Wind Turbine Hydraulic to Electrical Conversion

[deckart]

As a hobby for the last couple of years, I've been designing various theoretical wave and wind generator devices. One of the primary criteria is that the electrical power generation components have to be easily accessible.

For wave power, electrical power generation has to be on shore not in the water. For wind power, electrical power generation has to be on the ground not in the air.

That's where it gets tricky with a wind turbine. Mechanically, you can have a shaft transfer the torque to the ground components, but that same torque acts on the turbine head position. To avoid this, I've designed a means to convert the torque directly to hydraulic energy and transfer it via a rotary swivel and hydraulic lines.

Why hydraulics and not direct electrical? The main reason is that I'm a hydraulics guy and I know little about the intricacies of getting the wind turbine gen motor to produce 60Hz 240VAC electrically with a varying input velocity and torque. But I do know how to couple a hydraulic motor directly to a generator motor and spin it at the precise RPM required.

This idea is for on-grid supplementary use and for auxiliary shop hydraulic supply.

And that's where I'm going. But I'd love some input from fellow designers and hobbyists.

 

[jrmichler]

Some thoughts:
A well designed hydraulic motor or pump may be 90% efficient. Add in some line losses, and the system mechanical efficiency will be, at best, 70%. You will lose at least 30% of your power when you remotely locate the generator.

You could use the water as your hydraulic fluid in a wave generator. Any leaks would be zero pollution.

 

[deckart]

The motor that drives the generator can be 80-98% volumetrically efficient (80-90% mechanically efficient) depending on the type that is used. But, the "pump" at the turbine head will be near 100% (volumetrically) due to the use of hydraulic cylinders radially configured instead of a typical pump. Line loss will be nil because flow will be low in relation to line size. I dare say that the system will be comparable to the electrical equivalent net output.

And, in the end, any losses aren't really losses when the energy is free.

Water is superior to oil for transmitting energy. But, you lose lubricity and you have icing at low temp.

Thanks for input, jrmichler, I'm looking for holes in the idea!

 

[anorlunda]

How much is the financial benefit of locating the generator at the bottom of the tower instead of the top?

 

[deckart]

For a moderate residential installation, about 50 vertical feet.

 

[berkeman]

For wind power, electrical power generation has to be on the ground not in the air.

I know little about the intricacies of getting the wind turbine gen motor to produce 60Hz 240VAC electrically with a varying input velocity and torque.

You don't need to produce AC Mains frequency and voltage at the generator mounted to the top of the wind turbine -- you use whatever electrical generator works best up in the turbine body, and do the power conversion on the ground:

http://formatex.info/energymaterialsbook/book/559-571.pdf

This idea is for on-grid supplementary use and for auxiliary shop hydraulic supply.

Are you familiar with "Anti-Islanding" and other requirements for connecting your own power generation hardware to your grid connection?

 

[deckart]

Hi berkeman, thank you for posting that method of converting the input. It gives me confidence in the method that I've developed which is far less complex and far less expensive.

No, I know little about the requirements for connecting my own power generation to the grid. I'm sure my power company will give me all the direction I need on that end.

 

[berkeman]

No, I know little about the requirements for connecting my own power generation to the grid. I'm sure my power company will give me all the direction I need on that end.

Yes, Your local power company is definitely the right resource for that information.

 

[deckart]

This is where we exploit the advantages of pressurized fluid as a power transmission medium. Converting rotary motion directly to psi/in² energy units and converting it again to rotary motion of a much higher velocity with low energy losses. With electrical/mechanical component combinations doing this is very expensive.

Attached is a picture of the small actuators I will use for the radial pump located at the turbine head. Except the ones shown in the photo are 1" stroke, I will use 3" stroke cylinders for the "pump" in the configuration shown in the cut-away model pic. Each cylinder is $151.50/ea retail.

The cylinders can be turned off individually and allowed to float so that turbine can continue turn and produce energy at low wind speeds. This energy is stored in an accumulator until saturated, then released to the hydraulic generator motor.

 

[CWatters]

Is it possible to make a reliable rotating hydraulic coupling? eg to allow for changes in wind direction?

 

[deckart]

Is it possible to make a reliable rotating hydraulic coupling? eg to allow for changes in wind direction?

Yes, hydraulic swivels are available. That circular symbol on the bottom right of the schematic depicts a hydraulic swivel. This is how they work:

 

[CWatters]

Would the seals in the swivel be more reliable than say the bearings in a generator?

