ABB+SPT+AL+Transformer_00_October

Al i i T fMiljenko Hrkac, SPT Global Technology Manager , custonmer day, Guatemala october 16th/2012

Aluminium TransformersTechnical and Economical AnalysisTechnical and Economical Analysis

Topics

History of Aluminium History of Aluminium

Material selection in transformer design

Technical economical and environmental aspects Technical, economical and environmental aspects

K-factors and Aluminium

ABB experienceABB experience

Summary

History of AluminiumUnknown about knownUnknown about known

Aluminium is the third most abundant element of the Earths crust, behindAluminium is the third most abundant element of the Earth s crust, behind that of oxygen and silicon and the first of the metallic elements consisting 7.3% mass of the total crust.

Due to Aluminiums high affinity to bind with oxygen it is never found free in Due to Aluminium s high affinity to bind with oxygen, it is never found free in nature, but only in combined forms such as oxides or silicates.

The ancient Greeks and Romans used alumen (alum, potassium aluminium sulfate K2Al6(OH)12(SO4)4) in medicine as an astringentsulfate, K2Al6(OH)12(SO4)4) in medicine as an astringent

The metal originally obtained its name from the Latin word for alum, alumen.

Scientists suspected than an unknown metal existed in alum but they did not have a way to extract it until 1825. Hans Christian Oersted, a Danish chemist, was the first to produce tiny amounts of aluminium.

it would take years upon years of research to find an efficient method to extract the metal from its ore and even more years to create a production process that would allow the metal to be commercially practical.

History of AluminiumUnknown about knownUnknown about known

Mid 19th century, Deville, French chemist , develop process for commercial production of aluminium. As a result, the price of aluminium dropped from around $1200 per kilogram in 1852 to pp p garound $40 per kilogram in 1859.

With an easy way to extract aluminium from aluminium oxide and an easy way to extract large amounts of aluminium oxide from b it th f l i i h d bbauxite, the era of aluminium had begun.

In 1888, the Pittsburgh Reduction Company, which is now known as Alcoa produced about 25 kilograms of aluminium a day. By 1909 company was producing about 41 000 kilograms of1909, company was producing about 41,000 kilograms of aluminium a day. As a result of this huge increase of supply, the price of aluminium fell rapidly to about $0.60 per kilogram.

Today, aluminium and aluminium alloys are used in a wide variety y y yof products: cars, cans, foils and kitchen utensils, airplanes, rockets and other items that require a strong, light material but also in electrotechnic industry: transmission lines, cables and products.p

Conductor Materials in TransformersInformed ChoiceInformed Choice

Considering technical and economical characteristics and availability, the conductorConsidering technical and economical characteristics and availability, the conductor materials used in transformers are the following:

Copper (Cu)

Aluminium (Al)

The informed choice of Al and Cu conductors shall be based on technical,commercial/economical and environmental reasons such as: Conductivity

Density

Skin effect

Connectivity

Manufacturability

Thermal & mechanical properties

Cost

Environmental effects

Some customers strictly prescribe for copper windings only, for different reasons like

ABB Group October 12, 2012 | Slide 5

y p pp g y,conservatism, established custom and practice as well as perception of better quality.

Conductor Materials in TransformersHistorical price fluctuation of Cu Al Tin & ZincHistorical price fluctuation of Cu, Al, Tin & Zinc

LME STOCK

LME PRICE

LME STOCK

LME PRICE

LME PRICELME STOCKLME PRICELME STOCK


Conductor Materials in TransformersCopper historical price fluctuationCopper historical price fluctuation

In less than 10 years, between 2002 to 20122012, copper price have increased b 500%by 500%

The price of copper has historically been unstable. It jumped from 60-year low of 1.32USD/kg in June 1999 to 8.27USD/kg in May 2006. It dropped to 5.29USD/kg in Feb. 2007, then rebounded to 7.71USD/kg in April 2007. In Feb. 2009, weakening global demand and a steep fall in commodity prices since

th i ' hi h l ft i t 3 32USD/k


the previous year's highs left copper prices at 3.32USD/kg.

