ECE 4411 Transformer Construction

ECE 4412 Three-Phase Transformer

ECE 4413 Transformer Action -- DC

ECE 4414 Opposes battery voltageOpposes flux buildup

ECE 4415 Transformer Action -- AC

ECE 4416 Opposes V T Opposes Φ M

ECE 4417 “No-Load” Condition

ECE 4418 “No load” condition continued I o = I fe + I M I o = exciting current I o provides the “magnetizing flux” and the “core loss” I fe = core-loss currentI fe = V T / R fe I M = magnetizing currentI M = V T / jX M

ECE 4419 No-Load Excitation mmf No-Load Core Loss mmf Magnetizing mmf

ECE 44110

ECE Close the load switch Secondary current will set up an mmf in OPPOSITION to the primary mmf. The core flux will DECREASE to

ECE The decrease in flux causes a decrease in the counter-emf E P, and the primary current will increase by an amount known as I P,load, the load component of the primary current. Additional mmf due to this current adds to the magnetizing flux.

ECE Primary current increases until N P I P,load = N S I S. The flux Φ M and primary emf E P return to the same values as before the switch was closed.

ECE Final steady – state primary current under loaded conditions is

ECE Component Fluxes – Loaded Transformer

ECE Φ P = net flux in window of primary Φ S = net flux in window of secondary Φ lp = leakage flux of primary Φ ls = leakage flux of secondary Φ M = mutual flux Φ P = Φ M + Φ lp Φ S = Φ M – Φ ls