Author Topic: Induction generator VS standard generator.....  (Read 16881 times)

dkmc

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Induction generator VS standard generator.....
« on: March 21, 2008, 06:35:38 PM »
So I'm thinking again about the advantages/ disadvantages of a standard generator VS an induction generator as they apply to
reducing demand charges for my industrial 3 phase service.

It occurs to me that I have 2 choices with a standard generator:

1. Use it to power machines and the whole shop as far as the KW rating will go.
2. Use it only for base loads (lighting, boiler power, computer power,) and the stuff that's always a constant and known load.

Problem is, with the above loads, they will do little to affect my demand charges which increase based on what machinery I power up
during the course of the billing cycle. With industrial 3 phase service, the demand charges can be 50-70% of the total bill!
If I can't use a listeroid CHP setup to decrease my demand, there is no point to pursue it......which does not get me a Listeroid to play with, and therefore is not the fun result I am hoping for!   ;)

So.....question is.......with an INDUCTION generator, and using it to "push on the grid", and having it slow down the electric meter, that seems to be the way to reduce demand directly. 
Slowing the electric meter is the only way to incur less demand charges without having a generator big enough to handle the total
shop load. (Not practical, and too much power for a Listeroid solution)

Anyone here successfully running an induction generator and slowing the meter? Is this legal?
What hardware is required?  I have a 60 HP 3phase motor I could use as the induction generator.
Where can I read/ learn more about how to use a 3 phase motor as an induction generator? 
I am also considering the use of a WABCO air brake compressor off of a road tractor, belted to the Listeroid, to supply a certain amount of compressed air to the shop air system. These units are made to run continuously all day long, and load/unload as needed.
Most common sizes are in the 5-10 cfm range, which is not a lot of air, but could be helping to fill the air receivers on the electric compressors "all day long".  Why generate electricity -to run a motor....-to turn a compressor? Let the Listeroid turn the compressor directly and save conversion losses!
The Wabco units are water cooled, BUT they require oil pressure for lubrication, and I am not sure if the limited oil pressure from the listeroid oil system would be adequate........?

Induction Generator bad points:
1Down side to the I/G is that if the power goes out, it cannot (to my knowledge) be used as backup power.

And so goes the trade offs and dilemma....... ???


Appreciate your thoughts/ comments.....the battle for lower energy costs continues..... :'(

dk

ronmar

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Re: Induction generator VS standard generator.....
« Reply #1 on: March 21, 2008, 08:15:00 PM »
Well some of that depends on where you are at. ¬ There are a few threads here on selling power back to the grid, and doing it legally with an induction generator could be problematic. ¬ Squirrel cage motors are marvels of ingenuity. With outside excitation(power being fed into it)A squirrel cage induction motor simply needs to be attempted to be spun faster than it's resonant(rated) RPM. ¬ The torque being applied to spin the motor faster is converted into energy fed back onto the power lines. ¬ The more drag(load) you apply, the more current it draws, the more torque you apply, the more current it generates. ¬ Amazing!

As a generator the motor gets it's excitation from the energy already in the lines and in theory will stop generating when that power goes away. ¬ But enough capacitance in the circuit and it will self excite. ¬ If you had this thing on line and the power fails, you could in theory backfeed power down the line without anti islanding circuitry, hence the hardware and liscencing requirements for a legal connection. ¬ Power output from an inducton generator could offset the ammount of power used in your shop though, but at what cost, I don't know. ¬ A 60HP 3 phase motor might also be a little large and will suckup a ton of energy just to rotate the mass and move air around. ¬ You might have trouble coupling the roid torque pulses to such a high mass. ¬  ¬ 

To get an induction motor to work as a stand alone induction generator requires excitation. ¬ This excitation, can be provided by adding capacitance across the output legs, with the ammount of capacitance controlling the excitation/output voltage. ¬ But the catch is that it is not very effective powering inductive loads as most of your 3 phase loads probably are. ¬ An induction motor used this way can only start another induction motor maybe 1/6th it's size. ¬ For resistive loads such as lighting, it works good though.

