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TRANSFORMERS -

YESTERDAY, TODAY &

TOMORROW

: VK Lakhiani

Crompton Greaves Ltd.

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TRANSFORMER IS 117 YEARS OLD!

FIRST TRANSFORMER OF THE WORLD

60 W, 4.3 / 46.5 V, 18 Hz,

Single phase, Shell type, Dry type

Patented in 1985

by 3 Hungarian Engineers working in GANZ,

Budapest.

* KarolyZipernowsky

* TituszOtto’ Blathy

* MiksaDeri

Blathycoined the tame “Transformer”

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HOW IT ALL BEGAN !

•1831 -Faraday’s law of Electromagnetic Induction discovered

•1864 -Maxwell’s equations for mathematical models of

electromagnetic apparatus formulated.

•1885 -First real Transformer (single phase) Patented.

•1893 -First three phase Transformer was used in Hellsjon9.6

kV Transmission System in Sweden (Dry type 3 phase

transformers manufactured by ASEA)

•1900 -Oil Immersed Transformer was born.

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GROWTH OF LARGE POWER RATING TRANSFORMERS

World Scenario

1920s:

15 MVA

1930s:

45 MVA

1940s:

120 MVA

1960s:

1300 MVA 3-phase (Brown Boveri, 400 kV)

1970s :

550 MVA, 1-phase (1650 MVA Bank)

(Alsthom-France)

1998 :

775 MVA, 230 kV 60 Hz, SC Tested (ABB)

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GROWTH OF EHV TRANSFORMERS

World Scenario

1930s:

220 kV

1950s :

400 kV

1960s:

765 kV

1960s :

1150 kV (USSR)

Experimental Transformer -1785 kV / 1850 kV Class

2000s : 1200 kV (Japan, Italy, Canada, Brazil, USA)

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GROWTH OF TRANSMISSION VOLTAGES

Indian Scene:

1902: World’s first 78 kV, longest high rated voltage transmission line

on commercial basis in Mysore

State made operational -

Sivasamudram-Kankanhalli(about 150 km)

1931: 132 kV Introduced

1959: First 220 kV line become operative between Bhakrato Delhi

(300 km approx.)

1977: First 400 kV line commissioned between Obra-Lucknow

(370 km approx.)

1988:

HVDC Systems Introduced

2005(?):

800 kV AC

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LARGEST TRANSFORMERS (INDIA)

1968:

250 MVA 220 kV GT

1977:

240 MVA 400 kV GT

1980:

315 MVA 400 kV AT

1980:

600 MVA 400 kV Bank

1990:

315 MVA 1-phase HVDC Transformer

1995:

315 MVA 220 kV GT

2000:

320 MVA 275 kV GT

(Largest rating exported from India (CGL)

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CORE MATERIAL DEVELOPMENT

Year

Core Material

1885

Soft magnetic

1900

Non-oriented silicon steel

1935

Grain Oriented silicon steel

(Developed by Armco, USA)

1968

Hi-B (Developed by Nippon Steel Corpn.)

1980

Laser Scribed Hi-B

1990

Mechanically Scribed Hi-B

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GRADES & LOSSES OF ELECTRICAL STEELS

Type

Grade (Typical)

Loss w / kg at 1.7 T 50 Hz

Conventional

35 -M6

1.44

27 -M4

1.26

Hi-B

30 M2H

1.13

30 M0H

1.04

27 M0H

1.03

27 ZH 100

1.00

23 M0H

0.94

Laser Scribed Hi-B

27 ZDkH

0.92

23 ZDkH

0.85

Mechanically Scribed

27 ZDMH

0.92

23 ZDMH

0.85

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DEVELOPMENT IN CORE

•Reduction of core losses -Design & technology

-MitredJoints (1960s)

-2 x 2 blading

-10 mm over lap

-Minimum air gaps at joints

-Minimum burr level

-Yoke-less building

-Stepped lap core construction

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DEVELOPMENT IN CORE

•Bolt-less legs

-Banding with resi-glass tapes.

-Skin stressed cylinder.

-Semi conducting tape

•Bolt-less yokes

-Bolts outside the yokes.

-Resiglassbands with pressure buckles.

•Stainless steel clamp plate for stray-loss reduction or,

laminated CRGO clamp plates or, epoxy bonded legs.

•Optimum cross section or utility factor.

•Hotspot calculations and positioning of oil ducts.

