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Thread: Dry type Transformers versus Oil Filled

  1. #1
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    Dry type Transformers versus Oil Filled

    We are looking into the differences between dry type and oil filled transformer and understand the benefits of both types (somewhat). In this particular situation we are stepping up 480Y/277 to 12470 for a photovoltaic system. The 800kVA to 1500kVA transformers will be outside in the weather on a concrete pad. At what point should I consider oil filled or it there always a dry type that will work. I was under the impression we will need to use an oil filled outside in 90 deg ambient temps due to the dry types inability to disapate heat. Does anyone have any thoughts? Is it always a requirement or good practice to use oil filled outside?
    Chris Hill, EE,ME,GA-CR
    Power Factor Correction

  2. #2
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    Quote Originally Posted by aelectricalman View Post
    We are looking into the differences between dry type and oil filled transformer and understand the benefits of both types (somewhat). In this particular situation we are stepping up 480Y/277 to 12470 for a photovoltaic system. The 800kVA to 1500kVA transformers will be outside in the weather on a concrete pad. At what point should I consider oil filled or it there always a dry type that will work. I was under the impression we will need to use an oil filled outside in 90 deg ambient temps due to the dry types inability to disapate heat. Does anyone have any thoughts? Is it always a requirement or good practice to use oil filled outside?
    Liquid filled transformers are cheaper and more efficient. They will also lasts longer as long as you monitor the condition of the insulating fluid. Consider high-flashpoint biodegradable fuel for reduced fire risk and nitrogen padding for life optimization.

  3. #3
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    I agree with what weressl posted, another option is cast coil, more expensive but the best of both (Dry and liquid) worlds.

  4. #4
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    Quote Originally Posted by zog View Post
    I agree with what weressl posted, another option is cast coil, more expensive but the best of both (Dry and liquid) worlds.
    As long as you don't care about:
    1. initial cost,
    2. operating cost(efficiency), and
    3. BIL cost,
    4. service life.

  5. #5
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    Based on what?

    Quote Originally Posted by weressl View Post
    As long as you don't care about:[*]initial cost,
    Yep, initial cost is more
    Quote Originally Posted by weressl View Post
    [*]operating cost(efficiency), and
    ?? Opearting costs are minimal, they are essentially maintenence free, no cleaning (Dry) or oil analysis required. %Z is comparable (4-8%)
    Quote Originally Posted by weressl View Post
    [*]BIL cost,
    Cast coil BIL strength is superior to dry type and about the same as oil filled, BIL's of up to 200kV are available.
    Quote Originally Posted by weressl View Post
    [*]service life.
    Insurance company data shows cast coil failre rates are around 5% of standard dry types, expected service life is superior to dry type.

    Cast coils are also:
    - Moistyre proof
    - Fire retardant
    - Safe for environment, no toxic gasses or fluids can be emmitted to atmosphere
    - Smaller footprint for limited space applications
    -Higher overload capability than fry or oil
    -PD free
    -Superior short circuit capability to oil or dry
    Last edited by zog; 08-01-11 at 11:26 AM.

  6. #6
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    This is a good chart giving some options
    http://static.schneider-electric.us/...7300DB0401.pdf
    Ron

  7. #7
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    This is a paper regarding the special needs of the PV step up transformer

    http://www.transformerscommittee.org...Paper_Rev5.pdf

    I don't see it being all that special. Maybe some of the folks like Cooper are using it as a marketing opportunity.

    http://www.cooperindustries.com/cont...ansformer.html
    Ron

  8. #8
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    Quote Originally Posted by zog View Post
    Based on what?

    Yep, initial cost is more
    ?? Opearting costs are minimal, they are essentially maintenence free, no cleaning (Dry) or oil analysis required. %Z is comparable (4-8%) Cast coil BIL strength is superior to dry type and about the same as oil filled, BIL's of up to 200kV are available.
    Insurance company data shows cast coil failre rates are around 5% of standard dry types, expected service life is superior to dry type.

    Cast coils are also:
    - Moistyre proof
    - Fire retardant
    - Safe for environment, no toxic gasses or fluids can be emmitted to atmosphere
    - Smaller footprint for limited space applications
    -Higher overload capability than fry or oil
    -PD free
    -Superior short circuit capability to oil or dry
    The 150% premium can never be recovered unless you are paying 10 times the current electricity rates TODAY and inflation escalation will track with cost of power.
    Cast coils still have exposed leads, still relies on atmospheric cooling - unless they are in a sealed, pressurized tank - therefore still exposed to the outside atmosphere which needs to be largely free of chemicals that may attack. Square D still talks about "ease of cleaning coil".
    Efficiency still remains an issue. Of course they can build any efficiency you want, but at a cost.
    If you install it indoors, heat removal and real estate cost still comes into the picture, but liquid filled does not have to be indoors and outdoor space is considerably less costly.
    Non-toxic insulating liquids that are also high firepoint have Zero environmental impact. They fall into the same category as edible oils, just don't have FDA approval.
    PD issue still remains valid for the primary and secondary leads and their entry point into the cast body is the weakest point.
    Cast coils are also unrepairable.

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