Edit: Actually I'm not sure how they transmit the electrical power down from a conventional turbine. Do they use slip rings or a larger version of an electric toothbrush charger?

 

[deckart]

Would the seals in the swivel be more reliable than say the bearings in a generator?

As reliable, maybe. Hydraulic excavators use them to get power to the tracks and they work for decades without fail.

 

[deckart]

Here is an updated, complete schematic of the concept system. Very compact, simple, efficient, and cost-effective transfer of energy directly to a 60Hz 240VAC generator. And completely scalable.

After looking at other radial piston designs I've opted for a 5 cylinder pump system. Again, each cylinder is able to be turned off and allowed to float so that the lightest wind can keep the turbine rotating.

One of the reasons I'm sharing this is because I believe fluid power systems are being overlooked in the renewable energy industry. And there are a lot of applications, such as in wind turbines, that such systems are very well suited. This thread is also being shared on Reddit.

 

[CWatters]

I think you would need to quantity the costs and benefits compared to current practice before anyone would adopt the idea.

I wondered if one possibility would be to connect multiply turbines to one generator? Perhaps even run hydraulic lines from off shore turbines to on shore generators (10-20km?).

 

[deckart]

I think you would need to quantity the costs and benefits compared to current practice before anyone would adopt the idea.

I wondered if one possibility would be to connect multiply turbines to one generator? Perhaps even run hydraulic lines from off shore turbines to on shore generators (10-20km?).

Quantifying costs will be difficult. I will need to consult with engineers that design them and I don't know any, yet. I can only use general comparisons with the components that I work with.

It makes sense to convert the hydraulic energy to electrical energy close to the turbines. Energy travels long distances more efficiently as electricity.

The primary advantage of using hydraulics is going to be how it deals with a varying input RPM and load, and the energy conversion is very direct. The disadvantage is that you may have more moving parts. But the parts are simple, common, and relatively inexpensive.

 

[CWatters]

The primary advantage of using hydraulics is going to be how it deals with a varying input RPM and load,

I'm not an expert on turbines but I know they have developed power electronics to decouple what the generator is doing from what the grid is doing ...

Google found..
https://www.nrel.gov/docs/fy12osti/54605.pdf

Page 3..

Most large scale wind turbines installed during the 1980’s and 1990’s used gearboxes and fixed speed generators that produced voltage synchronous with the utility grid [6]. The wind turbine industry has since moved to using variable speed wind turbines that can maximize below-rated power production by matching blade tip-speeds against prevailing wind speeds to maximize aerodynamic efficiency, as described in Section II-C1.Variable speed operation is typically achieved by using one of two different configurations. The first employs a synchronous generator that spins at variable speeds and uses a full power converter to ensure the produced power matches in frequency and phase to that of the utility grid and is known as a ‘type 4’ wind generator [7]. The second, and most common way of achieving variable speed operation is to use a doubly-fed induction generator (DFIG), known as a ‘type 3’ wind generator [7]. The stator of a DFIG is directly connected to the grid while the electromagnets of the rotor are excited by a time-varying waveform that is produced by power electronics that need to only convert roughly 30% of the turbine’s rated power [7]. Almost all commercially available large scale wind turbines use either type 3 or 4 generators, both of which [are] effectively decoupled from the grid via their power electronics.

 

[deckart]

I literally just spoke to our Director of Research & Development while getting coffee, who has a Ph.D. in an Electrical Engineering discipline (I forget the exact title), and he described a couple of methods that are used, rectification/inverting and the one above (DFIG) to deal with the varying input velocities. Most of it is over my head but he says that it is an expensive problem. Apparently, he knows a lot about how these large wind turbines work.

I only get to speak to him in passing but I pick his brain his brain on occasion. While walking back with him in the hall I mentioned that I had created a hydraulic circuit easily captures the energy regardless of the turbine velocity and he thinks it is a great approach. Then he went on about how accumulators, like supercapacitors, are much better at absorbing a lot of energy quickly, more so than batteries... then electrical vehicle braking limitations, aircraft hydraulic hydrostat constant velocity generators to deal with varying input velocities, how leaky hydraulics doesn't have to be an issue... and back to his office he went. lol

I'm getting that using hydraulics with wind turbines just hasn't been explored entirely.

