TRANSFORMER LOSSES EFFICIENCY Lecture No 06 By Sajid

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 The load power factor is unknown Apparent Power

Problem S = 2 k. VA V 1 = 6, 351 V V 2 = 230 V Power output at unity PF ? Power = S x PF P = 2 k. VA x 1 P = 2 k. W

Problem S = 2 k. VA V 1 = 6, 351 V V 2 = 230 V Full load secondary current at 0. 8 PF ? I = 10. 87 A

Problem S = 20 k. VA V 1 = 1270 V (a) V 2 = 200 V Power output at unity power factor P = 20 k. W

Problem S = 20 k. VA V 1 = 1270 V (b) V 2 = 200 V Power output at 0. 8 power factor P = 16 k. W

Problem S = 20 k. VA V 1 = 1270 V (c) V 2 = 200 V Full-load secondary current at unity power factor I = 100 A

Efficiency Ratio between Input power and Output Power

Efficiency is normally expressed as a percentage

Transformer Efficiency Power In Power Out η = 100% Some Power is used to: Overcome Copper Losses Overcome Iron Losses

Problem S = 20 k. VA η = 90% V 1 = 230 V (a) V 2 = 32 V Power output of transformer P = 85 W PF = 0. 85

Problem S = 20 k. VA η = 90% V 1 = 230 V (b) V 2 = 32 V PF = 0. 85 Power input P = 94. 4 W

Problem S = 20 k. VA η = 90% V 1 = 230 V (c) V 2 = 32 V Losses P = 9. 4 W PF = 0. 85

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

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

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

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

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

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