Conductor Materials in TransformersCopper vs Aluminium price fluctuationCopper vs Aluminium price fluctuation

Cu is currently much more expensive than Al in terms of USD/kg. Cu s cu e t y uc o e e pe s e t a te s o US / gThe price of Cu has recently moved ahead much faster than the price of Al.


Conductor Materials in TransformersCu Al reserves and productionCu-Al reserves and production

World copper reserves are estimated to COPPER ppbe 480x106 metric tons

Considering an average consumption of 15x106 tons gives 32 years to reach full depletion

COPPER

full depletion Recycling is a major source of

copper in the modern world and the availability of copper can be longer.

World bauxite (Al) reserves are estimated to be 25000x106 which isALUMINIUM estimated to be 25000x106 which is more than 5 times of world copper reserves

Aluminium world production is almost 2 times as that of copper world production


Conductor Materials in TransformersSurge and Overload CurrentSurge and Overload Current

Mass of aluminium transformers is 0 488 times the copper ones Mass of aluminium transformers is 0.488 times the copper ones for a similar electrical performance

Heat (calorific) capacity = M x c

15.1)385904(488.0__ === AlAl cm

CitH tAlcapacityHeat

Aluminium transformers have superior thermal storage capacity

385__ CuCu cmCucapacityHeat

p g p ycompared to Copper wound units (15% higher for Al)


Conductor Materials in TransformersCopper Aluminium propertiesCopper Aluminium properties

Conductivity of Aluminium isPHYSICAL PROPERTIES COPPER ALUMINIUM Conductivity of Aluminium isapproximately 62% of Copperconductivity

This means for the same

PHYSICALPROPERTIES COPPER ALUMINIUM

Resistivity(microohmm) 0.01754 0.0282

Density 8.9 2.7

This means for the sameresistance, cross section of Alconductors must be 62%larger than the cross section of

ThermalConductivity(W/mK) 398 203

SpecificHeat(J/kgK) 385 904

Youngs modulus ofelasticity(dN/mm2) 11000 6500

Cu conductor( / )S.C(1sec)thermal currentdensity (A/mm2) 154 102

Larger cross section of aluminium is needed for having the sameresistance. This increases quantity of other materials used in powertransformers such as the core, tank and oil

But Aluminium density is less than Copper (2.7 vs 8.9 kg/dm3). We needa mass of aluminium half of the mass of copper for the same resistance


and the same winding length ( the same losses).

Conductor Materials in TransformersCopper Aluminium propertiesCopper Aluminium properties

Aluminium has a lower tensileYield stress ( N / mm2) typical value Aluminium has a lower tensilestrength than Copper however theincreased cross section ofaluminium, compared with copper

Yield stress ( N / mm2) typical value

Copper Aluminium

Soft strand conductor after annealing

40 25

for reaching the same resistivity,works to its advantage, since theincreased section helps to offsetthe lower ultimate strength of

Soft strand conductor after mechanical work hardening

80 65

Controlled hardned 120 180 110 - 130 the lower ultimate strength ofAluminiumconductors by heat treatment

COPPER vs ALUMINIUM CONDUCTOR FOR SAME LOAD LOSSES

Aluminium wound transformersLOAD LOSSES

Copper Aluminium

C ti 100 160

have better thermal performancesand in the most of cases alsomechanical during S.C w.r.tcopper wound one for the sameCross-section 100 160

Weight 100 48.5

copper wound one, for the sameload losses


S.C. Thermal Current 100 106

Harmonics, Transformers and K-FactorsEddy loss due to high harmonics: Al vs CuEddy loss due to high harmonics: Al vs Cu

According to classical theory the AC losses can be computed According to classical theory, the AC losses can be computedwith the following formula:

