200717 Meps Transformers

Technical Report

2007/17

Distribution Transformers: Proposal to Increase MEPS

Levels

Final Report October 2007

Prepared for Equipment Energy Efficiency Program

Prepared by T R Blackburn

_____________________________________________________________________ T R Blackburn Draft Report: Proposal to Increase Transformer Efficiency Standards 1

TABLE of CONTENTS

Page Number

Executive Summary 6 1 Introduction 10 2 Transformer Use in Electrical Networks 12 3 MEPS 1 Efficiency Levels 16 3.1 Application of MEPS 18 4 Transformer Efficiency 20 4.1 Losses in Transformers 20 4.1.1 No Load (Core) Loss 22 4.1.2 Load (copper or winding) Loss 24 4.2 Power and Energy Efficiency 24 4.2.1 Power efficiency of a Transformer 25 4.2.2 Energy Efficiency of a Transformer 26 4.2.3 Example of Energy Saving with Efficiency Improvement 27 5 Transformer Efficiency Standards in other Countries 29 5.1 US Proposed Efficiency Standards 29 5.2 European Union Proposals 34 5.3 Specified Efficiency Levels in other Countries 38 5.3.1 Canada 38 5.3.2 Mexico 39 5.3.3 China 40 5.3.4 India 40 5.3.5 Japan 42 6 Increase of Existing MEPS Levels 44 6.1 Comparison of New MEPS with other Standards 47 7 Why Increase MEPS Levels? 49 7.1 Better Use of Traditional Core and Winding Materials 50 7.1.1 Core Construction and Materials 50 7.1.2 Winding Conductors 50 7.2 Better Design Procedures 50 7.3 New Core Materials and Design 51 7.3.1 Amorphous Metal Core 51 7.3.2 The Hexaformer 52 7.4 Optimisation of Energy Efficiency 52 7.5 Total Life Costing of Transformers 53 7.6 Impact of Harmonics on Transformers 54 7.6.1 Non-linear Loads 54 7.6.2 Supply Voltage Power Quality 56 7.6.3 Example of Increased loss due to Harmonics 57 7.7 Increased Life of Transformers 58


8 Effects of MEPS 1 on Transformers in the Market 60

8.1 Australian Manufactured Units 60 8.2 Imported Transformers 60

9 Impact of Improved Efficiency on Greenhouse Gases 62 10 Exclusions from MEPS Compliance 63 10.1 Exclusions from MEPS 1 63 10.2 Comments on Exclusions 63 11 Testing of Transformers for Compliance 65 11.1 Testing Logistics 65 11.2 Test Procedures 65 12 Conclusions 66 13 References 68


LIST of TABLES

Page Number Table 1 Total Electrical Consumption on Network Losses 12 Table 2 Energy Saving potential and Greenhouse Gas 13 Mitigation from Transformer Loss Reduction Table 3 Distribution Transformer Numbers in Western Europe 14 Table 4 Existing and Proposed MEPS Levels for Liquid- Immersed Transformers 17 Table 5 Existing and Proposed MEPS Levels for Dry-type 18

Transformers

Table 6 USA Department of Energy Maximum Technologically Feasible Levels for Single and Three Phase Liquid-

immersed Distribution Transformers 31 Table 7 USA Department of Energy Maximum Technologically Feasible Levels for Single and Three Phase Dry-type Distribution Transformers 31 Table 8 USA Department of Energy Minimum Efficiency Levels

for Regulation of Liquid-immersed Distribution Transformers 32

Table 9 USA Department of Energy Minimum Efficiency Levels for Regulation of Dry-type Distribution Transformers 32

Table 10 No-load Losses for Dry-type Transformers (from HD 528) and of Liquid-immersed Transformers (from HD 428) 35

Table 11 Full-load Losses for Dry-type Transformers (HD 528) and

of Liquid-immersed Transformers (HD 428) 35 Table 12 Comparison of Efficiencies for CENELEC HD 428 and

C-AMDT Levels. 36 Table 13 Tabulation of Proposed European Levels pr EN5046-1 for

Oil-immersed Transformers and Comparison with C-C and C-AMDT Levels 37

Table 14 Canadian Standards for Dry-type Transformers 38


Table 15 Mandatory Efficiency Levels for Mexico 39 Table 16 Maximum Permissible Loss Levels for Liquid-filled

Transformers in Mexico 40 Table 17 Maximum Permissible Transformer Loss Levels for

the INDIAN BEE Star Classification. 41 Table 18 A Comparison of Efficiencies Calculated from the

Indian BEE- 3-Star Level with European Efficiencies from the HD 428 Loss levels 41

Table 19 Comparison of Japanese Top Runner Efficiency Levels

with other Countries for Liquid-immersed Transformers 43 Table 20 Comparison of Japanese Top Runner Efficiency Levels

with other Countries for Dry-type Transformers 43 Table 21 Comparison of Proposed New MEPS Levels for

Liquid-Immersed Transformers with other Countries 46 Table 22 Comparison of Proposed New MEPS Levels for Dry-type With other Countries 46 Table 23 Import Numbers of Transformers within the MEPS Range: July 1999 June 2007 61


LIST of FIGURES

Page Number

Figure 1 Single Phase Transformer Schematics 21 Figure 2 Examples of Liquid-filled and Dry-type Transformers 22 Figure 3 Transformer Loss Components and Power Efficiency Versus Load 23 Figure 4 New European Efficiency Level Proposal and Comparison with NEMA TP-1, Japanese Standards and the European A-A Combination 37 Figure 5 Loss Target Values for Distribution Transformers

in the Japanese Top Runner Program 42

Figure 6 Existing and proposed Transformer Efficiencies In various Countries and Regions and Comparison with New MEPS 45 Figure 7 Current Waveform and Harmonic Content Generated by a Non-linear Load 55 Figure 8 Typical Current Waveform and Harmonic Content of a Non-linear Load (Personal Computers) 56


Executive Summary In 2000 the then National Appliance and Equipment Energy Efficiency Committee of Australian Commonwealth, state and territory government officials initiated the development of Regulations to mandate Minimum Efficiency Performance Standards (MEPS) for electricity distribution transformers. This was part of the National Appliance and Equipment Energy Efficiency Program (now the Equipment Energy Efficiency Program)) run under the auspices of the Ministerial Council on Energy of Australian and New Zealand Energy Ministers. As an outcome of this work an Australian Standard was issued in 2003. This Australian Standard specified minimum permissible power efficiency levels for liquid-insulated and dry-type electrical distribution transformers with ratings in the range 10 2500 kVA and with primary voltage in the range 11 22 kV. The Regulations associated with the MEPS requirements mandated that no transformers covered by MEPS could be sold in Australia unless they complied with the MEPS. The MEPS requirements applied to both imported and Australian-made units. Compliance with MEPS for transformers came into force on 1 April 2004. The overarching objective of both the previous MEPS and the proposed new MEPS is to reduce greenhouse gas emissions related to energy losses from electricity distribution transformers below what they are otherwise projected to be, in a manner that is in the communitys best interests. The more specific aim of the MEPS program is to reduce energy losses associated with transformer operation in the electricity distribution system. Overall network losses in the electrical transmission and distribution systems used to supply power to consumers can be as much as 6-9% of the total power generated by large power stations. Transformers in the distribution networks, make up about 30-40% of the total network loss. The original MEPS stated that the efficiency levels specified would remain in force for four years and that they would then be reviewed in accordance with international trends in efficiency levels and would be made more stringent if international best practice indicated such change was achievable. Specifically, the original Standard gave a set of high efficiency levels that were not mandatory but were desirable levels. The review process of the original levels is now underway and this report has been prepared to discuss the change of mandatory MEPS levels to those high efficiency levels. Since the original MEPS levels were specified there has been significant development in transformer efficiency Standards and requirements in other countries including the USA, European Union, Canada, Japan, China, Mexico and India. The most detailed investigations of transformer efficiencies and the levels that are achievable have been undertaken by the US Department of Energy. In a seven year program they have audited manufacturing techniques, new materials, dissembled and re-assembled transformers and developed and applied testing methods. As a result of these investigations they produced tables of Maximum Technologically Feasible Efficiency Levels which were achievable in a theoretical sense. After applying practical constraints, such as manufacturing limitations, to these levels they then


