Loading

Mega May PDF Sale - NOW ON! 25% Off Digital Certs & Diplomas Ends in : : :

Claim My Discount!
Study Reminders
Support
Text Version

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Okay so typically if you see in this is sort of a summary we will come back to summary again as we close the class. So, it typically, for example, the rotors many of the companies these days have been using glass fibre reinforced plastics. So, plastic-based blades rotor blades are being made quite regularly. So, the most common one that you typically see as you you know if you drive around and see wind turbines a certainly most places in India and even internationally they are some plastic-based blade that you are seeing. And the glass fibres are included there to give them you know good stiffness and strength and people are looking at various types of fibres, usually, you are looking at high strength and high fatigue we will talk about these in a short while. The nacelle houses all of these in the yaw drive that we spoke about to and then there is something forbade blade pitch change we will look at that shortly; coolants, brakes, bearings, shafts, controllers and it has you know it could be made of steel or aluminium or other such materials and it would also have such parts in it. The gearbox has something called epicycle gears we will discuss that shortly, but it may get eliminated. So, that’s again something that we will look at shortly in the in this class. Most of the generators are requiring permanent magnets and so these magnets are present and you have a fair bit of copper inside that permanent magnet and the tower itself consists of either prestressed concrete or steel or some combination there off. So, broadly although I am going to get into the details of most of these parts in just a moment this slide sort of captures a reasonable summary of what you are going to see and then we will look at them in greater detail. (Refer Slide Time: 20:25) Okay so if you actually look at these parts and I also got together some data which tells us what is the relative cost to weight ratio okay. So, if you look at that you have here the rotor, the nacelle, the gearbox, the generator and the tower. So, if you look at it the if you take the tower, for example, it is an extremely heavy part of the structure. More than almost 50 per cent or even more than 50 per cent of the weight of the overall wind turbine is essentially the tower okay. So, the tower is pretty much the main heavy component of the structure and, so if you look at costs to weight ratio. So, if I have cost by divided by weight right it has a very high weight. So, it has some amount of cost, but significantly more weight is there. So, relatively you have you know the lower cost and higher weight associated with the tower it does have cost it is not that it is you know free or any such thing. In fact, in terms of transportation costs and all, there is a lot of things involved with the tower. So, cost to weight if you see that is it. The generator is in the scheme of the overall scheme of things relatively the cost is more and as a fraction of the overall weight it is also reasonably heavy, but it is not that heavy. So, the generator has this kind. So, you can see the cost factor is higher weight factor is a little bit relatively less. The gearbox is also is similarly you know it’s only one small component relatively speaking in terms of the overall structure. So, weight is also somewhat mediocre the cost is also mediocre and I will say that you know the gearboxes there is a very large industry which makes gearboxes for a wide range of applications. So, in terms of mass production gearbox is perhaps the relatively less costing component simply because there is such a large industry which produces gears for so many different applications automotive applications and a wide range of other applications require gearboxes. So, gearboxes are available in in a sort of a generic form or at least you can order a particular gearbox and it’s not going to be that complicated for some manufacturer to make it. Of course, specifications may be different. So, you might have to make something specific, but the industry is already in place. The tower, on the other hand, is very specific to the wind turbine, the specific tower that you use for the wind turbine is an onsite construction of in many ways and therefore, of course, the materials use our common materials relatively speaking. So, you are using concrete and so on, but it is still it is something that at least has to be assembled block by block in that location or built-in that location. Generators also are you know available in a wide range of capacities you know several tens of kilowatts to megawatts generators are available. So, again there is an industry associated with that from where you can get it. The nacelle and the rotor the nacelle is just the casing and the box that holds everything together. So, that is, of course, going to be specific to that particular wind turbine so, but it is not I mean it holds everything together functionally it keeps everything you know enclosed and in a compact, but beyond that, it is not you know very expensive part of the turbine so to speak and even functionally it is not the most critical in terms of the requirements of the overall turbine. The rotor on the other hand is very functionary very critical. So, this is the most critical. In some fundamental sense it is most critical because the design is very specific to the wind turbine I mean, of course, it takes you makes use of aerodynamic principles which are there I mean which are common across a wide range of you know technologies. But it is in terms of sizing you typically don’t have blades this size being used for almost anything else. So, manufacture of these blades is a challenge you need to make you know 60 meter long blades which is not a common