Amorphous Core Power Transformer

Although transformers, which are the indispensable component of transmission and distribution, are highly efficient comparing the other electric machineries, increasing global demand for electrical energy is resulted that efforts on improvements of energy efficiency of transformers has become an important current issue. Regarding efficiency of electrical energy distribution considering load ratio, no-load power losses of transformers are bigger part of total losses. In recent years some studies showed that no-load power losses of amorphous core transformers are less than laminated steel core transformers by 60-70%. In this paper, by manufacturing a prototype amorphous distribution transformer rated 33 kV and 1 MVA subsequently by quantifying its power losses, the energy efficiency value, gained by replacing laminated steel core transformer with this new type in a power disturbing system, are to be studied.

Keywords: Power distribution system, amorphous core, energy efficiency, transformer, no-load losses

INTRODUCTION

More than ever, electric utilities and industries today are searching for technologies that will reduce their operating costs and improve energy savings throughout their systems. New transmission and distribution (T&D) technologies are now available to help utilities meet these goals.[9] For high efficiency in transmission and distribution of electrical energy which is aimed at minimizing energy losses requires that an increase in voltage of conducted electric energy and to decrease current rewardingly as much as possible. It therefore resulted that voltage value of electric energy to be transformed to a high voltage where it’s generated.

The role of a transformer is to convert high-voltage electricity supplied from a power station into lower-voltage electricity for safe use. Transformers operate 24 hours a day, seven days a week during which time they undergo constant losses of 2 to 4% of the electricity that passes through them.

The size of Transformers used in electric distribution systems are specified according to:

Size
System design
Installed power
Maximum demand power

TRANSFORMER LOSSES

Although an ideal transformer would have no power losses, practically when energized a transformer will have some losses that occur in the windings, core and the surrounding structures. When the transformer is energized, but no load applied, the no-load power loss occurs due to the material that used in the core. This loss value is constant which occurs when both a load connected or not connected to the transformer. When a load connected to the transformer, a larger component of loss due to the flow of load current through the winding resistance is added to the no-load power losses. Thus, the total losses of the transformer can be determined with the following expression:

No-load Power loss/Constant Losses

Amorphous core transformers significantly reduce no-load losses by using an amorphous alloy *3 for the iron core, which the transformer windings that carry the electricity are coiled although it is caused regardless of whether a load is present. They are essentially the power required to keep the core energized. These are commonly referred to as “core losses,” and they exist whenever the unit is energized. No-load losses depend primarily upon the voltage and frequency, so under operational conditions they vary only slightly with system variations. They include losses due to magnetization of the core, dielectric losses in the insulation, and winding losses due to the flow of the exciting current and any circulating currents in parallel conductors. No-load losses can be calculated with the following mathematically expression [14-15]:

Hysteresis loss

Defined as the loss equal to the area of the static magnetization loop times the cycle rate. It’s the first component of the no-load power losses that is known “core losses”. The area of the Hysteresis loop times the frequency at very low frequencies is an accurate estimate of no-load losses. At low frequencies, the no-load power losses due to the eddy current losses and abnormal losses are very small when compared to the hysteresis loss

Eddy Current loss

Based on Maxwell’s equations, but does not including domain wall theory, Eddy current losses are the second component of the no-load power losses which caused by the change in the density of the flux with respect to time because of magnetic materials. In order to reduce eddy current losses, high-strength core material and laminating a thin core used.

Abnormal Loss

This loss which is not included in the two previous loss mechanisms. , and constants are obtained by the experimental data. Steinmetz constant n is 1.6. The no-load power losses due to micro-structure of the material, the conductivity is dependent on cross-sectional area and lamination. The equation is valid in a certain range of frequency and flux density. The last component of the no-load power losses is abnormal losses which appear on the tests that are not in the class of hysteresis and eddy current losses.

