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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

- 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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