EE2191 – Electrical Machines Transformers Chamali Gamage Department of Electrical and Electronic Engineering University of Sri Jayewardenepura Real Transformers • Magnetization current • Flux leakage from windings • Losses in the core • Resistance in the winding Equivalent circuit for a real transformer Simplification of the equivalent circuit Simplified equivalent circuit Voltage Regulation Quantity that describes the degree of constancy of the output voltage πΈππΏ − πΈπΉπΏ ππππ‘πππ π πππ’πππ‘πππ = π 100 πΈπΉπΏ Where, πΈππΏ = Secondary voltage at no-load (V) πΈπΉπΏ = Secondary voltage at full load (V) 6 Efficiency of a transformer PO = Output real power PI = Iron losses (Fixed losses) PC = Copper losses ππ πΈπππππππππ¦ η = ππ + ππ + ππΆ 7 All Day Efficiency of a Transformer ππ’π‘ππ’π‘ ππππππ¦ ππ ππβ ππ’ππππ π πππ¦ % π΄ππ πππ¦ η = π₯ 100 πΌπππ’π‘ ππππππ¦ ππ ππβ ππ’ππππ π πππ¦ ππ’π‘ππ’π‘ ππππππ¦ ππ ππβ ππ’ππππ π πππ¦ = ππ’π‘ππ’π‘ ππππππ¦+πΈπππππ¦ π ππππ‘ πππ π‘ππ‘ππ πππ π ππ π₯ 100 Energy spent on iron core loss =ππ x total time transformer is energized Energy spend on copper losses = πΏπππ πΎππ΄ 2 ( ) ππΆπ’ πΉπΏ x πΎππ΄ πππ‘πππ (total time of consumption) 8 Autotransformers π2 πΈ2 = πΈ1 π1 9 Autotransformer under load 10 Current across BC = πΌ1 Current across AC =πΌ2 − πΌ1 mmf produced by πΌ1 must be equal and opposite to the mmf produced by πΌ2 − πΌ1 Therefore πΌ1 (π1 − π2 ) = (πΌ2 − πΌ1 ) π2 πΌ1 π1 = πΌ2 π2 Assumptions Both transformer losses and exciting current are negligible π΄πππππππ‘ πππ€ππ ππππ€π ππ¦ π‘βπ ππππ = π΄πππππππ‘ πππ€ππ π π’ππππππ ππ¦ π‘βπ π ππ’πππ πΈ1 πΌ1 = πΈ2 πΌ2 11
