×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Submersible motors
3

Submersible motors

Submersible motors

(OP)
I am seeking Information on speed measuring of submersible motor.

RE: Submersible motors

Grover194

Our pumps do not directly bolt to the type motors you are looking at due to different bolt patterns, but we do use this type motor on occasion.  We have a machine shop make a spool adapter and coupling for us to fit between the pump and motor.  You could have an adapter made to gain access to the motor.

It depends on how the pump is made, but you may be able to gain access to the shaft at the top end of the pump with an adapter.

The amount of slip is going to be dependant on the motor design.  To make a reasonable calculation of rotating speed or slip you may want to contact the manufacture and see if they can offer possible information.

The amount of accuracy that you require is going to drive the cost of the method used.

Good Luck

RE: Submersible motors

Suggestion: A magnetic pick up sensor could be mounted to the frame and be directed toward the rotating part with a teethed wheel. It could count rotating part teeth/revolutions and send pulses to a speed indicator.

RE: Submersible motors

depending on how accurate you want to know speed - for approximate speed, you can ask the manufacturer for a running speed vs current curve at operating voltage and frequency.

RE: Submersible motors

Has anyone tried to use acceleration probes like those used for developing bearing signatures?  I'm sure you could rig up say 2 symmetrical features that make slight contact with something.....starting to sound like playing cards on the spokes of your bike.  Sounds hokey, but when I was doing PM surveys at a papermill, we could pinpoint the rpm's of the equipment fairly well.  Just a thought....

RE: Submersible motors

Hi Grover
The Idea of a vibration Accelerometer would be ok if you could transform that analogue signal into a Vibration Spectra.An Overall value would not tell you the RPM.
There are very small EDDY current probes/Gap probes, that can be installed close to a moving shaft and pick up a keyway or something.This is fairly simply technology and reasonably accurate.They are also called Proximity probles.Try Bentley Nevada /Entek/IRD/Kadon Eng.

Good Luck

GusD

RE: Submersible motors

2
Dear Mr. Grover,

Your basic problem semms to be measurement of the speed of a submersible motor, ie. when in submerged condition. I hope my assumption is correct.
There is a one method for measurement of the speed of submersible motors with much better reliability. However, this method can be used provided the performance test is being done in an open type of well or sump.
The main sensing device is called as Slip Coil, which is mounted over the stator portion of the motor.( at the centre of the stator ). As you may be aware, when the any induction motor starts, there is a back emf generated in the rotor. Due to the magnetic leakage, an emf is generated in the slip coil, with different frequency and is equal to the difference in the line ( supply frequency ) and the one generated by the rotor. To measure the slip, this signal is fed to a centre zero galvanometer, of which neddle oscillates exactly as per the differential frequency. this oscillations are counted and the speed is calculated.
In another method, a special disply instrument is connected to the out put of the slip coil and it displays directly the speed of motor.
The no. of turns and the I.D. of the coil is to be decided based on the stator length, operating voltage and this coil can be used for other motors having the O.D. smaller.
If you can provide me a little information about your motors, ie. the rating, operating voltage / frequency, motor OD etc. I can give you the details of this.

Before I end, let me tell you something about myself.

I am basically an electrical engineer working with KSB Pumps Ltd, India in Marketing department. I have 20 years of experience in the field of submersible bore hole pumps and submersible sewage pumps. My experience includes Research & Development for two years, design 7 years, projects 5 years and now looking after Projects in marketing department. In addition, I am excellent in the field of testing of motors, designing of instrument panels ( for performance testing )and control panels.
I hope this will be useful for you.

Rajendra Joshi
So if you have any problem like the one here, you ask and I will try to find a solution on it.

RE: Submersible motors

(OP)
Dear Rajeendra Joshi,

This is exactlly what I am looking for. Thank you for your input.

Alan

RE: Submersible motors

Question to AARVEEJE (Electrical) Mar 25, 2003:
Is that concept reliable and accurate considering its complexity? What about an accuracy in measuring the zero speed of the motor, i.e. whether or not the motor is at the standstill?

RE: Submersible motors

Some very good tips have been given such as the one from
AARVEEJE.My question with its use has to do with that stator  coil also known as "flux coil" which may indicate slip is problematic.We even considered using that for non-submerged motors but did not pursuit.The system is intrusive,complex and if the only thing you need is an RPM signal,I can't see anything much simpler than a "GAP probe " or Prox Probe.Easy to install, even for a submerged application,reasonably cheap and accurate.2 wires output pulses that can be easely converted to V/mV/or mAs .
Thank you.

