×
Follow Us
Page 2 of 2 FirstFirst 12
Results 11 to 17 of 17

XFMR test question - wye-delta TTR

 Jump to latest post
Page 2 of 2 FirstFirst 12
    #11
  1. Join Date
    Jun 2015
    Posts
    25
    Reputation
    Quote Originally Posted by Kalbi_Rob View Post
    WI | DE

    So, easy way to remember how to perform turns ratio is to start with the acronym WIDE where WI stands for Wye where current is equal between phase and line, and DE stands for Delta where E (electromotive force which also defines voltage) or voltage is equal between phase and line.
    So, on the Wye side of the transformer you need to take the voltage (assume to be phase voltage if not otherwise noted) and divide by square root of 3 (or ~1.73). So the equation is
    (7200V/(sqrt(3))/480V = 4156.9V/480V = 8.66 so the TTR = 8.66:1

    Turns ratio is only taken on single phases of a transformer, so all values need to be reduced to individual line values to represent each single phase. This is also why you see a 12kV/480 delta/wye transformer with voltage values of 12kV - 480Y/277V.
    If for whatever reason you needed to convert current values from phase to line on a Delta Xfmr, then you take phase current and divide by sqrt(3).
    thank you. this is very helpful.

  2. #12
  3. Join Date
    Dec 2018
    Location
    Atlanta, GA
    Posts
    26
    Reputation
    Quote Originally Posted by ElectricalTestTech View Post
    It is not a simple division. You have to pay attention to the Wye and Delta. Any winding that is Wye, you have to use phase to ground voltage. 7200/1.732. Delta windings use phase to phase.

    7200/1.732= 4160ish / 480 = ?

    Sorry Im doing the math in my head and on my cell phone.

    Hope this helps
    Is there any illustration that can show this math? Sorry i am a visual learner lol

  4. #13
  5. ryn_droma is offline Junior Member Pro Subscriber
    Join Date
    Nov 2018
    Posts
    2
    Reputation
    Quote Originally Posted by Ronwilson1801 View Post
    Is there any illustration that can show this math? Sorry i am a visual learner lol
    See if this helps

    Click image for larger version. 

Name:	picture 1.png 
Views:	16 
Size:	453.5 KB 
ID:	322

  6. #14
  7. dukeofsmooth's Avatar
    dukeofsmooth is offline
    WAR EAGLE!
    Junior Member Pro Subscriber
    Join Date
    Sep 2016
    Location
    Allentown, PA
    Posts
    8
    Reputation
    Quote Originally Posted by dbryce89 View Post
    A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?
    Your Answer: 15:1

    Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
    Wye VP = VL √3

    Delta VL = VP

    Wye VP = 7200 √3 = 4157
    Delta VL = 480
    4157/480 = 8.7:1
    *Give me a smart idiot over a stupid genius any day*

  8. #15
  9. akumar is offline Junior Member
    Join Date
    Oct 2018
    Posts
    7
    Reputation
    Quote Originally Posted by dbryce89 View Post
    A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?
    Your Answer: 15:1

    Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
    You did nothing wrong. I do not know why are assuming that you did anything wrong. Just FYI - I am not an administrator here or at NETA. Just a regular member. I am just baffled by the confusion here that should not have existed.

    The gentlemen on this thread have made all sorts of assumptions and tried their explanations. With all due respect to their efforts, I am not sure how many of these gentlemen or NETA question makers use a standard textbook definition of Turns Ratio.

    For Turns Ratio - You take identical parameters. Line parameters (LL) or Phase parameters (LN). If nothing is mentioned, automatic assumption is that the values are Line parameters NOT phase. These are the first concepts of power engineering.

  10. #16
  11. akumar is offline Junior Member
    Join Date
    Oct 2018
    Posts
    7
    Reputation
    Quote Originally Posted by ElectricalTestTech View Post
    It is not a simple division. You have to pay attention to the Wye and Delta. Any winding that is Wye, you have to use phase to ground voltage. 7200/1.732. Delta windings use phase to phase.

    7200/1.732= 4160ish / 480 = ?

    Sorry Im doing the math in my head and on my cell phone.

    Hope this helps
    "Delta windings use phase to phase"

    The fundamental is: In delta windings, V Line to Line or V subscript LL = V Line to Neutral or V subscript LN. So no conversion is required on Delta side.

  12. #17
  13. Join Date
    Jan 2019
    Posts
    2
    Reputation
    The way I taught my guys that seemed to stick with them was to visualize all transformer ratios as single phase devices.

    First off, it's important in this example to note that it's a WYE primary, which is not common and is an easy way to make a mistake.

    With a line voltage 7.2kV, we divide by 1.732 to find a phase voltage ~4.16kV.
    In the DELTA secondary, VL and VP are equal at 480V.

    At this point you can ignore the fact that these are part of a three phase system. You have three individual transformers with primary voltage of 4,160 and secondary at 480.

    4,160/480 = 8.67

Page 2 of 2 FirstFirst 12
Subscribe

Login or register to leave a reply!


Share this thread

Related Topics

  1. Insulation resistance test set question
    By mkennedyShermco in forum NETA Level 4 Exam
    Replies: 2
    Last Post: June 10, 2018, 12:52 PM
  2. Replies: 3
    Last Post: January 7, 2018, 01:23 AM
  3. Test Question--High Current Injection
    By alexlounsbury in forum NETA Level 3 Exam
    Replies: 5
    Last Post: July 10, 2017, 11:38 AM
  4. Replies: 2
    Last Post: February 2, 2016, 01:35 PM
  5. Replies: 4
    Last Post: January 24, 2015, 01:34 PM

Tags for this Thread



Related Content


Follow us


Explore TestGuy


NETA Certification Training


NICET Electrical Power Testing


Help and Support