×
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

MV motor winding PI

MV motor winding PI

MV motor winding PI

(OP)
Dear Folks,
Recently we have measured polarisation Index (PI) of one MV motor-11kV, 5100MW, we got the following values.
R -E --- 4
Y -E ---- 4
B -E ----4
R+Y+B-E --2.5

Anyone pl. discuss the reason for less PI if we measure all windings with respect to ground.
Thank you..

RE: MV motor winding PI

It is more like 5100 kW, isn't it?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: MV motor winding PI

(OP)
Sorry for wrong unit. It is 5100kW, 11kV motor.
Thank you Mr.Skogsgurra.

RE: MV motor winding PI

Above 2 we are  usually not concerned.

Can you give the values upon which the PI was calculated (1 minute and 10 minute readings)?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: MV motor winding PI

I've seen PI's skewed by failure to allow individual windings to adequately discharge before subsequent tests.  That might not be your reason, but it's an observable phenomenon.

My schedule:  Ground windings  B & C.  Test winding A.  Then ground winding A.  Go get cup of coffee and sip thoughtfully.  

Then remove ground from winding B and test it.  After testing, ground winding B.  Finish up old reports.  Chat with co-workers on jobsite.

Unground winding C.  Test it.  Ground winding C.  Carefully fill out more reports.  Go get second cup of coffee.  Ponder some problem that's bugging a co-worker.

Unground and connect all three windings, and do your overall PI.  Bring the results to the end user and have a cup of coffee from his pot.

Seriously, don't get in a hurry between tests.  Allow insulation to fully discharge.  A rule of thumb for this is to ground the winding for at least the amount of time that voltage was applied.  Some operators say "twice the time".

Also, keep in mind that the Polarization Index test is not a precision event.  Good care will produce reasonably useful results.  Any technician who brings me a PI calculated to two decimal places is due for some retraining.

NOTE:  This procedure also explains my predisposition to kidney stones...

old field guy

RE: MV motor winding PI

I couldnt have said it better myself oldfieldguy

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