 

[Punch-line]

This system is commonly known as a 'variable displacement hydrostatic transmission'. Mitsubishi Heavy Industries has invested somewhat in the idea with the purchase of Scotland-based Artemis Intelligent Power. Their design is also a radial piston pump with piston shut-off for low speed to maintain electrical output frequency. They are currently looking at applying it for wave energy converters.

I have also designed a variant of the hydrostatic transmission with a novel axial-piston reciprocating pump that does not require an eccentric driveshaft. I showed the design to the local Parker Hannifin office but they weren't interested.

It is a shame as the pump seems to be a promising alternative to permanent-magnet or gear-driven electric motors.

 

[deckart]

This system is commonly known as a 'variable displacement hydrostatic transmission'. Mitsubishi Heavy Industries has invested somewhat in the idea with the purchase of Scotland-based Artemis Intelligent Power. Their design is also a radial piston pump with piston shut-off for low speed to maintain electrical output frequency. They are currently looking at applying it for wave energy converters.

I have also designed a variant of the hydrostatic transmission with a novel axial-piston reciprocating pump that does not require an eccentric driveshaft. I showed the design to the local Parker Hannifin office but they weren't interested.

It is a shame as the pump seems to be a promising alternative to permanent-magnet or gear-driven electric motors.

That's great, Punch-line! I'd love to see your hydrostatic transmission concept.

I am familiar with the DDT (Digital Displacement Transmission), it is a cool technology that is gaining interest in the Fluid Power industry. Here is a recent article describing how it works in the Fluid Power Journal: http://fluidpowerjournal.com/2018/03/digital-displacement-pumps/

I'm in the process of developing a prototype of a transmission device, it is depicted downstream of the hydraulic motor that drives the generator in the schematic shown above. It will be the topic of a future post.

 

[deckart]

This system is commonly known as a 'variable displacement hydrostatic transmission'.

I want to add, there are some differences compared to the common hydrostatic transmission, though functionally, this circuit does operate as one. But the velocities are much lower than is common.

Primarily we are using individual stand-alone hydraulic cylinders as opposed to an actual pump unit. We don't have a minimum RPM in order to maintain the volumetric efficiency a typical pump requires due to machined clearances. Instead of a high-speed (1200-3600 RPM as in a gas or electric prime mover) low torque input, we are working with a low-speed (0-100 RPM, for example) very high torque input. This makes the design very scalable with common components.

I do appreciate the feedback and critique of the design.

 

[Punch-line]

I am by no means an expert on fluid dynamics and pump design so I do have a question about this design. Wouldn't an under square piston configuration with a 3" stroke require pivoting on each individual pump case to reduce side loading on the piston? Would an over square pump with a large bore and a wrist pin on the piston simplify construction in a radial configuration? Are off-the-shelf components in these dimensions readily available?

It would also depend on the torque requirement and form factor to suit it's location. So many factors to take into account.

 

[deckart]

To be honest, I don't know the terms "under-square" and "over-square" in this context but I think I'm following you...

The cylinders would have a pivoting mount where they attach to the outer frame.

One of the cylinder rods has to be fixed to the center lug that the rest of the cylinders are attached and be able to handle side loading. That particular cylinder may simply be a ram with no annulus or an oversized rod in order to be stout enough.

Yes, I'm looking at this as something that one could build themselves from common off-the-shelf components but scalable to industrial sizes.

 

[Baluncore]

If I had to use hydraulics, I would use a constant pressure, variable volume pump, driven by a wind turbine. That HP fluid would drive a constant speed hydraulic motor, coupled to an alternator. If the alternator used was a synchronous generator, spinning a few percent above synchronous speed, it could generate 3PH power directly to the grid.
If I needed to store some hydraulic energy I would build a thing like a gasometer, that is pushed upwards by a hydraulic ram. The vacuum pulled inside the gasometer would maintain a constant pressure on the hydraulic ram, avoiding the inverse law for compressed gas. When the wind stops and the pump pressure falls, the gasometer would push fluid out of the ram again to run the motor.

 

[deckart]

An updated model of the radial cylinder configuration:

 

[alantheastronomer]

For more input on your ideas, you might want to get in touch with "Renewable Energy Long Island", a not-for-profit organization, and "Deepwater Wind" a company currently constructing a wind farm off the shore of southern Long Island.

 

[anorlunda]

If the alternator used was a synchronous generator, spinning a few percent above synchronous speed, it could generate 3PH power directly to the grid.

Whoops, I think you meant induction generator. It runs a few percent faster than synchronous speed.

