Distribution Transformer Main Handbook

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Distribution Transformer

HANDBOOK

International Copper Association Southeast Asia Ltd

All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.

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Foreword|

t is hard to expect that energy prices will not continue to

increase in the next few decades. Climate change mitigation

will play an increasingly important role in the development of

power sector favouring renewable energy systems, energy

conservation and energy efficiency. Thus more and more

attention should be paid to energy losses.

According to our studies (“Global energy savings potential from high efficiency distribution transformers”, ECI 2004) technical energy losses in all of the world’s electrical distribution networks are at the level of one thousand TWh. About 30% of these losses occur in distribution transformers which are one of the two largest loss making components in electricity networks.

Although typical distribution transformers seem very efficient, the reduction of losses in transformers may have almost no limits. However there is a certain technological and economical optimum at which existing losses in distribution transformers may be roughly halved reaching life cycle cost minimum at the same time.

Replacing distribution transformers is relatively easy compared to lines or cables and in the event, of highly inefficient units it is worthwhile to do it even before they reach their technical lifetime. In the purchase decision process relating to newer equipment, it is imperative to include the cost of losses in the investment calculation.

As already stated, distribution transformers can bring economic benefits to users but also environmental benefits for the society. The economic benefits will not always remain in the investors’ hands as energy regulators may try to interfere in the balance of capital and operating cost of distribution companies in order to protect customers against rapid price increases. The customers will pay the cost of losses for the entire transformer life, but will not see any rapid change in their electricity bill.

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A good practice, in the purchase decision criteria, is to perform a lifetime cost analysis based on the capitalization formula. The relative data for this formula is: energy prices projections, interest rates, transformer lifetime, transformer loading and anticipated change in future loading. The other side of the equation presents the transformer price and its dependence on the level of rated losses.

The analysis is not extremely difficult but may be sensitive to a number of parameters, the most relevant of which may be interest rates, and lifetime but also changes in commodity prices. Planning on a broad scale is a key component to optimization. Large distribution companies quite often use procurement efficiency standards to specify transformers. Such practices help manufacturers so that they have prior knowledge of requirements and thus they know what they can expect from buyers. In this case, a well prepared procurement procedure may prove useful and will help to avoid misunderstandings between a buyer and a seller and should lead to optimum purchasing decision with losses kept sufficiently in focus. We think the rationale of this Handbook was to facilitate such a process.

Hans de Keulenaer Roman Targosz

Electrical Programme Manager Project Manager

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Introduction|

The Lower Mekong Subregion (LMS)

Harmonisation Programme

ambodia, Lao People’s Democratic Republic (Lao PDR),

Thailand and Vietnam have achieved different levels of

economic development. These countries in the Lower Mekong

Subregion (LMS) have strong economic inter-dependence.

Being developing countries, their power distribution systems, an

essential infrastructure, play a significant role in the economic

development. Energy end-users are dependent on the availability,

reliability, and quality of electricity from the power distribution

systems. The level of development and advancement of power

distribution systems has direct impact on the developmental

potential and economic growth, especially in urban cities.

The power distribution systems in the urban areas of these LMS countries, however, do not have the same level of development. It is widely acknowledged that harmonisation in the development of power distribution systems can benefit these countries and accelerate their economic growth.

In 2005, six power partners entered into a Memorandum of Understanding (MOU) to share the intent of working together towards harmonisation of power distribution systems in the following four LMS countries: Cambodia, Lao PDR, Thailand and Vietnam. The founding partners are:

• Electricité du Cambodge (EDC), Cambodia • Electricité du Laos (EDL), Lao PDR

• Ho Chi Minh City Power Company (HCMC PC), Vietnam • Hanoi Power Company (HNPC), Vietnam

• Metropolitan Electricity Authority (MEA), Thailand

• International Copper Association Southeast Asia (ICASEA) [formerly known as Copper Development Centre • Southeast Asia]

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This led to a study of power distribution systems of the power partners in Cambodia, Lao PDR and Vietnam; and the preparation of a regional cooperation roadmap and action plan.

