the maximum gyroscopic loads are significantly reduced by also moving the hub either away from the rear hub or decreasing the distance so as to increase the slip stream effect to the rear rotor which adds additional rotational lift by increasing the rear rotor turning moment and thus increasing the rotational velocity of the rear rotor to produce more electricity and improve overall efficiency.

The movement of the front hub on its horizontal plane either inwards or outwards to the rear hub to either increase slip stream effects to the rear hub to increase rear rotor rotational velocity also has the advantage of decreasing horizontal loads into the drive train and generator. The movement of the front hub along its horizontal axis is achieved either by a electric motor moving the hub on a screw thread, or a hydraulic ram moving the main shaft inwards or outwards.

026 The blade is harmonically balanced and incorporates inertia mass weights to balance the moments of inertia to ensure that the blade rotates in balance without increasing noise and vibration.

027 The hub and main shaft are also dynamically balanced to ensure that the rotation of all rotary parts are balanced thus increasing the reliability of all dynamic parts and ensuring tighter machine tolerances than would otherwise be possible. This allows for greater blade spans and thus greater yield than what is presently possible exceeding 35 year life cycles (achieved through Highly Accelerated Life Cycle Testing or HALT Accelerated Life Cycle Testing ALT).

028 The turbulence from each of the blade tips is reduced by the bending of the tips creating additional surface aerodynamic features to reduce wake related effects thus allowing multiple floating barges or fixed foundations behind the front floating barges or fixed foundations to carry additional counter-rotating wind turbines whose blades also have the same aerodynamic features thus not requiring complex wind farm formations and positioning of the Wind Turbine although this may also help improve yield.

029 Both front and rear blades can either have the teetering loads and subsequent movements either built into the carbon fibre blades at the root using selective carbon fibre fabric strengths or the a elastomer cushion in the hub is incorporated with a central pivot pin allowing up to two degrees of movement in the vertical axis at the pivot point to take place. The elastomer is placed at the front and rear of the blade hub pivot section located in the centre in between mounting plates at the front and at the rear section allowing the blade hub section to move to allow loads to be dissipated into the elastomer section which acts as a buffer.

The entire teetering mechanism is encapsulated by the aerodynamic slip stream inducing nose cone so that the extreme environmental effects are prevented from creating wear related problems.

031 Due to the carbon fibre material being used instead of glass fibre for the entire blade weight savings are approx 35% with the corresponding improvement in moment of inertia and reduced loads to rotate the blade and significant reduction in subsequent bearing loads on the generator increasing bearing life, cost of manufacture and reduced O&M costs.

032 Rear Blade The rear blades have a slightly smaller blade length compared to the front by a factor of up to 7/8 this is to allow the vortex and wake inducing loads to be offset and have a reduced effect to the aerodynamics of the rear rotor. The rear rotor also has either forward facing carbon fibre based twisting aero-foils at the tips on a single lead surface so that surface area presented to the front tip vortex loads instead creates better slip stream effects in the same way that a forward facing wing has to a rear swept wing on an aircraft especially at higher tip velocities. The blade tips on the rear rotor can also be facing rearwards in the same way as the front blade dependant upon prevailing environmental operating conditions and Wind Farm Wind Turbine Locations.

033 To offset reduced wind energy arriving at the rear blades the front blades lead the rear bladders by at least 9Odegrees so that clean air arrives at the blade surface. The rear blades are configured so that both front and rear rotors loads are balanced and movement is synchronized electronically with each other with the rotor brake control adding additional control to ensure that the rotors are synchronized to ensure maximum aerodynamic efficiency.

034 Direct Drive Axial multi stage stator and rotor permanent magnet Generator Energy from the rotor is transferred directly to the generator via a direct drive axial permanent magnet generator that has its permanent magnets and stator windings incorporated into multiple rotating discs.

Each disc caries the permanent magnets and stator windings were the magnets have their opposing poles facing each other unlike conventional permanent magnet direct drive generators where the magnets are incorporated along the perimeter of the rotor.

036 Both front main shaft and the rear shaft carry the rotor each carrying multiple discs that turn within the static stator which in turn carries permanent magnets and stator windings were the magnets have their opposing poles facing in between the discs attached to the rotor thus creating multiple magnetic flux shear.

037 Since the stator is static it can carry the wiring carrying the electricity generated without need for brushes and or slip rings.

038 The advantage of placing the magnets axially onto discs is that multiple discs can be incorporated thus increasing generating power very easily only increasing the length of the generator. Additional rotor and stator discs can be added in the form of cassettes that can be easily inserted thus increasing generator power without removing the whole generator giving additional flexibility and ease of maintenance where the discs can be replaced without removing the generator further increasing operational life.

039 The axial design means that there is zero cogging, reduced spiking effects and substantial increase in corresponding torque for each multi stages. The axial design can either be air cooled via the blades built in cooling vanes and or water cooled in a surrounding water jacket.