A synchronous generator runs at synchronous speed, a few degrees in phase angle ahead of the grid.

 

[Baluncore]

Whoops, I think you meant induction generator. It runs a few percent faster than synchronous speed.

Sorry, we all have to sleep sometime.

 

[Jon Richfield]

For various personal (abstract, not commercial nor professional) reasons I find this discussion very interesting
(see i.a. http://fullduplexjonrichfield.blogspot.co.za/2017/04/heavier-duty-banking-appendix-supplement.html)
And I called to mind a discussion about 48 or 50 years ago, when a then colleague in IBM, one James Philbrick (very intelligently creative, but since deceased, I am very sorry to say) described an invention that I admired. I know that he patented it in the same or following year, but I never saw that anyone took it up. I mention it here, as nearly as I remember it, in case anyone can put it to constructive use. Alternatively, if anyone happens to know that it is currently in use, I would be curious to know. Otherwise it would be a pity to waste it, I reckon.

James had been a hydraulics engineer with experience in designing systems for ships, and had recognised that a generalisation of the rotary vane pump could be used to power one flow of liquid by the input of another flow. By shifting the axis of rotation of the rotor, one could smoothly in effect change gear, either moving more fluid against lower resistance, or less fluid against higher resistance. I include a sketch of what I can remember from my distant youth. I omit the notional mechanism for moving the axis of the rotor (James represented it at the time simply as an external lever of type two, with the rotor axis in the middle).

The power is applied by one pair of opposed inlet-outlet channels (say the green arrows) which drives fluid through the other pair according to the position of the rotor in the outer drum. No doubt an arbitrary set of input-output channels could be combined for more complex requirements.

For your attention for what it is worth.

I apologise, but I failed to insert the diagram in usable form. In case my description fails to convey anything articulate (very likely!) I have posted it at:

https://www.facebook.com/photo.php?...5908628.111317.100001576411737&type=3&theater

Good luck to anyone interested.

If anyone could tell me how to include the image more conveniently, feel welcome.

 

[deckart]

HI Jon, I will look into this further but from what you just posted, it sounds like the VDT (Variable Displacement Transformer) concept that a friend and I are working on. He designed a version that uses a vane pump like you are describing. It is still a theoretical device but my friend, Dan Helgerson, an educator, has dedicated a lot of time trying to bring the concept some attention in the industry.

If it is the same type of device, it is depicted near the generator motor in the schematic in this thread.

Looking at your diagram, it is very similar in that it is used as a variable displacement flow divider. I will show this to Dan.

Here is a youtube video where he describes the vane version, it begins at minute 35:45

He describes the concept in many of the recent articles that he has posted on his website: www.danhelgerson.com , particularly the one titled, "Transformation Complete".

 

[anorlunda]

If anyone could tell me how to include the image more conveniently, feel welcome.

First, save the image on your own PC. Then use the UPLOAD button to insert it into a post.

 

[deckart]

First, save the image on your own PC. Then use the UPLOAD button to insert it into a post.

You are a staff member, you may have an upload button but I don't believe that we do. I have to use imgbb.com to post a picture URL.

 

[anorlunda]

You are a staff member, you may have an upload button but I don't believe that we do. I have to use imgbb.com to post a picture URL.

Here is a screen shot. Bottom right are buttons labeled POST REPLY and PREVIEW and UPLOAD. After it is uploaded, new buttona appear. Position the cursor to where you want to insert it and click FULL SCREEN. Note that this works with pictures stored on your PC (JPG, BMP, PNG, GIF, ...) , not a URL.

 

[deckart]

Here is a screen shot. Bottom right are buttons labeled POST REPLY and PREVIEW and UPLOAD. After it is uploaded, new buttona appear. Position the cursor to where you want to insert it and click FULL SCREEN. Note that this works with pictures stored on your PC (JPG, BMP, PNG, GIF, ...) , not a URL.

View attachment 223143

That's why we couldn't see it, it was right in front of us. :)

 

[Jon Richfield]

First, save the image on your own PC. Then use the UPLOAD button to insert it into a post.

Thanks anorlunda, let's see whether this works for me (thought I had tried that, but maybe I boobed )
Here goes: Ah. that worked. Maybe the previous time I didn't wait long enough. Thank you. I'll try to remember that, and try first to reduce the file size in case that contributed to the problem.

 

[Jon Richfield]

... youtube video where he describes the vane version, it begins at minute 35:45

He describes the concept in many of the recent articles that he has posted on his website: www.danhelgerson.com , particularly the one titled, "Transformation Complete".

