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Power transformers rating
This document discusses power transformer ratings, including rated power, voltages, tapping, short circuit impedance, losses, clock hour notation, and liquid immersed vs dry types. It provides details on calculating rated power based on load power and factors, selecting standard rated voltages, common tapping ranges, choosing short circuit impedance values, and standards for no-load and load losses. It also compares risks of liquid immersed and dry transformers in case of fire.
In this document
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Introduction of Angelo Baggini from Engineering Department of Bergamo University, Italy, and the focus on Power Transformer ratings.
Discusses fundamental parameters of power transformer ratings: rated power, voltages, tapping, losses, and types.
Importance of load power, network voltage, short circuit levels, reliability, and environmental considerations.
Covers rated power considerations including number of units, cooling methods, effects of harmonics, and oversizing.
Analytical calculations for different load types and their associated usage factors for accurate transformer sizing.
Proposes metrics for various industries' energy requirements, measuring power needs per square meter.
Address resilience in transformer design in the case of faults, ensuring reliability.
Emphasizes energy efficiency calculations and factors influencing transformer efficiency.
Discusses the importance of future needs in transformer sizing, including oversizing and potential loading.
Specifications for sizing low voltage sections, including standardized values in kVA.
Details on rated voltages selection based on network requirements and compliance with national standards.
Explains preferred tapping ranges for de-energized and on-load tap changers.
Discusses short circuit impedance impacts, standardized values, and implications for system design.Analyzes no-load and load losses in transformers and introduces new standards for oil-immersed transformers.
Calculates total owning cost for transformers based on performance and capital factors.
Presents case studies for different transformer sizes ranging from 150 to 600 kVA.
Introduces the clock hour notation system used in transformer ratings.
Compares liquid-immersed and dry-type transformers, discussing cost implications and fire safety risks.
Summarizes major factors affecting power transformer ratings discussed throughout the presentation.
Final remarks from Angelo Baggini and contact details for further information.
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Power transformers rating
- 1. Angelo Baggini, angelo.baggini@unibg.it,Bergamo University - Engineering Department Via Marconi 5, 24044 Dalmine (BG) – Italy Power Transformer rating
- 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. 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. Power Transformer rating Ratedpower … and number of units … and cooling mode
- 5. Rated power Load tobe 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. Rated power … incase of harmonics Voltage distortion → NO load losses Current distortion → Load losses Oversizing needs
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- 8. Load type ku Lamps1 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. Load type NumberkC 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. Number of loadskC 1 1 2 ÷ 4 0,8 5 ÷ 10 0,6 11 and more 0,4 Rated power Analytical calculations – Contemporaneity factors
- 11. Type of activityFactor 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. Rated Power Measurements, Hystoricaldata and trends
- 13. Type of activityPower (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. Type of activityPower (VA/m2) Offices 70 Schools 50 Hospitals 60 Hotels 80 Residential 40 Rated power Measurements, Hystorical data and trends
- 15. Rated Power Resilience incase of fault
- 16. Rated power 16 Resilience incase of fault
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- 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
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- 20. Rated power Future needs •Oversize* • Possibility of overloading* • At design stage: possiiblity to add a busbar * coherent sizing of LV section 20
- 21. Rated power LV sectionsizing 21 Ref. 400 V 3f 4% up to 630 kVA 6% upper 630 kVA
- 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. Power Transformer rating Ratedvoltages
- 24. Rated voltages to beselected on the basis of the voltages of the served networks
- 25. Rated voltages for windingwith 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. Rated voltages for windingwith 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
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- 30. Tappings DETC: De-energised tapchanger 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. Power Transformer rating Shortcircuit impedance
- 32. Shortcircuit impedance 1. Reactivepower: 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. Shortcircuit impendance Scheme’s effectson 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. Shortcircuit impedance Standardized values EUpractice fro MV transformers 4% ≤ 630 kVA 6% ≥ 630 kVA
- 35. Shortcircuit impedance Transformer inparallel Z V V Z CCA 21 A Z VV I • •• • − = CCB 21 B Z VV I • •• • − = Same: • Turn ratio • Clock hour figure • vcc
- 36. Power Transformer rating Loadand no-load losses
- 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. New EN 50588-1 Oilimmersed 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. Total Owning Cost (€/kWyear) (€/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. Load from 150to 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
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- 51. Power Transformer rating Clockhour notation
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- 53. Power Transformer rating Liquidimmersed and dry type
- 54. Liquid immersed anddry 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. 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. Thank you | Presentationtitle 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