thing that is done in most places. So, that takes some effort and so there are companies which specialize in it. So, it is not a mass-market product in the sense that you do not find a wide range of companies making these blades there are companies which specialize in this kind of activity which make these blades unlike say gearboxes. Gearboxes also if you want to get technical about them are you know a sophisticated piece of equipment, but it is not, it is still distinctly more commonplace because a wide range of technologies use them, but these blades in the manner that they are made for the windmills or wind turbines are exclusively only for the wind turbine. So, the wind turbine industry is pretty much the only customer for the blades of this nature. So, and it is also the first part that interacts with the wind and therefore, it defines many of the characteristics they are required of the rest of the turbine and places limits on what the turbine can do it also places an upper limit in terms of what we can expect from the turbine. So, given all this, that’s perhaps the most critical part of the wind turbine and even in terms of costing it is significantly expensive. (Refer Slide Time: 26:00) Okay so if you look at rotor blades. So, we will start with the rotor blades and see what materials are used what are some issues associated with them. So in fact, commonly these days as I mentioned composites is what is being used mostly it is glass fibre reinforced, glass fibre reinforced, but people are also looking at other reinforcements. So, you can have carbon fibre-based carbon fibres can be used carbon nanotubes are something that people are looking at. Primarily to ensure that it has a lightweight and many other properties, but lightweight and strength are two you know dominant properties, but many of the other properties are also there we will discuss them in detail in just a moment. But glass fibre and carbon are significantly being used. You may wonder why we mentioned steel and aluminium it appears to be a little bit old fashioned, but actually, it is both old fashioned and current. So, in many ways this the metal industry is like that we always keep thinking that you know you can get by without the metals and move way to something else which is all plastic and so on, but there are significant both performance issues, as well as environmental issues associated with the nonmetallic materials including you, know polymers and plastics that are used. So, the first thing most important thing with about all these plastics is that since you don’t want them to degrade very easily in the environment, you don’t want them to get spoiled, they are typically not biodegradable the ones that are used. So, that may not seem like much when you know you just have one wind turbine being set up in one locality, but if you are looking at you know trying to power a significant fraction of the world using wind energy then you are going to have wind turbines all over the place right. So, it is estimated that you know pretty soon we will have 15 20 per cent of the worlds energy requirements being met by wind turbines and a lot of countries are pushing hard to you know to get these wind turbines located in as many places as possible. So, then we have an issue it is not just one turbine you are looking at hundreds of thousands of wind turbines maybe even millions of wind turbines distributed across you know various locations. Again when it is new it doesn’t seem like an issue at that point only the manufacturing issue is there because there will be chemicals associated with that and you have to find a way to you know either consume the chemical completely or dispose of its safety. So, that disposing of waste safely. So, that issue is always going to be there. Any of these fibres, glass fibres etcetera can be you know hazardous. So, you have to worry about those glass fibres carbon fibres etcetera you have to worry about those in large scale manufacturing processes, but more importantly, if you put a million turbines out there or you know say tens of millions of turbines out there they will all have some finite lifetime. So, you are looking at you know let’s say 30 years down the road something like that let us say 20-30 years down the road when suddenly these turbines come to the end of their life say eventually those blades start wearing out or they start cracking up in some way and then and let’s say they reach a point when eventually they are beyond repair at that point you will have to dispose of those blades. Then when you have about a hundred million you know or maybe say 10 million such windmills around and they are all discarding their blade, blades you have a huge environmental mess. So, in the form of while you are addressing the environmental issue by using this wind clean energy solution of wind energy you have to be aware that how you use that wind energy shouldn’t create a problem again 20 years down the line right. So, we have to guard against that right away. So, that is where things like steel and aluminium still have a significant role to play. So, if you take steel and aluminium there is no problem at all in terms of recycling it you simply have to heat it melts it back and then you can recreate the blade in whatever manner you want you can always or you can even just do heat treatment to relieve any stresses etcetera if it is possible may not be that easy because it’s a longish structure and then you know bring it back into service. So, in terms of recycling ability the traditional materials are actually like steel and aluminium are still very promising and the steel and there is also a large industry there is a steel industry there is a lot of machine tools industry there is a machining industry etcetera. So, even if you want to change shapes you want to get some complex shape etcetera there is a lot of people, there are a lot of