Technical aspects of energyefficient distribution transformers

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Technical aspects of energy-efficient
distribution transformers

• Frederik Groeman

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Technical aspects of energy-efficient transformers

• Energy efficiency of distribution transformers
• Technological feasibility of energy-efficient
  transformers
• Economics of energy-efficient transformers

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Distribution transformer efficiency standards
Source CENELEC
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Standard transformer lossesat full load - HD 428
(538)
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Energy losses in distribution transformers

• Dependent on design and use
• No-load losses (iron losses)
• Load losses (copper losses)
• Standard levels in HD 428 A-AC-C
• A mixed population throughout Europe

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Efficient transformer designs

• No-load losses
• core material (e.g. high-grade steels, amorphous)
• core section
• core design
• Load losses
• increased conductor section
• lower temperature
• Even the lowest HD428 loss level does not require
  technical specialties

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Building distribution transformersmore
energy-efficient?
(technological)
No big ? problem!
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From nameplate losses toactual lossesthe
effect of loading
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From nameplate losses to real energy losses

• No-load losses (iron losses)
• voltage dependent
• always present, 8760 hours per year
• 1 kilowatt no-load loss ? 8760 kWh per year
• Load losses (copper losses)
• load dependent
• kilowatt load loss ? e.g. 2000 kWh per year
• Load power factor, harmonics

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Transformer efficiency
400 kVA, efficiency level A-A (HD428)
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Efficiency _at_ low load
400 kVA, efficiency level A-A (HD428)
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Examples of loaded transformers

• 100 kVA transformer
• A-A
• nameplate 97.7
• yearly basis 94.7
• C-C
• nameplate 98.1
• yearly basis 96.5

• 400 kVA transformer
• A-A
• nameplate 98.5
• yearly basis 98.0
• C-C
• nameplate 98.8
• yearly basis 98.6

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Energy-efficient application of distribution
transformers

• Match the transformer design to the load
• peak load
• running time of peak load
• Avoidance of over-excitation
• Always a compromise

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Economic aspects

• A balance between purchase cost and energy losses
• Loss evaluation as an alternative to standard
  loss values

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Loss evaluation

• Purchase costs

• Load losses
• No-load losses

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Capitalised cost of a transformer
CC Ct APo BPk

• Application data
• A cost no-load losses (/W)
• B cost of load losses (/W)

• Transformer data
• Ct purchase price ()
• Po no-load loss (W)
• Pk load losses (W)

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Application of capitalised cost

• Selection of the best (cheapest) transformer
• A and B reflect NPV of purchase costs of energy
  for the owner
• B also reflects the load pattern
• Low A/B values favour cheap transformers
• High A/B values favour efficient transformers
• The European standards leave some freedom for
  deviations

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A and B values for selected countries
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Two 400 kVA designs
No-load losses 4 /W, load losses 1.2 /W
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Conclusions

• Efficiency can be significantly increased at a
  price premium
• Fit transformers to their load
• Losses are typically as expensive as the
  transformer itself
• Kyoto commitments
• Take lifetime costs into account, not just first
  costs