The Lobby: Off-topic discussion

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Comments

On a Swedish-made chainsaw: “Warning: do not attempt to stop chain with hands”

Looking out of the window at the inevitable array of wind turbines dotted around the horizon, I was wondering whether the strength of the wind made any difference. They all seem to be turning at the same speed and do so day by day, probably because they are governed to a set speed. The question I pose is:
Does the extra force of the wind on the blades get translated into more power for the turbine via a gear box or similar? Might the blades automatically gain more resistance, making them more difficult to turn, but speeding up things inside the box at the back? Something is obviously stopping them taking off in a gale and they still rotate in a light breeze. Just curious, that’s all.

DerekP says:
21 March 2020

Hi Vynor, in general I would expect the available power to vary substantially with wind speed.

I think gear boxes are typically used to allow their generators to rate at about 1500 revs/minute (25 revs/per second) while the blades themselves will be designed for much lower rotational speeds.

For any given speed of rotation, the mechanical torque applied to the generator will determine the available power. Then, if the magnetic field strength (or excitation) of the generator is controlled to balance the electrical torque, the electric power output will balance the wind power input and the system will run at constant speed.

Any power imbalance will cause the speed to either increase or decrease.

Thanks for this explanation, Derek. I had been wondering for some time why the turbine blades appeared to be idling in a gale, unlike the whirly thing on a stick I used to have at the seaside [until I accidentally trod on it a few years ago].

Many thanks Derek. That would suggest that quite a lot of energy is being wasted because the system is geared to keep a constant speed of rotation – providing a constant generating speed – rather than increasing generation when the wind picks up. Perhaps I haven’t understood you correctly on that? Increased generating power doesn’t mean increased speed, but more things being driven by the force thereof and thus more power being produced? One might expect there to be a coupling and de-coupling of inner turbines depending on the pressure of the wind on the blades. Re-reading this, you might be suggesting that extra power generated provides resistance at the turbine which gets harder to turn as a result?

Wind turbines shut down to prevent the risk of self-destruction if the wind speed is too high. I believe that this is done by changing the blade pitch and braking.

I’ve noticed that too and times when they didn’t turn, presumably because they were not needed.

Late to the party on this. Power obtainable from a turbine is proportional to the cube of the wind speed – double the wind speed potentially 8 times the power generated.

The blade angular speed has to be kept to a safe value, so the power drawn must increase pro rated to the cube of the wind speed. If that cannot be done, the brakes go on and the blades get feathered.

There’s a good paper on this from a few years ago in a scientific journal – I’ll see if I can find it on line and if so drop a link in later.

I did not know that the power is proportional to the cube of wind speed, Roger. That explains why gales rapidly become more damaging as the wind speed increases.

Thanks Roger. Force on the outside is translated into power on the inside. Derek suggests that is through increased resistance as power output increases. What’s not clear to this novice is the way the speed of the blades is regulated so that power increases in output from the same generator in the box behind them. How does the generator generate more power when the wind picks up, when the magnets and windings are the same and the only variable is the way one turns within the other? What makes the generator sense there is more wind speed and therefore more energy to be dealt with? There must be some kind of mechanical switching or sensing to interpret this information.

I’ll follow Ian’s link in a bit, but in answer to your question, the overall system draws more from the windmill when the wind blows harder so as to impart more resistance to the blades to keep the speed nominally the same.

An analogy: If you imagine your plastic bird scarer windmill, but with the pin glued to the blade centre in a bearing through the shaft, with a cotton reel on the back driven by the pin you’d need next to no pressure in a light breeze to keep it at a sensible speed, but as the wind blows, to maintain that original speed you’d have to squeeze the cotton reel a little (drawing power from it to warm up your finger) and in a hooley, risk burning your palm to do the same thing. If the wind got up so that you could not hold the wheel, you’d put the brakes on and feather the blades to save the works and the shaft/foundation respectively!

Edited to add that Ian’s link is a nice Janet-and-John introduction to these things, but completely fails to answer the regulator question as to how the blades are kept in the desired rotational speed between lowest active and highest active wind speeds.

I’m assuming that most wind turbines use induction generators. I had to remind myself how those worked. For me, this rather technical article did that:-https://en.wikipedia.org/wiki/Induction_generator

Put simplly, an induction generator is similar to an induction motor, except instead of using the motor to drive something, you apply a drive to the generator, so that electrical power is produced rather than consumed.

