July 6, 2011

Distribution and Power Transformer Selection Guide

Power Transformer

Distribution and Power Transformer 
Selection Guide

Distribution & Power transformer selection, whether for residential, commercial, industrial, or utility application, has long-term ramifications. Transformers can have lives of 15, 30, and even 50 years or more, depending on their design, loading, application, protection, and maintenance. So it’s important to evaluate all of the transformer attributes that affect the final purchase decision. This guide provides the information needed to choose the best transformer for your application. Your transformer choices include:
  • Liquid-Filled:
                    Mineral Oil
                    Fire-Resistant Fluids (Less-Flammable) 
                High Molecular Weight Hydrocarbon (HMWH) (R-Temp®
                Silicone Oil (Polydimethylsiloxane) 
                Synthetic Ester (Envirotemp® 200
                Natural Seed Oil Ester (Envirotemp® FR3)

                    Standard Vented Dry
                    Vacuum Pressure Impregnated (VPI) Dry
                    Cast Resin
In order to make a fair comparison, equivalent transformer attributes should be compared. Installation flexibility, performance, accessory integration, environmental impact, and cost are all examples of attributes that should be considered.
  • Installation:
                    Public Access
                    Code Requirements

  •  Capabilities:
                    Electrical Withstand
                    Partial Discharge
                    Harmonic Withstand 
  • Performance:
                    Overload Capacity
                    Operating Temperature
                    Sound Level  

    Transformer Accessories:
    Accessory Integration 
    Total Life Cycle Cost:
                    First Cost
                    Installation Costs
                    Maintenance Costs
                    Environmental Impact
                Recycling and Disposal
                Environmentally Friendlier Fluids
                    Energy Costs
                    Total Life Cycle Cost Summary 


    Transformers for outdoor use and rated:
    Ø  Up to and including 1600 kVA shall be of the oil filled hermetically sealed type
    Ø  Above 1600 kVA and up to 3150 kVA should preferably be of oil filled hermetically sealed type, but may be of the oil filled conservator type
    Ø  Above 3150 shall be of the oil filled conservator type.

    Type of enclosure is only dependent on the kVA rating and not on the transformer voltages.

    For use in high-humidity tropical areas, a conservator that prevents contact between the oil in the transformer tank and the ambient air should be used. This may be either the membrane type or multi-compartment type of split conservator.

    In locations where fire risk must be minimised, e.g., in buildings, on offshore platforms, etc., the dielectric/cooling liquid of transformers shall be synthetic with reduced ignitability and flame-retardant characteristics, e.g., silicone fluid. In the above locations, dry-type transformers having cast resin encapsulated windings may also be used. Attention shall be paid to the shielding of live parts and possible capacitive currents when the encapsulation is touched.
    For oil transformer:
    Ø  Design life at least 25 years
    Ø  Shall be naturally air cooled (ONAN)

    Dry type transformer:
    Ø  Service condition : the transformer will be installed indoor
    Ø  IP protection at least IP21
    From VENDOR (cast resin transformers)
    Ø  Highest IP rating with AN cooling would be IP44 or IP33 only (if IP55 it’s possible also but for rating below 1000kVA)
    Ø  Higher than 1000kVA transformer with higher than IP44 should be AFWF(more maintenance works required) because we need to dissipate heat from the enclosure which is almost sealed condition
    Ø  Also more expensive, size and weight problems.
    Ø  Because we cann’t dissipate the heat generate by the transformer since with IP more than IP44, it’s completely sealed.
    Ø  Therefore, cast resin transformer for outdoor location may not be a good choice.
    Ø  Prefer oil or silicon type transformer.
    • For zone 2 transformers - only can use silicone oil for oil type transformer, cann't use mineral oil. 
    • If we use cast resin transformer with IP44 or below for outdoor applications(offshore), the salt & water molecule will deposited at enclosure and also at the winding because of the salt molecule is smaller than 1mm.


    Table below provides a comparison of transformer attributes:-

    Transformer Selection & Comparison Table
    • Giampaolo Roccatello & Andrea Caremi - Area Sales Manager
      Trasfor S.A - Switzerland
    • Tan Bin Chee
      General Manager (Swift Energy)
    • Logeswaran Sivapragasam
             Product Manager - Cast Resin Transformer
             AM SGB Sdn Bhd
             loges@amsgb.com - www.amsgb.com

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