developed efficiency levels that were used as their mandatory regulated efficiency levels. The European Union has developed a range of efficiency tables for their member countries. Some European countries have selected specific levels from these tables as mandatory requirements but in general the European Union efficiency levels are mostly voluntary. There is however a very active group (known as SEEDT Strategies for Energy Efficient Distribution Transformers) in Europe investigating feasible efficiency levels and the European Committee for Electrotechnical Standardization (CENELEC) has established a proposal that would give it attainable efficiency levels comparable to those developed by the US Department of Energy. Prior to development of the US DOE levels, the National Electrical Manufacturers Association (NEMA) in North America published a set of efficiency levels. Canada used these, with some small modifications, to produce two Standards giving efficiency specifications for distribution transformers. The Canadian efficiency levels were adopted, with small variations to adjust for the power frequency difference between 50 and 60 hertz, as the first Australian MEPS efficiency levels applied in 2004. Mexico has had mandatory efficiency standards for distribution transformers for many years. In general the efficiency levels are slightly lower than those of the Canadian Standards and NEMA levels. Mexico also specifies maximum permissible losses for transformers. Only liquid-immersed transformers are mandated. In China the current mandatory efficiency levels have been set down in a Chinese Standard and more recently the efficiency requirements have been increased but have not yet been made mandatory. The current levels are roughly comparable to the existing NEMA and Canadian levels. In India the Bureau of Energy Efficiency of the Ministry of Power has developed a star classification system for transformers, ranging from one to five stars, with five stars representing international best practice. The aim is to have three stars as a minimum efficiency standard and this requirement is being adhered to by many supply utilities. Power efficiencies relating to the star classes are not specified. Instead maximum permissible loss levels are specified. Only liquid-immersed transformers are considered. The Indian power efficiencies derived from the five star allowable losses are very high level by comparison with international practice. It is possible that some allowable tolerance may be included in the allowable loss levels. Japan has developed very stringent efficiency standards in their Top Runner Energy Efficiency Program. The Top Runner program covers a wide range of electrical equipment and appliances including distribution transformers. The Program specifies maximum target levels of total loss for use in determining transformer efficiency, and provides empirical formulae that can be used to calculate the losses and thence efficiency for any specific transformer rating.


The system of electricity distribution in Japan is somewhat different to that in most other countries in that it uses many more lower capacity units that are placed in quite close proximity to the ultimate load with transformation thus being done effectively at the site. There is thus a higher concentration of single phase transformers and smaller three phase units in Japan. Nevertheless the target values represented by the Japanese Top Runner program are close to the state of art in achievable transformer efficiency levels. When compared to the efficiency levels used for transformers in other countries the new MEPS levels that are proposed for Australia are seen to be consistent with international best practice in other developed countries. The new MEPS levels are below some achievable levels that are being instituted in other countries, for example the Japanese levels and a European proposal. These higher levels are based on the use of amorphous metal rather than steel cores loss, so that while they are achievable they would require a significant change in manufacturing capability and significant investment in new production facilities in Australia to implement. However they do represent an eventual benchmark efficiency. The most valid comparison of international levels for the new MEPS program is with: The original European Committee for Electrotechnical Standardization

(CENELEC) levels for the most efficient transformer configuration, designated HD428 CC,

The proposed new European Standard prEN50464-1 and The new USA Department of Energy levels that are to be mandated in 2010 Thus the new MEPS level proposals given here represent achievable efficiency levels that are consistent with current international efficiency Standards and proposals and are achievable in manufacturing terms. There are a number of factors that will enable the achievement of higher efficiencies and support the increase in the current MEPS levels. Better use of traditional materials to achieve loss reduction and improvement of

efficiency Better computer-aided design of transformers to reduce losses and improve

efficiency Use of low loss core materials such as amorphous metals New lower loss core configuration designs such as the Hexaformer Improved operational applications of transformers to optimize energy efficiency

in operation Consideration of total life cost of transformers: purchase cost plus operational

energy losses The effect of increasing harmonic levels from non-linear loads in increasing

losses and reducing efficiency Increased transformer life resulting from lower operating temperature with more

efficient transformers


The detailed impact of the reduction of transformer losses on global warming is difficult to predict and to model because detailed loading patterns are required for all types of transformer operation. However the detailed analyses used by the US DOE do provide such loading guides and the results in terms of energy saving and greenhouse gas reduction are outlined in the Federal Register document proposing the Rules for regulation of transformer efficiencies. Such parameters will be applied for the new MEPS levels in Australia. The testing of transformers for MEPS compliance is an important consideration as the testing of large transformers is not a logistically simple operation. Test procedures for MEPS 1 compliance are specified in the MEPS Standard which in turn refers back to the main Australian transformer Standard for the details of the test method. These test procedures lack some detail in the application of the loss measurements to the determination of efficiencies to an uncertainty of +/- 0.01% as is required by the Standard. Given the accuracy of the result required there should be some modification considered in the documented test procedures. It is suggested that the procedures given in the NEMA recommendations might be a suitable basis. In conclusion, the proposed increased MEPS levels have been compared in full detail to those transformer efficiency levels adopted or proposed in other countries. The proposed MEPS new levels are consistent and comparable with international levels for standard transformer designs and material applications. The new MEPS levels are achievable by manufacturers and will also provide significant energy conservation and positive environmental impact when they are implemented.


1 Introduction In 2000 the then National Appliance and Equipment Energy Efficiency Committee of Australian Commonwealth, state and territory government officials initiated the development of Regulations to mandate minimum efficiency performance standards (MEPS) for electricity distribution transformers. This was part of the National Appliance and Equipment Energy Efficiency Program (now the Equipment Energy Efficiency Program)) run under the auspices of the Ministerial Council on Energy of Australian and New Zealand Energy Ministers. As an outcome of this work an Australian Standard was issued in 2003 [AS 2374.1.2 2003: Power Transformers Part 1.2 Minimum Energy Performance Standard (MEPS) requirements for distribution transformers]. This Australian Standard specified minimum permissible power efficiency levels for electrical distribution transformers with nameplate ratings in the power range 10 2500 kVA and with primary voltage in the distribution voltage range of 11 22 kV. Details of the methods used for determination of the original transformer MEPS efficiency levels are given in reference [1]. Both liquid-insulated and dry-type transformers within the power rating range were included in the Standard. The Regulations associated with the MEPS requirements stated that no transformers falling within the specifications listed in AS 2374.1.2 could be sold in Australia unless they complied with the efficiency requirements. The MEPS requirements applied to both imported units and units made in Australia. The Standard was published in 2003 and the compliance requirements for transformers came into force on 1 April 2004. The main objective of both the previous MEPS and the proposed new MEPS requirements that are presented here is to reduce greenhouse gas emissions related to energy losses from electricity distribution transformers below what they are otherwise projected to be, in a manner that is in the communitys best interests. The specific purpose of MEPS for distribution transformers is to reduce the energy losses associated with transformer operation in the electricity distribution system. Overall network losses in the electrical transmission and distribution systems used to supply power to consumers can be as much as 6-9% of the total power supplied to the transmission and distribution networks by large power stations. Transformers, particularly in the distribution networks, make up about 30-40% of that network loss. All electrical power that is supplied to consumers has to pass through transformers at some stage and in some cases the power may pass through at least four or five transformers between the generator and the user. Usually, at least two of those transformers can be classed as distribution transformers. There will be power and thus energy losses at each transformer and thus reduction of loss in transformers will add greatly to reduction of greenhouse gas emissions. The original MEPS Standard stated that the levels specified would remain in force for four years and that they would then be reviewed in accordance with international trends of efficiency levels and would be made more stringent if international best practice indicated such change was achievable. Specifically, AS 2374.1.2 gave, in addition to the normal specified general levels of efficiency, a set of high efficiency levels that were not mandatory but were desirable levels. Only products which met