Old fashioned record players used to be powered by small “shaded pole” induction motors. These made use of an important property of the induction motors – i.e. they can be used to provide an (almost) constant speed drive, as required in a record player. This is achieved by supplying a.c. power to a fixed stationary (or “stator”) winding and then using the resulting magnetic field to move the motor’s armature. With an appropriate design of stator winding, the alternating current will cause the magnetic field to rotate about the motor’s axis of rotation.

In turn, that rotatng magnetic field causes or “induces” further currents to flow in the rotating armature (or “rotor”). Those currents then interact with the magnetic field, to produce torque on the rotor, so that it is dragged round by the rotating magnetic field.

At little or no load, the resulting speed will be just less than the “synchonous speed” of the motor. The latter is a rotational speed, set by the a.c. supply frequency and the number of magnetic poles on the stator windings. For example, a 4-pole winding gives a synchronous speed of 1500 rev/min when used on a 50 Hz supply.

Applying more load to the motor will increase its output power and cause it to slow down, but only by a little. Detailed analysis shows that the power transfer increases as a function of this small difference between the actual rotor speed and the synchonous speed. Also, this difference is termed the “slip”.

Mechanically overloading an induction motor can cause it to stall, but up to that point, small changes in slip correspond to give large changes in torque and power.

Then, for an induction generator, the overall setup is similar, except that the mechanical drive is arranged so that it can turn the rotor a a speed just faster than the synchronous speed. Changing the slip in this way reverses the power flow, thus giving a generator instead of a motor.

So in generation mode, quite small speed increases above the synchronous speed will be associated with quite large changes in the generator power output. This “electrical systems magic” is the key to answering Vynor’s original question.

Yes to all of that. However, even if it is a conventional generator (turn faster, up goes F and up goes V), load regulation can still work, just need somewhere to supply the power to, thereby reducing the primary speed.

Thanks Ian. Very clear and easy to understand -even for me. It was the generator bit and the increase/decrease of the wind that prompted my questions and the answer to them lies in the mystic powers of electricity itself and what it does to the generator. Derek has been very kind and explained this. I shall have another read of what he says and “think” about it.

Many thanks Derek. I can see that a generator is similar to a motor and its properties can be reversed. Presumably it is the change in the magnetic field strength, caused by the increased load/wind that actually mechanically makes the motor or generator work harder. Interesting too must be the way it instantly copes with ever varying wind speeds and gusts. The slightly less/more speed system is definitely electric magic and a wonderful bit of physics working for us. I think my curiosity is satisfied and I’m grateful for all the help received from you all.

If a loading on a winding of an ideal motor/generator increases at a given rotational speed, the current in the windings increases (without a change to the voltage or frequency) – and so does its magnetic flux, thereby imparting/receiving more rotational loading respectively. This is in the analogy I put above the equivalent of squeezing the cotton reel harder without the blades slowing down because the wind picked up.

Roger Pittock says: Today 14:15

Edited to add that Ian’s link…completely fails to answer the regulator question as to how the blades are kept in the desired rotational speed between lowest active and highest active wind speeds.

Have a look at 11/17, Roger. It is very simplified, I grant you, but seems to explain it quite well.

Re 11/17:
PITCH SYSTEM
Turns (or pitches) blades out of the wind to control the rotor speed, and to keep the rotor from turning in winds that are too high or too low to produce electricity.
This is the last ditch – for when the cotton reel in my example can’t be squeezed any harder without breaking something because the wind is picking up too much. It is not regulating load (which was the question asked) – but what happens when the regulator has secured its design load by routing to more demand and getting close to not being able to cope.

Phil says:
26 March 2020

It’s the reverse to the way modern aircraft and ship propellers work, the engine and prop turn at a constant speed for maximum efficiency and if there’s a need to go faster or slower the pitch of the blades is changed to take a larger or smaller ‘chunk’ of air/water.

That’s right. A variable pitch marine propeller can actually propel a ship in reverse by changing the angle of the blades. It will be less efficient in reverse because a marine propeller is optimised for forward motion, producing maximum axial and minimum radial flow.

Welcome to World Water Day, the day in 1995 the Deputy Governor of the Bank of England resigned following revelations of his affair with a freelance journalist and the day in 2006 when the Queen of the North Ferry ran aground on Gil Island, British Columbia, and sank; 101 on board, 2 presumed deaths

If at first you don’t succeed, you’re fired.