Load loss

Heat losses, or I ²R losses, in the winding materials contribute the largest part of the load losses. They are created by resistance of the conductor to the flow of current or electrons. The electron motion causes the conductor molecules to move and produce friction and heat. The energy generated by this motion can be calculated using different the formula It’s majorly caused by the load on the transformer during the use of electricity

DESIGN CONSIDERATIONS

A transformer is a static piece of apparatus used for transferring power from one circuit to another at a different voltage, but without change in frequency. It can raise or lower the voltage with a corresponding decrease or increase of current. Electrical energy generated at generating stations is transported to remote load centers. Between generating station and consumers we have transmission, sub transmission and distribution levels of voltage. Since the long distance transmission at high voltage is cheap and low voltages are required for utility purpose, the voltage levels goes on decreasing from the transmission system to the distribution system. For this high voltages and low voltages transformer is necessary in transmission and distribution system.[13]

An essential part of the design of a transformer consists of the determination of the ferromagnetic material cross-section core and the conductor’s cross-section area. These areas are determined from estimates of suitable values for the peak ﬂux density, the winding space factor, the stacking factor, and the full-load rms current density in the windings .Ferro-magnetism is the basic mechanism by which certain materials e.g. Iron form permanent magnets or attracted to magnets ,it’s the strongest type which creates forces strong enough to be felt. This current density depends on the mode the transformers will be operated, if intermittent or in a continuous form. Today the thickness of a sheet of grain oriented silicones id (0.18-0.30) mm.

Development of Fe-Si Steel has lead to production of a low material loss whereby:

Normal Si-Steel

(0.35 mm thickness and 1.5 %-3.5% of Si material)

0.9 To 1.1 Tesla

HRGO

Hot Rolled Grain Oriented Si Steel

1.4 To 1.7 Tesla

CRGO

Cold Rolled Grain Oriented Si Steel

0.14 to 0.28 mm thickness

Transformer cores are built from thin sheets of steel. These sheets are manufactured specifically for use in transformers. Core steel has low carbon content 0.1%.Increased carbon content has a detrimental influence on the hysteresis losses as well as the ageing properties. Its alloyed with silicon (Si) which increases the specific electrical resistance, reducing eddy current losses in the core and also makes the core brittle hence the content should be kept below 3%.Today only grain-oriented steel is used which is made by cold rolling the steel sheets making the magnetic domains in the steel sheet will tend to be oriented in the rolling direction. The material obtained has good loss properties in the rolling direction and the correspondingly poor properties in the transversal direction. The grain oriented core steel is available in several grades which have properties which occur due to raw material composition, the degree of cold rolling and different finishing treatments, for example laser treatment which is a mechanical treatment that divides the magnetic domains into smaller domains with lower losses as the result.

Another indication for the ease of magnetization of amorphous metals is the high value of their relative permeability which can also be read from the B-H curve given in Fig. 1, and is summarized in the values given in Table 1.

TABLE 1

Characteristics	Amorphous Metal	CRGO Steel
B saturation [T]	1.56	2.0
B design admisb. [T]	1.35	1.8
Magnetic permeability	3.5e5 for H<10A/m	6.0e4 for H<10 A/m

To minimize eddy current losses, the sheets must be insulated from each other using an inorganic material compatible with transformer oil and is corrosion and temperature resistant. The coating is very thin, 4µm which enhances a good core fill factor. The core is built up from many layers core steel sheets. Suppose the core limb was built from a solid iron bolt, the core would represent a short-circuit winding around itself, and the transformer would not work. The mutually insulated sheets prevent such a short-circuit .Eddy current losses in the core steel are proportional to the square of the thickness. Therefore the steel sheets have to be thin in order to reduce the no load losses. Typical thickness is from (0.18 – 0.3) mm. With the amorphous alloy this value is 0.025 mm and 7 to 12 times smaller than conventional silicon irons. This thinness, combined with its uneven surface, gives the amorphous material a space-factor of only 80% (86% that we can use Metglas) compared to 95% achieved with silicon-iron [3].In this paper, the amorphous alloy Fe ,B, Si, as produced by METGLAS 260HB1(not Allied Co), is the reference material. Since the amorphous alloys are produced as ribbons, they can be most naturally applied to the transformers designed with a shell-type core whereby we used five leg core types that’s why the outset amorphous alloy more longer than manufacturing availability. The reduced ﬂux density saturation of Fe-based amorphous alloys, less than 1.3T (based on our design and 1.4T For Metglas)versus the 1.7 T (For design value due to saturation) of Fe-3% Si has been a concern to some. Although some disadvantages of amorphous design value that causes big and expensive transformer, scientists have worked to solve this problems and it seemed that some working theoretically can achieve 1.90T [addition 1] and amorphous material tend to decline of the prices and serious saving because of load ratio of transformers. It should be noted, however, that the trend in Fe-3% Si-cored transformers is to lower operating inductions.