•Realisationof oil ducts with button spacers or dimple sheets

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FUTURE OUTLOOK ON CORE STEEL

Two needs:-

Energy Saving

Reduced Iron Loss

Environmental Problem

Reduced Noise

Latest Trends :

1) More outstanding grain oriented electrical steels by optimising

-Electrical Resistivity

-Steel thickness

-Domain width

-Grain Orientation alignment

-Roughness of the substrate steel & coating film interface

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FUTURE OUTLOOK ON CORE STEEL (Contd.)

2) Gap between calculated values and measured values to bridge

-6 sigma tools

3) Stepped lap core construction shall be the order of the Day !

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DEVELOPMENT IN WINDINGS

Windings Subjected to :

•Dielectric steady state stresses uptosystem highest voltage conditions

•Dielectric stresses under one minute power frequency induced over

voltages.

•Non Linear Transient Voltage Distribution

Under Lightning and Switching Conditions

•Corona Discharges

•Thermal Stresses

•Short Circuit / Mechanical Stresses

•Vibrations

•Stray losses

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DEVELOPMENT OF INSULATING OIL

••Fire resistant, non-flammable silicon based liquid.

•High grade mineral oil, with exceptional oxidation stability and

improved electrical properties

•Opticoolfluids with low viscosity for better cooling properties

•Thermally upgraded oils for operation upto150oC

•Super biodegradable eco-fluid made from vegetable seed oils

for environmentally sensitive locations.

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DEVELOPMENT IN WINDING CONDUCTORS

•Thermally upgraded paper insulated conductors

•Enamel insulated conductor

•Bunched conductors

•Epoxy bonded bunched conductors

•Continuously transposed cables (CTC)

•Epoxy bonded CTC

•Foil (and sheet) conductors

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DEVELOPMENT OF INSULATING MATERIALS

••

Softer Pressboard

•Pre-compressed Pressboard in 1960

•MouldedAngle rings, angle caps

•Special Insulation at ends of windings to match electrostatic

field plots

•Low permitivitypressboard (permitivityequal to that of oil)

-Futuristic

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DEVELOPMENT IN WINDINGS

Design and Technological Development

•Use of interleaved / PID winding / contra shield winding

•Optimisationof radial clearances on stress distribution concepts

•Optimisationof axial clearances and use of mouldedcomponents

•Reduction in solid pressboard insulation in sub-divided barrier

arrangement

•Optimum winding placement

•Use of guided oil flow

•Use of yoke shunt / wall shunt / flux trap to control stray losses

•Improvement in short circuit withstand capability

•Stressed oil volume concept for lead clearances

•Wave shape sensitivity analysis and part winding resonance

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DEVELOPMENT IN WINDINGS

Ongoing and FuturisticsTrends

•T50 concept for withstand of transient voltage

•Behaviourof steep fronted nanosecond waves in GIS operation

•Winding noise & vibrations

•Focus on winding manufacturing process to stay within the given

tolerances.

•Focus also on achieving the measured losses as calculated.

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DEVELOPMENT IN WINDINGS

•Requirement of low deviations between measured and

calculated winding temperature and thereby need to

control manufacturing process.

•Increased demand for short circuit test in developing

countries

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DEVELOPMENT IN PROCESSING

•Vapourphase drying system developed which ahs following

advantages over the conventional Heat / Vacuum System

-Uniform heating of entire mass

-Less heat up time

-Removal of dust and dirt

-More effective extraction of moisture

-Shorter drying time cycle

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DEVELOPMENT IN PROCESSING (CONTD.)

•Dew Point method of monitoring of dryness of the insulation is

developed -particularly useful at site after repair

•Low frequency induction heating technique

•Current areas of improvement

-RVM (Recovery Voltage Measurement)

-PDC ( PolarisationDepolarisationCurrent)

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DEVELOPMENT IN STRUCTURAL DESIGN

•Clamping Structure for core and coil should be capable or

withstanding the forces of short circuit apart from lifting and

clamping the core

-Use of HTS at the appropriate places e.g. flitch plate is desirable

in large capacity transformers.

-Better coil clamping methods e.g. use of dash pots, coil clamping

jack screws etc.

-Flat end frames to reduce stray losses.

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DEVELOPMENT IN STRUCTURAL DESIGN (CONTD)

•Tank is subjected to complex loading

Lifting -Vacuum -Pressure -Transport -Vibration

-Stress analysis is possible based on FEM

•Simplified rectangular tank construction with box type

vertical stiffeners is the trend.