these levels could use the high efficiency designation in promotional or advertising materials. The review process of the original levels is now underway and this technical report has been prepared to put the case for replacing the original general MEPS levels with the high efficiency levels quoted in the present Standard. This technical report examines current international developments in efficiency determinations and provides detail of levels adopted in other countries and gives detailed discussion to support the increase of the Australian MEPS levels. The report will examine benchmark efficiencies that represent the ultimate technological and manufacturing limit of efficiencies and put the new MEPS level in the context of these international standards and in the context of modern development of large integrated electrical distribution systems. In addition, the report also addresses the potential energy and greenhouse house gas savings achievable from the proposed MEPS levels. The previous MEPS addressed market failure in the private (industrial and commercial) transformer market, and the increasing risk of market failure in the utility transformer market, by enforcing investment in more efficient products so that the total life cycle cost of the transformers to users would be lower than otherwise, as discussed in the Regulatory Impact Statement for MEPS 1. These arguments remain for the proposed higher MEPS levels. In addition to support of the new proposed levels, the report also considers a number of other issues related to the implementation of the MEPS requirements. In the original Standard, there were a number of exclusions listed for what were considered to be specialised transformers only. This list of exclusions is reviewed in this report with the purpose of determining whether the current exclusions listed are fully appropriate for contemporary transformer applications and use. The test method for determination of losses and efficiency as given in the original Standard is based on the standard method of loss determination given in the main power transformer Standard AS 60076, with some additional specifications of uncertainty for the efficiency determination. The test method as specified at present will be examined to determine whether it is adequate for the purpose of efficiency calculation to the accuracy required by MEPS compliance.


2 Transformer Use in Electrical Networks In the alternating current (AC) electrical supply system that is used in all countries for supply to consumers, the transformer is an indispensable component. It is not possible to operate viable electrical supply systems without it. In the normal propagation of power to consumers, the power is generated at about 11,000-15,000 volts (11-15 kV). It is then passed through its first transformer stage to increase the voltage to the transmission level somewhere between 220-500 kV. When it reaches the end of the transmission route it is then transformed again this time down to the 132 33kV sub-transmission level. It is then sent to distribution utility zone substations where it is again transformed down to 11-22 kV and is then sent on its final path to local street or pole transformers where it is broken down again to the final voltage of 415/240 volts. All of the transformers involved will have energy losses and thus any reduction in the transformer loss will mean less generation requirement and less greenhouse gas emissions. In the main transmission systems the transformers are relatively few in number but in the final distribution system operating at 11-22 kV in Australia, there are hundreds of thousands of transformers and thus any reduction of loss in the distribution system transformers will have significant impact on ultimate overall loss in the networks. The total electrical energy use per annum of the world is estimated as 13,934 TeraWatthours [TWh] (1 TWh = 109 kWh) and it is further estimated [2] that the losses in all of the worlds electrical distribution systems total about 1215 TWh or about 8.8% of the total electrical energy consumed. About 30-35% of these losses are generated in the transformers in the distribution systems. Studies estimate that some 40-80% of these transformer losses are potentially saveable by increasing transformer efficiencies, i.e. 145-290 TWh. Table 1 gives some details of the major regions and their electrical system losses.

Table 1 Total electrical consumption and network losses [Source: IEA[39]]

Region Total electricity

consumption (TWh)

Network losses (TWh)

Network Losses (% of total use)

All Europe Western Europe

3046 2540

222 185

7.3 7.3

Former USSR 1135 133 11.7 North America 4293 305 7.1 South America 1057 192 18.3

Asia Total Japan

Australasia China India

3913 964 219

1312 497

381 44 21 94

133

9.7 4.6 9.5 7.2

26.7

Africa and Middle East 826 83 10.0 TOTAL 13934 1215 8.8


Modern distribution transformers are very energy-efficient in their design and operation (they are typically about 98-99% efficient). However, it is the very large number of transformers in use in distribution systems, supplying power to domestic, commercial, rural and industrial sites, that cause the total transformer loss to be such a significant contribution to global warming and climate change. Thus, even small improvements in transformer efficiencies will lead to significant reductions in generation capacity requirement and thus in greenhouse gas emissions. Table 2 below shows the potential for energy reduction and consequent reduction of greenhouse gases from transformer loss reduction.

Table 2 Energy saving potential and greenhouse gas mitigation

from transformer loss reduction [After [2]] Country/Region Annual loss in

Distribution transformers (TWh)

Annual energy saving potential (TWh)

Annual reduction potential in CO2 (Millions of Tonnes)

Western Europe 55 22 9 USA 141 84 60 Australia 6 3 3 India 6 3 3 China 33 18 13 Japan 44 31 12 TOTAL 285 161 100

In Australia the total annual electrical energy production is about 206 TWh. The overall electrical network losses in Australia are 5.9% [3] and the distribution transformer losses associated with supplying this are thus about 6 TWh or 3.3% of the total production. On the basis of international investigations it is estimated that this transformer loss could be reduced by 50% to about 3 TWh by use of more energy efficient transformers to replace the current stock and by optimising operational practice. 3 TWh of electrical energy production by total coal-fired thermal generation produces about 3 million tonnes of CO2 and about 750 tonnes of the NOx gases each year [4,5]. In countries where the generation mix includes nuclear and hydro such as the USA, China, Japan and Europe, the CO2 equivalents are lower, as can be seen in Table 2. Of the total distribution transformer population in use in developed countries about 55% are electrical supply utility transformers, 41% are used in industry, commerce and mining and about 3% in transport. Utility transformers are predominantly (about 90%) of the liquid-immersed (liquid-insulated) type. However in industry and commercial installations dry-type transformers, with no liquid, are the predominant type, principally because of their lower fire hazard without the flammable oil generally used in liquid-filled transformers. Liquid filled transformers are smaller in size than dry-type units for the same power rating capacity and have lower losses because of their better thermal dissipation characteristics.


The voltages used in distribution systems depend on the location (the country or region) and may vary between about 4 kV to 34 kV. In Australia the main distribution systems operate at either 11 kV or 22 kV, three phase. The power rating of such distribution transformers typically covers 10 kVA to 2500 kVA and this is the power range that MEPS AS2374.1.2 covers. In Australia distribution transformers are primarily three phase, with single phase units being used only in a minority of cases and then only at the low end of the power range covered by MEPS (up to 50 kVA only). Many of these will be single wire earth return (SWER) transformers used to supply single sites at remote locations. However in many countries (North America and Japan for example) single phase transformers are extensively used to supply large areas and thus those countries have much larger ratings of distribution transformers in general use in addition to three phase units. For example in the USA, single phase up to 833 kVA are used in distribution systems. Industrial transformers tend to dominate the higher end (above 750 kVA) of the MEPS power rating range, while electrical utility supply transformers are more evenly distributed over the lower end of the range, below about 750 kVA. Industrial transformers have, in many cases, specific design features incorporated, while utility transformers have a more standard liquid insulation-based design. The total numbers of distribution transformers used in developed countries are very large. Table 3 gives some detail of the application of distribution transformer ownership and types that are used in Western Europe. These are typical of most developed areas.

Table 3 Distribution Transformers in Western Europe [After [2]]

Type Owner Class

Liquid-insulated (less than 250kVA)

Liquid-insulated (greater than 250 kVA)

Dry-type (all ratings)

Total number of Distribution Transformers

Supply Utilities

1,900,000

1,100,000

----

3,000,000

Commercial buildings

50,000

150,000

300,000

500,000

Industry and mining

50,000

350,000

100,000

500,000

Total

2,000,000

1,600,000

400,000

4,000,000


In Australia the installed utility distribution transformer population is about 550,000 with a total power handling capacity of 100 GVA. The annual increase in the number of distribution transformers in Australia is 18,000 or 3.3% of the total installed number. Thus, the total market in Australia for new transformers that fall into the MEPS rating scope is about 20,000 units per year. In New Zealand the estimated distribution utility transformer population is about 160,000. The installed total power handling capacity is estimated to be about 25 GVA. The actual increase of distribution transformer numbers in 2005/2006 was 4400 single phase and three phase units, or about 3.2% of the total installed number. The number of distribution transformers in industry and mining in Australia is about 65,000 with installed capacity of about 46 GVA. On a pro rata basis assuming the same growth rate, their number would be increasing by about 2200 each year. The industry transformer numbers for New Zealand are not known. In general, except for the large distribution transformers, above about 1000 kVA, major repairs and refurbishment of distribution transformers (such as re-winding) are relatively rare. Replacement by new units is more standard.


