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Power transformers rating

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Rated power and voltages

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Power transformers rating

  1. 1. Angelo Baggini, angelo.baggini@unibg.it, Bergamo University - Engineering Department Via Marconi 5, 24044 Dalmine (BG) – Italy Power Transformer rating
  2. 2. Power Transformer rating 1. Rated power 2. Rated voltages 3. Tapping 4. Short circuit voltage 5. No-Load and Load losses 6. Clock hour figure 7. Liquid immersed and dry type
  3. 3. Min Input data • Load power and location • Network Voltage level • Short circuit level • Reliability and continuity of electrical service • Fire and environmental safety issues 3
  4. 4. Power Transformer rating Rated power … and number of units … and cooling mode
  5. 5. Rated power Load to be supplied or generated power* • Analytical calculations • Usage and contemporaneity factors • Measurements, Hystorical data and trends • Resilience in case of fault • Energy efficiency • Future needs * Not just at the rated frequency but taking into account the spectrum
  6. 6. Rated power … in case of harmonics  Voltage distortion → NO load losses  Current distortion → Load losses Oversizing needs
  7. 7. Rated Analytical calculation
  8. 8. Load type ku Lamps 1 Motors 0,5 - 2 kW 0,7 Motors 2 - 10 kW 0,75 Motors > 10 kW 0,8 Induction and resistence ovens 1 Rectifiers 1 Weldings 0,7 ÷1 Electrical heaters 1 Tools and transporters 0,6 ÷ 0,8 Elevators 0,8 ÷ 1 Pumps and ventilators 1 Rated power Analytical calculations – Usage factors
  9. 9. Load type Number kC Ovens Up to 2 1 Motors 0,5 - 2 kW Up to 10 0,6 Up to 20 0,5 Up to 50 0,4 Motors 2,5 - 10 kW Up to 10 0,7 Up to 50 0,45 Motors 10 - 30 kW Up to 5 0,8 Up to 10 0,65 Up to 50 0,5 Motors > 30 kW Up to 2 0,9 Up to 5 0,7 Up to 10 0,6 Rectifiers Up to 10 0,8 Weldings Up to 10 0,4 Elevators Up to 4 0,75 Up to 10 0,6 Ligthing 0,8 Rated power Analytical calculations – Contemporanity factors
  10. 10. Number of loads kC 1 1 2 ÷ 4 0,8 5 ÷ 10 0,6 11 and more 0,4 Rated power Analytical calculations – Contemporaneity factors
  11. 11. Type of activity Factor Hotels, colleges 0,6 ÷ 0,8 Hospitals 0,5 ÷ 0,75 Shopping Malls 0,7 ÷ 0,9 Schools 0,6 ÷ 0,7 Rated power Analytical calculations To be applied to the aritmetical sum of rated powers
  12. 12. Rated Power Measurements, Hystorical data and trends
  13. 13. Type of activity Power (VA/m2) Paper industry 120 Textile industry 100 Electronic industry 90 Mechanical industry 80 Wood industry 70 Rated power Measurements, Hystorical data and trends
  14. 14. Type of activity Power (VA/m2) Offices 70 Schools 50 Hospitals 60 Hotels 80 Residential 40 Rated power Measurements, Hystorical data and trends
  15. 15. Rated Power Resilience in case of fault
  16. 16. Rated power 16 Resilience in case of fault
  17. 17. Rated Power Energy efficiency
  18. 18. Rated Power Energy efficiency 18 *Usually40–50% )( 2 0 kr r PxPxP xP ++ =η kP P x 0 = Energyefficiency(%) Load (%) 100 0 20 40 60 80 100
  19. 19. Rated Power Future needs
  20. 20. Rated power Future needs • Oversize* • Possibility of overloading* • At design stage: possiiblity to add a busbar * coherent sizing of LV section 20
  21. 21. Rated power LV section sizing 21 Ref. 400 V 3f 4% up to 630 kVA 6% upper 630 kVA
  22. 22. Rated power Preferred values (kVA) (Renard R5 60%) 22 25 50 63 100 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 Ref. EU practice
  23. 23. Power Transformer rating Rated voltages
  24. 24. Rated voltages to be selected on the basis of the voltages of the served networks
  25. 25. Rated voltages for winding with Um > 1,1 kV Highest voltages for equipment 3,6 kV– 7,2 kV – 12 kV – 17,5 kV – 24 kV – 36 kV National practices may require the use of highest voltages for equipment up to (but not including) 52 kV, when the rated voltage is less than 36 kV (such as Um = 38,5 kV or Um = 40,5 kV). Insulation levels and dielectric test shall be in accordance with the requirements of IEC 60076-3. Ref. EN 50588-1
  26. 26. Rated voltages for winding with Um ≤ 1,1 kV Rated voltages 400 V – 410 V – 415 V – 420 V – 433 V – 690 V National practices may require the use of highest voltages for equipment up to (but not including) 52 kV, when the rated voltage is less than 36 kV (such as Um = 38,5 kV or Um = 40,5 kV). Insulation levels and dielectric test shall be in accordance with the requirements of IEC 60076-3. Ref. EN 50588-1
