EE-260 Lecture 14 AutoTransformer

8/9/2019 EE-260 Lecture 14 AutoTransformer

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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#


+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.


+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;



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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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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

=

=

=

=


c. ∆-= )onnections


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22


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

=

=

=

=


d. ∆- ∆ )onnections


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22


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


EE-260 Lecture 14 AutoTransformer

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