3 MEPS 1 Efficiency Levels The first MEPS efficiency levels for transformers were essentially based on proposed Canadian Standards for liquid-filled [6] and dry-type [7] transformers with some small appropriate variation to account for the power frequency variation from 60 Hz to 50 Hz. The electrical efficiency of a transformer is determined by the electrical losses that are generated within the transformer configuration. These losses occur in two separate parts of the transformer structure, core loss in the steel core which channels the magnetic field necessary for transformer operation and copper loss in the copper conductors, wound around the steel core, which carry the current in the transformer windings. The core loss and, to a lesser extent, the copper loss will both increase with increase in the AC power frequency and thus a frequency change from the 60 Hz used in North America to the 50 Hz used in Australia resulted in slightly lower losses and, consequently, in a slight increase in efficiency. The increase in the required minimum efficiency level due to the frequency change was about 0.1% in most cases. The Canadian efficiency levels for the liquid-filled transformers were based on American efficiency levels listed in a National Electrical Manufacturers Association (NEMA) Standard (NEMA Standard TP 1) [8]. The efficiency levels given in TP 1 were only used for voluntary application in the USA. They were determined from considerations of manufacturing and material best practice available at the time that they were developed in the late 1990s. In conjunction with NEMA TP 1, another Standard (NEMA Standard TP 2) [9] was issued to give detailed test requirements to enable adequate measurement accuracy of transformer losses as required to give adequate uncertainty in the transformer efficiency determination. In the current MEPS Standard, AS 2374.1.2 2003, two classifications of power efficiency levels for distribution transformers are given. These are: (i) General mandatory levels for MEPS regulatory application; and (ii) High efficiency levels which were not applied for regulatory compliance but can be used in promotional or advertising materials. At the time of publication of AS 2374.1.2, and since, the MEPS Regulations required manufacturing compliance with only the (lower) general efficiency levels. Transformer manufacturers or suppliers can have promotional and advertising material include the term High Power Efficiency Transformer if their transformers had power efficiencies that were equal to or higher than the high efficiency levels given in the Standard. It is now proposed to increase the mandatory efficiency levels in the MEPS 1 Standard for transformers. This will be done by using the previously specified High efficiency levels of MEPS 1 as the basic mandatory minimum efficiency levels required for all transformers under the amended MEPS of the E3 Program. The current general efficiency levels used for compliance will be removed from the new MEPS Standard.


Since MEPS 1 was issued there have been a considerable number of initiatives in various countries that have addressed the issue of transformer losses regulation to improve efficiency levels and reduce losses. In particular the Department of Energy (DOE) in the USA has undertaken, over a number of years, a very wide-ranging and detailed investigation of distribution transformer efficiency. This has been done to determine requirements prior to establishing new mandatory DOE Regulations to improve energy efficiency. The technical details and Rules have been published in 2006 [5] and will come into statutory force in 2010 in the USA. Since the first round of MEPS for transformers in Australia was published in AS 2374.1.2 a number of countries have either instituted or increased their transformer efficiency levels. In many cases these levels have exceeded the existing MEPS 1 specifications. These international developments will be described, discussed and summarised in a later section where they will be compared to the new MEPS proposals. The existing and proposed MEPS transformer efficiency levels are shown in Tables 4 and 5 below. Table 4 gives the efficiency levels for single and three phase liquid-immersed transformers, including single wire earth return (SWER) units used for rural distribution. Table 5 provides the same information for single and three phase dry-type transformers and for dry-type SWER units. Note that the minimum efficiency levels are specified at 50% loading of the transformer.

Table 4 Existing and Proposed MEPS levels for Liquid-immersed transformers.

[From AS 2374.1.2]

Transformer type kVA Power efficiency (%) at 50% load

Proposed New MEPS efficiency level

Single phase (and SWER)

10 16 25 50

98.30 98.52 98.70 98.90

98.42 98.64 98.80 99.00

Three Phase 25 63 100 200 315 500 750 1000 1500 2000 2500

98.28 98.62 98.76 98.94 99.04 99.13 99.21 99.27 99.35 99.39 99.40

98.50 98.82 99.00 99.11 99.19 99.26 99.32 99.37 99.44 99.49 99.50


Table 5 Existing and Proposed MEPS levels for Dry-Type transformers.

[Taken from AS2374.1.2]

Power efficiency (%) at 50% load Um = 12 kV

Power efficiency (%) at 50% load Um = 24 kV

Transformer type

kVA

Existing MEPS

Proposed new MEPS

Existing MEPS

Proposed new MEPS

Single phase (and SWER)

10 16 25 50

97.29 97.60 97.89 97.31

97.53 97.83 98.11 98.50

97.01 97.27 97.53 97.91

97.32 97.55 97.78 98.10

Three Phase 25 63 100 200 315 500 750 1000 1500 2000 2500

97.17 97.78 98.07 98.46 98.67 98.84 98.96 99.03 99.12 99.16 99.19

97.42 98.01 98.28 98.64 98.82 98.97 99.08 99.14 99.21 99.24 99.27

97.17 97.78 98.07 98.42 98.59 98.74 98.85 98.92 99.01 99.06 99.09

97.42 98.01 98.28 98.60 98.74 98.87 98.98 99.04 99.12 99.17 99.20

This report has been prepared to explain and to outline in detail the technical issues that have been involved in the move to specification of the higher mandatory efficiency levels. The report provides technical support for the application of the upgraded levels and compares the proposed new levels to current or proposed levels in other countries. The report is also aimed at providing a basis for public discussion of the new levels for manufacturers and users (electrical supply utilities and industry/commerce) of the transformers that fall within the scope of the MEPS program.

3.1 Application of MEPS In addition to providing technical support for the new levels, the report also considers other issues relating to transformer losses, including consideration of the cost of losses in initial transformer selection by purchasers. Consideration of both initial capital cost and the cost and effect of losses over the life of the transformer are important factors in both the economic cost of transformer operation and the losses which will be generated over the operational life. Transformer efficiency considerations are generally only secondary considerations when purchasing transformers for both industry and utility operations. However the application of energy efficient operation, in terms of initial capital cost and in terms of transformer loading to reduce loss, can have substantial long-term benefits in an economic and an environmental sense. In industry, the primary design features in the transformer specification are the ultimate application requirements. Achieving a long and energy-efficient operational life is not necessarily a major consideration. Thus initial capital cost is the usual major consideration in choosing transformers in industry. However, in addition to a


reduction of total life cost, improvements in energy efficiency by maintaining loading within ratings will increase the life of transformers and will reduce maintenance costs over the transformer life. An increase in transformer life will result whenever the long term operating temperature of the transformer insulation is reduced. A reduction in transformer loss will directly reduce this temperature. Hence, operation at higher efficiency and within the transformer rating limits will result in less degradation of insulation and thus less maintenance and longer life. In supply utilities, a long and efficient transformer life is a major consideration and requirement in the initial selection procedure but, as any cost of losses are generally able to be passed on to the consumer, the initial capital cost is again a primary feature of selection. This has been reinforced in recent years with the de-regulation of the industry where the utility ownership may change many times over the life of the transformer. In such circumstances short term capital benefits are more attractive than long-term total life costs of infrastructure. It is noted in the considerations of the US DOE outlined in [5] that, whereas total life costs were the basis for selection in about 75% of US supply utilities some years ago, since de-regulation of the electrical supply industry that percentage is now down to 50%. As will be discussed later, the MEPS regulations do not apply to all transformers. So-called power transformers, used in very high voltage electrical transmission systems for point to point transfer of power, as opposed to electrical distribution systems where power is supplied to many general consumers, are not included because they are relatively small in number and are generally designed on a one-off basis to high quality standards, including their energy efficiency. They have much higher ratings than distribution transformers, being typically in the range 10,000-500,000 kVA. Similarly, small transformers with rating less than 10 kVA single phase, are too small for general electrical distribution applications. They are used for more general applications rather than power distribution and are thus not included here. They are generally less efficient than the distribution transformers included in the MEPS scope (transformer efficiency increases with increase in rating), but their very small number in the distribution system, low rating and small energy handling capacity mean comparatively low overall losses in absolute terms. Thus they would not contribute significantly to total energy saving. For this reason they are not included. There are also a number of other exclusions from the coverage of MEPS, mainly for transformers for quite specific applications. These will be discussed in further detail later when the case for their exclusion is considered.


