Energy Saving Opportunities for Transformers

1. Energy Saving Opportunities for Transformers Hans De Keulenaer Outokumpu Tara Mines Energy Efficient Motors & Transformers Workshop May 7, 2002

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

3. 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

4. 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, …)

5. 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)

6. 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 €

7. Historical evolution in the production of magnetic steel

8. Evolution of magnetic steel since the introduction of cold-rolled magnetic steel

9. 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 * 0.5^2 = 37.2 MWh/yr • 30 yrs = 1.11 GWh • Emissions (0.4 kg CO2 / kWh) = 444 tonnes • 5 c / kWh = 55,500 €

10. Loading • Case 1: • 30% of time 80% load • 70% of time 10% load • Case 2: • 8 hours @ 80% • 8 hours @ 40% • 8 hours @ 10% 20% 30%

11. Typical load profile

12. 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%

13. Transformer efficiency 400 kVA, efficiency level A-A’ (HD428)

14. Efficiency @ low load 400 kVA, efficiency level A-A’ (HD428)

15. 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%)

16. Distribution transformer efficiency standards Source: CENELEC

17. Extreme cases High loss >> AA’ Low loss >> CC’

18. Comparison of efficiency at 50% load

19. 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

20. Copper and Aluminium Designsfor the same efficiency

21. 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

22. Full load losses in a 100kVA C-C’ transformer Total loss = 1685 W

23. Harmonic profile of a typical Personal Computer

24. Full load losses in a 100kVA C-C’ transformer Total loss = 3245 W

25. 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

26. Harmonic culture

27. 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%

28. 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 €

29. A and B values for selected countries

30. Lifetime owning cost400 kVA oil-cooled

31. Beyond the magic of A & B

32. 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% @ 30 years

33. 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

34. Soft benefits • Save energy • Save emissions • Noise? • Reduced heating • Improved lifetime • Reliability? • More robust against harmonics

35. What’s the catch? • Increased capital outlay • Commercial policy of suppliers • Small amounts • Risk of being a pioneer

36. Energy & emission savings potentials related to transformers & standby power

37. 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

40. Super-trafo demonstration

41. 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