I found these links a while back. ¬ I have been studying this also as I think a 3 phase induction motor has real potential as an efficient DC source like an auto alternator, without the efficiency losses of an alternator.

The first is from a Danish wind power site and does an excellent walkthru of types of generators and explains how a squirrel cage induction motor operates as a generator.
http://www.windpower.org/en/tour/wtrb/electric.htm ¬ 

The second contains a bunch of links on this subject. ¬ Interesting reading.
http://www.educypedia.be/electronics/generatorasync.htm

Edit:  Wrong second link...

Ron
« Last Edit: March 25, 2008, 12:40:27 AM by ronmar »
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Jim Mc

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Re: Induction generator VS standard generator.....
« Reply #2 on: March 22, 2008, 02:23:03 AM »
...
If I can't use a listeroid CHP setup to decrease my demand, there is no point to pursue it......which does not get me a Listeroid to play with, and therefore is not the fun result I am hoping for! ...

You need to be honest with yourself.  The list of folks who  are successfully lowering utility costs with a Listeroid prime mover is, well, uh... pretty short.  If your  fuel is free, the numbers can work out in a CHP set up.  If you're buying #2 fuel oil, forget it.

But, hey, if you just like to tinker at these things, then go for it.

Take the time to do the math. 

Let's start here:  How much is your demand charge per month?  And for what kW demand?  In other words, what are you paying per kW of demand?  How much per kWh of usage?




dkmc

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Re: Induction generator VS standard generator.....
« Reply #3 on: March 23, 2008, 01:09:42 AM »

I don't need anyone telling me to "do the math" as I've been doing it for several years now.

Who would buy No 2 at near $4 a gallon in hopes of making cheap electricity??

Of course my fuel would be ......near.......free. WVO isn't FREE.......no matter who tries to kid who into thinking it is.
Unless someone delivers it for free and your slaves filter it for you at no cost.

The short answer is that when I divide my total electric bill by KWH I get about 24 CENTS/ KWH.
My highest demand is usually about 6 KW....

Is that electricity expensive enough to warrant an alternate method?

Doug

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Re: Induction generator VS standard generator.....
« Reply #4 on: March 23, 2008, 01:47:27 AM »
You can be reasonably sure that the motor in question can deliver around 85-90% rated name plate power to the line drivin by a prime over with 60 Hp.

The less input power the lower the efficency but if the fule is near free I guess its not so bad.

Guess I should add more info since there are more questions....

You can induction generate with single or three phase.

The efficency of induction machines is lower because unlike a machine that has field windings and an exciter the induction machine must transfer power to the rotor acoss the air gap to build the magnetic field and this means more air gap losses, more iron inthe core and more copper inthe stator to handle the extra current. Most people never notice but two identical hp machines one syncronous and one induction side by side the Induction is larger in all respects because of the need for more iron and copper in the stator to provide that extra excitation current to the rotor.

You can do all kinds of neat stuff with the induction generator. Because the power output is directly proportional to the slip above syncronous speed its very easy to tell how much power you are generating ( once you know the charateristics of the machine from testing and observation ) just buy monitoring the speed ( 1800 rpm means you doing nothing but abosorbing reactive power form the line at 1875 you may be producing full power anything in between is a fairly steady ratio ) .

Inspite of the slightly lower efficiency Induction generation is a very simple and reliable way to make grid connected power 
« Last Edit: March 23, 2008, 01:58:27 AM by Doug »
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MacGyver

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Re: Induction generator VS standard generator.....
« Reply #5 on: March 23, 2008, 01:49:51 AM »
Of course my fuel would be ......near.......free. WVO isn't FREE.......no matter who tries to kid who into thinking it is.

This would be a thread I'd like to see started:

"How much does it cost to process free oil"  (both WVO & WMO)

I'd be curious to know what the REAL cost per Gallon is, including materials (replaceable filters, etc), energy input (pumping, heating the oil for processing, filtering, etc), and human labor (how much of your time does it take to process 10 gallons of oil?).