people who are experienced in this area and a lot of industries that are there a lot of machinery that is already in place which can create what you want. And therefore, this is still an industry that competes in almost any technological sphere and the windmill or wind turbine sphere is not an exception. So, there also you have the metal industry trying to make its case and I mean people are continuously doing research to see if that can be done, but still as of now what is coming out is typically composite. So, that is the largest contributor at this point to the rotor blades. So, what are we looking for? Of course, we are looking for lightweight this is important because the wind has to push the turbine right, it has to or rather I mean the base based on the lift that is generated the turbine should start rotating now the heavier the turbine is due to gravitational forces etcetera you are going to have a lot of inertia right. So, you are going to have a lot of inertia you have to push past the inertia and to get this or you have to have enough lift which is over and above this inertia to get this turbine to rotate. So, it may not move as effectively and therefore, lightweight is a very important aspect of the turbine design. So, inertia is an issue okay. So, this is inertia is an issue. Fatigue resistance, fatigue is the idea that materials deteriorate or fail at loadings well below they are rated loading. So, you take a material you do a test to make a new component you do a test you put a tensile test and you would you know pull it apart and see at what level of loading the material fails okay. So, based on some standards and standards ways of testing you can say that you know the failure of this material will happen at this load if you make this is the material with these standard dimensions failure will happen at this load or this stress value okay some specific stress value it will fail. So, the stress will take care of the cross-sectional area you do not have to worry about whether it’s a larger part of a smaller part all that is accounted for if you look at the stress it's normalized concerning the cross-sectional area. So, its load per unit area. Now, that will be some reasonably high value let’s say there is some particular value and therefore, you feel that this is adequate for the utility that you are trying to put this structure too, but if you have cyclic loading and almost all components in regular use have some cyclic loading right. So, cyclic loading in the sense you load the component a little bit then you release the component it could be anything if you are on a vehicle. So, the vehicle goes over bumps and you know various roughness factors in the road just because it goes in you know the poorly built road does not mean all the parts in the vehicle have failed. But those parts have been stressed in one direction and stressed in the other direction repeatedly, but with very small stress levels the stress level was not so, high enough to damage the part, but it did go through an increase in stress, a decrease in stress, increase in stress, decrease in stress and it may not even have been periodic it will just go up and then stay up for a little while and then suddenly drop down come back up etcetera. So, you will have a wide range of loading. So, people test that for tests to see if the materials will fail under such cyclic loading conditions okay. So, it’s generally found that our large vast set of materials have a situation where if you put them through cyclic loading and of course, in an in a systematic test you put them through a known frequency loading and known you know load level etcetera when you do that you find that many of these materials will fail at a value of stress which is significantly lower than the rated stress of that material. So, you did the original test and you came up with some value, but under cyclic loading even though you are loading it up with much less load just because it is cycling repeatedly over a long period it fails. So, fatigue is very important and this phenomenon is called fatigue. So, it is repeatedly loading and unloading a structure and it tends it will fail at a value of load significantly less than the rated load. So, the fatigue is very important for most structures which are facing cyclic loading and a wind turbine is a classic example of it because the wind will come on at some point wind is not going to be steady you will have wind you know velocity is continuously varying even as you know over several minutes. So, you will have suddenly a slightly faster way and slightly slower wind. So, you push the blade a little bit more, it comes back to the front direction even as and that is also that is when you have just variations in the wind flow. Even if you take the windmill structure itself if you look at the fact that you have a blade there, and a blade here and I am just drawing two blades at the moment and let’s say you have a tower here. Then clearly the blade that is at the bottom is getting some shielding because there is a tower right behind it right whereas, the blade at the top is not getting any shielding because there is nothing behind it. So, even if the wind were steady you have a steady breeze that is flowing as the blade rotates through the, you know through its standard cycle. When it comes to the top or for a significant fraction of the cycle it is you know not having anything the back and so the wind is continuously relatively uniform, but then when it comes down and it gets shielded by the or gets some kind of you to know blockage effect because there is a tower right behind it suddenly there is a drop in the wind loading on the blade. So, the stress on the blade suddenly decreases as it comes off the shadow of that the tower it will again go up in loading. So, you are guaranteed that in every circle, every circle that it makes the there will be cyclic