Dual direct Drive Permanent Magnet generator option Instead of a single combined dual multistage generator two similar large direct drive permanent magnet generators each driving their own rotor attached to the combined generator and main foundation casting which is the P being protected. Fig 3 041 The Generator combined mounting, foundation and tower bearing casting allow the loads to be transferred to the base of the tower. Tower

042 The top section of the tower is a complete aerodynamic structure directing and accelerating front air to the rear rotor creating a slip stream effect allowing the rear rotor to accelerate to offset inefficiencies related to the shrouding effect of the tower to the rear rotor.

043 The main bearing is located one fifth from the top of the tower to reduce shrouding of the air to the rear rotor. This part of the tower moves in the direction of the wind allowing the air to accelerate to the rear rotor. Fig 2

Claims

042 What is Claimed 01 A complete fully assembled Wind Turbine for offshore that does not require prior disassembly or does not have to have its main components such as tower, nacelle, hub, blades assembled offshore prior to installing onto a foundation. The entire Wind Turbine is transportable onto sea worthy surface ships/barges fully assembled and only needs to be installed onto the foundation and have the electrics connected and commissioned.

02 This a fully dedicated offshore wind turbine that can be installed effectively on any platform or foundation including floating beds were the turbine would then operate its twin dual blades in a counter rotating fashion to reduce the effects of gyroscopic forces that could create undue unstable turning moments in the base of the floating foundation. In other words it is designed specifically to be installed on floating foundations creating a stable platform on which to generate electricity than a 3 blade design mounted on a floating bed.

03 The Wind Turbine has built in transport fixtures both at the base of the tower and in the Nacelle negating the need for additional fixtures to transport the entire fully assembled wind turbine which can then be transported by sea on almost any ship and assembled without the need for special fixtures reducing costs and the use of special ships.

04 The use of dual front and rear blades is mainly to ensure that the entire wind turbine in the fully assembled condition can be transported on any surface vessel easily with the blades parked in the same direction as the tower not feasible with a 3 bladed design.

The Fully assembled Wind Turbine can be installed onto the foundation with limited operations, limited equipment, limited resources, limited time, limited cost, limited number of additional vessels whencompared to a prior art 3 bladed design.

06 Both the front and rear blades are manufactured from pre-formed and pre-preg carbon fibre material with Kevlar re-enforcement specifically to allow lighter, stronger, longer and bigger blades for offshore use.

07 Both front and rear carbon fiber Kevlar reinforced blade design incorporates torsional adjustment flexibility along the trailing edge of the blade to further enhance energy generating performance at both high and low wind speeds. At high wind speeds the trailing edge of the blade bends curling the surface to allow reduced drag resistance however at lower wind speeds the trailing edge remains in position to capture as much wind as possible this allows for more alternate shapes and forms of the blade so as to increase the wind capture capability at the root of the blade previously not feasible due to the very large thickness at the root of the blade using glass fiber pre-preg material.

08 The root of the twin dual rotor wind turbine blade is 20% less than for a lOOm length blade than would be possible using predominant prior art material this allows for a lighter, stronger and more aerodynamic configuration especially at the root of the blade to allow greater air pressure to be created and thus lift than using current prior art materials or blade forms.