Thanks, Interesting video. Still going through the whole one. Good luck if the info I regurgitated is of value.

 

[deckart]

Thanks, Interesting video. Still going through the whole one. Good luck if the info I regurgitated is of value.

It's interesting to see that the idea has been around a long time. It's a very simple concept that is common in electronics but just hasn't been exploited in fluid power.

 

[Baluncore]

it sounds like the VDT (Variable Displacement Transformer) concept that a friend and I are working on.

In post #24, I suggested a constant pressure, variable volume pump driven by the wind turbine, with the fluid driving a constant speed hydraulic motor. That is really a VD transformer with a hydraulic loop connecting two rotating shafts.

If instead you have a fluid input loop, couple the shafts together and have a fluid output loop, then it is more obviously a VDT described from the viewpoint of an hydraulic engineer.

In the wind generator application there is a shaft input and a shaft output, coupled by a pump and motor hydraulic circuit. Inserting a VDT into that loop would be less efficient than migrating the transformation to the ends of the system by using a VD CP pump and a VD fixed speed motor. That technology has been available for many decades. These days there are more efficient electrical solutions.

 

[deckart]

In post #24, I suggested a constant pressure, variable volume pump driven by the wind turbine, with the fluid driving a constant speed hydraulic motor. That is really a VD transformer with a hydraulic loop connecting two rotating shafts.

If instead you have a fluid input loop, couple the shafts together and have a fluid output loop, then it is more obviously a VDT described from the viewpoint of an hydraulic engineer.

In the wind generator application there is a shaft input and a shaft output, coupled by a pump and motor hydraulic circuit. Inserting a VDT into that loop would be less efficient than migrating the transformation to the ends of the system by using a VD CP pump and a VD fixed speed motor. That technology has been available for many decades. These days there are more efficient electrical solutions.

The reason this has not been done is that the input velocity is too low for a variable displacement constant pressure pump to operate. It is not a feasible circuit.

Pumps are not designed to operate at such low velocities which is why I designed it using hydraulic cylinders (0-100 RPM maybe, the lower the better). What happens on the other end, at the generator, has to be done at higher velocities that are typical for generating electricity.

The electrical problem is dealing with the low and inconsistent wind speeds. It is not that efficient, from what I've read. Using hydraulics, you capture more of the energy at any speed. As long as the there is motion, there is energy being converted to hydraulic energy. And that is easily converted back to mechanical energy to drive a generator.

So, I disagree that the current electrical solutions are more efficient or less expensive. At least to the point that it is worth research. I have not seen any studies regarding this. My opinion is that because the product is electrical energy that the development of these types of devices has been electrical-centric and the use of fluid power as a means of interim power transmission has not been explored.

What you described in post #24 is conceptually the same thing it's just not using the same components. Hydraulic pumps, in general, are designed to be driven at velocities typical of fuel or electrically driven prime movers. 1200-3600 RPM.

 

[Jon Richfield]

It's interesting to see that the idea has been around a long time. It's a very simple concept that is common in electronics but just hasn't been exploited in fluid power.

Yes, I can't remember whether James showed it to me in 1968 or 1969, but I think he had had the idea some years before. I sometimes wonder whether something of the kind shouldn't be more efficient and versatile than our current transmission in automatic cars.

 

[Baluncore]

My opinion is that because the product is electrical energy that the development of these types of devices has been electrical-centric and the use of fluid power as a means of interim power transmission has not been explored.

I remember reading reports in the 1970s of prototypes of hydraulic systems using VDT being built and evaluated in the USA and UK for wind generators. Even with hydraulic transformers, they were not as efficient as multi-pole alternators and I believe were upgraded or sold. That is probably why you have not come across them.
There were a couple of bright engineers in my lab who evaluated hydraulic VDTs to improve the efficiency of wind turbine generators, but they could not show a competitive advantage over existing electrical alternators.
The subject keeps coming up as a search of google images for 'hydraulic wind turbines' will show you.

 

[anorlunda]

The primary advantage of using hydraulics is going to be how it deals with a varying input RPM and load, and the energy conversion is very direct.

When you talk about advantages of one design versus another, starting with RPM as the independent variable masks part of the problem. You should start with available energy. At low wind speeds, low energies make power production unattractive regardless of the efficiency of the mechanical/hydraulic/electrical mechanisms.

