×
Follow Us
Results 1 to 1 of 1

LTC Transformer circulating current from a one-step tap discrepancy

    #1
  1. SecondGen's Avatar
    SecondGen is offline
    I push buttons.
    NETA Level III Pro Subscriber
    Join Date
    Jan 2014
    Location
    United States
    Posts
    508
    Reputation

    LTC Transformer circulating current from a one-step tap discrepancy

    There are two identical LTC transformers (12/16/20 MVA, 115 kV to 13.8kV, 9%Z, ±10% in 5/8% steps) which are operating in parallel on differing taps, one step removed from each other. Calculate the resulting circulating current from a one-step tap discrepancy.

    Step 1: Find the voltage driving the circulating current

    Each transformer is one tap apart so the difference in voltage is: 5/8% (0.00625 pu)

    V = Difference x (Vsec / 1.73205)
    V = 0.00625 X (13,800 / 1.73205)
    V = 0.00625 X 7967.438
    V = 49.796
    V = 49.8V

    Step 2: Find the transformer base impedance
    Z(base) = kV^2 / MVA
    Z(base) = 13.8^2 / 12
    Z(base) = 190.44 / 12
    Z(base) = 15.87 ohms

    Step 3: Find the transformer loop impedance
    Z(loop) = 2 x Z(transformer)
    Z(loop) = 2[9% x Z(base)]
    Z(loop) = 2[0.09 x 15.87]
    Z(loop) = 2[1.4283]
    Z(loop) = 2.86 ohms (reactive)
    Z(loop) = j2.86 ohms

    Step 4: Calculate the resulting circulating current from a one-step tap discrepancy
    I(circ) = Voltage / Z(loop)
    I(circ) = 49.8 / j2.86
    I(circ) = -j17.413 Amps

    https://beckwithelectric.com/wp-cont...pp-Note-11.pdf

Subscribe

Share this thread

Related Topics

  1. transformer excitation current readings
    By kcorpuz in forum NETA Level 3 Exam
    Replies: 3
    Last Post: June 24, 2022, 12:25 PM
  2. Step up transformer vector group
    By Diarymh in forum Electrical Testing Talk
    Replies: 0
    Last Post: March 26, 2019, 06:23 AM
  3. Total burden on current transformer
    By Sanjayo in forum NETA Level 3 Exam
    Replies: 1
    Last Post: February 19, 2016, 01:50 PM
  4. Easy way to calculate transformer fault current
    By SecondGen in forum Electrical Testing Talk
    Replies: 0
    Last Post: June 11, 2015, 06:40 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