Tie in an induction head and synchronous head

[muns53]

My idea is to have an induction genny (3-5 KW) run by a Listeroid 6/1 for grid-connected net-metering and a synchronous genny (3-5 KW) run by a second Listeroid 6/1 for backup power (non grid-tied). The purpose of the net-metering is to cancel out my electrical bill. The purpose of the backup power is to run the essentials when the grid goes down (several times a year where I live). Both prime movers will be primarily fueled by WVO.

Then, what I want to be able to do is tie in the induction motor to the synchronous motor for larger power needs. I was thinking of either a 5KW ST or Utterpower's 3KW PMG for the synchronous motor and a Baldor 3-5 HP motor for the induction piece. (Reference for the latter is Bill Rodgers' book (The Home Power Producer's Guide to Electrical Reality).

Anyone doing this? What are the considerations? What are the potential pitfalls?

Thanks!

[ronmar]

What are you planning on using as anti-islanding circuit with the grid tied induction generator? 

Connecting an induction gen to a syncronous gen to double your output capacity...   Hmmm....  I don't know of anyone who is doing it.  I don't have a clue how the syncro would react to the inductive gen exciting off of it.  Linking an induction gen to the grid is one thing, it has that near infinite(by your homes standards) load capacity and frequency stability.  YOu just have to try and increase the output freq of the induction gen(I say try:)) and you are pushing current back into the grid.  the induction can't alter the frequenbcy of the grid though.  The syncronous gen on a 6/1 prime mover has frequency that is all over the place with load changes.  As the induction gen ramps up to put out power it will take load off teh syncro which will unload and speed up, which will reduce the output of hte induction gen as it's "grid" frequency tries to speed away.  This shifts load back to the syncro gen.  I could see these things fighting each other for control, but I have never tried it either...

[Doug]

It will work.

Pitfalls:
PF will need to be adjusted.
Frequency drift will be higher because as the load increases and decreases the Asyncronous head not only put out different voltages but it will try and change frequency. The governer on the roid can't be  set in any way to change the speed to compensate.

[muns53]

Thanks guys.

Ronmar, I'm not sure what you mean about an anti-islanding circuit. Is this because the inductor and synchronous motor will "fight" a little if the load varies?

Doug, what would I be aiming for with adjustiing power factor? And do you mean with capacitors on the induction motor?

Regarding the drift and load shifting... so, for the situation where the motors are tied, would it help to push the power first through an inverter or some type of power conditioner to clean it up?

[Doug]

You would have to PF correct the motor to unity.

Nothing I can think of would condition the power although the synchronouse head would probably drag the induction motor back some if the frequency got much above the no load base. You would need to baby sit the thing basicly like a system opperator and adjust the governer constantly as the load changes to keep the frequency tight. .

[buickanddeere]

  yes, no and maybe.
  You will be happier just limiting the electrical loads to allow limping along with one 6/1 instead of trying to sync two generators. Plan B would be an oversize sync gen and tie the two 6/1's together on one large generator.
  Why are you so keen on messing with an induction generator?

[Jim Mc]

What are the potential pitfalls?

In a nutshell; the economics of selling power back  to the utility.

[ronmar]

Thanks guys.
Ronmar, I'm not sure what you mean about an anti-islanding circuit. Is this because the inductor and synchronous motor will "fight" a little if the load varies?

I am refering to a circuit to disconnect your induction generator from the grid automatically.  In a perfect world, when you loose the incomming power from the grid to the induction motor, it will no longer excite and stop generating power.  In the real world, the nature of the capacitance in the line connection itself coupled with residual magnetism in the motor head may allow the induction motor to self excite and continue to generate power if the commercial power fails.  If this happens, you will continue to generate power and feed it to the grid and possibly injur a lineman trying to repair the system.  An anti islanding circuit monitors the commercial power and if the commercial power is lost, it physically breaks the connection to the induction motor.  An approved and legal installation to backfeed the grid will require this circuit for safety purposes.  This also works both ways as the grid power when it is restored may not be at the same spot in the sine wave that your induction generator is running at.  This will force the induction motor to attempt to physically re-align itself to the grid power and this could possibly damage your motor or the engine driving it...

All the grid-tie capable inverters that the solar net metering folks are using have this circuitry built in, and will not make any AC power unless there is valid incomming commercial power available.  Not quite sure where you would get an anti-islanding circuit for an induction generator setup... 

[Doug]

" In the real world, the nature of the capacitance in the line connection itself coupled with residual magnetism in the motor head may allow the induction motor to self excite and continue to generate power "

A fact many people do not understand. A long power line looks like a capacitor to the utility ( even a correct line ) hence most power station are generating a lagging powerfactor. The lines themselves use reators to ground to help compnesate for this. Next time you drive downa rural road and see transformers on the poles look to see how one end of the primary is very often going to ground and not another conductor. Many of these are not transformers at all.....

[buickanddeere]

" In the real world, the nature of the capacitance in the line connection itself coupled with residual magnetism in the motor head may allow the induction motor to self excite and continue to generate power "

A fact many people do not understand. A long power line looks like a capacitor to the utility ( even a correct line ) hence most power station are generating a lagging powerfactor. The lines themselves use reators to ground to help compnesate for this. Next time you drive downa rural road and see transformers on the poles look to see how one end of the primary is very often going to ground and not another conductor. Many of these are not transformers at all.....