4 Transformer Efficiency It is of relevance at this stage to discuss the factors that determine the power and energy efficiency of transformers. These factors will be discussed in some detail in the later considerations and comparisons, so that some explanation of them is needed. The basis on which efficiency levels of transformers is considered and specified varies in some countries and regions. For example, the Australian MEPS regulations and the North American Standards use a specified power efficiency level of the transformer which is determined and specified at a particular loading level of the transformer. This particular loading is normally 50% of the full load, or Nameplate rating of the transformer. (In some cases it may be specified at 40% of load.) The loading is an important consideration as the efficiency will vary with the load. Generally, a transformer has maximum power efficiency at about 50% of full load, hence the general choice of this test load condition. Other countries, such as Japan, the European Union and India, do not specify power efficiency but instead specify maximum levels of power losses for the particular transformer ratings at full load. The transformer losses are tested and must fall within the maximum loss limits laid down in Standards. It is a simple matter to translate the power losses of the transformer into power efficiency levels by scaling the specified full load losses to 50% load. There is no major difference in the two approaches and they are easily convertible into the other form. Ultimately, the energy efficiency of overall energy use in a specified period of time is the main consideration for greenhouse purposes. Determination of this energy use over a period of time from the efficiency or losses requires knowledge of the loading of the transformer and its variation over that period. The losses and efficiency vary with loading of the transformer. The major problem occurs in the determination of the loading levels of the transformer as this must be known to calculate the total energy loss over a period and hence to determine the energy efficiency of the transformer. 4.1 Losses in Transformers In essence, the standard single phase transformer comprises a soft magnetic metal core built up from thin laminations which are made of highly refined magnetic steel sheets. Wound around the magnetic metal core are two electrical windings, the primary and the secondary, which are insulated from each other. The two windings carry current and transform the voltage of the power supply according to the relative number of turns in each winding. The magnetic steel core is used to contain and channel an alternating (AC) magnetic field around the core structure (the magnetic circuit). The magnetic field in the core is generated by passing a small electrical current (the magnetising current) through one of the windings (the primary) which is connected to the power source (in this case the general distribution grid system operating usually at 11,000 volts (11 kV) 3-phase or 6,350 (6.35 kV) single phase. The secondary winding is normally designed to give 415 volts 3-phase (240 V single phase) to any connected load (although there will be


a gradual change in these levels over the next few years to standardise them at 400/230 volts.). Figure 1(a) shows the general features of the single phase transformer construction and the major relevant components (the iron or steel core that contains the magnetic field (flux) and the windings). Three phase transformers have three sets of primary and secondary windings, each set usually wound on a separate leg of a multi-limb transformer core. (see for example Figure 2(c)).

(a) Figure 1 Single Phase Transformer Schematics

(b) In a simple single phase transformer the windings are contiguously wound on the transformer core with the magnetic field coupling through both windings (Figure 1(b)). The primary winding is the high voltage (outer) winding, connected to the distribution grid and the secondary winding is the low voltage (inner) winding, connected to the load(s) supplied by the transformer. The power taken to the load is transferred from the primary winding to the secondary winding and the load via the magnetic field generated in the core by the primary winding. Figure 2 shows some examples of liquid-insulated and dry-type distribution transformers. In liquid insulated transformers the windings and the core are immersed in insulating oil which provides both an electrical insulation function and a thermal transfer function to dissipate the heat generated by the transformer losses. See for example Figure 2(a). In dry-type transformers (Figure 2(b) and 2(c)) the insulation is provided only by solid materials with insulating paper wound over the windings and then all is filled by a solid casting of epoxy resin (2(c)), or alternatively in the open winding type (2(b)) the windings and paper insulation are provided with a thick varnish-type coating. In


dry-type transformers the heat generated by losses must be dissipated by thermal conduction of the solid insulation, which is less efficient that oil in removing heat.

(a) (b) (c)

Figure 2 Examples of liquid-filled and dry-type transformers

(a) 1000 kVA liquid-filled (b) 750kVA dry-type: open winding (c) 500 kVA dry-type: cast resin The establishment of the magnetic field in the core requires some current flow from the distribution system into the primary winding, so that even when there is no load connected to the secondary winding, magnetising current is still required to be taken from the grid to establish the magnetic field so that power transfer between the windings can occur whenever a load is connected to the secondary. In effecting transfer of electrical power from the distribution grid to the load the transformer itself consumes some power and hence energy loss within its structure. These losses generate heat in the transformer and this must be dissipated to the ambient. In order to maintain the transformer insulation within its operational limits. There are two quite different components making up transformer loss. These are:

(i) the No load (or core or iron) loss and (ii) the Load (or copper or winding) loss.

4.1.1 No Load (Core) Losses Whenever an AC magnetic field is generated in the steel core, it will cause an energy loss in the core material. This is the No-Load Loss or core loss of the transformer. There are, in turn, two components of the No Load Loss: (a) hysteresis loss and (b) eddy current loss. Hysteresis loss is generated due to the effect of the alternating magnetic field on the soft magnetic steel of the core. As the magnetic domains in the steel try to follow the changing orientation of the AC magnetic field they generate frictional heat in the core: this is the hysteresis loss. The level of hysteresis loss depends on the magnetic field magnitude (the core flux density), the AC power frequency and on the specific material used for the core.


Eddy current loss in the core steel arises from the intrinsic effect of the AC magnetic field on the electrically conducting core material. The AC magnetic field generates (induces) eddy currents in the core steel due to the magnetic interaction. These induced eddy currents generate heat (and energy loss) in the metal core material in the same way that any electrical current flow generates heat in the resistance of an electrical conductor. The eddy current loss depends on the electrical resistance of the core material and the AC frequency. The resistance can be increased and the eddy current loss decreased by using thin laminations or by using a core material with an inherently high electrical resistance, such as amorphous magnetic metal. Both of these components of core loss are dependent on the AC frequency at which the magnetic field alternates, so that when frequency increases, the core loss will increase. Hysteresis loss increases linearly with frequency but eddy current loss scales as the square of frequency. Thus any higher harmonic components in the exciting voltage will cause increased core loss. The magnetising current required to establish the AC magnetic field in the core, and hence the core losses associated with maintaining the magnetic field, are independent of the load connected to the secondary winding. The magnetic field flux density in the core is always constant and independent of the load current. Thus the core loss is the same for all levels of transformer loading, whether there is no load, half load or full load. Hence the No Load core losses are fixed losses, as shown in Figure 3, and they will be produced and present in the core whenever the primary winding is connected to the distribution grid voltage system. The core loss is voltage-dependent and also slightly temperature dependent. Thus, if the distribution grid voltage level changes, the core loss will also change. A higher voltage will generate higher losses and a lower voltage lower losses. The temperature dependence is complex in that the hysteresis loss will increase slightly with increased temperature but the eddy current loss will decrease with temperature increase because of increase of resistance with temperature. Thus, measurement of fixed losses in performing efficiency tests requires that test voltage and temperature must be specified and measured accurately. In some cases it may be necessary to use multiplying factors to adjust measured losses to specified standard conditions.