GusD

RE: Submersible motors

Grover,

Is the pump a centrifugal type or is it a positive displacement type ?

Also, what is the significance of knowing the speed at which the motor/pump is operating ?

Thanks

RE: Submersible motors

(OP)
jOmega,
thank you for your interest, see my question Feb 20 Speed of submersible motors.
 Regards  From Oz.......

RE: Submersible motors

(OP)
Dear Rajeendra Joshi,
I would be gratefull for details of this Slip Coil .
Typical motor....Eg  Hitachi Plueger Franklin  8"  100hp
Continous rating
Voltage      415
Frequency    50 hz
OD           8"   200mm
Lamination iron length   31.9"  800mm
Rotor   Aluminium or copper bars
Please ask for any further information required.
Regards Alan.

RE: Submersible motors

(OP)
Dear GusD,
Can you steer me towards obtaining details on the Gap Probe or Proximity Probe.
What physical size are these?
Can they operate in a water filled motor?
Room available is very very restricted,in some cases less than half inch diameter one -two inches long,ie they have to fit into the crown of the winding with the internal cable joins / splices.
I like the simple two wire signal idea,as this is what is required to bring to the surface control box.

Thanks Gus,
          Regards Alan......

RE: Submersible motors

Hi Grover

Yes ,I will try to give you all the info that you need on  GAP /Prox probes,costs and whatever goes with it.

Good luck

GusD

RE: Submersible motors

Dear Mr. Grover,

I am unable to attach the file to this message, which gives the construction of slip coil and method of measurement of speed. Please mail me on " rvjoshi@ksb.co.in " so that I can send it by mail.

Regards,

Rajendra


RE: Submersible motors

Grover,

Your 2/20 post answered my question as to the significance of the speed.... but didn't address the type of pump...i.e., centrifugal or positive displacement.

Is my assumption that it is a centrifugal type correct ?

RE: Submersible motors

(OP)
JOmega, And GusD,
Hi, The pumps are multi stage centrifugal type,can be up to 20 plus stages ,or impellers.

Regarding accesability to the shaft, internally the shaft in most subm motors is "covered" by the snout or bearing mount,most have carbon guide bearings that extend almost to the laminations,on both the drive and non drive end.This makes it not possible to have access to the bear shaft.

The internal room in the connection area is very restricted,and only allows enough room for the 3( in most cases )internal leads.Hence installing a device in the crown area is not a option.
Please keep up the discussion       
......Grover  ( Not From Sesame Street ).....

RE: Submersible motors

I don't know what type of submersible pump you have.It may or may not be an easy task to adapt a gap/prox probe unless you have access to at least 1/2" of shaft showing.
If you just want to take  a spot measurement of pump speed at full load to verify slip,I would wait for a time when you have highest load and do a current measurement.
Your Pump curve should give you a fairly good indication of what you have.The probes I suggested would be for a continuous speed measurement.

GusD

RE: Submersible motors

(OP)
GusD,
Yes from FLC  I can read the curve of say a Hitachi Motor and this will give me an indication of the speed.Most Submersible data sheets are calculated data rather than actual data .I have proved this and have been told this by motor manufactures.A true indication is required when a motor is in field ,coupled to the correct size pump,to give the optimin ( best) performance characteristics, at what ever actual voltage and frequency is being supplied (mains or alternator) ( dedicated line or other large equipment on the same grid).
It is surprising how much varation there is between two different brands of motors.
The power authorities and large end users are very selective and particular in maximum performance.
Hence my initial enquiry to the forum.I am enjoying the response.

No , there is not any exposed motor shaft,as the pump housing covers the coupling,and the only way to see if the shaft is free is to lever with a screwdriver usually in the grub screw hole to see if you can turn the shaft.
 
Ernie is resting now, Regards  Gggrover.
alan@downundersubmersibles.com.au


RE: Submersible motors

Grover:

Danfoss has recently introduced a "sensorless" centrifugal pump contoller that consists of a variable frequency drive with special algorithms that enable controlling the flow to within a close tolerance without having to have a sensor mounted to provide flow feedback. It also does NOT require a tach or encoder on the motor.

Does require knowledge of both the pump and the motor characteristics.

Interested?

RE: Submersible motors

HI Grover

I understangd Some VFDs have one feature(DTC)which is direct torque control.This would allow you to run the drive without speed feedback from Encoder or tacho.
Once the drive has the motor finger print it will know what the speed/versus torque should be.
 This feature should give you a reasonable accurate RPM
measurement.

GusD

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources