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Thread: Three winding transformer

  1. #1
    Join Date
    Jan 2010

    Lightbulb Three winding transformer

    Three winding transformer

    Regarding to three winding transformer usage I know the below information. If there is any other usage please advise me.

    1-To elminate the third harmonics currents from flowing into the system delta connected tertiary winding is used. This is know as three winding transformer.

    2-Sometimes the tertiary winding is connected with a reactor or capacitor for reactive power compensation.

  2. #2
    Join Date
    Jan 2009
    Well yes there is another 1# usage there used during construction buy other trades as a work bench .

    Another use would be 2# the electricians use them to keep our lunches warm .

  3. #3
    Join Date
    May 2005
    Richmond, Virginia
    Years ago, I built a heavy duty power supply for a set of four 75w mono amplifiers I was bridging into two 300w amps. Each amp originally came with a +/- 40v (80v CT) 3a supply, so I built a +/- 40v 25a supply for all four amp channels.

    I bought a pair of 40v 25a surplus transformers that I paralleled the primaries for 120v and placed the secondaries in series to form an 80v CT supply and used a pair of high-current rectifiers and a bunch of filter capacitors.

    In addition to the usual primaries and secondaries, the transformers had what were called tertiary windings, and each one came with a capacitor that was to be connected directly to these windings (one cap per transformer).

    The effect was to make the supply "stiffer." The power supply output voltage remained at the peak filter-capacitor charging voltage even under load, almost as if the transformers put out a square wave instead of a sine wave.

    These were regular 1ph single transformers, and they were heavy. I built the supply in a plastic milk crate. I think I still have the supply in storage somewhere. That's the limit of my experience with it. Hope that helps your searching.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  4. #4
    Join Date
    May 2006

    Three-Winding Transformer

    Greetings Hameedulla-Ekhlas,

    Here is what I found in one of my books. Handbook of Power System Engineering, Yoshihide Hase, pp 99-100.

    To isolate the zero-sequence circuit of the delta winding side from that of the wye winding side. In other words, to intercept zero-sequence currents from flowing across the different winding side circuits.

    To reduce largely zero-sequence reactance of the transformer, thus to reduce and stabilize neutral point voltages, and then to reduce phase overvoltages under normal and fault conditions.

    To intercept the pass through of dc or harmonic currents from the high to low side equipment protecting generators and other such equipment.

    To protect the transformer itself against the inflow of harmonic currents.

    To reduce zero-sequence impedance and stabilize neutral voltages under normal conditions.

    Best of luck,

  5. #5
    Join Date
    Jan 2009
    Well on a good note this time tertiary winding are also used for earth fault protection .

    auto transformer with series & tertiary windings .

    Question would you consider a flyback transformer a tertiary type ?
    Last edited by ohmhead; 03-20-10 at 08:32 PM.

  6. #6
    Join Date
    Jun 2007
    CTs are placed on the tertiary winding to served as a source for polarizing current for directional comparison distance relays

  7. #7
    Join Date
    May 2005
    Redmond, WA

    3-Winding transformers at Power Plants

    Power plants use three winding transformers to keep capital costs down.

    Example: a plant with two 220 MVA gas turbines operating at 18 kV with a 230 KV utility tie.

    Option #1 -Use two 230kV-18 kV Generator Step Up (GSU) Transformers, 220MVA, each with its own foundation and high voltage circuit breaker.

    Option #2 - Use one with three winding transformer rated 440MVA/220MVA/220MVA, 230kV/18kV/18kV (H/X/Y). It is on one foundation with one 230 kV circuit breaker. Total cost and space is less. You give up some operating flexibility but save a lot of money up front.

    If we tried to connect both generators onto one 18 kV winding, the 295kA short circuit will be greater than available equipment can handle. The three winding transformer is like two transformers in the same tank. The impedance between the X & Y 18 kV windings is enough to keep the short circuits to manageable levels.
    Bob Wilson

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