The penetration depth of Cu at 50 Hz is 9.4 mm, while for Al is12 3 mm The conductivity of Cu at 75C is 0 4703 108 [Ohm12.3 mm. The conductivity of Cu at 75 C is 0.4703 10 [Ohmm]-1, while for Al is 0.28935 108 [Ohm m]-1

Cu AlConductivity 100% 62%Penetration Depth 100% 127%Eddy losses 100% 62%

Eddy loss in aluminium winding is 38 % less w.r.t eddy losses in copper with same volume of conductor


pp

Harmonics, Transformers and K-FactorsEddy loss due to high harmonicsEddy loss due to high harmonics

Once the K-Factor of the load has been determined, it is a simplematter to specify a transformer with a higher K-rating from the standard range of 4 9range of 4, 9, 13, 20, 30,40,50

K-Factor

In US practice, the K-factor is the ratio of eddy current losses when driving non-linear and linear loads :

Harmonics, Transformers and K-FactorsEddy loss due to high harmonicsEddy loss due to high harmonics

Harmonic currents are generated whenever a non linear Harmonic currents are generated whenever a non-linear load is connected to the mains supply.

The problems caused by harmonic currents include overheating of cables especially overheating and vibrationoverheating of cables, especially overheating and vibration in induction motors and increased losses in transformers.

What is effect of harmonics on the transformers and how designers can use to account for them and ensuredesigners can use to account for them and ensure reliability.

Losses in transformers are due to magnetic losses in the d dd t d i ti l i th i dicore, and eddy current and resistive losses in the windings.

Eddy current losses are of most concern when harmonics are present because they increase with the square of the ffrequency.

The harmonic spectrum of the load current must be known to determine eddy losses due to harmonics

Harmonics, Transformers and K-FactorsEddy loss due to high harmonics: Al vs CuEddy loss due to high harmonics: Al vs Cu

Copper Windings Al mini m Windings RatioK-Factor

Copper Windings Aluminium Windings Ratio Eddy

(Al/Cu)Pdc Peddy Ptotal Pdc Peddy Ptotal

K1 4997 111 5108 4997 70 5067

63%

K4 4997 444 5441 4997 280 5277

K9 4997 999 5996 4997 630 5627

B l i l f 400KVA VSD t f ith l N

K13 4997 1443 6440 4997 910 5907

K20 4997 2220 7217 4997 1400 6397

Below is an example, for 400KVA VSD transformer with equal No Load and Load losses designed with Copper and Aluminium conductors

Eddy losses are reduced by approx. 37% in case of aluminium

As we can see from table, a K20 rated aluminium wound transformer have approximately Eddy losses as K13 copper wound


transformer have approximately Eddy losses as K13 copper wound transformer

Aluminium Conductor in TransformersEconomic ConsiderationsEconomic Considerations

Copper represents one of the most expensive materials used in Copper represents one of the most expensive materials used in transformers

Besides its cost, price of copper is highly unstable.

The price of aluminium is lower than the price of copper and it fluctuates, but not as much as copper.

World copper reserves are limited and a big debate on, when will be the full depletion. It is reasonable to expect future copper prices to be both high and volatile.

The amount of Al now produced annually exceeds Cu production by two. Economies of scale, supply and demand, and other factors such as Al being the most plentiful metal in the earth have g pthe potential to make the Al prices more stable and lower than the Cu prices in the future.


Aluminium Conductor in TransformersEnvironmental ConsiderationsEnvironmental Considerations

For evaluating the environmental impact of Cu and Al European For evaluating the environmental impact of Cu and Al, EuropeanUnion Eco-Indicator is used as an indication.

The values given in Eco-Indicator 99 Manual for Designers2000 for primary Cu and Al are 1400 mpt/kg and 780 mpt/kg2000 for primary Cu and Al are 1400 mpt/kg and 780 mpt/kgrespectively.

As with cost, comparisons based on volume are more useful thancomparisons on mass: per volume the values can be expressedcomparisons on mass: per volume, the values can be expressedas 12.5 mpt/cm3 for Cu and 2.1 mpt/cm3 for Al.

