Electric motor overspeed and grid backfeed

[veggie]

Hello ?....Hello?....anybody here ?    

I had a thought the other day and I want to get some comments on this.
I am not advocating the idea, but I wonder if it could be done safely.

It is my understanding that when an electric motor is running (say 1800 rpm, 60hz for this example) it is basically in sync....or synchronous with the grid at 60hz.
Now... if the machine that the motor is driving were to try and push the motor into and overspeed condition, much like a car going down a hill and driving the engine faster than it would otherwise be running, then that electric motor would generate power back into the grid.?

Setting aside the safety issues for the moment, lets discuss the principle of the idea.

One of the biggest problems with getting a small generator to be "grid tied" is the synchronizing of the Grid and Generator frequencies so that the generator head does not lock and explode.
Consider the following solution for a Listeroid (or similar) engine which is normally started by hand crank.

A 110 volt AC motor is mounted on the Listeroid base and belt driven with a ratio which equates to 1800 rpm (or 60hz) motor speed when the Lister is at 650.
When mains power is applied to the motor it runs at 1800 rpm and drives the Listeroid at say 650 rpm ( a 2.76:1 ratio ).
After a bit of spinning, the operator throws the decomp lever and the engine springs to life but at zero load.
A few moments later the operator increases the throttle in an attempt to bring the electric motor up to say 62 hz. However, the Listeroid cannot over power the grid and the motor stays at 60 HZ but is now generating power back into the grid. The only change is that the Listeroid is grunting a bit while trying the make the motor spin faster than synchronous speed.

There was no issue in trying the sync the motor to the grid because it was already running at synchronous speed before the Listeroid tried to over speed it.
In essence, a system with a starter motor and a grid tied power saver.

So, does this theory hold water ?

From a safety point of view, there was a reason why I chose to back feed the house with 110 volt.
The back feed would only be attached to one leg of the house system.
A relay energized by the none-back feed leg of the main panel would break the back feed connection if the grid power ever failed.

thoughts, discussion, caveats ?

Veggie

[mobile_bob]

do a google on induction generators

bill rogers wrote a book that utterpower used to stock and sell, Bill went into the details
of doing what you are talking about.

yes it will work, and yes there are some safety concerns

but iirc it is fairly easy to do, efficient, and is burnout proof

most induction motors run with "slip" which means an 1800rpm nominal motor will run at about 1740, or so given its slip  to produce its rated power.

the same motor overdriven to around 1860 will produce power if it is also connected with a set of capacitors to provide for excitation.  it is in choosing the right amount of mf of capacitance that the output voltage is set.

so yes it can be done, but it is unlikely that your power company is going to sign off on a diy system. 

pirate operation not with standing of course.

the thing is the motor now generator must see power from the grid to generate, if the gird fails the thing is supposed to stop generating, and it probably will 99.999% of the time in an equal amount of installations, however it is "possible" even if unlikely that there might be some guys shop with a capacitor back phase converter running when the grid goes down and this might under perfect conditions allow for your motor now generator to continue to put power out onto the local grid...

not likely, but enough that your local power company isn't going to approve in likely 99.999% of cases.

look on the net, there are countless examples of what you are talking about doing.

bob g

[veggie]

the thing is the motor now generator must see power from the grid to generate, if the gird fails the thing is supposed to stop generating, and it probably will 99.999% of the time in an equal amount of installations, however it is "possible" even if unlikely that there might be some guys shop with a capacitor back phase converter running when the grid goes down and this might under perfect conditions allow for your motor now generator to continue to put power out onto the local grid...
not likely, but enough that your local power company isn't going to approve in likely 99.999% of cases.

bob g

Hi Bob, note that I did propose a relay which would disconnect the motor if the grid went down.

As I recall, Bill Rogers book only deals with the use of a synchronous motor as a generator and not as a starter motor.
In my scenario, the motor would be used to start the engine and later to generate power. Changing of capacitors may hinder the "starter motor" part of the scenario.?

Veggie

[BruceM]

Veggie, alas your safety feature of the relay on the second hot leg isn't going to work.  When you drive the first hot leg winding of your power company's transformer secondary winding, you energize the other.

[Jens]

Have the new electronic power meters not made their way to you yet? The power company has the capability to look at your feed on an almost continuous basis. As far as I know they don't do that yet but it is definitively on the horizon. It would be foolish to try this unless you have the old meter (for how long?) and have a real desire to live in government housing and to eat government food.
Power companies also use statistical methods to trace theft and these will likely reveal your setup as well.
Since you can never feed more than you consume over a billing cycle (sure way to get the electrical inspector to show up), why not just spend a few dollars extra, generate DC and feed a lithium battery bank. Power some of your circuits from an inverter and anything that draws heavy current (stove) you leave on the grid.
Yes, there will be a significant hit for the batteries but then you will be completely legal and don't have to grow eyeballs in the back of your head

Why are you asking the question ..... we all know that the economics of generating power is iffy at best. If you are generating heat and the power is a by-product then this is a viable way of using that.