How about "incidental costs"?  Things like reduced injector life, increased piston/cylinder/whatever  wear?

Obviously no "free" fuel source is really free unless you can just pour it into the tank without additional processing and there are no other penalties like increased maintenance costs, engine wear, etc.

So how much does your "free" waste oil really cost?  Anyone?


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mike90045

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Re: Induction generator VS standard generator.....
« Reply #6 on: March 23, 2008, 01:55:57 AM »
What is the size of your Diesel motor ?  figure 2HP = 1 KW roughly   
 
Can 3 - 4 KW  be enough to offset your electric usage ?

You can generate DC, feed it into an appropriate sized Grid Tie inverter, and if allowed by your power company, would be legal. An induction motor *as a generator) would not pass inspection.

What if your ran a shop air compressor off the lister, instead of it's regular motor?

Jim Mc

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Re: Induction generator VS standard generator.....
« Reply #7 on: March 23, 2008, 02:58:00 AM »
...The short answer is that when I divide my total electric bill by KWH I get about 24 CENTS/ KWH.
My highest demand is usually about 6 KW....

Is that electricity expensive enough to warrant an alternate method?

Beats me.¬† You've provided essentially zero details about your bill, usage, loads, or even how much heat you could use.¬† $0.24 sounds high, but how much of that is facility charge?¬† 6kW of demand around here would generally cost around $60.¬† Since you implied that's about half your bill, I can only assume your monthly bill is $120, and you use, what, 500kWh?¬† Makes no sense to me -¬† here 3-phase Industrial rates include a $400/month fixed equipment charge.  If I was using only 500 kWh/month with 6kW demand, I'd be looking at single phase (non-demand charge) service and a phase copnverter...

Since you've already done the math, I guess you already know the answer.  Why am I wasting my time???

As for using induction generator vs. synchronous,  they're great - mainly because they can operate with very little auxiliary equipment since they needn't be synchronised to the line frequency.  But,  your local power company will be the only ones to advise you on exactly what you need in the way of auxiliary protection and saftey equipment.  But you already knew all that, right?  Again, pretty small group of folks that have made this work...  I can only remeber one thread of one guy that's running a cogen here...






M61hops

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Re: Induction generator VS standard generator.....
« Reply #8 on: March 23, 2008, 08:23:20 AM »
If I was in your position, from the info you've given, I think the best plan might be to use a 'roid to run a compressor with an electric clutch to provide all your shop air and a DC generator with a battery and inverter to provide some of your base loads like lights, computers etc.  This way you could keep your system isolated from the grid while cutting a percentage of KW use off your meter bill, but, depending on how the power company figures things might not lower your cost.  Lots of the time utilities measure the peak current draws of starting your motors and if you do much of that at the wrong time of day you pay extra.  If that is your situation it would probably require a more complicated approach.   You'd need to spin your 3 phase motor fast enough to generate power to help carry your base loads and the starting loads; while providing anti-islanding protection.  I'd be afraid that a 'roid couldn't provide good enough speed regulation for an application like this; you might see flicker in your lights and the motor might slow down and draw power from the grid when you switch on something that has a high starting current.  The combined draw of the machine you want to start and the motor you are using as a generator could be bad for your meter charges; this might be a case where you have to try it and see what happens.   And you would have to have a need for the waste heat or there is no chance of saving any money from this project.   :-\                                  Leland
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mobile_bob

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Re: Induction generator VS standard generator.....
« Reply #9 on: March 23, 2008, 02:55:35 PM »
here is what i would do :)

look for a huge industrial UPS 3 phase type,, they can be had very cheap used
use your lister to drive a couple of alternators to charge the ups batteries

plug the output of the ups into a #4 or #5 reversing contactor (used backwards) and  hook the grid into the other contactor
set he control circuit up to a timer so that when the demand charge time of day occurs the timer switches you offgrid seemlessly over to the ups.