Figure 3

Transformer loss components and power efficiency versus loading [Note that peak efficiency occurs when load loss and no-load loss are equal] [From [18]]


4.1.2 Load (copper or winding) loss The Load Loss is generated in the two windings by load current flow in the electrical resistance of the two windings, generating simple ohmic heating from the effects of current on the winding resistance. (The magnetising current in the primary is very low in magnitude compared to normal load currents and will give negligible contribution to Load Loss). The Load Loss is load-current dependent as can be seen in Figure 3 and scales as the square of the load current (and the load level in kVA) so that, for example, the load loss at 100% loading will be four times the load loss at 50% loading. Load losses are relatively insensitive to grid voltage change. They are however very sensitive to temperature variation of the windings and this is an important consideration in analysis of the test results of efficiency determinations. Test temperature must be recorded and the results normalised to specified standard temperatures in any loss and efficiency determinations. (Although copper loss is a widely used term for Load Loss, the windings are not always made of copper. In modern distribution transformers, the secondary winding may be wound in the form of a cylindrical sheet of aluminium. This is an important consideration in adjusting losses for temperature variation.) As can be seen in Figure 3, the load loss becomes the dominant component when the transformer is more than about 50% loaded. The load dependence also means that any overloading of the transformer will cause significant increase in load loss and decrease in efficiency. Load loss is also dependent on the frequency content of the load current. When higher frequency harmonics are present in the load current due to non-linear loads, for example, eddy currents are generated in the windings and these cause higher levels of loss. The higher the harmonic frequency content, the greater the load loss. In addition to the load loss due to winding resistance, there is another component of loss that is generally included in the load loss but is not part of the actual winding loss. This is stray loss in the metal structural parts of the transformer tank and similar metal components. Stray loss arises from eddy currents set up in the metal parts when the magnetic field of the secondary current in the transformer interacts with them. The eddy current flow causes heating in the tank and other metal structural components in the same way that they are caused in the core laminations. Stray losses are typically about 5-10% of load loss. Non-magnetic metals such as aluminium will have lower stray loss than magnetic metals such as steel. 4.2 Power and Energy Efficiency Having outlined the losses that affect the efficiency of power transfer by transformers it is necessary to differentiate between the Power Efficiency which is the defining quantity used in the MEPS Standard and the Energy Efficiency of a transformer. These two quantities are not quite as intimately or simply related for transformer operation as they are in some other items of electrical equipment. This complexity arises because of the operational load dependence of the total losses in transformers


and the need for transformers to be connected to the grid voltage at all times whether loaded or not. In an electrical distribution system, the transformers are always left connected and energised even when no power is being taken from them by consumers. When they are not supplying power transformers will still generate no load loss with the result that the unloaded transformer is a simple power drain on the grid. Even when lightly loaded (up to 15% of rated load), the transformer power efficiency is very low. Figure 3 shows the dependence of losses and efficiency of a typical transformer on the load level. For this reason the loading of the transformer is an important consideration in terms of the energy efficiency. The loading will depend on the application and the type and number of consumers connected and will be quite different, for example, between utility and industry/commercial application. Supply utility transformers have a complex loading pattern that is often dominated by domestic loading requirements while transformers supplying industry and commerce have a more predictable load that can be more readily modelled in energy loss calculations. Typically a general utility supply transformer will have an averaged load of about 25-30% over a year while an industrial transformer will have an average load of about 50%. These differences can mean that the energy efficiencies of the same transformers with different loading will be quite different. 4.2.1 Power Efficiency of a Transformer The power efficiency of a transformer is a property that is only able to be defined for a specific load It gives an instantaneous measure of the transformer power loss relative to the power supplied to that specific load at any particular time. Then the power efficiency EP is defined as:

EP = Load power/ [Load power + Power loss] = PL / [PL + PC + PW] where The real power delivered to the load is: PL watts The No Load core loss is: PC watts The Load Loss is: PW watts The real power in watts supplied to the load, and hence the power efficiency of the transformer, is dependent on the power factor of the load. The power factor is the ratio of real power (in watts) used by the load to the apparent power (in kVA) required by the load conditions. Thus PL = Voltage x Current x Power Factor. Typically domestic loads have almost unity power factor, while industrial loads will have lower power factors. If the power factor of an industrial or commercial load is too low (say less than 0.8) the supply utility may require increase of the load power factor (power factor correction) by installation of capacitors at the load. Using the power factor, the full definition of the power efficiency is then:


EP = VICos / [VICos + PC + I2RW] where: The power factor is: Cos The load voltage is: V volts The load current is: I amps The total winding resistance is: RW ohms Obviously, if the supplied power to a load is zero, the efficiency is zero and the transformer represents a simple power and energy loss to the supply grid system. As can be seen in Figure 3 the power efficiency is very low below about 10% of loading. While the power factor can be an important consideration in determining the overall energy efficiency, when testing transformers for their power efficiency, unity power factor load conditions (Cos = 1) are used. Maximum power efficiency occurs when PC = PW, when the load loss is equal to the no load loss. As a rule of thumb, maximum efficiency often occurs at about 50% of the full rated load of the transformer. Thus when efficiency testing is performed it is normally done at 50% of full load. [In fact, for modern transformers with low no load loss the above rule of thumb may not work because the no load losses are decreased. However the 50% test load is still used. Dry-type transformers, in particular, have higher core loss than liquid-insulated transformers and so the 50% load may not correspond to peak efficiency in that case either.] MEPS requirements are that the efficiency must be determined at 50% of full load and thus the specified minimum efficiency levels are about the peak values for general transformer operation. 4.2.2 Energy Efficiency of a Transformer The power efficiency is an efficiency level determined by the instantaneous load power and the power losses in the transformer. The energy efficiency is an integrated quantity characterising energy supply and energy loss over a specific period of time. Thus it is necessary to determine the energy supply from the load power levels and durations of the particular loads imposed on the transformer during the period that the energy efficiency is calculated for. Thus the energy efficiency is necessarily specified over a period of time, which may be a day, a week, a month or a year. The loading pattern of the transformer then becomes an important consideration in energy efficiency and there is thus some variation in energy efficiency between the domestic, industrial and commercial applications of transformers because of the different load patterns. The loading of industrial transformers is higher than that of utility distribution transformers [5] and thus their energy efficiency is usually higher than that of utility transformers. If a transformer has a load pattern consisting of, say, three periods of different constant loads (L1, L2 and L3) over defined periods T1, T2 and T3 with no load supplied for a period T4, the energy efficiency of the transformer over that period is:


EW = [L1T1 + L2T2 + L3T3]/ [L1T1 + L2T2 + L3T3 + (T1+T2+T3+T4)PC +

(PW1T1 + PW2T2 + PW3T3)]

= [L1T1 + L2T2 + L3T3]/ [L1T1 + L2T2 + L3T3 + (T1+T2+T3+T4)PC +

(L12.T1+L22.T2+L32.T3)PWR/LR2]

where: L1, L2 and L3 are the loads in kVA that are sustained for periods T1, T2 and T3 T4 is the duration of the no-load period of the transformer PC is the core power loss (no load loss) PW1, PW2 and PW3 are the load losses at loads L1, L2 and L3 PWR is the full load (copper) loss at nameplate-rated load LR. In terms of load voltage (V) and currents (I1, I2 and I3 and IR) the energy efficiency is:

EW = [VI1T1 + VI2T2 + VI3T3]/ [VI1T1 + VI2T2 + VI3T3 +

(T1+T2+T3+T4)PC + (I12.T1+I22.T2+I32.T3)PWR/IR2]

[It is assumed that the voltage regulation maintains V constant, independent of load.] Calculation of the energy efficiency and the total energy over a period thus requires details of the transformer loading pattern in addition to the loss details. The loading pattern is often difficult to determine, particularly in a large distribution system with many transformers and it is necessary to use some empirical modelling procedures to simplify loading patterns into two or three equivalent periods of constant loads so that total energy loss calculations can be performed. Transformer loading Standards such as AS 2374.7 (Loading Guide for oil-immersed power transformers) [11,12] are useful in providing standard methods of determining such load models. Such modelling is necessary to determine accurately the overall energy saving potential of any targeted improvements in the power efficiency of transformers. Much effort was expended by the US Department of Energy in developing load models for use in analyses of the impact of their proposed efficiency regulations [13]. 4.2.3 An example of energy saving by improvement of power efficiency For a 1000 kVA transformer with MEPS 1 efficiency level of 99.27% and with a daily load cycle consisting of the following:

8 hours at full load unity PF, 6 hours at 50% load unity PF, 6 hours at 25% load unity PF and 4 hours at no load,

the daily energy efficiency is 99.07% and the energy loss per day is 117 kWh. For the same transformer rating with the new proposed MEPS power efficiency level of 99.37% and the same load cycle, the energy efficiency is increased to 99.24% and the energy loss per day is reduced to 101 kWh.


