30hp motor conversion....hypothetically

[bigrockcandymountain]

I might have an opportinity to get a 30hp 6 pole motor for free.  A friend saw my current turbine, and thought maybe I need this motor to convert. 

Tell me your thoughts.

My quick calculations look like this. 
It's likely 37a 3 phase so could be expected to make 64a on the dc side of the rectifier.  I would run about 150v so that's almost 10kw continuous!!

The shaft size is 2-1/8" which i think would swing a 20' rotor easily. 

Its wired 460v. My 5hp now hits 48v at about 160rpm.  Wired 460 that would be 80rpm.  This one has a much larger armature, but I'm not sure what that would do to voltage.  It should land within range of a 6m / 20' diameter for cutin though.


I would mount it on a fixed tower on one of our hills.  Probably 16" heavy wall pipe.  I would go about 18' to the shaft.  Just high enough that you can't get hit by the blades.

I don't think I'll start on this any time soon. 

[Adriaan Kragten]

A simple and cheap way to convert a 6-pole asynchronous motor into a PM-generator is described in my public report KD 747 which you can copy for free from my website www.kdwindturbines.nl. The geometry of the armature is given for certain dimensions of the armature and the chosen magnets and for a stator with 36 slots, so with 36 stator poles. The armature has 30 mechanical poles but 6 magnetic poles. So six stator poles poles are opposed to five mechanical armature poles resulting in 6 * 5 * 6 = 180 preference positions per revolution and therefore in a rather low peak on the cogging torque.

I don't know if your motor also has 36 stator poles. Very big 6-pole motors sometimes have 54 stator poles. If this is the case, you can use an armature with 48 mechanical poles. In this case there are nine stator poles opposed to eight mechanical armature poles resulting in 9 * 8 * 6 = 432 preference positions per revolution resulting in an even lower peak on the cogging torque. I don't know if magnets of the correct size are available for your armature geometry.

[Adriaan Kragten]

If you use the standard 3-phase winding and rectify the current with a 3-phase rectifier, you have only two options; star rectification or delta rectification. The DC voltage for star rectification is a factor square root of three higher than for delta rectification. The disadvantage of delta rectification is that the unloaded torque rises much faster than for star rectification because higher harmonic currents can circulate in the winding for delta rectification. A disadvantage of a 6-pole winding is that it is normally a 3-layers winding. A 4-pole winding is normally a 2-layers winding and for a 2-layers winding it is possible to halve the voltage by connecting the first and the second layer in parallel in stead of in series. This is explained in chapter 4 and figure 2 of report KD 341.

I expect that the DC voltage of your 6-pole motor will be much too high for 24 V battery charging if you make a strong armature. The winding of a 6-pole motor with 36 stator poles is given in figure 1 of report KD 747. Every phase has 6 coils. A phase consists of three bundles of two coils. The two coils of a coil bundle are laid around each other. All six coils U1 - U6 are lying in the outer first layer. All six coils V1 - V6 are lying in the middle second layer. All six coils W1 - W6 are lying in the inner third layer. All six coils of one phase are connected in series. It is possible to disconnect the three coil bundles of one phase and to connect these three coil bundles in parallel. This results in decrease of the voltage by a factor three and increase of the current by a factor three. It might be that with this modification, the winding can be used for 24 V battery charging if the winding is connected in star. But if the matching in between the rotor and the generator is acceptable, depends also on the optimum cubic line of the wind turbine rotor (see report KD 35 formula 8.1)

[bigrockcandymountain]

I expect that the DC voltage of your 6-pole motor will be much too high for 24 V battery charging if you make a strong armature.

I'm pretty flexible on output voltage.  My system is 48v, so it would be good if it somewhat works with 48v, but I will probably use a mppt controller, so the voltage can be quite a lot higher than battery voltage. 

If i take a wild guess at the stator dimensions, lets guess it is 10" (250mm) diameter, 9" (225mm) long. 

3" x 1/2" x 1/4" magnets are $6

Say 9 magnets per N pole is 27 magnets the rotor is 3 magnet lenghts long so 81 total. 

