transformers yesterday,today & tomorrow

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TRANSFORMERS YESTERDAY, TODAY & TOMORROW

: VK Lakhiani Crompton Greaves Ltd.

1

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 by 3 Hungarian Engineers working in GANZ, Budapest. * Karoly Zipernowsky * Titusz Otto Blathy * Miksa Deri2

Patented in 1985

Blathy coined the tame Transformer

HOW IT ALL BEGAN !

1831 - Faradays law of Electromagnetic Induction discovered

1864 - Maxwells equations for mathematical models of electromagnetic apparatus formulated.

1885 - First real Transformer (single phase) Patented.

1893 - First three phase Transformer was used in Hellsjon 9.6

kV Transmission System in Sweden (Dry type 3 phase

transformers manufactured by ASEA)

1900 - Oil Immersed Transformer was born.3

GROWTH OF LARGE POWER RATING TRANSFORMERS

World Scenario15 MVA 45 MVA 120 MVA 1300 MVA 3-phase (Brown Boveri, 400 kV) 550 MVA, 1-phase (1650 MVA Bank) (Alsthom-France) 775 MVA, 230 kV 60 Hz, SC Tested (ABB)4

1920s :

1930s :

1940s :

1960s :

1970s :

1998 :

GROWTH OF EHV TRANSFORMERS

World Scenario220 kV 400 kV 765 kV 1150 kV (USSR)

1930s :

1950s :

1960s :

1960s :

Experimental Transformer - 1785 kV / 1850 kV Class 1200 kV (Japan, Italy, Canada, Brazil, USA)

2000s :

5

GROWTH OF TRANSMISSION VOLTAGES Indian Scene :

1902:

Worlds 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 Bhakra to Delhi

(300 km approx.)

1977:

First 400 kV line commissioned between Obra- Lucknow

(370 km approx.)

1988:

HVDC Systems Introduced6

2005(?): 800 kV AC

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)7

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

8

GRADES & LOSSES OF ELECTRICAL STEELS Grade (Typical)35 - M6 27 - M4 30 M2H 30 M0H 27 M0H 27 ZH 100 23 M0H 27 ZDkH 23 ZDkH 27 ZDMH 23 ZDMH 1.44 1.26 1.13 1.04 1.03 1.00 0.94 0.92 0.85 0.92 0.859

Type

Loss w / kg at 1.7 T 50 Hz

Conventional

Hi-B

Laser Scribed Hi-B

Mechanically Scribed

DEVELOPMENT IN CORE

Reduction of core losses - Design & technology

- Mitred Joints (1960s) - 2 x 2 blading - 10 mm over lap - Minimum air gaps at joints - Minimum burr level - Yoke-less building - Stepped lap core construction

10

DEVELOPMENT IN CORE

Bolt-less legs

- Banding with resi-glass tapes.

- Skin stressed cylinder.

- Semi conducting tape

Bolt-less yokes

- Bolts outside the yokes.

- Resiglass bands 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.

Realisation of oil ducts with button spacers or dimple sheets11

FUTURE OUTLOOK ON CORE STEEL

Two needs :Reduced Iron Loss Reduced Noise

Energy Saving

Environmental Problem

Latest Trends :

1) More outstanding grain oriented electrical steels by optimising

-

Electrical Resistivity

-

Steel thickness

-

Domain width

-

Grain Orientation alignment12

-

Roughness of the substrate steel & coating film interface

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 !

13

DEVELOPMENT IN WINDINGS

Windings Subjected to :

Dielectric steady state stresses upto system 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

Vibrations14

Stray losses

DEVELOPMENT OF INSULATING OIL

Fire resistant, non-flammable silicon based liquid. High grade mineral oil, with exceptional oxidation stability and

improved electrical properties

Opticool fluids with low viscosity for better cooling properties

Thermally upgraded oils for operation upto 150oC

Super biodegradable eco-fluid made from vegetable seed oils

for environmentally sensitive locations.15

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

16

DEVELOPMENT OF INSULATING MATERIALS

Softer Pressboard

Pre-compressed Pressboard in 1960

Moulded Angle rings, angle caps

Special Insulation at ends of windings to match electrostatic

field plots

Low permitivity pressboard (permitivity equal to that of oil)

- Futuristic17

DEVELOPMENT IN WINDINGS

Design and Technological Development

Use of interleaved / PID winding / contra shield winding

Optimisation of radial clearances on stress distribution concepts

Optimisation of axial clearances and use of moulded components

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 clearances18

Wave shape sensitivity analysis and part winding resonance

DEVELOPMENT IN WINDINGS

Ongoing and Futuristics Trends

T50 concept for withstand of transient voltage

Behaviour of 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.

19

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

20

DEVELOPMENT IN PROCESSING

Vapour phase 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

21

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

( Polarisation Depolarisation Current)

22

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.23

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

24

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.

Pressurised chambers used for windings and insulating parts to protect against pollution and dirt.

High frequency brazed joints / Improved crimping joints

Vapour phase drying for effective and fast cleaning of core and windings.25

Particle count for oil contamination

IMPROVEMENTS IN BUSHING TECHNOLOGY

`SRBP to `OIP to `RIP to SF6 Practically Non-existent Upto 800 kV Upto 500 kV Upto 1000