loading you will be loaded up and then you will release the load you will again load it up and so on. So, every cycle that every time it rotates once, it is going to be loaded once and released after that and every blade is going to undergo this. So, you are guaranteed of cyclic loading. So, this is guaranteed to happen. If the windmill is operating you are guaranteed to have cyclic loading. So, this is something. So, therefore, we need to look at fatigue resistance. The strength is overall loading that is there because of you know its weight the wind that is pushing against it etcetera. So, you do need to have significant strength and you are looking at longer and longer blades because that helps you reach access more you know higher wind speeds etcetera. So, that is something we have to look at. Stiffness, so this relates to the integrity of the shape. So, if the blade is not stiff then it will a flap around in the winds in strong winds and you have to keep in mind that there is not much of a distance here between the tower and the blade. So, if the blade were twisted too much it can even hit the tower right if it were not so stiff and it and you could you know go down go backwards. So, the wind if the blade tended to was not so stiff and it could just bend backwards it can even hit the tower. So, for a wide range of wind speeds, you have to be confident that the blade is stiff enough that it will not go and hit the tower. So, that’s something that you have to keep in mind. And that is why again you have some rating some wind speed rating and you say that you know it is only within the scope of this rating that you will use this wind turbine if the wind speeds are higher you will stop the turbine. Then there is the issue of how it interacts with the environment. So, given that it is out there you are not you know shielding it in any manner you are just putting it out there in the sum. So, it is going to face a lot of heat and cold. So, the cyclic temperature is going to be there, the night it is going to be cold, the day it’s going to be hot. There’s a lot of humidity you could have rain you could have dry conditions a wide range of conditions and of course, lightning strikes you are going to put this out there and you are bound to have I mean it is guaranteed to have lightning hits because you have put this tall structure out there and typically an open area you put a tall structure that is exactly what is required to you know to attract lightning and it will get a lightning strike. So, you have to be prepared that materially it is in a position to handle it there are lightning arresters. So, there are ways to take the lightning hit down to the ground and have it grounded okay. So, this is something that you have to be worried about. And of course, as I mentioned right at the beginning blade recycling in terms of material recycling and this is something which may not be an issue today because today is when we are you know all into this wind energy field and every country is putting all this effort to put these windmills out there if you look 30 years down the line this is an issue. And this is something that we need to address right away. We have already made this mistake in the past where we said you know oh we found petroleum great, let’s use the petroleum that is exactly why we are in this situation today that we need to worry about the environment right. So, 30-40 years of extensive petroleum usage and we suddenly have this problem and now we have to do something urgently to deal with it. So, we don’t want to wait 30 years and then have a major problem we would like to address it ahead of time so that we are, because now we are seeing this cycle of you know how something we use hits us 30 years down the line. So, we might as well plan for it and you know do something appropriate. So, that’s the rotor blades I spend significant time on it because it is the as I said the most important critical part of the wind turbine and the first part that gets the whole thing operational. (Refer Slide Time: 39:32) Then you have the tower, the tower structure itself. As I said mass wise that is the most massive of part of the wind turbine in structure, the blades are very light, the tower is quite heavy. So, it has to deal with wind shear this is simply the variation in wind speed as a function of altitude, it may not be much I mean it may be you know the difference of say 10-20 kilometres per hour something like that. So, for example, if you double the height of the structure your wind speed increases by about 10 per cent okay so, but at the same time, it’s a difference of 10 per cent of stress from the top of the structure to the bottom of the structure and it is there continuously, I mean based on you know the height of the tower. So, you have to have a structure that deals with this wind shear and does not get affected by it. As I said we are always interested in increasing the height of the wind turbine because the power available in the wind increases as the cube of the velocity of the wind. So, if the wind speed, for example, you double the height of the structure right and I said wind speed goes up by a factor of 10 per cent. So, if you have wind original wind speed was v we now have 1.1 v, 10 per cent mode. So, what will happen to the power? If you originally had P if you do the calculation this is 1.1 into I mean 1.1 into 1.1. So, 1.1 cubed is what the power will become times P and that is approximately equal to some 0.3 some something some 1.33 p something like that approximately. So so, this means this is approximately 30 per cent increase, by doing nothing by simply pushing the windmill to a higher location that’s it you just pushed it to a higher location it caught you 33 per cent or not that, it is some 30, 30 plus per cent of the increase in power that’s a huge increase in power for you know nothing else changing everything