Transformer Selection

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™)
  
  
  Dry-Type:
                  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:
                  Outdoor
                  Indoor
                  Public Access
           Code Requirements
•  Capabilities:
                  Electrical Withstand
                  Partial Discharge
                  Harmonic Withstand
• Performance:
                  Efficiency
                  Overload Capacity
                  Operating Temperature
                  Sound Level  
  
  
  Transformer Accessories:
  Accessory Integration 
   
  Total Life Cycle Cost:
                  First Cost
                  Installation Costs
                  Maintenance Costs
                  Reliability
                  Environmental Impact
              Repairability
              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.

  
  
  Summary 

  
  

  Table below provides a comparison of transformer attributes:-
  
  

  

  Click to enlarge

    
  References:- 
  
  
  

  • Cooper Power Systems - www.cooperpower.com 
  • Giampaolo Roccatello & Andrea Caremi - Area Sales Manager

  Trasfor S.A - Switzerland

  andrea.caremi@trasfor.ch

  http://www.trasfor.com/

  • Tan Bin Chee

  General Manager (Swift Energy)

  bctan@senergy.com.my

  http://www.senergy.com.my/

  • Logeswaran Sivapragasam

           Product Manager - Cast Resin Transformer
           AM SGB Sdn Bhd
           loges@amsgb.com - www.amsgb.com
  
  

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