If only . . .

My thoughts exactly…

I’ve worked myself up from nothing to a state of extreme poverty

You tried your very best and failed miserably The lesson is never try.

Kevin says:
22 March 2020

But if it keeps on happening, cheerfully ignore it and go into politics.

Welcome to Near Miss Day, the day in 1743 when the Messiah was first performed and the day in 1693 when James Bradley, the astronomer who discovered Earth’s nutation motion, was born in Shelborne.

If at first you don’t succeed, try management.

Try them by all means, but they cannot all be guilty.

There are two rules for success in life: 1. Never tell anyone everything you know.

If at first you don’t succeed, redefine success.

Laugh of the day on the Microsoft home page. “Let’s stay at home.” This has an Enid Blyton-esc ring to it as if it seems to be a good idea from the Famous Five.

I am going to risk a walk to the post box [about 100 yards each way] on my own today and hope the police interceptors are not out in force.

On Thursday I shall be making my weekly visit on the bus to the clinic for a dressing change; I have been a little apprehensive about that ever since this outbreak broke out

We’ll shortly be heading out for a walk but, as always, our only companions will be sheep and goats. We never see others, anyway, but it’s been even quieter, lately, with no RAF activity, no big passenger jets from one of the major airports, so we can enjoy cloudless sky, contrail-free solitary walks.

Welcome to World Tuberculosis Day, the day in 1882 when German scientist Robert Koch discovered and described the tubercle bacillus and the day in 1998 Mitchell Johnson and Andrew Golden, aged 11 and 13 respectively, fired on staff and pupils at Westside Middle School in Arkansas killing five and wounding ten.

On a spiritualist’s door: to avoid confusion, please use bell.

That’s a good one.

I was thinking that with a well-positioned Aldiss lamp we could keep in touch with a number of our neighbours and we are in line of sight to the local church tower which could pass signals on to the clock tower on the City Hall.

I will go for my permitted walk for exercise this afternoon. I hope I don’t meet a spiritualist on the psychic path.

All those who believe in Psychokinesis raise my hand.

Telepath wanted. You know where to apply.

One of the problems with sorting things is the inevitable side track. I came across this and reproduce an edited version. Not belly laughs but a few wry smiles perhaps.

Aircraft maintenance reports.
Left inside main tyre almost needs replacing.
Almost replaced left inside main tyre.

Test flight OK except auto land very rough.
Auto land not installed on this aircraft.

Something loose in cockpit.
Something tightened in cockpit.

Dead bugs on windshield.
Live bugs on back-order.

Evidence of leak on right main landing gear.
Evidence removed.

Friction locks cause throttle levers to stick.
That’s what friction locks are for.

DME volume unbelievably loud.
DME volume set to a more believable level.

Suspected crack in windshield.
Suspect you’re right.

Number three engine missing.
Engine found on right wing after brief search.

Target radar hums.
Reprogrammed radar with lyrics.

Mouse in cockpit.
Cat installed.

Aircraft handles funny.
Aircraft told to straighten up, fly right and be serious.

IFF inoperative in off mode.
IFF always inoperative in off mode.

Quite a few laughs here, Vynor. Thanks for the amusement.

Kevin says:
24 March 2020

Ryanair aircraft, evidence of customer service in cabin.
Identified and implemented level of ‘premium’ charge that passengers will accept for maximum revenue.

Getting by probably happens more often than we would like to know about.

Out of interest I checked departures from Heathrow and Gatwick airports. There are still rather a lot of flights scheduled.

One more to add to the above.
Noise coming from behind the control panel just as if a midget was hitting it with a hammer.
Took hammer away from midget. .

Vynor’s list of aircraft maintenance reports has probably been around as long as computers. One item that has been omitted is:

> Pilot’s clock inop.
> Wound pilots clock.

I suppose that younger people cannot be expected to understand winding a clock. 🙂

Talking of mice . . .

We have unset the mouse traps in the garage as we release them a few miles away. Just hope they don’t breed too quickly.
🐭🐭
🐭🐭🐭🐭🐭🐭
🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭🐭 😱

Kevin says:
24 March 2020

Hi Alfa
I seem to recall you need to release them a surprisingly long distance away for effective ‘social isolation’ if you don’t want them back, can’t remember the detail though? ‘Homing’ mice does sound a bit for fetched, so this may be an urban myth, perhaps it only applies to town mice…

They say you need to release them 10 miles away otherwise they can find their way ‘home’ again.