09 The special shape and form of blade is possible by using various material fiber strengths orientated such that the fibers of the carbon fiber blade material either result in increased strength or greater flexibility to twist without inducing unwanted shear and strain loads. This is achieved throughout the entire length of the blade so that the leading edges have built in movement of the fibers so as to either incrementally increase lift or decrease lift this is also the case for the trailing edges optimizing flow and stall angles simultaneously reducing turbulence and vortex related wake generating conditions.The tips of the blade have additional built in weak points allowing the tip to bend completely backwards above speeds of 4m/s in order to reduce wake related effects. The adjustment is further increased by further twisting in the vertical plane of the net aerofoil to reduce the size of the vortex and increase the front slip stream effect to the rear rotor. Fig4 liThe effect of counter rotation is electronically controlled to ensure that the maximum gyroscopic loads are significantly reduced by also moving the hub either away from the rear hub or decreasing the distance so as to increase the slip stream effect to the rear rotor which adds additional rotational lift by increasing the rear rotor turning moment and thus increasing the rotational velocity of the rear rotor to produce more electricity and improve overall efficiency.12 The movement of the front hub on its horizontal plane either inwards or outwards to the rear hub to either increase slip stream effects to the rear hub to increase rear rotor rotational velocity also has the advantage of decreasing horizontal loads into the drive train and generator. The movement of the front hub along its horizontal axis is achieved either by a electric motor moving the hub on a screw thread, or a hydraulic ram moving the main shaft inwards or outwards.13 The hub and main shaft are also dynamically balanced to ensure that the rotation of all rotary parts are balanced thus increasing the reliability of all dynamic parts and ensuring tighter machine tolerances than would otherwise be possible. This allows for greater blade spans and thus greater yield than what is presently possible exceeding 35 year life cycles (achieved through Highly Accelerated Life Cycle Testing or HALT Accelerated Life Cycle Testing ALT).14 The turbulence from each of the blade tips is reduced by the bending of the tips creating additional surface aerodynamic features to reduce wake related effects thus allowing multiple floating barges or fixed foundations behind the front floating barges or fixed foundations to carry additional counter-rotating wind turbines whose blades also have the same aerodynamic features thus not requiring complex wind farm formations and positioning of the Wind Turbine although this may also help improve yield. Fig 4 Both front and rear blades can either have the teetering loads and subsequent movements either built into the carbon fiber blades at the root using selective carbon fiber fabric strengths or the a elastomer cushion in the hub is incorporated with a central pivot pin allowing up to two degrees of movement in the vertical axis at the pivot point to take place. The elastomer is placed at the front and rear of the blade hub pivot section located in the centre in between mounting plates at the front and at the rear section allowing the blade hub section to move to allow loads to be dissipated into the elastomer section which acts as a buffer.16 The entire teetering mechanism is encapsulated by the aerodynamic slip stream inducing nose cone so that the extreme environmental effects are prevented from creating wear related problems in the teetering mechanism. Fig 1 17 The rear blades have a slightly smaller blade length compared to the front by a factor of up to 7/8 this is to allow the vortex and wake inducing loads to be offset and have a reduced effect to the aerodynamics of the rear rotor.18 The rear rotor also has either forward facing carbon fiber based twisting aerofoil's at the tips on a single lead surface so that surface area presented to the front tip vortex loads instead creates better slip stream effects in the same way that a forward facing wing has to a rear swept wing on an aircraft especially at higher tip velocities.19 The blade tips on the rear rotor can also be facing rearwards in the same way as the front blade dependant upon prevailing environmental operating conditions and Wind Farm Wind Turbine Locations.To offset reduced wind energy arriving at the rear blades the front blades lead the rear blades by at least 9odegrees so that clean air arrives at the blade surface. Fig 3 21 The rear blades are configured so that both front and rear rotors loads are balanced and movement is synchronized electronically with each other with the rotor brake control adding additional control to ensure that the rotors are synchronized to ensure maximum aerodynamic efficiency.22 Energy from the rotor is transferred directly to the generator via a direct drive axial permanent magnet generator that has its permanent magnets and stator windings incorporated into multiple rotating discs.Each disc caries the permanent magnets and stator windings were the magnets have their opposing poles facing each other unlike conventional permanent magnet direct drive generators where the magnets are incorporated along the perimeter of the rotor.23 Both front main shaft and the rear shaft carry the rotor each carrying multiple discs that turn within the static stator which in turn carries permanent magnets and stator windings were the magnets have their opposing poles facing in between the discs attached to the rotor thus creating multiple magnetic flux shear. Fig 124 The advantage of placing the magnets axially onto discs is that multiple discs can be incorporated thus increasing generating power very easily only increasing the length of the generator. Additional rotor and stator discs can be added in the form of cassettes that can be easily inserted thus increasing generator power without removing the whole generator giving additional flexibility and ease of maintenance where the discs can be replaced without removing the generator further increasing operational life.The design also incorporates an outer Bernoulli Nacelle to increase laminar flow to the rear rotor without shrouding either the front or rear rotor but guiding front low pressure air over to the rear rotor to further increase air flow over the low pressure area of the rear rotor root area creating a more effective slip stream effects using Bernoulli principles. Fig 1 26 Instead of a single combined dual multistage generator two similar large direct drive permanent magnet generators each driving their own rotor attached to the combined generator and main foundation casting which is the IP being protected Fig 1 027 The Generator combined mounting, foundation and tower bearing casting allow the loads to be transferred to the base of the tower.028 The top section of the tower is a complete aerodynamic structure directing and accelerating front air to the rear rotor creating a slip stream effect allowing the rear rotor to accelerate to offset inefficiencies related to the shrouding effect of the tower to the rear rotor. Fig 1 029 The main bearing is located one fifth from the top of the tower to reduce shrouding of the air to the rear rotor. This part of the tower moves in the direction of the wind allowing the air to accelerate to the rear rotor. Fig 2 Advantages of the multi-stage permanent magnet rotating disc based generator 1. No need for converters although these can be added as separate items if required
2. Powerful generator with high torque with direct drive via twin rotating shafts
3. Easy scale up of generator output via additional multi stage stators and rotors through an axial drive rotating disc arrangement that holds the permanent magnets and windings axially saving space
4. Easy access to the rotating discs as they are coupled via a slotted shaft that carries a set number of discs that are incorporated into an easily insertable cassette to increase generator output without replacing the generator
5. Ease of maintenance of generator as the discs carrying the permanent magnet are un-shrouded and easily accessible and replaceable as they are on a slotted shaft arrangement that can be removed in the form of a cassette.
6. Permanent magnets un-shrouded using both poles rotating against static stator discs
7. Stators fixed within housing
8. High torque
9. No cogging
10. No arcing or limited spiking
11. Instant ramp up
12. Low maintenance
13. High reliability/High life