•Bell shaped construction developed for ease of site inspection

•Welded curb flanges

•Gaskets in machined grooves

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DEVELOPMENT IN MFG. TECHNIQUES

•High degree of automation is employed to achieve high dimensional

accuracy for lamination for reducing air gaps and to improve

efficiency.

•Vertical winding machine for winding large capacity transformer

coil.

•Pressurisedchambers used for windings and insulating parts to

protect against pollution and dirt.

•High frequency brazed joints / Improved crimping joints

•Vapourphase drying for effective and fast cleaning of core and

windings.

•Particle count for oil contamination

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IMPROVEMENTS IN BUSHING TECHNOLOGY

•`SRBP’ to `OIP’ to `RIP’ to SF6

SRBP

Practically Non-existent

OIP

Upto800 kV

RIP

Upto500 kV

SF6

Upto1000 Kv

•RIP with Silicon rubber sheds composite insulated for heavily

polluted atmosphere (Futuristic trends)

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IMPROVEMENTS IN BUSHING TECHNOLOGY (CONTD)

•Condition Monitoring of Bushings (on-going developments)

-Online infra-red scanning for hot spots

-Dissolved gas analysis

-Particle count of oil

-RIV Measurement to detect corona

-Tan δ δδδMonitoring

-Capacitance Monitoring

-PD

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IMPROVEMENTS IN OLTC

•Reactor type switching OLTC patented 1905 & 1906

(still popular in USA)

•High speed resistor type OLTC developed based on

Dr. Jansen’s patent (1926) (used in large scales)

•Improvement in construction features to increase reliability

of operation

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IMPROVEMENTS IN OLTC (CONTD.)

FUTURISTIC

•Maintenance free OLTC

•Use of semiconductors and vacuum for switching

•Dry type OLTC

•Condition Monitoring of OLTC

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OIL PRESERVATION SYSTEMS

Isolation of oil from moisture and oxygen result in slower deterioration

of oil

Popular preservation systems are :

•Nitrogen Sealing -Inert dry atmosphere of N2is created over the oil in

conservator

•AtmosealSystem -Rubber pouch placed inside the conservator inflates

or deflates with contraction / expansion of oil

•Diaphragm System -Rubber diaphragm creates a partition between oil

and outside air

•ThermosyphonSystem -Part of the oil circulated through an absorbent

sieve of Alumina by thermosyphonaction

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NEW ADDITIONS TO FAMILY OF TRANSFORMERS

AMORPHOUS METAL TRANSFORMERS (AMT)

•Amorphous metal has a non-crystalline structure (like glass)

with molecules in random pattern -results from rapid solidification

of molten alloy @ one Million Degrees celsiusper second.

•Gives 80% reduction in no-load losses compared to conventional

CRGO.

•Substantial reduction in magnetisationcurrent and hence low

reactive VAR consumption.

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AMORPHOUS METAL TRANSFORMERS (AMT) (CONTD.)

•Low harmonic losses

•Present limitation -distribution range upto5 MVA.

•(Futuristic) energy efficient cast resin transformers

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DRY TYPE TRANSFORMERS

•Two types (i) Conventional (ii) Cast Resin or Resin Impregnated

•Class `C’ or `F’

•Suitable for indoor application with low fire hazard

•Nomexpaper / board used has temperature withstand capability

of 2200C

•Vacuum pressure impregnation (VPI) with polyestermide

resin ensures high mechanical strength

•Initial higher cost than that of oil cooled

•Maintenance free

•Future trends -ratings beyond 33 kV

•Problems related to PD and UV radiation

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SF6 GAS INSULATED TRANSFORMERS

•Technology more popular in USA and Japan.

•Conductor Insulation is PET (Polyethylene Terephthalate(No

reaction with SF6 and has high temperature withstand)

•20% reduced weight, 15% reduced size compared to oil

immersed transformers.

•Suitable for installation in high fire risk elimination of fire

hazards and explosion that exist with transformer oil.

•Cooled by Gas to liquid heat exchangers.

•Pressured SF6 Gas provides dielectric strength during the start-

up period.

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SF6 GAS INSULATED TRANSFORMERS

•Liquid fluorocarbon is dispersed over the magnetic circuit

and the windings. When the transformer is loaded where it

is vapourised. The vapoursincrease the dielectric strength

and also provide cooling.

