Energy Saving Opportunities for Transformers

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Energy Saving Opportunities for Transformers

• Hans De Keulenaer
• Outokumpu Tara Mines
• Energy Efficient Motors Transformers Workshop
• May 7, 2002

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Content

• Introduction
• Technical issues standards
• Economic equations
• Ecological equations
• The business case for high efficiency
  transformers
• Conclusion

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Why transformer efficiency is an issue?

• All electricity passes through several stages of
  transformation
• Savings potential of 22 TWh / year for EU
• Technology exists
• Economic potential
• Many pieces to the sustainable energy puzzle

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Losses in distribution transformers

• No load loss, or iron loss (Po)
• Load loss, or copper loss (Pk)
• DC loss
• Extra losses
• eddy current loss in windings
• stray loss
• Other losses (ventilation, )

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Losses in distribution transformers
Extra loss
Load loss
Extra loss due to harmonics
Resisitive loss
Conventional load loss excl harmonics
No load loss
Unloaded Rated load Actual
load Actual load (excl
harmonics) (incl harmonics)
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Iron loss

• Occurs 24 hours / day, 365 days / year
• Example 1,600 KVA, Po 2,600 W
• Annually 2,600 W 8,760 hrs 22.8 MWh / yr
• 30 yrs 684 MWh
• Emissions (0.4 kg CO2 / kWh) 274 tonnes
• 5 c / kWh 34,200

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Historical evolution in the production of
magnetic steel
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Evolution of magnetic steel since the
introduction of cold-rolled magnetic steel
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Copper loss

• Occurs only when transformer is loaded
• Varies quadratically with the load
• Example 1,600 kVA, Pk 17 kW, 50 loaded
• Annually 17 kW 8,760 hrs 0.52 37.2 MWh/yr
• 30 yrs 1.11 GWh
• Emissions (0.4 kg CO2 / kWh) 444 tonnes
• 5 c / kWh 55,500

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Loading

• Case 1
• 30 of time 80 load
• 70 of time 10 load
• Case 2
• 8 hours _at_ 80
• 8 hours _at_ 40
• 8 hours _at_ 10

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30
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Typical load profile
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Results

• Energy transformed
• 1,600 kVA 0.5 8,760 7,008 MWh / year
• Efficiency
• ? 7,008 / (7,008 22.8 37.2) 99.2
• Lifetime cost
• Transformer 10,000 10
• Iron loss 34,200 35
• Copper loss 55,500 55
• Total 99,700 100

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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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Efficiency standards

• Two approaches
• European approach specify Po and Pk
• CENELEC HD428 (oil) Po class A, B, C Pk
  class A, B, C (nine combinations)
• CENELEC HD538 (dry) one class for Po, Pk
• US approach specify efficiency at average load
  (typically 35-50)

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Distribution transformer efficiency standards
Source CENELEC
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Extreme cases
High loss AA
Low loss CC
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Comparison of efficiency at 50 load
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Conductor materials

• Cu and Al transformers can be built to comply to
  the same performance and quality standard
• Smaller ratings are typically cheaper with Cu
• In general, use of Cu leads to
• heavier, but more compact windings
• a smaller core
• a smaller, more compact transformer
• a lower noise level
• less oil-content

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Copper and Aluminium Designsfor the same
efficiency
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Dry-type versus oil-filled transformers

• higher initial cost
• higher no-load losses
• lower load losses
• harmonics cause less extra heating and ageing
• better fire protection
• no oil spilling container

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Full load losses in a 100kVA C-C transformer
Total loss 1685 W
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Harmonic profile of a typical Personal Computer
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Full load losses in a 100kVA C-C transformer
Total loss 3245 W
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Effect of additional losses on life-time
where T is working temperature at rated
fundamental power, Pf,, Pk is the total power
and T is the rated life-time in years
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Harmonic culture
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Economic evaluation

• 2 approaches to buy a transformer
• Specify Po and Pk
• Specify A B factors
• Ct Purchase price A Po B Pk

With I interest rate 7 n lifetime 30
yrs CkWh cost / KWh 0.05 c Il/Ir
loading 50
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Example

• 1600 KVA, 50 load, oil-cooled
• (A 5.4 euro / Watt B 1.3 euro / Watt)
• Efficiency AA CC
• Purchase 9,700 10,300
• Load loss 22,100 18,200
• (1.3 17,000) (1.3 14,000)
• No load loss 14,040 9,180
• (5.4 2,600) (5.4 1,700)
• Total 45,840 37,680

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A and B values for selected countries
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Lifetime owning cost400 kVA oil-cooled
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Beyond the magic of A B
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Example - revisited

• 1600 KVA, 50 load, oil-cooled
• Efficiency AA CC
• Purchase 9,700 10,300
• Load loss 1,850 / yr 1,533 / yr
• No load loss 1,140 / yr 745 / yr
• Result
• Payback 10 months
• IRR 119 _at_ 30 years

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Ecological evaluation

• 1600 KVA, 50 load, oil-cooled
• Efficiency AA CC
• Energy 210 GWh 210 GWhtransformed
• No load loss 684 MWh 447 MWh
• Load loss 1,110 MWh 921 MWh
• Emissions 718 tonnes 547 tonnes
• Emission savings 171 tonnes

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Soft benefits

• Save energy
• Save emissions
• Noise?
• Reduced heating
• Improved lifetime
• Reliability?
• More robust against harmonics

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Whats the catch?

• Increased capital outlay
• Commercial policy of suppliers
• Small amounts
• Risk of being a pioneer

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Energy emission savings potentials related to
transformers standby power
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More information

• www.efficient-transformers.org
• electronic library
• calculation tools
• K-Factor Factor K
• Investment evaluation spreadsheet
• www.supertrafo.com
• daily, on-line measurement of energy saving for 4
  high efficiency transformers installed in Poland

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Super-trafo demonstration
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Conclusions

• Evaluate transformers for lifetime cost
• oil-cooled
• Buy only CC or higher
• Evaluate transformer with 15-20 less loss than
  CC
• dry-type
• if you need the advantages
• evaluate transformer with 15 less loss than
  HD538
• Check harmonic culture
• Consider replacement of veteran transformers