×
Follow Us
Results 1 to 4 of 4

Transformer winding resistance, balance ?

 Jump to latest post
    #1
  1. rgrabis is offline Junior Member Pro Subscriber
    Join Date
    Jun 2015
    Posts
    11
    Reputation

    Transformer winding resistance, balance ?

    Winding resistance is one of the more common tests we perform. However, unlike insulation resistance or conducting path (contact) resistance, I am not aware of any specs. or rule of thumb for the allowable variation in resistance readings between phases. Does anyone know of any or have any thoughts on this issue? Thanks

  2. #2
  3. SecondGen's Avatar
    SecondGen is offline
    I push buttons.
    NETA Level III Pro Subscriber
    Join Date
    Jan 2014
    Location
    United States
    Posts
    508
    Reputation

    A Guide to Transformer Winding Resistance Measurements

    So I did some searching and I found this from Megger:

    The transformer winding resistance test is very useful in identifying and isolating the location of suspected problems. Winding Resistance Measurements are evaluated by:

    • Comparing to original factory measurements
    • Comparing to previous field measurements
    • Comparing one phase to another


    The latter will usually suffice. The industry standard (factory) permits a maximum difference of 1/2 percent from the average of the three phase windings. Field readings may vary slightly more than this due to the many variables. If all readings are within one percent of each other, then they are acceptable.

    Variation from one phase to another or inconsistent measurements can be indicative of many different problems:

    • Shorted turns
    • Open turns
    • Defective DETC or LTC
    • Poor connections (brazed or mechanical)



    See the PDF attached to this post, it will pretty much explain everything you need to know about winding resistance.
    Attached Files Attached Files

  4. #3
  5. rgrabis is offline Junior Member Pro Subscriber
    Join Date
    Jun 2015
    Posts
    11
    Reputation
    Hey, that's great. Thanks for the help

  6. #4
  7. wooddy is offline Junior Member
    Join Date
    Jan 2018
    Posts
    8
    Reputation
    Quote Originally Posted by SecondGen View Post
    So I did some searching and I found this from Megger:

    The transformer winding resistance test is very useful in identifying and isolating the location of suspected problems. Winding Resistance Measurements are evaluated by:

    • Comparing to original factory measurements
    • Comparing to previous field measurements
    • Comparing one phase to another


    The latter will usually suffice. The industry standard (factory) permits a maximum difference of 1/2 percent from the average of the three phase windings. Field readings may vary slightly more than this due to the many variables. If all readings are within one percent of each other, then they are acceptable.

    Variation from one phase to another or inconsistent measurements can be indicative of many different problems:

    • Shorted turns
    • Open turns
    • Defective DETC or LTC
    • Poor connections (brazed or mechanical)



    See the PDF attached to this post, it will pretty much explain everything you need to know about winding resistance.
    couple things that you can do to ensure that your readings are consistent, usually start with centre phase readings first, this way you have equal flux flowing between windings for all of the testing, another thing we run into with our cold weather is to be careful of how much current and how long the machine is on for each readings, we have found that if ur using say 50 amps and its taking a long time for the machine to balance and the transformer windings are really cold there is actually enuf heating provided by the winding resistance tester to progressively change the resistance of the winding as you go through the taps thus giving you readings that are out of balance compared to the other windings and or taps, obviously if you can do the testing while the transformer is still warm this is better, obviously record the winding temperature so all readings can be corrected and compared to original manufacters readings

Subscribe

Share this thread

Related Topics

  1. 230kV Auto-Transformer (Insulation Resistance Test)
    By rizza_gay in forum Electrical Testing Talk
    Replies: 8
    Last Post: January 19, 2018, 11:27 AM
  2. winding resistance tester and CPC 100
    By moon1958moon in forum Electrical Testing Talk
    Replies: 8
    Last Post: August 4, 2017, 12:09 PM
  3. winding resistance of power transformers
    By Sanjayo in forum NETA Level 2 Exam
    Replies: 4
    Last Post: March 27, 2016, 07:13 PM
  4. winding resistance tolerance for a transformer test
    By Larry5441 in forum Electrical Testing Talk
    Replies: 6
    Last Post: June 29, 2015, 04:33 PM

Tags for this Thread

Follow us


Explore TestGuy


NETA Certification Training


NICET Electrical Power Testing


Help and Support




You are viewing the archives. Enjoy new features and join the conversation at wiki.testguy.net