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Transformer Losses & Efficiency

Transformer Losses & Efficiency. Lecture No. 06 By. Sajid Hussain Qazi. Transformer Ratings. Transformers are rated to supply a given output in Kilo Volt Amps or KVA at a specified frequency and terminal voltage. Transformer Ratings. They are NOT rated in Watts

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Transformer Losses & Efficiency

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  1. TransformerLosses & Efficiency Lecture No. 06 By. SajidHussainQazi

  2. Transformer Ratings Transformers are rated to supply a given output in Kilo Volt Amps or KVA at a specified frequency and terminal voltage.

  3. Transformer Ratings They are NOT rated in Watts The load power factor is unknown Apparent Power

  4. Problem S = 2 kVA V2 = 230 V V1 = 6,351 V Power output at unity PF ? Power = S x PF P = 2 kVA x 1 P = 2 kW

  5. Problem S = 2 kVA V2 = 230 V V1 = 6,351 V Full load secondary current at 0.8 PF ? I = 10.87 A

  6. Problem S = 20 kVA V1 = 1270 V V2 = 200 V (a) Power output at unity power factor P = 20 kW

  7. Problem S = 20 kVA V1 = 1270 V V2 = 200 V (b) Power output at 0.8 power factor P = 16 kW

  8. Problem S = 20 kVA V1 = 1270 V V2 = 200 V (c) Full-load secondary current at unity power factor I = 100 A

  9. Efficiency Ratio between Input power and Output Power

  10. Efficiency Efficiency is normally expressed as a percentage

  11. Transformer Efficiency PowerIn PowerOut η = 100% Overcome Copper Losses OvercomeIron Losses Some Poweris used to:

  12. Problem S = 20 kVA V1 = 230 V η = 90% V2 = 32 V PF = 0.85 (a) Power output of transformer P = 85 W

  13. Problem S = 20 kVA V1 = 230 V η = 90% V2 = 32 V PF = 0.85 (b) Power input P = 94.4 W

  14. Problem S = 20 kVA V1 = 230 V η = 90% V2 = 32 V PF = 0.85 (c) Losses P = 9.4W

  15. Transformer Losses Copper Losses (Cu) • Varies with load current • Produces HEAT • Created by resistance of windings • Short circuit test supplies copper losses

  16. Short Circuit Test Copper Losses (Cu) Limited Supply Voltage ≈ 5-10 % Secondary Short Circuited Wattmeter indicates Copper Losses (Cu)

  17. Short Circuit Test Copper Losses (Cu) • Finds Cooper losses at full load • Copper losses vary with the square of the load Full load Cu loss = 100 W Transformer loaded at 50% PCu = 25 W

  18. Copper Losses (Cu) Cu Losses (W) % Load

  19. Transformer Losses Iron Losses (Fe) • Fixed • Always present • Related to transformers construction Eddy Currents Hysteresis Reduced by laminations Produces HEAT Reduced by using special steels in laminations

  20. Open Circuit Test Finds Iron Losses (Fe) Full Supply Voltage Secondary Open Circuit Wattmeter indicates Iron Losses (Fe)

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