$486 plus shipping for magnets. 

That's just a guess based on made up measurements. 

[Adriaan Kragten]

Say 9 magnets per N pole is 27 magnets the rotor is 3 magnet lenghts long so 81 total. 

[/quote]

To prevent strong preference positions for a 6-pole generator, the number of mechanical armature north poles must be one less (or one more) than the number of stator poles used for one magnetic stator pole. If the stator has 54 mechanical poles, there will be 9 mechanical stator poles for one magnetic stator pole. If you use 27 magnets per north pole and if there are three magnets in one groove, a magnetic armature north pole will have nine mechanical poles. This means that there is just one mechanical armature pole opposed to one mechanical stator pole. This will cause very strong preference positions.

So if the stator has 54 mechanical poles, the armature must have 48 mechanical poles. This means that a magnetic armature north poles has eight mechanical poles. If there are three magnets in a groove, you need 3 * 8 = 24 magnets for one magnetic north pole and so totally 3 * 24 = 72 magnets for the three magnetic north poles. A magnetic south pole is formed by eight rows of the remaining material of the armature. It seems that you haven't understood the trick which I used to reduce the peak on the cogging torque.

[SparWeb]

Wow!
Kinda gritty but interesting nonetheless.

Can I suggest that it may have better uses than wind?
The same conversion but in a hydro installation would deliver that 10kW continuously, like 7,200 kWhr per month.  That's how much electricity I use in a year.

300 kg = 660 pounds.  For wind, this will require a completely different kind of tower, as you say. I wouldn't want to make too many guesses about the tower until the performance of the WT is known.  Unfortunately that piles one guess on top of another guess.  Prepare for expensive footing and column, even doing it yourself.

I think Adriaan is on to something about split poles, too.  The conversions I've done always run in parallel-star, because I make sure to disconnect the star point and separate the groups in each pole.  Whenever I get around to upgrading my 24V system to 48V, then I'll reconnect the groups in series.  A 6-pole motor may have an uneven number of coil groups per pole, so you can't divide three in half.  Maybe you can split them 3 ways, so instead of 2 groups in parallel, you can have 3 groups in parallel.  That lowers the volts per RPM- maybe too much.  If so, then leave the groups in series, and maybe you'll enjoy very low RPM at the rated speed.  The only way I know to be sure is to do the conversion and then bench test it.

Assuming you will craft the blades yourself, then you can choose the diameter, chord, taper, twist, and incidence according to the power output and speed profile of the converted generator.

I've typed this out because the image is really hard to read-

TEFC
Westinghouse T30/25/2006TE4
Poles 6
Frame 326T
60 Hz
Ambient 40C
volts 460
HP 30 / 25 / 20
Amps 30 / 31.0 / 25.0
RPM 1120 / 1120 / 1110
Weight 300 kg
PF 88.5%
Service Factor 1.1
Bearing 6312 6212
Ser. No. JS70791081005

[Adriaan Kragten]

The weight of the armature can be reduced by making it hollow. The normal short-circuit armature consists of an iron lamination with aluminium short-circuit bars cast in it. So the average density will be about 5 kg/dm^3 which makes a big armature very heavy. This armature has to be removed and replaced by a new mild steel armature in which the grooves for the magnets are made. On You Tube there are films from people who use the original short-circuit armature but if you cut grooves in this armature, you will cut the aluminium bars and these bars don't guide a magnetic flux. In my drawing of the 6-pole armature, I have used a massive iron bar which is pressed on the original motor shaft. But the magnetic flux flowing inside this bar is using only the outer side. So it seems possible to use a thick wall pipe for the outside of the armature. The pipe is welded to two disks and the two disks are welded to a central bush which fits around the shaft. The pipe must be that thick that there is no magnetic saturation. Another way to make the armature lighter is to start with a massive bush but to turn a chamber at the left and at the right side of the bush.

It might also be possible to use the original armature and to reduce the outside diameter. Then glue a thick wall pipe at this armature and make the magnets grooves in this pipe. But this construction isn't reducing the weight.