•GIS is the trend, right upto1200 kV

•Environmental concerns, sealing problems and high cost of

manufacture may restrict the growth of SF6 transformers

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CONDITION MONITORING TECHNIQUES

Diagnostic methods & Online Off-line Fields of application

Measuring Quantities

--------------------------------

---------

----------

-----------------------------

•Gas-in-oil analysis x x

Core & coil assly-Therm

al

faults and elect.discharges

•Fibreoptic sensors

xWinding hot-spots -loading

embedded in wdg. For

capability

hot-spot measurement

•RVM, PDC, Tan Delta

x Dryness of insulation

•C, Tan delta of

x x Healthiness of bushings

bushings

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CONDITION MONITORING TECHNIQUES (CONTD.)

Diagnostic methods & Online Off-line Fields of application

Measuring Quantities

•PD measurement

x x Core & coil assembly, ageing,

and location

incipient faults

•Transfer function x Core & coil assly. Winding

displacement,

winding

faults

•PPM x x Active part dryness

•OLTC monitoring

x x Arcing and contact wear

•FRA,LV1,HV1

x Winding displacement during

transport, short circuit

•Furfural Content

x x RLA

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TRANSFORMERS FOR TOMORROW

•Power-former

•High voltage Electric Generators employing XLPE

cable are being developed upto400 kV

•First Power-former : a hydro machine rated at 11

MVA, 45 kV commissioned at the PorjusHydro Power

Centre in Northern Sweden in 1998.

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TRANSFORMERS FOR TOMORROW

DRYFORMER -LATEST BREAKTHROUGH

♦First patent filed in February 1997 : 10 MVA, 52/17 kV

♦First commercial installation in 1999 : 2 x 20 MVA, 140/6.6 kV at

BirkaEnergi’sLotteforsHydropower Station

♦Result of marriage of high voltage cable technology and

transformer technology

♦It is oil free, dry type transformer which is a complement to, and

an extension of existing range of conventional high voltage

transformers using XLPE cable as winding conductors.

♦Claimed advantages: positive environ-mental impact, enhanced

safety, flexible placement, higher reliability; hence suitable for

placement in densely populated urban areas and environmen-

tally sensitive areas

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DRYFORMER (CONTD.)

♦Better short-circuit strength as windings are held in a place in

a cage like structure that provides both axial and radial

supports

♦Windings are self supported (not clamped from yoke / frame)

♦Mechanical behaviourof XLPE changes especially at high

temperatures (upper temperature limit 900C)

♦New dry type OLTC and new cable to air terminations are

under development

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HIGH TEMPERATURE SUPER CONDUCTING

TRANSFORMERS (HTS)

TRANSFORMER FOR NEAR FUTURE (Next 5-10 Years)

•Reduces energy losses by approx. 50%

•Reduces weight and size as much as 50%

•Elimination of oil

•Used with non-flammable liquid N2as a coolant and dielectric

•About 100 compounds now classified as HTS, some of them becomes

super conducting at temperature as high as 1350C

•Two important types :

YBCO -Yttrium barium Copper Oxide

BSCCO -Bismuth Strontium Calcium Copper Oxide

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HIGH TEMPERATURE SUPER CONDUCTING

TRANSFORMERS (HTS)

•World’s First Operational HTS Distribution Transformer

630 kVA, 18.7 kV / 420 V Commissioned in Geneva, Switzerland in

March 97, using BSCCO-2223 PIT windings cooled in liquid N2.

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DISTINCT TRENDS AT THIS TIME

•The continued interest and emphasis on improved reliability for

both transformers and accessories

•Research and Development of condition monitoring techniques

to ensure trouble free service

•Estimation of remnant life of transformers and accessories

•Diagnostic methods for fault locations

•Microprocessor based monitors

•Electronic instrumentation for controls and protection

•Future is for dry technology

-Dryformer

-Dry bushings

-Dry static tapchangers

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BUSINESS TRENDS AT THIS JUNCTURE

•Business around aging population of transformers shall increase

-Consultation business to grow to help utilities plan for

replacement or refurbishment

-RLA will have good business potential

•Upgrading will be a large business

-New windings and new insulating material can increase the

rating upto50%

•Site repair, site refurbishment, site dry out and site testing may

develop as good business

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BUSINESS TRENDS AT THIS JUNCTURE(CONTD.)

•Trend towards specialisationand segmentaionto

achieve high quality and stay competitive and

concentrate on Niche Products

•Focus on efficient and fast manufacturing.

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( TODAY )

•TRANSFORMER INDUSTRY IS NOW

COMPLETELY GLOBALISED LIKE

AIRCRAFT OR AUTOMOBILE OR IT

INDUSTRYOF TODAY

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( TOMORROW )

TRANSFORMER WILL CONTINUE

TO SERVE MANKIND SELFLESSLY

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