Instead, the focus should be on efficiency in the attractive range of wind speeds, roughly 15-25 mph (7-11 mps). So, the hydraulic method might still be interesting, but not at low wind speeds. Also, there are freedoms in the design of the wind turbine (such as variable pitch) as well as the conversion mechanisms, so you have to evaluate the entire system to determine attractiveness.

Conservation of mass requires that the amount of air entering and exiting a turbine must be equal. Accordingly, Betz's law gives the maximal achievable extraction of wind power by a wind turbine as 16/27 (59.3%) of the total kinetic energy of the air flowing through the turbine.[15]

The maximum theoretical power output of a wind machine is thus 16/27 times the kinetic energy of the air passing through the effective disk area of the machine. If the effective area of the disk is A, and the wind velocity v, the maximum theoretical power output P is:

{\displaystyle P={\frac {16}{27}}{\frac {1}{2}}\rho v^{3}A={\frac {8}{27}}\rho v^{3}A}

,
where ρ is the air density.

 

[deckart]

I remember reading reports in the 1970s of prototypes of hydraulic systems using VDT being built and evaluated in the USA and UK for wind generators. Even with hydraulic transformers, they were not as efficient as multi-pole alternators and I believe were upgraded or sold. That is probably why you have not come across them.
There were a couple of bright engineers in my lab who evaluated hydraulic VDTs to improve the efficiency of wind turbine generators, but they could not show a competitive advantage over existing electrical alternators.
The subject keeps coming up as a search of google images for 'hydraulic wind turbines' will show you.

In the 70's variable displacement pumps and motors were not common at all. Most hydraulic applications used low efficiency fixed displacement devices. One of the first articles that came up when I googled "hydraulic wind turbine" is this: http://www.machinedesign.com/energy/hydraulic-wind-turbines describing very similar configuration but the author is considering the use of traditional high RPM pumps which are inefficient to drive at low speeds. I address this by simply using hydraulic cylinders which are 99% efficient.

You have not convinced me that this approach has been evaluated. Also, the VDT is a theoretical device that has never been commercially manufactured. I believe you are thinking of a hydrostatic transmission. The variable pump/motor relationship is virtually the same concept.

 

[deckart]

When you talk about advantages of one design versus another, starting with RPM as the independent variable masks part of the problem. You should start with available energy. At low wind speeds, low energies make power production unattractive regardless of the efficiency of the mechanical/hydraulic/electrical mechanisms.

Instead, the focus should be on efficiency in the attractive range of wind speeds, roughly 15-25 mph (7-11 mps). So, the hydraulic method might still be interesting, but not at low wind speeds. Also, there are freedoms in the design of the wind turbine (such as variable pitch) as well as the conversion mechanisms, so you have to evaluate the entire system to determine attractiveness.

The hydraulic method IS interesting because of its efficiency at low wind speeds (using a hydraulic cylinder pump) vs electrical-mechanical. Input energy is a different conversation. I'm proposing a different method of transmission.

How hydraulic energy is converted back to mechanical energy to drive a generator can be done with a common variable displacement motor as opposed to a VDT. In fact, I should change that in the schematic to prevent any confusion around a device that doesn't even exist yet. The advantage of a VDT is that it can be used to maintain a target RPM passively. With currently available components the RPM would be controlled by modulating the displacement of the motor in a closed-loop.

 

[deckart]

For various personal (abstract, not commercial nor professional) reasons I find this discussion very interesting
(see i.a. http://fullduplexjonrichfield.blogspot.co.za/2017/04/heavier-duty-banking-appendix-supplement.html)
And I called to mind a discussion about 48 or 50 years ago, when a then colleague in IBM, one James Philbrick (very intelligently creative, but since deceased, I am very sorry to say) described an invention that I admired. I know that he patented it in the same or following year, but I never saw that anyone took it up. I mention it here, as nearly as I remember it, in case anyone can put it to constructive use. Alternatively, if anyone happens to know that it is currently in use, I would be curious to know. Otherwise it would be a pity to waste it, I reckon.

James had been a hydraulics engineer with experience in designing systems for ships, and had recognised that a generalisation of the rotary vane pump could be used to power one flow of liquid by the input of another flow. By shifting the axis of rotation of the rotor, one could smoothly in effect change gear, either moving more fluid against lower resistance, or less fluid against higher resistance. I include a sketch of what I can remember from my distant youth. I omit the notional mechanism for moving the axis of the rotor (James represented it at the time simply as an external lever of type two, with the rotor axis in the middle).