[bigrockcandymountain]

I didn't expect to dive quite so deep as decogging in the hypothetical stage, but it's all good to think about. 

Here's a question? Adriaan has in his plans only the N poles covered in magnets.  The S poles are formed from the armature iron.   If you went with half the thickness of magnets, and covered the S poles also, would you get less, more or the same flux? I expect a small amount higher density. 

I would try doing like i did with my last conversion.  Turn the existing armature down in a lathe, to make room for the magnets.  Drill and tap holes and bed the magnets in epoxy and screw down with stainless screws. That is the easiest machining for me to accomplish.  I have a lathe but no milling machine.

Do you guys think 1/8" thick magnets on 100% of the armature would be enough?

[makenzie71]

That would have to go on a 100ft commercial tower...it might be interesting but no way I could do it myself.  Might be a fair candidate for a HUGE geared up VAWT, though.  A 20ft darrieus turbine with large sails could generate enough torque to gear it up, even though it wouldn't be as efficient.  There's a much bigger problem than how you use it, though, and it will required SERIOUS thought before even beginning the project.

I took apart one of my i1500's and damn dead was unable to get it reassembled properly because of the magnetic pull.  Getting enough magnet material in this thing to generate the kind of power it's capable of would mean some very interesting machinery would have to be used to assemble the generator.  The armature in that thing probably weighs close to 100lbs all by itself...you wrap it in 81 powerful magnets and it's going to have a pull measured in tons.

[SparWeb]

Do you guys think 1/8" thick magnets on 100% of the armature would be enough?

No.  I spent a lot of time with my conversions, working out the ideal magnet thickness.  For exactly this reason, cost/effectiveness.
I found that 1/8" and 1/4" magnets don't have enough field to overcome the back EMF when current flows in the windings.
All of my conversions have been done with magnets 1/2" thick and I don't regret the extra few bucks.

I agree with your lathe approach. Without a milling machine (and an indexer chuck) you won't be able to machine cavities for magnets on only some parts of the rotor and not the others.  With the entire rotor turned to the same diameter, 100% coverage of N and S poles with magnets makes sense.
When I converted the Toshiba 7.5hp motor, I added a step to mill flats on it after turning on the lathe.  That step I could have done with a draw file.  But I could use the Bridgeport at work on weekends, so...  anyway if you don't have a mill but want flat faces for the magnets to stick to, consider some elbow grease and a sharp new file.

Making a whole new rotor is also an option, which I did with my Blador conversion many years ago.  However, buying material to make the new rotor from can be as expensive, or more, than the magnets.

Wait...  do you have a shaper? 

some very interesting machinery would have to be used to assemble the generator. 

Also a good point.  A jack or some other device is needed to control the insertion process.

[Adriaan Kragten]

I didn't expect to dive quite so deep as decogging in the hypothetical stage, but it's all good to think about. 

Here's a question? Adriaan has in his plans only the N poles covered in magnets.  The S poles are formed from the armature iron.   If you went with half the thickness of magnets, and covered the S poles also, would you get less, more or the same flux? I expect a small amount higher density. 

I would try doing like i did with my last conversion.  Turn the existing armature down in a lathe, to make room for the magnets.  Drill and tap holes and bed the magnets in epoxy and screw down with stainless screws. That is the easiest machining for me to accomplish.  I have a lathe but no milling machine.

Do you guys think 1/8" thick magnets on 100% of the armature would be enough?

Yes, if you use half the magnet thickness and cover the south poles with magnets too, you will get the same calculated magnetic flux in the air gap. In chapter 3 of KD 747 I have calculated the flux density in the air gap and I came to a very high value of 1.02 T even for magnets with a thickness of only 4 mm and for an air gap at the south poles of 0.3 mm. However, for this calculation it is assumed that the iron of the stator is not saturated somewhere. The iron of the stator can be saturated at the spokes or at the bridge in between the bottom of a sleeve and the outside of the stator. For the very high calculated value of 1.02 T in the air gap, the iron of the stator will probably be saturated somewhere which means that now it is no longer allowed to neglect the magnetic resistance of the stator iron. This means that the real flux density in the air gap will be lower than 1.02 T. But even for a lower value, the stator iron will be close to saturation. Therefore I think that it is useless to take thicker magnets or to use magnets for the south poles too. The magnet costs increase about proportional to the total magnet thickness in one magnetic loop and so increasing of the total magnet thickness will make the generator a lot more expensive.