PROTOTIP DESIGN

Unlike many countries around the world, Europe has no mandatory standard on energy efficiency of distribution transformers. The two main documents which describe losses in transformers are: the European Standard EN 50464-1, which has superseded the harmonized document HD428 for oil cooled transformers, and the harmonized document HD538 for dry type transformers, which is still valid (or their various country equivalents, e.g., DIN, etc.)[17] Oil cooled distribution transformers are used C₀₃₆ B_k36 energy class in Turkey due to EN 50464-1. Electric distribution system operates at 33 kV, 15.8 kV, 10.5 kV, and 6.3 kV in Turkey

While in France the distribution level is 11KV, United States 11kV, United Kingdom 33KV, New Zealand and Australia 11kV and 22KV common in South Africa.[18] As to total transformer quantity in Turkey, 86% of transformers are rated 33/0.4kV. The ratio of distribution transformers rated 33/0.4 kV is approximately 72% of installed power. It is estimated that 25% of these distribution transformers are rated 1000kVA [16] .

The Hitachi/Metglas group manufactures amorphous metals and is the biggest promoter of amorphous technology in distribution transformers. Metglas introduced a new amorphous material, HB1, (improved from the earlier SA1 material) which compensates for the deficiency of reduced saturation induction. The new material reaches saturation at induction levels close to those typical of traditional magnetic steel. To manufacture an amorphous core prototype transformer is used Metglas 2605HB1M core alloys. [7]

Metglas amorphous metal material is the earth-friendly high-technology material for distribution transformers that can reduce no-load loss (standby electricity) in distribution transformers to about one-third the level compared to those using grain-oriented electrical steel.

Amorphous Data Sheet (Key Design Information) [10]

	23M3	Amorphous	Comment

Resistivity (μΩm)	45	135	Significantly less sensitive to harmonics than Si Fe. Suited to high frequency applications.
Stacking Factor	0.96	0.84	14% larger build than Si Fe is required for the same core area
Saturation B (60 Hz)	2.03 tesla	1.5 tesla	23% lower design flux density, requiring additional build &/or lower volts per turn
Standard widths	Up to master coil (~36”)	3 widths 213mm 170mm 142mm	Amorphous manufacturing equipment limitation
Max Operating Temperature	650oC	150oC	Possible limitation in dry types (heat distortion temp. of epoxy coating)

To manufacture an amorphous core prototype, transformer is used a Metglas 2695HB1M core alloys. Prototype amorphous core transformer which can be used in Turkish electrical distribution system, design values to be manufactured is shown in Table 2 and electrical design parameters are shown in Table 3.

Table 2: Prototype Amorphous Core Transformers Design Value

Table 3: Electrical design values

The prototype transformer and classical electrical steel core transformer conforming to EN 50464-1 with energy class A₀₃₆ A_k36that same characteristeics were tested. Test values is shown in Table 3.

Table 3: The Comparison of Transformers Test Results

A CASE STUDY ON AN ELECTRICAL DISTRIBUTION SYSTEM

Taking into account of different load rates, the ratio of no-load losses to the total losses of the transformer conforming to EN 50464-1 with energy class C₀₃₆B_k36.In spite of reduction in ratio between everlasting no-load power losses and load power losses increasing by load rate, the ratio of no-load losses to the total losses of the transformer increases.

The ratio between no-load losses and the total losses according to the EN 50464-1.

Considering geographical structure, population, industrialization, etc. of distribution system of Turkey, it is decided to deliver the distribution system, diving into 21 regions, to private sector companies, in order to provide electricity to the use of the consumers in a quality, continuous, without effect of loss/theft ratio, cost-effective and environment-friendly way. In this context, Başkent EDAŞ (an energy distribution company) is one of region that was made private with ratios of 10.1% of subscribers of distribution system and 8.3% of total consumption and 3.08% of internal loss/theft ratio.

Examining real time data taken from the transformer rated 1000kVA in the distribution region and located in urban area, the maximum peak load rate of the transformer is 70% and the average load rate is 39%. The total annual loss of the transformer under examination conforming to EN 50464-1 with energy class C₀₃₆ B_k36 is 34.477 kWh per year. In case prototype amorphous core transformer is used under same conditions, total annual loss will be 18.167 kWh per year and reduce by 47%.

Examining real time data taken from the transformer rated 1000kVA in distribution region and located in rural area, the maximum peak load rate of the transformer is 40% and the average load rate is 22%. The total annual loss of the transformer under examination conforming to EN 50464-1 with energy class C₀₃₆B_k36 is 22.872 kWh per year. In the case where prototype amorphous core transformer is used under same conditions, total annual loss will be 8.552 kWh per year and reduce by 62%.

