Author Topic: gear up or smaller runner or double the poles?  (Read 6249 times)

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mab

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gear up or smaller runner or double the poles?
« on: November 06, 2014, 01:03:53 PM »
hello all,

My hydro system is running with a 7.5" pelton wheel on a 4 pole 3ph induction motor with capacitor exitation (nominal: 240v 50Hz 3ph Delta) which generates at about 110v 26Hz. Ideally I'd like to get it running closer to normal grid - a convenient factor of 2 up.

I've been looking for an 8 pole motor but they're a bit rare above 200watts and whilst one has become available, it's 400v delta rather than 230v meaning I'd need a transformer as well; but the cost of the motor, delivery, caps and a transformer make it quite an expensive upgrade.

An alternative method would be to buy/make a smaller pelton wheel but with the existing spoons I think I'd struggle to halve the diameter and wonder if it would work as efficiently with just 8 or 10 spoons.

The third option I was considering is a belt drive system which would not be too technically challenging to do, but I wonder how lossy it would be when there's little water?

The main reason for wanting to upgrade - aside from convenience - is that I'm already running at the motors rated (Y) amps (3.9A), and although it's wired Delta, as the fans are running ~ 1/2 normal speed I worry about overheating the motor, especially when running non-unity power-factor loads like a battery charger.

There's plenty of water at the mo' and it seems a shame not to use some more  :) , but I'm struggling to decide which way to go.
 

dbcollen

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Re: gear up or smaller runner or double the poles?
« Reply #1 on: November 06, 2014, 02:31:50 PM »
the 8 pole motor would likely generate fine at 220v and 46hz. I run a 1hp tefc 8 pole induction motor at 380v and 110hz on the 240v wiring(1400w continuous). it is never more than warm to the touch and has no fan on it, just the cast steel housing and fins. They are very forgiving on the speed, just adjust cap values for maximum power.

mab

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Re: gear up or smaller runner or double the poles?
« Reply #2 on: November 06, 2014, 03:10:41 PM »
thanks

my only problem with the 8 pole motor is the cost - and figuring out what caps I need (and the cost of the caps). I don't think I need to worry about overspeed as my pelton wheel seems to run around 800 ish RPM (I guess).

1400W from a 1hp motor! that's good going.

hydrosun

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Re: gear up or smaller runner or double the poles?
« Reply #3 on: November 15, 2014, 07:59:28 PM »
The easiest way to go would be to use a smaller pelton wheel. Harris hydro uses a 4 inch pelwheel which can take up to a 1/2 inch nozzle. If a 1/2 nozzle doesn't run enough water you can use  multiple nozzles. Conversely a turgo can handle more water in the same diameter wheel. You might find what you need at hhydro.com. They have different sized spoons and arbors to attach to your motor.       
Chris

joestue

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Re: gear up or smaller runner or double the poles?
« Reply #4 on: November 16, 2014, 03:37:59 AM »
I had a 1/3rd hp 6 pole induction motor, running at nominal rated nameplate voltage from the grid it had higher actual no load losses than did a 1/2 hp 2 pole motor wound with aluminum wire.

By gearing up the system you can use a smaller, faster, more efficient induction motor, especially if you run the motor at nominal name plate volts per hz.

I seem to recall back driving my 1/2hp 8 pole single phase, permanent capacitor run induction motor, at nominal nameplate voltage and frequency, I seem to recall I had to shove at least 1/4th hp into the motor to just start the watt meter spinning backwards.
I will have to repeat this test and make much more accurate measurements, but i think you will have better efficiency with even the crudest PM conversion than you will with capacitor exciton.

Flux

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Re: gear up or smaller runner or double the poles?
« Reply #5 on: November 16, 2014, 05:26:08 AM »
Many options, much will be decided by costs to you.

Changing the Pelton for smaller diameter or a Turgo ( higher specific speed) is one way to go, but having got a working turbine rotor that may not be a cheap option.  Gearing makes sense but depends on your low water conditions. Timing belts are better than v belts but the pulleys are expensive.

Chain drive is the most efficient option but needs lots of work to be satisfactory in most hydro environments, an open chain is unlikely to survive long.

Self excited induction motors are not the best for efficiency or flexibility but are simple. At high pole numbers they are not the easiest of things to deal with, 8 pole may or may not behave, depending on various factors so unless you can get one cheap to try I wouldn't go that way, if you can try it before paying then ok.

I agree that any form of true synchronous alternator , motor conversion or axial air gap is likely to be more efficient than a SEIG, motor conversions better protect neo magnets than axials in wet environments.

If your low water conditions are not particularly bad and you can get reasonably priced timing pulleys I would be tempted to raise the speed of your existing motor with a timing belt.

