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By | July 2013
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EHV Power Transformers

J S Sastry GM (EHV Transformers) Vijai Electricals

Topics to be covered
• • • • • • • • What is a Transformer Transformer principle Basic design concepts Construction features Materials used and improvements Types of failures and diagnostics Challenges to Transformer Designers Reactors

IF YOU HAVE NO DOUBTS YOU HAVE NOT UNDERSTOOD ANYTHING.
- a Spanish proverb.

What is a Transformer
• A transformer is a static equipment which transformers power from one circuit to another by stepping up or down the primary voltage without any change in the frequency. • The two circuits may or may not be connected but are magnetically coupled.

Features of Power Transformers
• Single Phase • Three phase
– Star or Delta connected Primary – Star or Delta connected Secondary – With or without Tertiary winding

• Provided with Off-circuit tap switch or On-load Tap Changer for voltage regulation

Transformers in Network

Transformer Operating Principle

Operating Principles Equivalent Circuit

Specification Parameters for Generator Transformer

Specification Parameters for Network Transformer

Design Principles - Core

Design Principles - Core
 Higher the number of steps in cross section, better is space utilization and smaller is the core diameter. 90 to 95 % utilization factor is optimal.

 Core area (A) is determined by the Flux Density (B) which in  turn depends on many factors - like loss capitalization and overall design economics. As the no load losses attract very high capitalization, attempts are continuously made to reduce them.

Design Principles - Core
• Improved manufacturing techniques like core building with 2-lamination packets, steplap joints, v-notched laminations, bolt-less cores are used. • Hi-β core steels like M0H, ZDKH, etc are available in which the specific core losses are lower than normal grades. • Amorphous steels drastically reduce no-load losses, but are now being used only in...

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