Although it is not 10 miles, ours get released in a woody area and have a bit of an obstacle course to get back to us, with a build-up area and river to cross so hopefully they find a new home somewhere.

Morning everyone – how are you all doing? Keeping well I hope.

We are navigating lock down, home schooling, trying to figure out the heating system in our new house and unpacking all at once. Which is interesting. 😉

Hi Abby, I was wondering if you made it back.

When we bought our home, the previous people took all the curtains except the rags they left us for the bedroom, curtain fittings, light bulbs, some light fittings, etc. I hope you don’t have all that to sort out.

Morning Abby – If you have not been left the instructions for the heating you can probably find them online. It must be a very exciting time for you and your family.

We have brilliant sunshine at the moment and it’s time to cut the grass for the first time.

@alfa We have some of that to sort out. Thankfully we have curtains in the most important rooms. The biggest pain is we didn’t realise how horrific the oven was! There is no handle and even if there was it is so disgustingly dirty I would be too scared to use it. We knew we had to redo the kitchen as soon as we moved in but that is all on hold. I am doing a lot of cooking in the pressure cooker and thankfully our microwave is a combination oven.

@wavechange. Slight problem – the boiler is behind a locked door and the key disappeared on the first day here! I think the system needs flushed as some of the radiators downstairs don’t come on unless all the others are off.

It was exciting until the lock down. We have met our new neighbours through the hedge but that is about it. I am missing catching up with my mum and friends – one of the big reasons we moved!

I think a grotty oven is what everyone moving home should be prepared for. Ours was disgusting but it was fairly new and didn’t need changing – we just replaced the hob. But we had to employ an oven cleaning specialist to tackle the oven and it took about three hours. The cooker hood was in a bit of a state as well but the cleaning guy got it back cooking like new. It had been about three months since viewing the house and moving in during which time it looked as though no cleaning had been done.

There’s a lot to be said for turning up on the day before exchange of contracts and checking that the place is good enough to move into but we hadn’t thought of that.

Hi Abby,
Sounds like you are making the most of your trying circumstances. When we lost our kitchen the combi microwave was so useful along with the slow cooker. I have never owned a pressure cooker as when I was young a relative had one explode that put me off owning one for life even though they are probably much safer these days.

Abby – I hope you find the missing key. If you heating does require flushing to remove sludge it’s important to add corrosion inhibitor.

My main oven was incrusted with grease and required hours of effort to get it clean. The rest of the house was fine.

Welcome to Kidney Month, the day in 1807 when Parliament abolished the slave trade throughout the British Empire and the day in 1895 when Italian troops invaded Abyssinia.

We seem to get very little credit for having abolished slavery across half the globe over two hundred years ago.

Phil says:
25 March 2020

Whilst the buying and selling of slaves was abolished in 1807 it wasn’t until 1833 that it became illegal to own slaves apart from in the territories administered by the East India Company, India, Ceylon (Sri Lanka) and St Helena, who had to wait another ten years.

The edge might’ve been taken off things by the way the slave owners were compensated for their loss but not the slaves.

Yes, the slave traders and merchants involved in shipping the slaves across the Atlantic Ocean were handsomely compensated, that is for sure. Slaves were effectively profitable ballast in a triangular trade with capital goods being exported to Africa, slaves loaded up to go to the Caribbean and America, and tobacco and sugar being shipped across to the UK.

Boycott shampoo; demand the real poo

Phil says:
25 March 2020

If you want to rub real poo into your hair that’s entirely your choice. Just don’t stand near me afterwards.

Kevin says:
25 March 2020

I like to round off a good shampooing with a Kopi luwak coffee and a nice Andouillette sausage.

We learned about the civet and coffee beans on Which? Convo a few years ago, Kevin. Normally I’m keen to experiment with different beans but this time I will make an exception. 🙂

I’ll skip on the sausage too, but thanks.

Kevin says:
25 March 2020

You should see how sophisticated my bean-to-cup machine is…

Chacun à son goût.

This is what I like about Which? . . . It is an inclusive medium and tries to cater for a broad spectrum of society in a non-judgmental manner.

That reminded me of Flanders and Swann.

I told my son shampoo was the poo of a sham – a small creature that is farmed for their poo. I was so disappointed to find nothing on the internet to back this up!