  27. 27. Ref. IEC 60071-1
  28. 28. Ref. IEC 60071-1
  29. 29. Power Transformer rating Tappings
  30. 30. Tappings DETC: De-energised tap changer Preferred tapping ranges • ± 2,5 % with 3 tap positions • ± 2 x 2,5 % with 5 tap positions On special request ±4 x 2,5 % with 9 tap positions can be provided. Tapping ranges greater than ± 10 % or with more than 9 tap positions are unusual and subject to specific agreement. OLTC: On load tap changer • smaller than ± 15 % with a maximum of 17 tap positions. Tapping ranges greater than ± 15 % or with more than 17 tap positions are unusual and subject to specific agreement. Tapping ranges outside the above definitions have to be specified by agreement between manufacturer and purchaser. Ref EN 50588-1
  31. 31. Power Transformer rating Short circuit impedance
  32. 32. Shortcircuit impedance 1. Reactive power: directly prop (cost of PFC) 2. Voltage drop: directly prop 3. Shortcircuit current: inverserly prop (cost of LV system) The Minimum value compatible with shortcircuit needs • Loads subdivision (single TR power decreasing) • Distribution scheme (NO TR in parallel) • Different voltage value I Z V I V
  33. 33. Shortcircuit impendance Scheme’s effects on the the shortcircuit current Trip time (s) TRs in parallel TRs working separtely Section (mm2) 0,04 50 25 0,1 70 35 0,4 150 70
  34. 34. Shortcircuit impedance Standardized values EU practice fro MV transformers 4% ≤ 630 kVA 6% ≥ 630 kVA
  35. 35. Shortcircuit impedance Transformer in parallel Z V V Z CCA 21 A Z VV I • •• • − = CCB 21 B Z VV I • •• • − = Same: • Turn ratio • Clock hour figure • vcc
  36. 36. Power Transformer rating Load and no-load losses
  37. 37. Power transformer losses P = P0 + x2 Pk Losses: No-Load (P0) • Mainly into the magnetic circuit Load losses (Pk) • Mainly into the windings Forced cooling system consuptions 37
  38. 38. New EN 50588-1 Oil immersed 1,1-24 kV Excluding pole mounted TIER 1 - July 1st 2015 Sr AAAo AAo Ao kVA W W W 25 35 63 70 50 45 81 90 100 75 131 145 160 105 189 210 250 150 270 300 315 180 324 360 400 220 387 430 500 260 459 510 630 300 540 600 800 330 585 650 1000 390 693 770 1250 480 855 950 1600 600 1080 1200 2000 730 1305 1450 2500 880 1575 1750 3150 1100 1980 2200 Sr Vcc Ak Bk Ck kVA % W W 25 4 600 725 50 750 875 100 1250 1475 160 1700 2000 250 2350 2750 315 2800 3250 400 3250 3850 500 3900 4600 630 4 or 6 4600 5400 800 6 6000 7000 1000 7600 9000 1250 9500 11000 13500 1600 12000 14000 17000 2000 15000 18000 21000 2500 18500 22000 26500 3150 23000 27500 33000 NOloadlosses Loadlosses EN50588-1
  39. 39. Total Owning Cost (€/kW year) (€/kW year) (capitalisation factor) k0l PBPAC ⋅+⋅= ( ) c r L e F S S hCB ⋅      ⋅⋅= 2 ( ) ( )n n ii i Fc +⋅ −+ = 1 11 ( ) ced FCCA ⋅⋅+⋅= 876012
  40. 40. Load from 150 to 600 kVA Analyzed cases: • 2 x 400 kVA • 2 x 500 kVA • 2 x 630 kVA • 1 x 800 kVA 40 Example A00 – A00AK – A00BK A0 – A0AK – A0BK – A0CK
  41. 41. 41 200 kVA
  42. 42. 42 200 kVA
  43. 43. 43 250 kVA
  44. 44. 44 300 kVA
  45. 45. 45 350 kVA
  46. 46. 46 400 kVA
  47. 47. 47 450 kVA
  48. 48. 48 500 kVA
  49. 49. 49 550 kVA
  50. 50. 50 600 kVA
  51. 51. Power Transformer rating Clock hour notation
  52. 52. Clock hour notation
  53. 53. Power Transformer rating Liquid immersed and dry type
  54. 54. Liquid immersed and dry type Risks in case of fire A B SAFE AREA SAFE AREA Cost comparison A – liquid immersed B – Dry type Unitary cost minor greater Transformer losses minor greater Installation costs ? ? MV cable cost and installation minor greater V cable cost and installation greater minor Cable losses greater minor
  55. 55. Power Transformer rating 1. Rated power 2. Rated voltages 3. Tapping 4. Short circuit voltage 5. No-Load and Load losses 6. Clock hour notation 7. Liquid immersed and dry type
  56. 56. Thank you | Presentation title and date For more information please contact Angelo Baggini Università di Bergamo Dipartimento di Ingegneria Viale Marconi 5, 24044 Dalmine (BG) Italy email: angelo.baggini@unibg.it ECD Engineering Consulting and Design Via Maffi 21 27100 PAVIA Italy

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