Flux

dbcollen

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Re: gear up or smaller runner or double the poles?
« Reply #6 on: November 16, 2014, 11:20:35 AM »
Not trying to argue with Flux, But I find my induction generator to be quite flexible, I run it with jet sizes between 1/8th inch and 5/8ths inch, you just need to add capacitance with bigger jets. I even ran it through a clipper and classic 250 and got the same amount of power as running just the 3 transformers and rectifier. I did let the smoke out of my Beta Clipper trying that experiment, the clipper can't act fast enough to catch the voltage excursions that an induction setup can create if unloaded. I have measured 1.6Kv on mine unloaded. I have 346ft of head with 1100ft of 2in poly pipe as my penstock.

Flux

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Re: gear up or smaller runner or double the poles?
« Reply #7 on: November 16, 2014, 12:01:00 PM »
It depends so much on the motor, possibly on the rotor cage resistance, that is why I said that it would be a good idea to try the motor before an expensive purchase.

With 2 or 4 pole virtually any motor will excite with capacitors. As the pole count gets higher they seem more fussy, I have heard of people trying 10 pole motors and not being able to get them to self excite.

I didn't intend to imply that it couldn't work, just was worried that the original poster was looking at purchasing an expensive motor with no assurance that it would behave. 8 pole and above are not common and are most likely made for a special purpose, certainly any version of an ac servo motor would almost certainly not excite.

Flux

mab

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Re: gear up or smaller runner or double the poles?
« Reply #8 on: November 16, 2014, 01:25:50 PM »
That's good to know Flux - The motor I was looking at was not very cheap TBH, just cheaper than buying new - add to that some different caps then I'd rather not find out it doesn't want to go.

I have thought about PMG conversion - though I'd still worry about exceeding 3.9A at 1/2 nominal rpm - but I'm assuming most of the heat I'm getting at the moment is generated in the stator not the rotor (presumably with a PM conversion you don't generate heat in the rotor? I do have another 4 pole motor (3hp) that I was thinking of doing the conversion on, but I guess if it's a bigger motor I'll need more magnets.

I may ask Harris about the price of their 4" pelton although I suspect it won't be cheap, but a smaller runner would surely be the simplest to do.

Timing belt sound's doable - in fact if I can find an old engine it should have 2:1 ratio sprockets anyway - if I can do the engineering to mount them true - otherwise it means buying new ones. But the water does occasionally run down to the point where I can't get it to run as-is.

Well thanks folks - I'll do some more thinking...

 

joestue

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Re: gear up or smaller runner or double the poles?
« Reply #9 on: November 16, 2014, 02:50:01 PM »
High pole count induction motors operate at lower power factor, requiring more current to self excite.

Converting an induction motor to permanent magnet will practically cut the losses in half, because not only do you cut the losses in the rotor to nearly zero, but the reactive current in the stator is done away with as well. so if it was 70% as a self excited generator, as a pm conversion it should be as high as 85% netting you 15% real gain.

A 3 hp conversion may be too large unless you run it at reduced volts/hz. how much hydro power do you have?

mab

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Re: gear up or smaller runner or double the poles?
« Reply #10 on: November 16, 2014, 04:54:53 PM »
not sure: it's currently running ~340w and there's enough water for as much again at the moment.

it does sound like a PM conversion may be worth it - it's finding the time. if the 3hp is too big then I'm sure I can find another smaller 4 pole - it's the 8 pole that are a bit rare.

thx


mab

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Re: gear up or smaller runner or double the poles?
« Reply #12 on: November 17, 2014, 08:21:57 AM »
that would do, though I'll probably look a bit closer to home to save on postage

XeonPony

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Re: gear up or smaller runner or double the poles?
« Reply #13 on: November 30, 2014, 09:50:08 AM »
http://h-hydro.com/New_Site/turgo-runners/ < Corrected link to not go to a dope shop lol.
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udos46

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Re: gear up or smaller runner or double the poles?
« Reply #14 on: April 22, 2015, 12:45:08 AM »

watch these videos with synchronous 10-poli


Absolutely NO LINKS on your first post!  DamonHD
« Last Edit: April 22, 2015, 02:38:15 AM by DamonHD »

Harold in CR

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Re: gear up or smaller runner or double the poles?
« Reply #15 on: April 22, 2015, 07:43:32 AM »

 A note on cog belt/timing belt pulleys. On an electric bicycle forum I frequent, someone made cog pulleys by taking a belt and measuring pulleys, to see where a belt could be cut and joined to fit exactly flush with the pulley.

 Then, use good epoxy to fill in the pulley and press the belt into the epoxy and tape it around the pulley.

 Inexpensive way to make durable cog pulleys. He rode that bike a lot, then sold it to build another.

skid

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Re: gear up or smaller runner or double the poles?
« Reply #16 on: April 24, 2015, 12:57:24 PM »
Regarding efficiency of V belts, I've read that vbelts cost ~10% efficiency...