but then again you have to have the engine running before switchover can occur, so use the output of the genset to provide power to switching circuit

i don't know what your peak kwatt needs are, but i bought a 15 kva ups surplus a few years ago for 25 bucks, that just needed batteries
it is a 208 Y connected setup.  with new batteries (240vdc front end) one could rectify an st head to keep the charge up on the battery bank.

or...

move all your lighting, computers, aircompressor loads etc over onto the listeroid as mentioned,, maybe there is enough loads there to offset all or most of your needs
during that time of day?

it is my understanding from a very knowlegable source that an induction generator (if based on a high efficiency 3 phase motor) can be well over 90% efficient
used as an induction generator.

another consideration you might want to look into,, that is what is your overall powerfactor?  you might very well trim a significant amount of your problem
if you have poor power factor and take steps to correct it.  most residential users are not charged for power factor issues,, but my bet is as an industrial user you are
charged for poor power factor.  machine tools can have miserable power factors i might add, lightly loaded motors have poor power factors, floresent lighting can also have poor power factors, computers and other stuff can as well.  it is something you wanna know about especially if you are charged for it either directly or indirectly.
and in any event your going to want to know that you have a good power factor if you are planning to produce your own power, where  poor power factor does nothing but eat up your generating capacity without producing useful work.

just some thoughts

bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

dkmc

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Re: Induction generator VS standard generator.....
« Reply #10 on: March 24, 2008, 01:54:46 AM »
Quote
If I was using only 500 kWh/month with 6kW demand, I'd be looking at single phase (non-demand charge) service and a phase copnverter..

Do you have a Listeroid Jim? If so, what do you DO with it....watch it run?

Apparently you don't know so much about utility companies and how they charge for commercial electricity.
There are no single phase non-demand meters for commercial users here. (Upstate NY).
Even houses converted to legal offices or dentist offices get single phase  :-\ demand :-\  meters now.
Any commercial customer that pulls over 5KW demand gets a demand meter. And very very few of the commercial customers
pull less than 5KW. I pull 5.2 minimum. I guess weather I really do, or weather they adjust the bill accordingly!  They have also changed the rules, you must be below 5KW demand for 6 months to qualify for "no demand charge billing". 
I am lucky to have a night rate meter, they don't install them anymore. No demand from 11PM to 7AM.
And 11PM friday to 7AM monday. Who wants to work those hours all the time tho...??

 With energy costs rising, I am sure more people will be using CHP setups in the future, so if only one person has done that so far,
that means nothing to me as far as it being a viable process for my situation.
Something tells me I could write a ream of details about my assorted costs and you'd find immediate fault with my proposal anyway.
So thanks for your info and words of wisdom. Please don't let me waste any more of your time.

I am glad there are more positive and open minded people here willing to discuss these ideas......
Yes, ideas. The 60HP 3phase motor was totally free, and I can always EBAY it.
Haven't invested 5 bucks in hardware yet....because it may not be a viable option.
 
YMMV....

Waste heat:
I would transfer what little waste heat is available to the hydronic baseboard system in the building.
The ending solution to the "problem"  ;D of having this " near-free" fuel available, may be to just burn it for heat in
winter. But burning it to first turn a generator sounds like better use of the "free" fuel ......maybe it turns out it's not.

Fuel costs:
I will try to filter as little as possible.  I will use a centrifuge. No filters to replace.

Bob G
I will be on the lookout for large UPS units.....interesting idea.
And I will learn about the power factor at my facility........thanks for that info also.
 
Thanks for the input and points of view.
« Last Edit: March 24, 2008, 02:23:37 AM by dkmc »

Jim Mc

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Re: Induction generator VS standard generator.....
« Reply #11 on: March 24, 2008, 04:08:14 AM »
Do you have a Listeroid Jim? If so, what do you DO with it....watch it run?
Yep, going on 9 years now,  and I enjoy every minute of it...

