Electric Motors driving Sucker Rod Pumps (oil pump jacks): correctly measure their Power consumption

[mrspcs]

We need to measure the Electric Power consumption (kW power intake) of electric motors driving Pump Jacks in oil wells.
I am pretty sure this requires the use of a special type of meter due to the cyclic nature of the pump operation (along its cycle it goes from high to low % Load values). Something like the Dranetz Demand Analyzer (e.g. take readings over a certain time interval).
Common hand-held, single digital output devices (e.g volts, amps, kw etc) won't do for this particular application.
I have seen this issue documented in a few papers (e.g. from the Society of Petroleum Engineers -SPE-).
I would appreciate if someone can indicate specific references regarding applicable standards for this measurement (like API, IEEE, etc).
Comments and suggestions on this issue will also be greatly appreciated.

 

[davidbeach]

kW will be continuously varying, other than peak kW, what can you gain? kWHr on the other hand would be useful measure of the energy consumed (directly related to cost of operation) and shouldn't be that difficult to measure.

 

[HTNeighbors]

I used to work for a contractor and did a lot of oil-field work. When we would take hand clamp-on AMP measurements, we would always take 4 readings and average them out. We would record the readings when the weights were in the following positions:
1) top
2) mid-way down
3) bottom
4) mid-way up

For long-term power consumption over specific times, we have had the utility company connect a recording meter at the service. We also had a 3PH Fluke recording meter we would use as well.

 

[itsmoked]

A standard kWhr meter will give you the correct energy consumption. Let it record for a specific period, like an hour, then divide the reading by that period,(in hrs), for the Average Power in kW. If you happen to use an hour your math will consist of dividing the reading by (1). That is, the Average Power equals the kWhrs.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Further to itsmoked's post:
Look on the utility meter for the kH factor. This is the watt hours for one revolution of the disk. Count and time the disk revolutions for 5 or 10 pump-jack cycles. Now you have the WHr consumption over a measured time period. Do the math. Don't forget to factor in the meter multiplier if applicable and divide by 1000 to get KWHrs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Here's a picture of a meter showing a kH of 7.2 Every revolution of the disk represents a consumption of 7.2 Watt Hours.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

A meter with a disk!!?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Yeah, really, who makes those anymore? ;-)

 

[waross]

Now you look at the travel of the pseudo disk. There is a set of dots that move across the viewing area. One transit of the dots equals one revolution of the disk.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cranky108]

I would think the ups and downs of the pump could be balanced out by adjusting the weight of the counter balance. Some utilities will use a peak Amp meter to record the peak, and mutply this by the voltage to calculate a demand KVA for the customer. Sort of a way to punish customers who don't attempt to balance there pump jacks.

I would expect two cycles per stroke in the electric demand if the counter balance is matched correctly with the down hole rod. If not perfectly aligned, and they never are, one of the two cycles will have a greater demand than the other. The problem lies in that several of these pump jacks will sync themselves and cause some very noticable voltage fluxuations that other customers will notice.

If the jack is greatly unbalanced, the two single phase Watt meter method will not work well, as part of the cycle will be generation back into the power system. This is confusing and I have seen arguments because the calculations don't work as expected. I would recommemnd a recording meter over the whole stroke to best determine the consumption.

 

[waross]

Here is a picture of an electronic meter with a Kh of 7.2. It will have a pseudo disk comprised of dots moving across the display. These are used to determine the equivalent of mechanical disk revolutions. Why spend time money to duplicate equipment that is already in place.

http://www.ebay.ca/itm/ABB-Asea-Bro...-State-Watthour-Meter-Class-200-/180667954742

I previously used kH. It should have been Kh

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Bill I hope you know I was just teasing you.. All the meters around here have wheels or fake wheels just as you describe.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Grin. David is probably correct though. I don't think that they are made any more but the old electro-mechanical meters are still available rebuilt. The price of around $15 or $20 makes them attractive.
Ya got me Keith!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mrspcs]

Thanks to all for the contributions and comments. Much appreciated.

cranky108: I think you are right.
The "recording" type meter is the way to go, there are some that in fact go longer than just the full cycle of the pump.
The problem with the Pump Jack is the high variability of the % Load on the motor. Just the opening of the traveling valve introduces a huge "point" variation.
There are a number of 'recording meter'types (under the general category of "demand analyzer") and they are expensive. Some even offer "leasing" the instrument.
Like I mentioned, the need for this type of instrument has been described at various times in literature (e.g. Society of Petroleum Engineers).
For our purpose, optimizing energy use, determining the % Load profile of the motor is fundamental (e.g. amount of time and intervals it operates 'underloaded' and by how much).
What I have not been able to find, and if anyone knows anyghing about it I'd appreciate it, is specific information on applicable standards (API, IEEE, NEMA etc.) for the task of determining/measuring Power intake [kW] in a Pump Jack type rig.
Again thanks to all.

 

[itsmoked]

mrspcs; You are driving us nuts. You are not being clear on your question. You asked "how do I measure the kW consumption of your pump motor". You've speculated you "think you need a special meter".
We've told you how to accurately measure "the kW" of your pump motor.

You now speculate that due to the variability of the motor load. You must use an "expensive" special meter. You do not. Any junk kWhr meter will do a better job than you would ever need of measuring the average kW power usage of your pump motor.