It would be a good test to make two different armatures; one with magnets for only the north poles and one with the same magnets for both north and south poles. Then measure the open voltage for a certain rotational speed. I expect that this voltage will be only a little higher if the double total magnet thickness is used. I think that you will find the same ratio for the maximum electrical power at a certain rotational speed.

Using magnets for both the north and the south poles has another important disadvantage. When the armature is mounted in the stator it will always be pulled to one side. The armature will only be centred after connection of the bearing covers. If magnets are only used for the north poles, only the south poles will make contact with the stator during mounting and so you will get no scratches on the magnets. So if the test with two different armatures would show that there is a big difference in between the maximum power at a certain rotational speed, it would be better to use thicker magnets for only the north poles than to use thinner magnets for both north and south poles.

The required magnet thickness will also depend on the generator size. The bigger the generator, the longer the path of the magnetic flux in the stator iron and the thicker the magnets must be to overcome the magnetic resistance of the stator iron if this iron is close to saturation.

[Adriaan Kragten]

Determination of the optimum magnet thickness for a new generator type is difficult. The best way is to build a prototype and test it on an accurate test rig. I won't do this for this new type of PM-generator with many magnets for one north pole but I have built and measured several 4-pole generators with magnets in inclined radial grooves. A picture of such a generator is given in figure 1 of report KD 341. The biggest generator which I have built makes use of a housing frame size 132 with an enlengthened stator. The measurements of this generator are given in report KD 82. I think that the proper way to judge the strength of a PM-generator is to compare the peak torque of the generator with the nominal torque Q of the original asynchronous motor.

The original 3-phase, 50 Hz motor has a nominal power of 10 kW at a nominal rotational speed of 1440 rpm and an efficiency of 87 %. So the ingoing mechanical power is 10000 / 0.87 = 11494 W. The angular velocity is 2 * pi * 1440 / 60 = 150.8 rad/s. So the nominal torque Q is 11494 / 150.8 = 76.2 Nm.

The generator armature has a diameter of 122 mm and a length of 190 mm. The stator length is 180 mm and so the armature juts out 5 mm at each side of the stator. The stator has 48 slots. The stainless steel shaft has a diameter of 44 mm at the armature. The mild steel armature is provided with four 10.2 mm wide and 38 mm deep grooves which make an angle of 2.5 ° with the shaft axis. Three neodymium magnets size 63 * 36 * 10 mm are glued in each groove with anaerobe glue. As the groove depth is 38 mm, it isn't possible to make the groove narrower if the grooves are made with a milling cutter. So for this generator type, the minumum magnet thickness is determined by the groove depth. The inside diameter of the stator is 122.6 mm and so the air gap is 0.3 mm. So the magnets of this rather big PM-generator have a thickness of only 10 mm.

The torque measurements for short-circuit in delta and star are given in figure 4 of KD 82. The peak torque for short-circuit in delta is much higher than for short-circuit in star because higher harmonic currents can circulate in the winding for short-circuit in delta. The peak torque depends also somewhat on the temperature of the winding. It is about 113 Nm for a warm winding in delta and about 85 Nm for a warm winding in star. Loaded measurements have only been performed for a constant DC voltage of 52 V rectified in star. The Q-n curve for 52 V star is given in figure 8 of KD 82. It can be seen that the maximum torque is about 86 Nm. This is about the same as for short-circuit in star. So the maximum loaded torque for 52 V star is higher than the nominal motor torque of 76.2 Nm and this is an indication that this is a rather strong generator for its size. I doubt if the generator would have been much stronger if thicker magnets would have been used. For this generator, there is only one magnet in a magnetic loop and so it isn't necessary to use very thick magnets for this type of armature construction. I think that the same counts for a generator of the same frame size if the magnets are orientated differently.