[SteveU.]

  Ha! Ha! Jens! Well said. I wished we had a "like" button here.  
Been living with telemetric/radio from the road pinged grid meters since ~2008.  
THEY do NOT want your power!   No matter what any laws may say.    
Back feeding to the Grid is a passe' dream.  

IMHO the freedom goal should be to not need/want Them anymore.  
As long as you are plugged into Them . . . they still own you.    
Give Them as little ownership power over you as is personally, affordable, possible.  
I near zeroed out consumption usage the one oldshop/woodshed/greenhouse/freezer shed grid meter back in May/June doing extended running inverter-generator testing. Do that too long would have triggered an on-site/demand inspection.

Regards  
Steve Unruh

[mobile_bob]

yup, our little town, pop. 450 or so, got fitted with smart meters this year,

i have about 1700watts of grid tie solar on my shop roof, not hooked up yet
and i don't plan on doing so until i can get time to rig up a control/relay system
that connects them to the grid only when i have enough load to warrant them being connected
without backfeeding the grid.

in the summer months that is easy enough, just connect a control line from the A/C blower motor
and the hvac, it runs nearly continuously during the hot months, most especially during the day time.

if i ever get back to the tri-gen project it will certainly be controlled in a similar manner as i don't want the headache of dealing with the power company and them giving me grief about backfeed
and other NEC/UL issues.

ideally i would like to get enough control over things to provide for all my loads, under a load management system, much like living off grid with batteries.  then just use the grid when i need peaking or backup?

i do however like the induction motor starting, then going to generator mode one running, much like the old hohler (and others) did with their smaller generators. they of course were not induction motors but combination units.

glad to hear you guys are still alive and kicking

bob g

[veggie]

Hi Jens,
As I stated in my original question, I am not advocating this idea. Just wondering if it could be done.
I thought of it while driving the other day and wondered if it was possible.
I have no need for AC motor backfeeding as my Roid already has electric start and a connection to key house circuits.
My current system has solar ---> batteries ---> Inverter ---> 6 circuit transfer switch, which allows me to run 6 house circuits on solar or grid, so what you suggested is already in place.
I have no desire to turn my meter backwards (currently the old style).
My batteries are 6V Solar deep cycles. I may consider Lithium when these Bats wear out.... but man those Lithium Bats are expensive right now.

Hey StevU,
I picked up a 3000W inverter gen a couple weeks back. Nice and quiet. Especially in economy mode.
Did you say to change the oil every 25 hrs under heavy use ?  I'm running Synthetic, and I'm planning to add an hour meter to the unit.

Veggie

[SteveU.]

Hey Mr veggie
100 hours on a synthetic oil.
50 hours on a standard dino oil.
Regards
Steve Unruh

[LowGear]

Educational Moment Please:

Of what is synthetic oil made.

Casey

[veggie]

Hi Casey,

Syn oil stands up better in extremes (Hot and cold)
So here in the frigid north for example, it helps during cold starts.  

https://en.wikipedia.org/wiki/Synthetic_oil

cheers,
veggie

[Henry W]

Hey guys,
It's been quite a while. Glad to know your all ok. I've been thinking of selling power back to the power company. Some of the issues I would face is being able to find someone sign off on a home built system. Having it insured would also be a problem. The only way it can be done is, you would have to have a licensed electrical contractor install a system that's been built by a manufacture a that's been approved by power companies and the county inspectors. But who has $30,000.00 to $50,000.00 to shell out to get a return. And how long will it take to have the investment paid off. For me it's not worth it. I would rather put a transfer switch in and have a system support the house just on ideal days and than go back on the grid when it can't support your needs.

About synthetic oil, that's all I use in air cooled engines. I use a group 4 synthetic.

[Henry W]

I am planning to down size to a smaller home. Looking to build a single story home on a slab. Thinking of a 700 - 800 sq. foot build. Something that will be wheel chair accessible if needed. I am looking at the possibility of using 2x4 staggered studded walls. This will help reduce the heat and cooling transfer to the inside walls.

[veggie]

Henry,

Good luck with your house project!
A new house is an excellent opportunity to incorporate energy saving designs at very little cost.
Im sure you will find it very challenging and rewarding 

Veggie

[Tom Reed]

A slab heated with a hydronic loop, heated by engine coolant/solar is a nice way to go.