This begs the question, is your question wrong? Are you really needing something else? What exactly are you needing this 'power' measurement for? Is it only for adjusting the counter-weights?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

You seem to want to measure the energy used or kWh and not the power or kW. What exactly are you trying to accomplish with this metering?

How cheap do you want this power meter to be? AccuEnergy makes some cheap meters that have tons of features.

http://www.accuenergy.com/?discography=acuvim-l-series

http://www.powermeterstore.com/p8153/acuvim_al.php

Throw some CT's and PT's at this meter and you can easily have a permanently installed meter for <$500 in parts. You can go around to your pump jacks and log the kWh of each site and then reset the meter to record for the next session. Heck, the meter even has RS-485 communications so you can set-up automatic data logging if you wanted. If you don't like that meter, they have fancier ones that cost more of course.

If you want to try and determine some kind of pump jack efficiency rating then you'd have to measure some other parameters from the pump jack outside of the motor energy usage, such as amount of material pumped, speed being used and valve positions. Feed it all back to a computer and log the data to see what operating point gives the most material pumped per kWh used.

 

[DRWeig]

Veris Industries, Kele, Honeywell E-mon, and a number of others have kW / kWh meters that will do the job. Your load variability is not a concern. These meters are generally under USD$800.

I suggest you call one of these companies and speak with a technical representative. They will know the limitations of their meters. Typically, though, the sample rate is far higher than what you need.

Disclosure: I am a former employee and currently am a consultant for Kele.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[waross]

We need to measure the Electric Power consumption (kW power intake) of electric motors driving Pump Jacks in oil wells.

Cheapest way; Use your wrist watch or cell phone to time the existing utility meter, use the Kh number and do the math.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Hi mrspcs, I'm as confused as itsmoked...

It would be very helpful indeed if you can state WHY you wish to measure and record - what? Power? Energy? Peak demand? In other words, what is your end goal? Are you trying to correctly size the drive motor and its supply conductors? Or, as itsmoked asked, are you trying to adjust the counterweights so the heights of the two load 'scallops' on your power versus time trace are identical? Or maybe add customized power factor corrective elements to each jack?

Carl

 

[mrspcs]

Again thanks to all for the comments.
One final post regarding some of the answers.
There seem to be some confusion as to the original question. Some seem to not understand whether I want to measure "Power" or "Energy". Others indicated that although I want to measure "Power" (as in [kW]) I should be measuring "Energy" (as in [kWh]) instead.
The original question clearly states that the objective is to measure "Power" (as in [kW], power intake to the loaded motor, for instance).

As to the reason for wanting to measure that, I suggest reading (among the many references in literature) the Fact Sheet "Determining Electric Motor Load and Efficiency" from the Motor Challenge Program of the US Dept. of Energy.
The Power Intake of a loaded motor can be measured directly or calculated as: Pi = f (V,I,PF) where Pi is the input Power in [kW].
Once Pi is obtained, the "% Load" (output power as % of rated power) of the motor is calculated as: (Pi/Pir)x 100 where Pir is the input Power at full rated load.
Once the % Load is known, the Efficiency at which the motor is operating can be estimated.
That and the difference between "% electric load" and "% mechanical load" (e.g. in the motor shaft) are also well explained in the Fact Sheet.

HOWEVER, directly measuring the Power intake or the variables needed to calculate it (V, I and PF) in the case of a highly variable load like the Pump Jack (as indicated in my original question) requires a particular type of instrument, one capable of recording the values of the variables vs. Time (my original question mentions one such instrument, there are many in the market).
In loads of this type, the I and PF are varying constantly and rapidly. Hence the need for this particular type of instrument.
There are MANY articles and literature references about this. One that I think covers the subject rather well is a paper from the Society of Petroleum Engineers (paper SPE 16363: Electrical Savings in Oil Production by J.E. Bullock, Pacific Gas & Electric Co.. Presented at the Society's regional meeting in California in 1987). Regarding the proper equipment for these measurements in the particular case of Pump Jacks, the paper indicates that meters whose output is instantaneous values of the measured parameters are "not suited for measuring pumping unit motors" due to the cyclic nature of their operation (e.g. highly variable % Load condition).

The foregoing I hope clears that the objective is to measure POWER intake of the loaded motor (e.g. [kW] (to be used in determining % Load and Efficiency of the motor) and that a particular type of instrument is required in the case of the Pump Jack and similar types of loads.
Should anybody question any of that, I'd suggest taking the case up with the authors and/or organizations providing the material. I am merely a reader/user of it.

About the reason for wanting to measure/calculate those parameters:
This is also covered in the two references mentioned (and there is a score of others...). There are a number of reasons, all having to do with Optimizing Energy Use in Oil Production: advisability/convenience of replacing a motor with one of higher Efficiency, installing any of various options for energy savings, determine which pump jacks are the better candidates for any of these actions... etc etc.

That said, let me go back to the ORIGINAL QUESTION:
Does anyone know of any specific STANDARDS from any reputable organization or professional society (e.g. IEEE, API, SPE etc etc.) relevant to the case of pump jacks, referring to the measurement of the Power intake of electric motors (or their Efficiency) in the specific case of pump jacks or similar highly variable loads ?? (e.g. type of instrument, minimun length of recording time or any other aspect of this task).
(NOTE that I have made reference to publications, articles and papers but NOT to Standards. That's what I’m trying to find out).
Thanks and best regards to all.