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#72107 - 11/18/06 09:36 PM Meter that runs forwards and backwards
Ann Brush Offline
Member

Registered: 12/27/05
Posts: 155
Loc: Ohia
Just got back from a trip to Holmes Co. Ohio (Amish), anyway they have a little oil beneath them and there are numerous small grass hoppers (coloquial term for an oil well and rocking headgear) about. The cottage were we stayed was on a farm and one well head was in a pasture a few hundred yards from the cottage. I walked up to it to take a closer look. The electrical metering caught my eye. It looked like a standard "glass bowl" encased meter. As the rocker entered the upstroke (pulling oil up and out of the ground) the meter spun as usual - forward, however as it entered the downstroke (pump gear returning down into the shaft) the meter stopped spinning and started spinning the other way (in reverse), at the end of the down stroke the meter wheel stopped and again went forward. The reverse spin time/distance was not as much as the forward so there was always a net forward spin for each complete stroke (kind of like two steps forward and one step back etc). Anyway I was amazed to see this, they had harnessed the falling weight of the pump gear to generate electricity on the down stroke and was selling it back to the grid - all this in a little rural oil well that stood on a 8' by 8' pad. It flies in the face of discussions we have had here regarding the inability of getting meters to turn in the reverse direction. Anyone else seen this type of setup or wish to comment - I was impressed.

Edited for typo's

[This message has been edited by Ann Brush (edited 11-19-2006).]

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#72108 - 11/18/06 11:09 PM Re: Meter that runs forwards and backwards
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
Very interesting what you described from there and great observation !
When the asynchronous drive motor runs on overspeed which seems to happen when the weight goes down there will be electricity generated, hence the meter going backwards.
The utilities are most likely to be aware of it and accept this way of metering the latter.
When more of these oil pumps in an area are near each other these overspeed extra's will be absorbed by the loads drawn by the other machines and shouldn't give any problems to the supply feeder line.
_________________________
The product of rotation, excitation and flux produces electricty.

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#72109 - 11/19/06 10:29 AM Re: Meter that runs forwards and backwards
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
Me again, Ann

Regarding the meters running backwards,

Some type of electromechanical meters may have a reverse running stop built in as well.

This is usually a type of free running latch arrangement which engages with a ratchet sprocket mounted on the disc spindle.
Some allowe half a turn and others may allowe one turn of the disc backwards.

In some AEG VAr meters I have seen registers designed to register always forwards, regarding the rotation of the disc.

Electronic meters are a different topic, these usually don't run backwards because that is set up in the electronics circuit.
_________________________
The product of rotation, excitation and flux produces electricty.

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#72110 - 11/19/06 02:03 PM Re: Meter that runs forwards and backwards
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
Depending on the meter - If you install it up-side down it will spin in reverse. How do I know? Well once in a big rush I put on in that way, and got a call from the poco to put it back the right way....

Never heard of generation from an oil well, but hey, anything is possible. Weather or not this was the intent is a question that looms for me, as it is drawing on the up-stroke. There may be actually something wrong here - the motor may be generating unintentionally.....
_________________________
Mark Heller
"Well - I oughta....." -Jackie Gleason

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#72111 - 11/19/06 03:19 PM Re: Meter that runs forwards and backwards
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
Any asynchronous motor which is ran at a higher speed than the nominal speed + slip will generate power when the motor coils are energized.

So a 1800 RPM motor ran at 1854 RPM because of the weight of the load will generate power.
( say a 1800 RPM motor with 3% slip will run up to 1854 RPM, then the motor will act as brake and generates power.)

This method is also used in ac crane motors, to reduce wear and tear on brakes while a load is hoisted down.

AC electric locomotives can also "generate" power this way in a descend with heavy freight trains while an uphill going train absorbs the extra power available.
_________________________
The product of rotation, excitation and flux produces electricty.

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#72112 - 11/19/06 03:27 PM Re: Meter that runs forwards and backwards
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Looking at pics of 'Nodding Donkeys', they don't appear to have any counterweights on the beams, so regeneration on the downstroke may be economic, [ plus the braking effect you mentioned Rod]. A reversing meter though; - would that be a feasible or accurate method of measuring net power consumption?

Alan
_________________________
Wood work but can't!

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#72113 - 11/20/06 05:02 PM Re: Meter that runs forwards and backwards
WFO Offline
Member

Registered: 09/03/05
Posts: 206
Loc: Cat Spring, TX
It is "Net" metering, pure and simple.
Like Rodalco said, Poco's that were worried about it put detents on the discs to prevent reverse rotation. Others didn't worry about it.
Where it becomes a factor now is with AMR (automated meter reading) technologies that depend on a light reflecting off the disc to count rotations. The light can't differentiate direction, so it counts forward and reverse rotations equally. As a result, the consumer gets billed too much if a detent is not installed.

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