The 30-pole generator as described in KD 747 has an armature diameter of 114.4 mm and magnets with a thickness of only 4 mm. This diameter is only somewhat smaller than the diameter of 122 mm of the 4-pole generator with 10 mm thick magnets as measured in KD 82. So I agree that the magnets of the 30-pole generator are relatively thin. But it still seems worth while to build a prototype and to measure what maximum torque level can be obtained for these thin and cheap magnets.

[bigrockcandymountain]

Wait...  do you have a shaper? 

Why, yes i do.  Thanks for asking. I could machine grooves with the shaper.  I even have a dividing head that could be used.  The problem i see with a dividing head in the shaper is rigidity.  The tool pressures are very high, and a dividing head has very limited holding power. I bet i would learn a lot though.   

I wish magnets weren't so darned expensive these days, and i wish i had more of a need for a bigger turbine.  It would all be much more justifiable that way. 

No.  I spent a lot of time with my conversions, working out the ideal magnet thickness.  For exactly this reason, cost/effectiveness.
I found that 1/8" and 1/4" magnets don't have enough field to overcome the back EMF when current flows in the windings.
All of my conversions have been done with magnets 1/2" thick and I don't regret the extra few bucks.

I used 1/4" and covered the whole surface, with a very small air gap on my 5hp  I'm happy with the performance.  I'm thinking 1/4" is the magic number for me here.  I certainly don't need 100% of the potential out of a motor that big.  If it makes 3kw on a normal wind day I would be quite happy. 

[joestue]

I didn't expect to dive quite so deep as decogging in the hypothetical stage......

Do you guys think 1/8" thick magnets on 100% of the armature would be enough?

I rewound a 1/3rd hp 1200 rpm induction motor with 18 individual coils, 30 poles, 36 slots, 120vac at 400hz at 1750 rpm ish. 2 inch long armature, about 2.75 inch diameter.
So instead of a 50% efficient 1/3rd hp motor it was able to overload  a 1/2 hp dc drive. (So probably .75 to 1 hp at 1700 rpm)

Its short circuit current was 9 amps, which suggests it would be able to supply 4.5 amps times 1.73 times 120vac, at 1750 rpm, while dissipating only 60 to 90 watts of copper losses.

The magnets were 1/4 inch wide 2 inches long, 30 of them. 36 slots in the stator, 18 actual copper coils.


.

[ruddycrazy]

Just one thing to remember with a huge motor like is putting the magnet into the motor housing, now let me tell you how my 4Kw motor conversion insertion went.

I put the motor in a 'G'' sized Warman Bearing housing I got for free with the end cap just big enough to fit the magnet rotor, then I used a chain block on the lifting jib on my tractor.

Well when it hit home the front wheels on the tractor came off the ground and that 400 kg bearing housing went up with a thump and the magnet rotor was home. Now as this motor is a heap bigger than mine better to start thinking on just how your going to fit this magnet rotor as going the wrong way it will bite and bite hard. Doing this the correct way is the key to the success of these motor conversions and steps do need to be taken to ensure this process is done properly and safely.
so mate have a real good think on how you can do this as yes it will be a daunting task

[bigrockcandymountain]

When i did mine, i bolted the motor frame to the loader frame of the tractor.  I then ran a bottle jack up through the bottom, fully extended.  Then i just set the rotor on top, and let down the bottle jack.  It went surprisingly well.  I did line the inside of the stator with 6 mil poly to prevent scratches. 

After putting the magnets on, i was extremely careful with the rotor.  I moved it around in a big plastic picnic cooler iined with blankets.  The threat of it jumping out and smashing in to something metal was always there.

[joestue]

On the order of a maximum of 100 pounds per square inch at 1T field strength. (Goes with the square)

So for the 3x diameter 2.5 inch long ferrite armature mentioned in my last post, on the order of 10 pounds force to pull the rotor out.

Neodymium would be on the order of 10 times that, assuming the stator was designed for neos in the first place and didn't saturate.