else is the same you simply push the windmill up to a higher location you are getting 30 per cent more power. So, naturally, there is you know interest to get this windmill to be as high as possible so that you can get this benefit out of the power that is available and therefore, people try to have tall towers. But at the same time if you double the height of the windmill you are going to have to also double you have to also do something about the diameter of that tower so that it stays stable and usually. That means, 4 times the diameter these are you know approximate numbers they do not they are not hard and fast numbers it will depend on the type of structure you are making and all, that just to give you an idea that material required for that turbine is going to I mean for the tower itself is going to go up significantly if you sort of double the height of the turbine. The material choice will impact things like transportation and construction of that structure because if you are using, for example, there are people who use tubular stainless steel based structures. So, those tubes have to be transported to that site and, concerning windmill construction, this transportation is a fairly significant activity maybe over the lifetime of the wind turbine the cost is perhaps not that much it is distributed across the cost of that lifetime. But still, transportation is a major activity if you ever go to one of these sites where they are setting this up you have to keep in mind that let’s say even the wind windmill blade is you know say 50 meters long. So, you need to actually have a truck which has 50-meter long carrying capacity behind it and place this you know single blade there and then carry it carefully to that site. So, it is a fairly you know involved activity they have I ensure that the roads are capable of handling a truck that long it is not heavy, but it is just long it’s an awkward shape. So, you have to find a way in which the road will be able to handle this structure and this truck will have to be guided to the location. So, concerning this tower itself people use concrete it increases life and it's better for taller towers. So, therefore, this is how people are working with it in more, specifically, they used what is referred to as prestressed concrete. So, that helps increase the life and is ideally suited for taller towers. Interestingly, some people are even you know relatively recently looking at wood as a way in which you can make these constructions it has good fatigue properties and therefore, this is something that they are actively looking at. So, this is related to the kinds of you know design restrictions and construction ideas and aspects associated with the tower design. (Refer Slide Time: 44:11) Then we will look at the hub, the hub if you go back to our diagram here this is the hub this part here is the hub okay. So, this is the central part of the wind blade arrangement. So, it does a specific activity primarily the blades are bolted to the hub. So, the bolt blades are attached to the hub, and you could do it two ways you can directly bolt the blade onto the hub, but usually, that is not the preferred way to do it instead the blades are bolted to something called the pitch bearing and this pitch bearing is bolted onto the hub okay. And the idea is simply that you may have you know wind may be coming at some velocity and then the blade will have a particular we will talk about this how you angle the blade concerning the; how you angle the blade concerning that wind, incoming wind we will depend on ideally it depends on the wind speed only then you get the best benefit out of the wind that is flowing. So, if you get it fixed rigidly to the hub you are not in a position to reorient the blade gets stuck in that one position and therefore, it’s not ideally suited to pick up the best you know energy from the wind. So, it is better to fix it to some other bearing which is referred to as the pitch bearing which would sit somewhere here. So, some pitch bearing that sits there and using that you can reorient the blade based on the location of the breeze and in fact, you can also use this to help stop the blades to assist you in stopping the blades if you know you want to shut down this generator for some purpose. So, there is a pitch bearing on which the blades are attached and that pitch bearing is attached to the hub and then that hub is attached to the rest of the structure. So, this is the other way in which this is done and so this is the central part of the wind turbine. (Refer Slide Time: 46:13) And then we have the gearbox. So, there is a shaft which comes from the blade and that goes to the generator right and this shaft that goes from the blade to the generator does not go typically does not go directly to the generator although we are going to discuss that right now it goes through a gear. So, if you go back to our drawing which we just put down you can see that. So, this is the drive train or the shaft and this is coming from the blades from the hub right, it is coming from the hub, it comes to this gearbox that you are seeing here this gearbox and from the gearbox, it is attaching to the generator. So, it is attaching to the generator out here. So, that is where; you can see that it is attaching in this region right. So, this gearbox is there to attach, to connect the blades the rotating blades to the generator. So, why do we need it? Okay so, it is specifically required because if you go and stand in front in one of these locations where these wind turbines are operating you will find that the winds the turbines are rotating, but you can easily see you know road each blade can be comfortably seen with your right you don’t your I mean it is not rotating. So, fast that you do not see anything even you are the ceiling fan in your house is rotating much faster than the wind turbine is rotating right.