   Not to find fault but I've stood in the Pickering Nuclear A control room and watched the operators increase the generator excitation to provide a leading PF as morning load increases/motor loads are started by industry etc.
   Long lines do have a capacitive effect but it's too limited. Most switchyards and sub-stations contain banks of oil filled PF correction capacitors.
   The "inductors" on the poles are actually auto-transformer voltage boosters.

  b&d

[ronmar]

Having worked with some large banks of PF correction caps, I mainly recall they were in place to get our facilities load(very inductive) within the utilities specs for power factor.  Loads outside the specified limits caused a higher electrical rate...

[muns53]

Jim Mc - Power is expensive in my part of NY and only going up. Depending on the project budget, I'm figuring on a project ROI of 2-4 years - and a "free" backup genny - and "low cost" energy thereafter (maintenance on the system and replacement parts basically). My veg oil fuel is "free" - just my time that's invested in collecting and cleaning (only a few hours/week), so I'm happy with the economics of it.

All - I don't plan to grid-tie without consulting the utility. Based on your feedback, maybe an induction generator isn't the way to go. I was just thinking that tieing two smaller generators together (one inductor and on synchronous) would be more economical than setting up one larger generator for backup power and one smaller generator for net-metering. Maybe the simplicity of that is better than trying to get fancy...

They don't credit for net-metering where I live without solar, wind or bio-gas. So, I figure I'll have to have at least a small wind or solar PV project along side this. The wind would spin an alternator to produce DC into an inverter; the solar also produces DC. Then, they are tied to the grid with anti-islanding circuitry (now I know where I've heard that term, Ronmar).

So that makes me think of another approach. Would it be simpler to run a DC alternator off a 6/1 and just size up the inverter to handle the current input from the solar/wind genny and the Listeroid/alternator? Then, I could invest in a battery backup setup instead of a second generator. When the grid goes down, I could just run the house off the battery bank & use the 6/1 to recharge the batteries when they get low through the same inverter.

Potential budget:
1) $1200 Listeroid
2) $2800 3KW Outback Inverter/Battery/Circuitry (after rebates - retail price is $7K)
3) $1000 1KW Solar panels (after rebates - retail price appx. $2500); $1000 1KW Wind turbine (after rebates - retail price appx. $2500)
4) $250 Permanent Magnet, Brushless DC alternator
5) $500 Miscellaneous
Total: $5750 - ROI = 2.2 years

Thoughts?

[ronmar]

Like I mentioned earlier, most of the net metering inverters don't work at all without grid power available.  There are systems that have backup capability when the grid goes down(my neighbor has one), but that option will cost you.  You need to be specific in your specifications to the folks who are supplying/installing your system.

I am contemplating a grid tied solar system with my new home build.  Once inplace, that opens the door to any other DC source I can come up with, such as a capacitor excited 3 phase induction generator and monster rectifyer.  This should work ok as the load back to the grid should be fairly constant.  I have a seasonal source for microhydro, so this seems like it might work ok, as  once on line, I don't think the grid tied inverter really cares where it gets it's DC from...   

[mike90045]

Depending on the "ripple" or "lumpyness" of the rectified AC - DC for battery charging, the charge controller may have trouble with it, and regulate poorly. Outback is known to have problems, Xantrex fewer, and the new Monringstar 60A MPPT very resistant to "ripple".  Ripple on batteries is also caused by the load of the inverter supplying a heavy load @ 60 hz, which can knock off a charger just when you need it most.
 Also, outback inverters are 120VAC only, Xantrex XW's are 240V, with 70% imbalance OK  Also price out the control/programing module & adapters for each.

[Doug]

Lines are capacitive and the longer the more trouble it becomes ( also series inductive ). All power lines are compensated to correct for this though.

Please do find fault if I am wrong but generaly I been told ( by the power dept this would include the guys at places like big Eddy dam ) we generate slightly lagging to compensate for or short lines ( that were for 25 cycle way back in the day ). We also have reactors to compensate our lines as well as synchronous reactors and caps.

I do see auto transformers on poles far more than any line correction these days.

The need to correct lines is serious buisness and a long un corrected line would be useless to transmit any power without it.
One of the reasosn Manitoba hydro and Quebec are using DC transmission....

BUT.......
Buck works for a Utility I work for big consumer. If someone is wrong/out of date or simply used to very old out of date equipment, its probably not the Utility guy.

Side note Buck if you and the fellows have nothing to do this week end could you send a massive power spike to copper cliff  ?

" In the real world, the nature of the capacitance in the line connection itself coupled with residual magnetism in the motor head may allow the induction motor to self excite and continue to generate power "

A fact many people do not understand. A long power line looks like a capacitor to the utility ( even a correct line ) hence most power station are generating a lagging powerfactor. The lines themselves use reators to ground to help compnesate for this. Next time you drive downa rural road and see transformers on the poles look to see how one end of the primary is very often going to ground and not another conductor. Many of these are not transformers at all.....

   Not to find fault but I've stood in the Pickering Nuclear A control room and watched the operators increase the generator excitation to provide a leading PF as morning load increases/motor loads are started by industry etc.
   Long lines do have a capacitive effect but it's too limited. Most switchyards and sub-stations contain banks of oil filled PF correction capacitors.
   The "inductors" on the poles are actually auto-transformer voltage boosters.

  b&d