Quote
Apparently you don't know so much about utility companies and how they charge for commercial electricity.
There are no single phase non-demand meters for commercial users here. (Upstate NY).
I never professed to be an expert  in all utility rate structures.  I made some clearly stated ASSUMPTIONS about your situation - clearly stating I was assuming it might be the same as my situation.  Apparently not.  I make no apologies for that.

Quote
Something tells me I could write a ream of details about my assorted costs and you'd find immediate fault with my proposal anyway. 
If your math is at fault, you can be absolutely assured I'd point it out.  But, you seem to be a bit defensive about the details, so I may never have the chance...

Convince me - I'd really like to see how this works out!  I'd  like to see your utilities rate structure. 

You never stated what size Listeroid you're considering, but a 60HP motor may not be a good match.  Its line current, even when lightly loaded will be significant - maybe in the 50-100 A range.  Its power factor will be very low.  As cheap as 3 phase motors are, you might think about getting a smaller motor, better matched to the kVAs you plan to generate. 

Two other things to keep in mind - Induction generators generate only leading VARs.  This might 'raise the eyebrows' of the engineering folks at your utility.  Certainly not an insurmountable problem, but something to keep in mind.  Also, read the fine print about your utilities willingness to buy back power, and offer net metering.  My utillity, for example, says they net meter.  Great, eh?  But the detail  is that they buy back power at their avoided cost.  So every kW I'd generate is only used to defer their avoided cost, which is only about $.02 per kWh.  For me, it's not true net metering, since they install a 2nd meter to measure my generation, and credit for avoided cost.  Stinks.  I'm not asserting your situation is the same - just a suggestion to find out the details, in case you've not done it yet.

Quote
I am glad there are more positive and open minded people here willing to discuss these ideas...
....because it may not be a viable option.
Excuse me, I'm a scientist.  I just like to see how this is gonna work...  You claim to have 'done the math'  Just curious about the details.  In a forum like this we each have very little respect or reputation on which to ride. 

« Last Edit: March 24, 2008, 12:18:34 PM by Jim Mc »

buickanddeere

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Re: Induction generator VS standard generator.....
« Reply #12 on: March 25, 2008, 11:36:57 PM »
  Where are you located? Most utilities are forced to provide net metering by their government. The fees,regulations and equipment requirements can be daunting.
  If the roid was used for peak shaving and it was located inside the shop during fall/winter/spring. It would also offset 3-4 KW of heating loads.
  If using a syncronous generator and using a proper transfer switch. The roid could produce basic emergency power for lights and heat during a power outage.
  Using a synchronous generator, a rectumfire ( no that isn't a miss-spelling) and a grid tie inverter would be my personal choice. And forget to tell the utility about the peak shaving equipment.     

Doug

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Re: Induction generator VS standard generator.....
« Reply #13 on: March 26, 2008, 01:32:49 AM »
¬†  a rectumfire ( no that isn't a miss-spelling) and a grid tie inverter would be my personal choice.

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oliver90owner

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Re: Induction generator VS standard generator.....
« Reply #14 on: March 26, 2008, 07:23:20 AM »
I'm with Jim Mc here.  As a scientific type I read the initial posts and thought it so defensive and short on content that it deserved awaiting some replies before I dived in with any thoughts/observations (not that generators are my strong point).

'Thinking again' relays some kind of effort has already been applied to solve the problem previously but there appears to be little groundwork even considered excepting maybe the titles and subtitles for discussion.

None of the replies so far seem to have gone further than your previous assessment would have if you have combed the forums and other internet sources, excepting Bob's suggestion of a UPS. 

Waste Heat.
The reason you have so little waste heat is because you are not running anything!  There is at least 100% spare heat produced if and when you actually run one (even, let's say, 200% waste heat!).  That is not an inconsiderable amount of energy if you have calculated costs.

So, come on dkmc, give us a few details and you might just get an objective reply or three or four :)

Regards, RAB