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Thread: Transformer Issue

  1. #11
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    We had a similar situation with the UPS powered down. Almost 40 amps in our case.
    We found main electrical system neutral connected to ground in 7 different locations.

    Once they were removed this current disappeared.

    Good Luck
    May the force be with you

  2. #12
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    Grounds were checked throughout the distribution system and minimal ground current 2-3 amps. The levels exterior to the transformer remain the same with the transformer on or off.
    Brian John
    Leesburg, VA

  3. #13
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    Update to this ground current issue than a question


    The transformer was meggered and TTR'ed (Turns Ratio Tested) no problems there.




    The transformer is a 480 to 208/120 transformer Delta Wye.


    The distribution system is solidly grounded.


    The excitation current is A-12, B-8, C-7 Amps, Generally, I believe we see A and C phase higher than B phase.


    At no load, the current on the frame ground is 15.9 amps. This current is only measured on the frame ground conductor installed by the factory


    No one including the manufacturer can give me an answer.


    There is a sticker I noticed today that says due to high leakage current this transformer must be grounded.


    Now my question


    The manufacturer says to ground the UPS one way if the distribution system is high impedance grounded and ground another way if low impedance grounded. THE UPS IS NOT THE SOURCE OF THE GROUND CURRENT, this has been ruled out by isolating the transformer from the UPS. But I still have a question.


    I believe that a low impedance ground is the same as solidly grounded the engineer says no it is similar to a high impedance grounded system just a different value impedance, the manufacturer says that is a design issue and not their concern.


    Thoughts?
    Brian John
    Leesburg, VA

  4. #14
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    Quote Originally Posted by brian john View Post
    The manufacturer says to ground the UPS one way if the distribution system is high impedance grounded and ground another way if low impedance grounded. THE UPS IS NOT THE SOURCE OF THE GROUND CURRENT, this has been ruled out by isolating the transformer from the UPS. But I still have a question.


    I believe that a low impedance ground is the same as solidly grounded the engineer says no it is similar to a high impedance grounded system just a different value impedance, the manufacturer says that is a design issue and not their concern.


    Thoughts?
    For generator protection, a low impedance ground is similar to a high impedance ground. Low impedance uses a series resistor in the ground path. A high impedance ground uses a grounding transformer with a resistor on the secondary side that reflects impedance to the primary/ground path side (this is what I am used to). Both will clamp ground faults to levels much lower than a solid ground so are similar in that respect. Think of solid as hundreds to thousands of amps, low as tens to hundreds, and high as tens of amps or less.

    It sure sounds like a shield drain issue since the other data does not indicate a fault.
    Not sure what is up with the transformer.
    Do you have a transformer manufacturer contact? I usually don't use shielded units but could ask our rep and he might could hunt down an applications engineer at the plant.
    BB+/BB=?

  5. #15
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    Quote Originally Posted by mivey View Post

    It sure sounds like a shield drain issue since the other data does not indicate a fault.
    Not sure what is up with the transformer.
    Do you have a transformer manufacturer contact? I usually don't use shielded units but could ask our rep and he might could hunt down an applications engineer at the plant.

    Tamura Elcomponics Technologies Pvy. Ltd
    Pandithanahalli, Karnataka 572104, India

    The weird thing about the nameplate, It states Primary 480 Secondary 208, Transformer is a Delta Wye 480 to 208/120. Generally, I would expect the name plate to state 208/120. on a Delta Wye.


    Brian John
    Leesburg, VA

  6. #16
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    As mivey pointed out, the issue may be with transformer shield. Is it possible to disconnect the shield from ground temporarily?

  7. #17
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    It appears the shield ground is internal and not accessible.
    Brian John
    Leesburg, VA

  8. #18
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    Quote Originally Posted by brian john View Post

    There is a sticker I noticed today that says due to high leakage current this transformer must be grounded.

    Thoughts?
    The leakage current may be due to electronics circuitry in UPS such as filter capacitor and flows to ground via EGC.But the ground current you are observing is not flowing in EGC but circulating and so abnormal.

  9. #19
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    The transformer was isolated from the UPS no connections. The same level current exists when the transformer is totally isolated, in Bypass, on-UPS and on battery.
    Brian John
    Leesburg, VA

  10. #20
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    We may check whether it is an induced current. Measure no load transformer current and the ground current. Calculate the ratio between the two. Load the UPS. Measure transformer current and ground current and calculate the ratio for these values also. If the ratios are close, the ground current is induced one.

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