transformers yesterday,today & tomorrow
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1
TRANSFORMERS -
YESTERDAY, TODAY &
TOMORROW
: VK Lakhiani
Crompton Greaves Ltd.
2
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”
3
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.
4
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)
5
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)
6
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
7
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)
8
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
9
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
10
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
11
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
12
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
13
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 !
14
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
15
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.
16
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
17
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
18
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
19
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.
20
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
21
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
22
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)
23
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.
24
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
25
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
26
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)
27
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
28
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
29
IMPROVEMENTS IN OLTC (CONTD.)
FUTURISTIC
•Maintenance free OLTC
•Use of semiconductors and vacuum for switching
•Dry type OLTC
•Condition Monitoring of OLTC
30
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
31
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.
32
AMORPHOUS METAL TRANSFORMERS (AMT) (CONTD.)
•Low harmonic losses
•Present limitation -distribution range upto5 MVA.
•(Futuristic) energy efficient cast resin transformers
33
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
34
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.
35
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
36
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
37
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
38
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.
39
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
40
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
41
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
42
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.
43
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
44
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
45
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.
46
( TODAY )
•TRANSFORMER INDUSTRY IS NOW
COMPLETELY GLOBALISED LIKE
AIRCRAFT OR AUTOMOBILE OR IT
INDUSTRYOF TODAY
47
( TOMORROW )
TRANSFORMER WILL CONTINUE
TO SERVE MANKIND SELFLESSLY
48
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