Even considering the 62% additional Al needed for equali ti it Al h h l i t l i t th Cresistivity, Al has much less environmental impact than Cu

needed for the same winding by this measure.

Eco-indicator method quantifies environmental impact in terms of i t h 1000 i t hl d t th lpoints, where 1000 points roughly corresponds to the annualimpact of an average European. Millipoints (mpt) are often theappropriate units for evaluating practical decisions in designwork


work.

Practical issues in using Al in TransformersTermination & ConnectionTermination & Connection

To avoid interconnection To avoid interconnection problems, ABB uses proper connectors for internal connectionsconnections

Using cables, rings and g , gspecial weldings for proper connections it is possible to provide necessary elasticity in joints without compressing aluminium too much and having the same efficiency


as copper terminals.

Aluminium Conductor in TransformersReliability ConsiderationsReliability Considerations

Transformers life is defined by the life of its insulation system.

In transformers, limiting temperatures are specified mainly to limit the ageing of paper insulation in contact with the conductor.

Hot spot temperature is mainly located where eddy losses concentrated

For every 6 8 C rise in temperature the life of paper insulation is For every 6 - 8 C rise in temperature, the life of paper insulation is halved

The higher resistivity of Aluminium gives inherently lower eddy l i th i di Thi iti t th i k f h t tlosses in the windings. This mitigates the risk for hot spots.

The transformers are designed to comply with the temperature limits, whichever the conductor type is.

The maximum allowed temperature during S.C for oil-immersed transformers is 250oC for copper conductor, whereas the same is 200oC for an aluminium conductor without any detriment to


mechanical properties.

ABB Aluminium Wound TransformersExperienceExperience

More than 40 ears of More than 40 years of experience with aluminium wound transformers

Experience of several million aluminium wound di t ib ti t fdistribution transformers

Experience of several thousand aluminium wound power transformers above 10 MVA

Well proven and established ABB technology up to 170


kV class and 63 MVA

ABB Aluminium Wound TransformersSome customers using aluminium transformersSome customers using aluminium transformers


Aluminium Conductor in TransformersSummarySummary

Transformers with Aluminium windings having the same losses as that of Copper Transformers with Aluminium windings having the same losses as that of Copper windings are technically feasible and economically advantageous.

Copper is extensively used in power transformer windings.

The price of copper fluctuates heavily during the last years and the price level is The price of copper fluctuates heavily during the last years and the price level is expected to be at high levels, due to limited copper reserves.

As the price of Cu has recently moved ahead much faster than the price Al, usage of Al in winding conductors has become more viable option.

Descriptions True False Aluminium price is more stable because of its market availability (twice copper worldwide production); Xpp p );Aluminium windings are lighter than copper windings; X

Copper winding transformers better bear short-circuit efforts; X

Al i i t f h bi lAluminium transformers have bigger losses; XAluminium winding transformers are not compatible with copper connectors; X

Copper transformers are more compact than aluminium ones; X


X

Interesting facts about Al

Every minute of every day, an average of more than 123,000Every minute of every day, an average of more than 123,000 aluminium cans are recycled.

Since 1972, an estimated 660-plus billion beverage cans have been recycledplaced end-to-end, they could stretch to the moon nearly 300 timesnearly 300 times.

If each person recycles one aluminium can each month, energy savings equal 1,750 to 3,500 gallons of gas.

American consumers and industry throw away enough aluminiumAmerican consumers and industry throw away enough aluminium to rebuild the entire U.S. commercial air fleet every three months.

One pound of aluminium can replace twice that weight in steel in most applications.

Rubies, emeralds and sapphires consist mainly of crystalline aluminium oxide.

Aluminium is light, strong, corrosion-resistant, nonmagnetic, nontoxic and naturally good lookingnontoxic and naturally good looking.

ABB Group October 12, 2012 | Slide 25 ABB Group October 12, 2012 | Slide 25

ABB+SPT+AL+Transformer_00_October

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