ee-260 lecture 14 autotransformer
TRANSCRIPT
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EE-260 : Electro-Mechanical Systems(EMS)EE-260 : Electro-Mechanical Systems(EMS)
Lecture#14Lecture#14
Text oo!: "hater 02 (Stehen $% "haman 4th E&)
'nstructor: Miss eelma a
"lass: EE 4 "*+
School o, Electrical Enineerinan& "omuter Science
+eartment o, ElectricalEnineerin
1
2%. T/E TT3S3ME3 5ae 10.
2%10 T/3EE-5/SE T3S3ME3 5ae 116
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1. Auto-Transformer1. Auto-Transformer• Auto-Transformer is a transformer with only one winding.transformer with only one winding.
• That means, the primary and secondary windings are notnotelectrically isolated form each other electrically isolated form each other . In other words, the
primary and the secondary of autotransformer are
physically connected. physically connected.
• The theorytheory is almostalmost the samesame as two winding transformer.two winding transformer.
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4
1. Autotransformer
Some times it is desirable to change oltage leels by only small
amount.
!or e"ample
11# $ to 1%# $ or 1&.% ' to 1&.( '.
)onentional Transformer Autotransformer
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• The winding across which both the
primary and secondary oltages
appear is called )ommon *inding and the smaller winding which is
connected in series with the common
winding and across which only one
oltage +primarysecondary appears
is called Series *inding.
1. The Autotransformer +cont
• The oltage at the output of the autotransformer is the sum of the
oltage on the first winding and oltage on the second winding.
&
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/
1. The Autotransformer +cont
Step down autotransformer
Step up autotransformer
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0
1. The Autotransformer $oltage elationships
+cont..
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1. The Autotransformer )urrent elationships
+cont..
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1. The Apparent 3ower ating Adantage
+cont
L
H
SE C
C
H
L
I
I
N N
N
V
V =
+
=
The input and output apparent power may
be defined as
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1#
1. The Apparent 3ower ating Adantage
+contThe apparent power in the transformer
winding is gien by
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• The S IO
is the apparent power entering the primary and leaing the
secondary of transformer,
• The S w is the apparent power actually traveling through the transformer’s
windings, the rest passes from primary to secondary without eingcoupled through the transformer winding .
• The smaller the series winding the greater the adantage will be.
1. The Apparent 3ower ating Adantage
+cont
1#
The e6uation describes the apparent power rating adantage of thetransformer oer a conentional transformer.
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7ome *or'
*or' out and understand8"ample %-0
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14
%. Three 3hase Transformers
• The ma9or power generation, transmission, and distribution
systems are three phase systems. Therefore, it is necessary tounderstand the design and operation of a three phase
transformers.
• A three phase transformer can be constructed in one of the two
waysa. Simply ta'e three single phase transformers and connect
them in three phase ban'.
b. :a'e a three phase transformer consisting of three sets of
windings wrapped around a common core.
• A single three phase transformer is the preferred practice today
because it is lighter, smaller, cheaper, and slightly more efficient.
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1;
%. Three 3hase Transformers
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1/
%. Three 3hase Transformer )onnections
+cont•
The 3rimary and secondary winding of a three phasetransformer can be independently connected in either wye +=
or delta +∆.
• !our possible connections for a three phase transformer.
1. =-= %. =-∆ &. ∆-= 4. ∆-∆
• Any single transformer in the ban' behaes e"actly li'e a
stand alone single phase transformer.
• The impedance, oltage regulation, efficiency, and similarcalculations for three phase transformer can be done on per
phase basis using the techni6ues established for single phase
transformer.
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10
%. Three 3hase Transformer
a. =-= )onnections
& & L! ! L
!
S
L
L
S
!
S S
V V a
V V V V
aV V
ϕ
ϕ
ϕ
ϕ
=
=
=
=
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16
%. Three 3hase Transformer
a. =-= )onnections
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%. Three 3hase Transformer +cont
b. =-∆ )onnections
17
&
& !
L! ! L
L!
S LS
S S V V V V
V V a a
V V
ϕ
ϕ
ϕ
ϕ
=
=
=
=
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%. Three 3hase Transformer +cont
b. =-∆ )onnections
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&
&
L! ! L
! L!
S LS
S S V V V V V V a
aV V
ϕ
ϕ
ϕ
ϕ
=
=
=
=
%. Three 3hase Transformer +cont
c. ∆-= )onnections
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22
%. Three 3hase Transformer +cont
c. ∆-= )onnections
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23
L! !
!
S
L!
S
LS
S L
V V V V
V V a a
V V
ϕ
ϕ
ϕ
ϕ
=
=
=
=
%. Three 3hase Transformer +cont
d. ∆- ∆ )onnections
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22
%. Three 3hase Transformer +cont
d. ∆- ∆ )onnections
Th Ph T f
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2
Three Phase Transformer
Connections
1) -
2) -∆
∆-
4 ∆-∆
aV
V
aV
V
V V V V
LS
L!
S
!
S LS ! L!
&
&
==
==
φ
φ
φ φ
&
&
a
V
V a
V
V
V V V V
LS
L!
S
!
S LS ! L!
==
==
φ
φ
φ φ
aV
V a
V
V
V V V V
LS
L!
S
!
S LS ! L!
==
==
φ
φ
φ φ
aV
V aV
V
V V V V
LS
L!
S
!
S LS ! L!
==
==
φ
φ
φ φ &&
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"onclusion
26
1. Auto Transformers
%. Three 3hase Transformers