WEL-COME

TO

POWER GRID OFFICIALS

DESIGN & DEVELOPMENT OF POWER TRANSFOMERS

Presented by-

J.K.JAIN – Sr.DGM(TRE)

Special Characteristic Features of Transformer Designs

• Tailor made designs to suit customer requirements.

• Design Problems – Two fold.

> Associated with high voltages (Dielectric design,

behaviour under transient voltages, PD).

> Associated with high currents (Electromagnetic.

problems related to stray losses and hot spots,

thermal design, mechanical short circuit forces).

• High cost of losses demand low loss designs with high material content (Transport and handling problems), better methods of stray loss control.

• No two designs of same MVA and Voltage rating are comparable in terms of weights and losses owing to different capitalization, Impedance, Tapping range, Limiting current densities, Flux density etc.

Constituents of a Transformer

• Windings

• Core

• Insulation Structure

• Tank

• Cover

• Core clamping Structure

• Pipe Work

• Cooling Equipment

• Bushings

• Leads (Terminal Gear)

• Fittings

• Control Equipments

• Oil

Type of Windings

• SPIRAL WINDING

• HELICAL WINDING

• CONTINUOUS DISC WINDING

• PARTIALLY OR FULLY INTERLEAVED DISC WINDING

• SHIELDED LAYER WINDING

Type of Windings

Spiral winding Helical winding

(No radial duct)

(a) cross-section (b) connections

SINGLE LAYER DISC COIL

INTERLEAVED DISC WINDING

INTERLEAVED DISC WINDING

(4 discs per group)

Transposition

Transposition at each cross-over in

Continuous Disc Winding

Transposition in Spiral/Helical Winding

(a) Complete Transposition

(b) Partial Transposition

Directed Oil Flow Arrangement

WINDING

• USE OF SPECIAL TYPE OF COPPER CONDUCTORS (BUNCHED PICC, GLUED PICC, WORK HARDENED etc.)

• OPTIMUM WINDING PLACEMENT• USE OF GUIDED OIL FLOW AND FORCED

DIRECTED OIL FLOW IN WINDINGS FOR CONTROL OF HOT SPOTS

• USE OF YOKE SHUNT/WALL SHUNTS/FLUX TRAP TO CONTROL STRAY LOSSES

DESIGN TRENDS IN RECENT YEARS

• USE OF INTERLEAVED/PARTIALLY

INTERLEAVED DISC WINDING (LAYER WINDING, IN SPECIFIC CASES)

• OPTIMISATION OF RADIAL CLEARANCES BY STRESS DISTRIBUTION CONCEPT INCLUDING TG & BUSHING CLEARANCES

• OPTIMISATION OF AXIAL CLEARANCES AND USE OF INSULATION MOULDINGS

• REDUCTION IN SOLID PRESS BOARD INSULATION BY SUB-DIVIDED BARRIER ARRANGEMENT

Insulating Area

A: Vertical Area B: Horizontal Area C: Area between A&B

Core Nomenclature

• L= Leg Length• C= Distance

between leg centres

• W=Main leg width

Top Yoke

Bottom YokeAuxiliary

Limb

WA AL

C C

D= Max. core diameter

Section through ‘A-A’

Cooling Duct

D

W

Type of core forms

Single Phase, Core type 2 legs wound

SC

W

WL

Single Phase, core type middle leg wound

SM

W

W/2

W/2

Single Phase, core type 2 middle legs wound

SMC

W W

W/2

W/2

Three Phase, core type

TC

W

W

W W

Three phase, core type, 5 limb

TCF

0.43 W

0.57 W

Inside Yoke Length

W W W

Core ConstructionsA. Three phase- 3 limb core

INTERLEAVED THREE QUARTER MITRED

FULLY MITRED FULLY MITRED SPLIT WITH DIAMOND INSERT

Three phase, five limb coreB: Three phase, five limb core

FULL WIDTH

SPLIT WIDTH

CORE:

USE OF BUTTON SPACERS IN CORE FOR BETTER SPACEFACTOR AND OIL FLOW

USE OF HI-B GRADES OF STEEL FOR REDUCTION OF NO LOADLOSSES

USE OF LASER SCRIBED CORE STEEL FOR FURTHER LOSSREDUCTION

USE OF NON-MAGNETIC STEEL FOR CLAMP PLATE FORHIGHER CAPACITY TRANSFORMER FOR STRAY LOSSCONTROL AND IMPROVED OVERFLUXING CAPABILITY

ELIMINATION OF YOKE BOLTS REDUCED NO. OF PACKETS IN YOKE FOR IMPROVED

PRODUCTIVITY

DESIGN TRENDS IN RECENT YEARS

Radial Short Circuit Stress

Short Circuit Stress in Core Type Transformers with cylindrical windings

Internal sketch of Transformer

PLAN VIEW

ELEVATION VIEW

Types of Transformer Tank

1) Conventional Tank

- Bolted Tank

- Welded Tank

2) Bell Type

Conventional Tank

Tank Cover Turret

Tank Body

Stiffner

Core Clamping structure

ResiglassTape

Clamp Plate

End

Frame

Leakage Flux

Flux entering the tank

Flux enters the Shunt

Clearance between Windings and YokeAngle rings and Caps with Field

Fittings and Accessories• Buchholz Relay• conservator• Breather• Magnetic Oil Level gauge• Winding Temperature Indicator• Oil Temperature Indicator• Fans• Radiators• Pressure relief Device• Thermometer• Oil Preservation System

• Marshalling Box

• Bushings

• Post Insulator

• Current Transformer

• On Load Tap Changer

Oil Preservation System

Breather

Air cell

Typical Outline General Arrangement

A: ELEVATION

B: PLAN

Thanks