CONCLUSION

In this study, an amorphous core distribution transformer was designed, manufactured and tested. The results were compared with classical steel core transformer performance which is used in a real electrical distribution system. It is known that Turkey electrical distribution system has not yet been using amorphous transformer. Although there have been lots of working on this subject around the world, the distribution voltage level of Turkey is different of the general level of the world. In this study, it is proved that amorphous no-load power can be less than 76.5% cold rolled grain oriented transformer with C₀₃₆ B_k36efficiency standard that used generally in Turkey. But, the significant of the amorphous core transformer gets more important when focus on a real electrical distribution system. Due to the load of the transformer in the real system the total loss of the transformer decreases by 47% in urban area and 62% in rural area excepting harmonic effects on the losses.

Typically, core loss can be 70–80% less than with traditional crystalline materials. This leads to a reduction of generation requirement and, when using electric power generated from fossil fuels less CO2 emissions [11][12] It has been widely adopted by large developing countries such as China and India where energy conservation and CO2 emission reduction have been put on priority. These two countries can potentially save 25–30 TWh electricity annually, eliminate 6-8 GW generation investment, and reduce 20–30 million tons of CO2 emission by fully utilizing this technology.

Significant results acquired in this study are given below:

By manufacturing and testing the prototype amorphous core transformer rated 36kV, 1000kVA, it is realized that no-load losses are reduced by 67% of classical electrical steel core transformers conforming to EN 50464-1 with energy class A₀₃₆A_k36 .
By manufacturing and testing the prototype amorphous core transformer rated 36kV, 1000kVA, measurement results showed that load losses was reduced by 3% of classical electrical steel core transformers conforming to EN 50464-1 with energy class A₀₃₆ A_k36 .
By analyzing load ratios of transformers used in real distribution system, it is demonstrated that using amorphous core transformer in rural areas, where load ratio are less, result in more significant energy-savings.
Although the utilization of amorphous core transformer in distribution system provide with significant energy-savings, as result of design limitation of technical values of amorphous material, the size of the transformers is bigger than the classic core transformers. The progressive development of materials science may result in the usage of amorphous material widely.
As a result of the thin and fragile nature of amorphous strips, the manufacturing of amorphous core transformer requires the high cost of workmanship hence the cost is high.

REFERENCES

[1] S. J. Chapman, Electric Machinery Fundamentals. New York: McGraw-Hill, 1991, p. 716.

[2] H. Matsuoka and M. Okamoto, “Recent development of grain-oriented silicon steel, “Rapidly Quenched Metals,S. Steeb and H. Warlimont,Eds. Amsterdam, The Netherlands: Elsevier, 1985, pp. 1633–1636

[3] E. L. Boyd and J. D. Borst, “Design concepts for an amorphous metal distribution transformer,”IEEE Trans. Power Apart. Syst., vol. PAS-103, no. 11, pp. 3365–3372, 1984.

[5] Advanced in Superconductivity IV, Publisher Springer-Verlag Tokyo Hitachi Metals America LTD

[6] Wilson Power Solutions

[7] WWW.metglas.com

[9]Distribution Electrical Transformer Steel.

[10]Cognet Power Inc

[11]Li, Jerry (2005), Climate Change and Energy—Opportunities in China, presented in Climate Change: The Business Forecast” Conference, London, Oct 2005. (Available from links on Jerry Li ‘s page at http://www.jerryli.co.nr)

[12]Li, Jerry (2000), Use of Energy Efficient Transformers in Asia, presented in Asian Energy Conference 2000, Hong Kong. (Available from links on Jerry Li’s page at http://www.jerryli.co.nr)

[13] http://www.scribd.com/doc/45739281/Final-Soft-Copy-of-Projectauthor Murthypln Murthy.

[14]. C.P. Steinmetz, on the law of hysteresis (originally published in 1892), Proc. IEEE, 72(2):196-221.

[15]. G. Bertotti G, General Properties of Power Losses in Soft Ferromagnetic Materials, IEEE Transactions on Magnetics, 24: 621-630.

[16]. Turkish Electricity Distribution Co. APK Presidency, “Production Capacity of Electricity Turkey Report 2011-2020”, November 2011.

[17]. Polish Copper Promotion Centre and European Copper Institute, “Selecting Energy Efficient Distribution Transformers A Guide for Achieving Least-Cost Solutions”, SEEDT, First Published June 2008.

[18] Wills, H.L, Power Distribution Planning Reference Book,Marcel Dekker INC 2^nd edition 2004

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