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ECE 4411 Transformer Construction Slide 2 ECE 4412 Three-Phase Transformer Slide 3 ECE 4413 Transformer Action -- DC Slide 4 ECE 4414 Opposes battery voltageOpposes flux buildup Slide 5 ECE 4415 Transformer Action -- AC Slide 6 ECE 4416 Opposes V T Opposes M Slide 7 ECE 4417 No-Load Condition Slide 8 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 Slide 9 ECE 4419 No-Load Excitation mmf No-Load Core Loss mmf Magnetizing mmf Slide 10 ECE 44110 Slide 11 ECE 44111 Close the load switch Secondary current will set up an mmf in OPPOSITION to the primary mmf. The core flux will DECREASE to Slide 12 ECE 44112 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. Slide 13 ECE 44113 Primary current increases until N P I P,load = N S I S. The flux M and primary emf E P return to the same values as before the switch was closed. Slide 14 ECE 44114 Final steady state primary current under loaded conditions is Slide 15 ECE 44115 Component Fluxes Loaded Transformer Slide 16 ECE 44116 P = net flux in window of primary S = net flux in window of secondary lp = leakage flux of primary ls = leakage flux of secondary M = mutual flux P = M + lp S = M ls