The power is applied by one pair of opposed inlet-outlet channels (say the green arrows) which drives fluid through the other pair according to the position of the rotor in the outer drum. No doubt an arbitrary set of input-output channels could be combined for more complex requirements.

For your attention for what it is worth.

I apologise, but I failed to insert the diagram in usable form. In case my description fails to convey anything articulate (very likely!) I have posted it at:

https://www.facebook.com/photo.php?...5908628.111317.100001576411737&type=3&theater

Good luck to anyone interested.

If anyone could tell me how to include the image more conveniently, feel welcome.

Jon, can you reference the patent number? I am not finding it.

 

[Jon Richfield]

Jon, can you reference the patent number? I am not finding it.

I have not the faintest clue, sorry. I never knew that. James just mentioned it to me afterwards. I seem to remember it was a world patent or something, and we were in South Africa. I know nothing about the practicalities of patents now, and less than that then. It would have been about 1968 or 1970.

 

[Baluncore]

but the author is considering the use of traditional high RPM pumps which are inefficient to drive at low speeds.

Obviously high speed pumps will be optimised for high speeds. The same type of pump can be scaled to operate at low speeds. A bent-axis swash-plate motor uses hydraulic cylinders with variable stroke. The swash plate was and still is most commonly used for adjustable rate pumps and motors. There is little difference between axial hydraulic cylinders with a swash-plate and your proposed radial configuration.

... I address this by simply using hydraulic cylinders which are 99% efficient.

The movement of hydraulic fluid through the lines and valves connected to the hydraulic cylinder is where the majority of the loss occurs. Those ancillary losses usually amount to between 10% and 20%. Long hydraulic lines between pump and motor will greatly improve oil cooling and oil life, but will also reduce the efficiency overall.

Hydraulic systems have a very high power to weight ratio, but that comes with poor efficiency. When you double the RPM of a hydraulic pump or motor you double the power for the same weight, while the flow is doubled at the same pressure. That is why small high speed motors are more common than big, heavy and very expensive radial cylinder pumps or motors like your design. Since hydraulic losses increase in proportional to the square of the fluid velocity. Bigger, more expensive hydraulic lines and valves must be used not only with big and slow rotary devices, but also with small and fast rotary systems. The maximum pressure is also limited for larger diameter hoses. That cuts the maximum power transmitted.

You have not convinced me that this approach has been evaluated. Also, the VDT is a theoretical device that has never been commercially manufactured. I believe you are thinking of a hydrostatic transmission. The variable pump/motor relationship is virtually the same concept.

What do you mean by “hydrostatic transmission”, a toroidal flow torque converter? I see any hydraulic pressure transmission as a “hydrostatic transmission”, be it a VR pump and VR motor combination or the return of the VDT concept under another name.
“The variable pump/motor relationship is virtually the same concept” as what? The newly named VDT or the combination of VR pump and VR motor I suggested. I think they are the same. Your requirement was to have hydraulic flow up and down the tower. That requires a separate pump and motor, with a fluid reservoir = header tank and a filter system high on the tower where fluid must be pushed into the pump inlet.

One of the reasons I'm sharing this is because I believe fluid power systems are being overlooked in the renewable energy industry.

This has been a common theme. Every five years there is someone who jumps on the hydraulics bandwagon. They focus on rediscovering hydraulic technology and pump design. Then they go quiet when they find out how inefficient hydraulic transmission systems can be. A hydraulic system is not as efficient, nor as flexible as today's electrical technology, control systems and accumulator technology.

 

[deckart]

Obviously high-speed pumps will be optimised for high speeds. The same type of pump can be scaled to operate at low speeds.

Sure, high-speed pumps can be scaled to operate at low speeds. But they aren't. There is no market for them and that is why they don't exist. Pumps require a prime mover, something to drive them. The common items that drive pumps operate at high-speeds, i.e. gas engines, electric motors. There are no prime movers to drive low-speed pumps. What would be the point? Where is the market? So, I propose a pump design that CAN operate efficiently at low speeds. It is just a combination of common, inexpensive, hydraulic cylinders. I didn't redesign a wheel. I just made a low-speed pump suitable for this application.

A bent-axis swash-plate motor uses hydraulic cylinders with variable stroke. The swash plate was and still is most commonly used for adjustable rate pumps and motors. There is little difference between axial hydraulic cylinders with a swash-plate and your proposed radial configuration.

