Transformer Construction

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ECE 441 1 Transformer Construction

description

Transformer Construction. Three-Phase Transformer. Transformer Action -- DC. Opposes battery voltage. Opposes flux buildup. Transformer Action -- AC. Opposes V T Opposes Φ M. “No-Load” Condition. “No load” condition continued. I o = I fe + I M - PowerPoint PPT Presentation

Transcript of Transformer Construction

Page 1: Transformer Construction

ECE 441 1

Transformer Construction

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ECE 441 2

Three-Phase Transformer

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Transformer Action -- DC

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11

de N

dt

2 2

de N

dt

Opposes battery voltage Opposes flux buildup

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Transformer Action -- AC

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max4.44P PE N f max4.44S SE N f

Opposes VT Opposes ΦM

max

max

4.44

4.44PP P

S S S

N fE N

E N f N

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“No-Load” Condition

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“No load” condition continued

Io = Ife + IM

Io = exciting current

Io provides the “magnetizing flux” and the “core loss”

Ife = core-loss current Ife = VT / Rfe

IM = magnetizing current IM = VT / jXM

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O fe M

P O P fe P M

I I I

N I N I N I

No-Load Excitation mmf

No-Load Core Loss mmf

Magnetizing mmf

P MM

core

N I

R

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T P P P

T PP O

P

V I R E

V EI I

R

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Close the load switch

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

P M S SM

core

N i N i

R

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

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,P M P P load S SM

core

N i N i N i

RPrimary current increases until NPIP,load = NSIS. The flux ΦM and primary emf EP return to the same values as before the switch was closed.

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Final steady – state primary current under loaded conditions is

,

0 ,

P fe M P load

P P load

I I I I

I I I

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Component Fluxes – Loaded Transformer

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ΦP = net flux in window of primary ΦS = net flux in window of secondary

Φlp = leakage flux of primary Φls = leakage flux of secondary

ΦM = mutual flux

ΦP = ΦM + Φlp

ΦS = ΦM – Φls