Electrical Machine - IES Academy
Electrical Machine - IES Academy Electrical Machine - IES Academy
India’s No. 1 IES Academy Transformer Chapter-1 Transformed VA Input VA ( V − V ) I V 1 (1 k) VI V 1 2 1 2 = = − = − 1 1 1 Conducted VA Input VA V − V VI 2 1 = = 1 1 k As a' = N1/N2 approaches unity, (VA)' >> (VA) Hence, auto- transformer is used for required turn-ratio is 2 or less. Copper requirement For a two-winding transformer and auto-transformer having same voltage-ratio and VA rating, the weight of copper required by both of them is as below: G G auto TW = I ( N − N ) + ( I −I ) N IN 1 1+ IN 2 2 1 1 2 2 1 2 = 1 – N V 2 N = 1 – 2 1 V 1 Copper saving = GTW – Gauto = 1/a' GTW 1 R2' = ⎛ N ⎞ 2 ⎜ −1 R2 ⎟ and X2' = ⎛ N1 ⎞ ⎜ −1⎟ ⎝ N 2 ⎠ ⎝ N 2 ⎠ 2 X2 Three Phase Transformers There exist two arrangements: (i) A bank of three single – phase transformers (ii) A three – phase transformer (single unit) Fig. (a) Three-phase transformer bank, both windings in star (b) three-phase core-type transformer www.iesacademy.com E-mail: iesacademy@yahoo.com Page-24 25, 1 st Floor, Jia Sarai, Near IIT. New Delhi-16 Ph: 011-26537570, 9810958290
India’s No. 1 IES Academy Transformer Chapter-1 Three-phase transformer is cheaper (about 15% less cost) than a bank of three single-phase transformers, occupies much less space and are more efficient. But single-phase units are easier to transport. Moreover, in case of fault they can be used as open-delta with 58% rating. Types: (i) Core type; and (ii) Shell type Transformer Labeling and Connections Terminals on HV side in each phase – A, B, C (in capital letters) Terminals on LV side in each phase – a, b, c (in small letters) Similar polarities are indicated by similar suffices 1 or 2 on both sides. Labelling for transformer terminals Star/Star (Yy) Connection – (0° and 180° connections are obtained) www.iesacademy.com E-mail: iesacademy@yahoo.com Page-25 25, 1 st Floor, Jia Sarai, Near IIT. New Delhi-16 Ph: 011-26537570, 9810958290
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India’s No. 1<br />
<strong>IES</strong> <strong>Academy</strong><br />
Transformer<br />
Chapter-1<br />
Three-phase transformer is cheaper (about 15% less cost) than a bank of three single-phase<br />
transformers, occupies much less space and are more efficient. But single-phase units are<br />
easier to transport. Moreover, in case of fault they can be used as open-delta with 58% rating.<br />
Types: (i) Core type; and (ii) Shell type<br />
Transformer Labeling and Connections<br />
Terminals on HV side in each phase – A, B, C (in capital letters)<br />
Terminals on LV side in each phase – a, b, c (in small letters)<br />
Similar polarities are indicated by similar suffices 1 or 2 on both sides.<br />
Labelling for transformer terminals<br />
Star/Star (Yy) Connection – (0° and 180° connections are<br />
obtained)<br />
www.iesacademy.com E-mail: iesacademy@yahoo.com Page-25<br />
25, 1 st Floor, Jia Sarai, Near IIT. New Delhi-16 Ph: 011-26537570, 9810958290
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