Thus, the daily energy saving is 16 kWh, which is 5.8 MWh per annum for this load pattern, corresponding to about 6 tonnes of CO2-e greenhouse gas emissions avoided per annum or 180 tonnes of CO2-e over the expected 30 year life of the one transformer.


5 Transformer efficiency standards in other countries Other countries have put forward minimum efficiency standards or proposals for transformers in recent years. In particular the USA, the European Union, India and Japan have undertaken extensive investigations to determine minimum power efficiency levels that are technically achievable by manufacturers and that will provide significant energy savings when adopted. It will be seen from the following survey that the proposed new MEPS efficiency levels for distribution transformers in Australia are quite consistent with the minimum efficiency level standards that are being developed and applied internationally. 5.1 US Proposed Efficiency Standards In America the voluntary NEMA TP 1 Standard [8] has been used as an interim measure while new efficiency standards have been developed for future mandatory application. In developing the new efficiency standards the Department of Energy in the USA has undertaken a very substantial and lengthy investigation of transformer efficiencies in order to determine technically appropriate and achievable efficiency levels for adoption. This work was started in 1996 with the publication of DOE commissioned reports by the Oak Ridge National Laboratory [14,15] into energy conservation standards for distribution transformers. This involved a detailed investigation of the whole range of factors involved in distribution transformer manufacture and operational efficiency. Subsequent to those initial commissioned reports, extensive work was undertaken by the DOE itself which involved having their technical staff use state of the art computer design procedures to develop a number of transformer designs to determine the sensitivity of efficiency to a variety of design factors so that achievable best practice efficiency levels could be specified. They also purchased a range of transformers from manufacturers and then dismantled and re-assembled the transformers to examine component quality and to test manufacturing quality control features in order to determine whether they could be improved so as to increase energy efficiency. In addition they used utility and industry data from detailed surveys of transformer loading data from utilities and industry to develop mathematical models of loading patterns for all typical applications distribution transformers. These were then used in life cycle models of the transformers to determine the total life cycle costing of transformers, including capital cost, cost of losses and maintenance costing over the life of the transformer. Using all of this data and modelling of energy savings from the effect of new imposed higher efficiency levels they were able to model and determine the impact of the efficiency savings on the environment, particularly in the case of reduction of carbon dioxide emissions and reduction of the NOx gas emissions from thermal power stations when the higher efficiency transformer units were used.


Detailed consideration was also given to the testing methods specified in NEMA Standard TP 2 [9] for determination of transformer losses and calculation of the power efficiencies. Documents relating to this work included an environmental assessment of the proposed energy standards for distribution transformers [16], a Framework Document for the new Standards for public comment [17] and a Technical Support Document for Advanced Notice of Proposed Rule-making [13] giving full details of modelling procedures and technical discussion. The final result of this work was publication in the USA Federal Register, on 4 August 2006, of a Proposed Rule for distribution transformer energy conservation Standards [5]. Distribution transformers manufactured after 1 January 2010 will have to have power efficiencies that are no less than the specified values under the test conditions given in the Rules. Some further discussion on test procedures and amendments to the NEMA TP 2 test methods were given in another Rule in the Federal Register [10]. As a result of the work the DOE published two sets of efficiency tables for transformers. One set represented what were considered to be the Maximum Technologically Feasible Levels (MAX-TECH LEVELS) which were based on use of the most efficient materials and use of sophisticated design parameters and software to create designs at the highest efficiencies possible. The other set of efficiencies given in the Rules were the proposed efficiency standard levels that were chosen from a number of various designs and combinations investigated. Six Trial Standard Levels representing the short list of most efficient designs were devised for detailed investigation. The one chosen for application in the Rules was Trial Standard Level 2 [TSL2]. Tables 6 and 7 below show the MAX-TECH LEVELS for liquid-insulated transformers (Table 6) and dry-type transformers (Table 7) that were decided on the basis of the extensive investigations described above. Tables 8 and 9 show the proposed efficiency levels [for TSL2] chosen for implementation of the Energy Conservation Rules. It should be noted that the efficiencies listed in the DOE tables are specified for 60 Hz operation. For equivalent 50 Hz operation as used in Australia (and Europe) the corresponding minimum power efficiency levels would be expected to be slightly higher (by less than about 0.1%).


Table 6 USA Department of Energy Maximum Technologically Feasible Levels

for Single and Three Phase Liquid-immersed Distribution Transformers. Tests to be done at 50% of rated loading according to test procedures in reference [10]

Table extracted from reference [5]. Figures are for 60 Hz operation.

Table 7 USA Department of Energy Maximum Technologically Feasible Levels

for Single and Three Phase Dry-Type distribution transformers. Tests to be done at 50% of rated loading according to test procedures in reference [19]

[Figures for BIL of 46-95 kV will correspond to rated voltage of about 11 kV.] Table extracted from reference [5]. Figures are for 60 Hz operation.


Table 8 USA Department of Energy Minimum Efficiency Levels for Regulation

of Liquid-immersed Distribution Transformers at 60 Hz. Table extracted from [5]

Table 9 USA Department of Energy Minimum Efficiency Levels for Regulation of

Dry-type Distribution Transformers at 60 Hz. Table extracted from [5]


The detailed testing that was done did not cover all of the rating levels in the range. For other ratings not covered by testing, the designated efficiencies were determined by scaling losses. The (0.75) exponent scaling rule was used on the ratings to determine losses from known loss characteristics at other ratings. Thus the No Load Loss (NLL) and Load Loss (LL) at some kVA rating level (S) was determined from the known losses NLL0 and NL0 at rating S0 by the following scaling equation: NLL = NLL0 (S/S0)0.75 LL = LL0 (S/S0)0.75

The reason for the inflexion in the proposed three phase efficiency levels for liquid-insulated transformers (the efficiency decreases at 333 and 500 kVA and then increases again) is not known. It obviously does not follow the above scaling rule. The work leading to the proposed levels also involved a detailed screening process that removed a number of material or design types from consideration if they were not considered viable for manufacturing procedures. Thus for example they excluded high temperature superconductor transformers and also amorphous metal use in stacked core configuration (though amorphous metal use in wound-core configuration was considered). The DOE levels provide a basis for comparison for the proposed new Australian MEPS levels. While the three phase range of transformers in Tables 8 and 9 have similar equivalents in Australia, single phase distribution transformers are more extensively used in the USA and thus the single phase rating range given is much broader than is available in Australia where single phase ratings only up to 50 kVA are used in distribution systems. In any specific comparison of efficiencies, the effect of the frequency difference (60 vs. 50 Hz) should be considered. In general, the efficiency for the same power rating at 50 Hz will be a little less than 0.1% greater than the efficiency at 60 Hz. In the case of the dry-type transformers, three design cases (PC or Product Cases) are listed. They are distinguished by the Basic Insulation Level (BIL) which is the designed lightning impulse withstand voltage level for the transformers. The comparable class for the Australian distribution situation would be that for a BIL of 46-95 kV. This will correspond roughly to the Australian 11 kV transformer class. A comparison of the levels with the new Australian levels will be given later. It should be noted here that there has recently been some criticism of the US DOE proposals by NEMA, who claim that transformer materials costs (particularly of silicon steel for the cores) have risen very significantly since 2003 when the DOE investigations were carried out. NEMA claim that this increase will affect the economics of the procedure used to determine achievable efficiency levels [26]. They have asked the DOE to consider using newer data in the analysis of efficiency levels. The listing of the above Tables in the Federal Register specifies that the efficiencies must be determined at a specific reference temperature and at 50 % of nameplate-rated load. For both liquid-immersed and dry-type transformers the no-load losses must be determined at a temperature of 200C. For the load losses used in the