Actually, there are significant differences. One of which is that I'm not adjusting flow (or in your words, "rate"). This is a fixed displacement device. Flow is dependant on RPM, RPM is the variable. The problem this solves is that it captures energy efficiently regardless of how low the RPM is. Electro-mechanical systems do not do this efficiently as you claim. The systems that are used employ a lot of expensive techniques to address this. Some of them are very ingenious from what a colleague has described to me, though I can barely follow the theory behind it.

The movement of hydraulic fluid through the lines and valves connected to the hydraulic cylinder is where the majority of the loss occurs. Those ancillary losses usually amount to between 10% and 20%. Long hydraulic lines between pump and motor will greatly improve oil cooling and oil life, but will also reduce the efficiency overall.

This is a very ambiguous paragraph. There are always losses when you transmit energy, whether electrical, mechanical, or hydraulic. Let’s say there is a total of 10% line and valve loss. Which is high, imo, because the only valves I’m using for the work lines are check valves. Consequently, I may be capturing 30% more energy. I really don’t know yet but I have a system that could be used to find out.

Hydraulic systems have a very high power to weight ratio, but that comes with poor efficiency. When you double the RPM of a hydraulic pump or motor you double the power for the same weight, while the flow is doubled at the same pressure. That is why small high speed motors are more common than big, heavy and very expensive radial cylinder pumps or motors like your design. Since hydraulic losses increase in proportional to the square of the fluid velocity. Bigger, more expensive hydraulic lines and valves must be used not only with big and slow rotary devices, but also with small and fast rotary systems. The maximum pressure is also limited for larger diameter hoses. That cuts the maximum power transmitted.

This is riddled with ambiguity and incorrect generalization. With higher pressures densities you transmit the same power with less flow, smaller lines. Just as you can deliver the same power with a higher voltage and less current, smaller lines. Regardless, extremely large ID high pressure hose is available (see Parker 797 series 6000 psi hydraulic hose).

What do you mean by “hydrostatic transmission”, a toroidal flow torque converter? I see any hydraulic pressure transmission as a “hydrostatic transmission”, be it a VR pump and VR motor combination or the return of the VDT concept under another name. “The variable pump/motor relationship is virtually the same concept” as what? The newly named VDT or the combination of VR pump and VR motor I suggested. I think they are the same.

Fine, semantics. It isn’t really the point of the system.

Your requirement was to have hydraulic flow up and down the tower. That requires a separate pump and motor, with a fluid reservoir = header tank and a filter system high on the tower where fluid must be pushed into the pump inlet.

Up/down, yes. No, it does not require a separate pump and motor. I’m using the radial pump to circulate all fluid in the system. Filtration, yes, and yes, the reservoir will be pressurized to aid pump inlet delivery. It is a closed system. Much like a hydrostatic transmission, in fact. And remember, fluid head coming down the tower is the same as is going up, energy-wise, they are equal.

This has been a common theme. Every five years there is someone who jumps on the hydraulics bandwagon. They focus on rediscovering hydraulic technology and pump design. Then they go quiet when they find out how inefficient hydraulic transmission systems can be. A hydraulic system is not as efficient, nor as flexible as today's electrical technology, control systems and accumulator technology.

You still haven’t proven your point beyond making vague generalizations.

 

[deckart]

This forum makes for a good chalkboard!

I've been doing some more research into the challenges of current large-scale wind turbine arrays. One of the problems, of course, is energy storage. There are often demands when the wind isn't blowing. There are meteorological projections considered in advance for opportune times to bring the arrays online. Tesla and their mega-battery systems, as demonstrated in Australia, work great in this capacity.

The wind-turbines themselves can provide a good piece of energy storage when a hydraulic system is utilized with the use of the basic hydraulic accumulator. A good deal of energy can be stored for use during those opportune periods. The limitations are only in the capacity of accumulators that are utilized and with the large numbers wind turbines that some of these wind farms employ, this can be a very substantial amount of energy.

Here is a schematic illustrating how such a system might be configured:

 

[NTL2009]

What would these accumulators physically look like? I assume these are oil pumped into a chamber with air/gas, so the energy storage mechanism is compressed gas?

I was under the impression there is a fair amount of loss in a system like that. Compressing a gas heats it, and that heat is lost over time, which could be many hours if you are trying to smooth wind differences over the course of the day.

How large would accumulators be per MW-Hr of storage?