efficiency calculation, the specified reference temperatures to be used are 550C for liquid-immersed transformers and 750C for dry-type transformers. Reference [10] published in April 2006 discussed in detail the test procedures to be used and gives, in its Appendix A, a Uniform Test Method for Measuring the Energy Consumption of Distribution Transformers. This procedure is to be used in performing tests for compliance with the proposed DOE Rules. The test procedure used also gives sampling details for effecting a proper random selection of test objects. These test procedures are more detailed and specific than those available for use with the Australian MEPS test procedures. 5.2 European Union Proposals There has also been much activity in recent years in the European Union countries with regard to transformer efficiency standards. An organisation named SEEDT (Strategies for Energy Efficient Distribution Transformers) has been established recently with the express aims of promoting the use of energy efficient transformers and proposing and applying strategies for reducing energy losses associated with distribution transformers. SEEDT held a conference in March 2007 at which new proposed transformer efficiency levels for European application were outlined. [18]. In addition to SEEDT, another organisation was established with wide international membership, including Australia. This group is PROPHET (Promotion Partnership for High Efficiency Transformers). PROPHET issued a detailed position paper on transformers in February 2005 (The Potential for Global Energy Savings from High Efficiency Transformers) [19]. In the European Union the relevant Standards for distribution transformer efficiency are CENELEC HD 428 [20] for liquid-immersed units and CENELEC HD 528 [21] for dry-type units. These Standards do not specify power efficiency levels but take the other option of specifying maximum allowable No Load and Load Losses for different transformer rating classes. The Standards [20, 21] do not give mandatory levels to be complied with by member countries. Instead the Standards provide a number of different levels of losses (and thus different efficiency levels) for different transformer combination types. It is the left to member countries to adopt (or not to adopt) any of these levels for implementation. HD 428 [20] specifies no-load loss levels for three different core types (designated A, B and C, with C having the lowest loss and A the highest). It also gives load losses for three different winding types (designated A, B and C, with C being the lowest loss and B the highest loss). HD 528 [21] gives just one loss combination. There are thus nine different transformer combinations of No load and Load loss in HD 428 in terms of overall losses, but only one for dry-types. Tables 10 and 11 below show the various loss levels specified in HD 428 and HD 528. Table 10 gives no-load losses and Table 11 gives the load losses. Amorphous core materials were not included in the specified no load losses in the Standards. However later European proposals have used amorphous core materials to reduce no load loss.


The B-A combination of load and no load loss is the highest loss and represents the least efficient transformer type. The C-C combination of load and no load loss has the lowest total loss and thus corresponds to the highest efficiency transformer type. HD 528 gives only one possible combination of load and no load loss for dry type units with the dry-type no-load losses being higher than for A for all power ratings, as would be expected from the general properties of dry type transformers. In the case of load losses the dry-type losses are lower than the B levels, comparable to A levels and less than the C levels for liquid-immersed transformers.

Table 10 No-load Losses for Dry-type Transformers (from HD 528) and for Three Classes

(A, B and C) of Liquid-immersed Transformers (From HD 428).

Table 11 Full Load Losses for Dry-type Transformers (HD 528) and for Three Classes (A,

B and C) of Liquid-immersed Transformers (HD 528).


The adoption of the HD 428 and HD 528 loss levels as maximum loss specifications levels for transformers is not mandatory in the European Union. Some countries have used the efficient C-C combination as a requirement and others have adopted lower efficiency combinations such as the B-B. For example the following table indicates the levels used in some European countries [4]. Belgium: C-C France: A-A and B-B Germany: A-C, B-A and C-C Italy: B-C Netherlands: Has levels better than C-C Spain: Half the transformer population meet the C-C levels It is considered [4] that the C-C combination of loss levels and the corresponding efficiencies are not difficult for manufacturers to achieve and thus there has recently been a move to combine the more efficient C load loss levels with no load losses typical of amorphous cores to achieve a benchmark level of attainable efficiency, designated C-AMDT [19]. Table 12 shows the efficiencies at the Standard 50% load level determined from the loss specifications for the C-C combination, for the C-AMDT combination and the dry type from HD 428 and HD 528. The efficiencies have been calculated and tabulated so that some comparison can be made later with efficiency standards in other countries.

Table 12 Comparison of the Efficiencies for the Three Phase C-C Combination from

CENELEC HD 428 and the C-AMDT levels. Also shown are the efficiencies for the Dry-type units from HD 528.

Trans. Type Rating (kVA)

C - C efficiency at 50% load

C-AMDT efficiency at 50% load

Dry-type Efficiency at 50% load

50 98.65 99.01 ---- 100 98.86 99.16 97.76 160 99.03 99.28 98.10 250 99.13 99.36 98.41 400 99.23 99.42 98.60 630 99.31 99.50 98.67 1000 99.32 99.51 98.82 1600 99.36 99.52 99.02 2500 99.37 99.52 99.06


There is a new proposed efficiency Standard for liquid- immersed transformers in the European Union, designated prEN50464-1, which proposes new efficiency levels that lie between the C-C and the C-AMDT levels shown in Table 12 above. These new proposals are shown in Figure 4 below as the light blue curve. Also shown are the NEMA TP-1, 50 Hz levels which are the same as the existing Australian MEPS 1 levels for liquid-filled transformers and the Japanese levels, which will be discussed in the next section. The proposed new European efficiency levels Pr EN50564-1 are also tabulated with the existing HD428 C-C levels for more detailed comparison in Table 13.

Figure 4 New European Efficiency Level Proposal (Pr EN50464) and Comparison with

NEMA TP 1, Japanese Standard levels and the A-A combination. [From [18]]

Table 13

Tabulation of the Proposed European Levels prEN5046-1 for Oil-immersed Transformers and Comparison with C-C and C-AMDT levels

Type Rating (kVA)

C - C efficiency at 50% load

C-AMDT efficiency at 50% load

Proposed Standard prEN5046-1

50 98.65 99.01 98.90 100 98.86 99.16 99.10 160 99.03 99.28 99.22 250 99.13 99.36 99.30 400 99.23 99.42 99.38 630 99.31 99.50 99.45 1000 99.32 99.51 99.46 1600 99.36 99.52 99.48 2500 99.37 99.52 99.49


5.3 Specified Efficiency Levels in Other Countries As well as the USA and European efficiency levels outlined above there are other distribution transformer efficiency Standards in other countries that are either already in force or are about to be imposed. The other countries using efficiency ratings for transformers include Japan, Canada, China, Mexico and India. 5.3.1 Canada Canada uses the two Canadian Standards CSA C802.1 [6] and CSA C802.2 [7] for efficiency specifications of liquid-immersed and dry-type distribution transformers respectively. The levels set for liquid filled transformers follow the specifications of NEMA TP-1 [8] and the current Canadian levels are still the same as when they were adopted, with small variations, as the first Australian MEPS efficiency levels. They are thus essentially the same as MEPS 1 levels and for this reason are not listed here. The current dry type levels in Canada differ from the NEMA TP 1 levels because of specific local Canadian manufacturing situations. They are shown below in Table 14. Because first phase of MEPS levels were based on the Canadian levels, which have not changed, th

200717 Meps Transformers

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