Building on the success of the first MOU, ICASEA and MEA inked a second MOU to continue their strategic partnership in conducting further studies and facilitating programmes as outlined in phase 2 of the road map and action plan. This impetus is to enable the LMS countries to make further progress towards harmonisation and the realisation of the objectives as set out in the MOU with all the power partners.

The study of power distribution systems in the LMS countries under the first MOU had revealed that there are many differences in the power distribution systems in this region. The objective of this second MOU was to narrow down the differences in six key areas and enable the LMS countries to move towards greater harmonization of their power distribution systems.

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Preface|

Loss in the Power Distribution System is a common and

pressing concern expressed by Utilities in the LMS. Reducing

loss is the priority given the energy shortage arising from rapid

economic growth and high oil prices.

A Regional Loss Reduction Workshop for LMS Utilities was held in Phnom Penh, Cambodia on 18 & 19 March 2008. It concluded with a consensus to, amongst other areas of collaboration, reduce losses in the Power Distribution Systems of EDC, EDL, HCMC PC and HNPC by harmonising technical specifications and developing a best practices handbook for energy efficient equipment based on international standards.

The views of and input from participating Utilities were crucial in the development of technical specifications for the harmonisation of power equipment in the LMS. Only with acceptance and implementation of the technical specifications can LMS Utilities reduce losses associated with inefficient power equipment. Hence, a 6-member Technical Working Group (TWG) comprising a senior technical representative from each Utility and ICASEA was formed to participate and contribute in discussions and meetings.

The objective of the TWG was to start with the development of technical specifications to harmonise low loss power transformers in the LMS. This step-by-step approach was to enable the participating Utilities to review and evaluate the result of this Technical Working Group before collectively moving to the next step of harmonising other equipment.

This handbook was developed to help LMS Utilities implement low loss transformers. Reduction will only come when the minimum performance guidelines are followed and implemented by all associated with the design of the electricity grid, specifying the standards of equipment for procurement and subsequently operating or maintaining them.

Members of the Technical Working Group: Chairman

Mr.Surapon Soponkanaporn

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Electricite Du Cambodge (EDC), Cambodia

Mr. Lim Sisophuon

Deputy Chief, Dispatching Control Centre

Electricite Du Laos (EDL), Lao People’s Democratic Republic

Mr. Xanaphone Phonekeo

Deputy Manager, Technical Standards Office

Ho Chi Minh City Power Company (HCMC PC), Vietnam

Mr. Nguyen Duy Hoang

Electrical Engineer, Technical Department

Hanoi Power Company (HNPC), Vietnam

Mr. Vu Quang Hung / Mr Trinh Xuan Nguyen

Vice Director, Technical / Manager, Technical Department

Metropolitan Electricity Authority (MEA), Thailand

Mr. Werawat Buathong

Deputy Director, Power System Planning Division Mr. Somchai Homklinkaew

Senior Electrical Engineer Mr. Sompong Sittichaiyanan Electrical Engineer

International Copper Association Southeast Asia (ICASEA)

Mr. Louis Koh

Project Leader, Power Distribution Mr. Piyadith Lamaisathien Country Manager, Thailand

MEA Project Support Team

Ms. Sutida Sindhvananda, Director of Int’l Services, Business Div. Ms. Sasianong Vacharasikorn, Electrical Engineer

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Acknowledgements|

he harmonisation of power distribution systems in the

LMS will contribute to the expansion of the ASEAN

Power Grid. However, harmonisation requires a robust

partnership and sustained effort over many years.

The harmonisation of technical specifications together with the development of this handbook is taking the process a step closer towards the realisation of the objectives as set out in the strategic roadmap for the harmonisation of power distribution systems in the LMS.

Strengthening regional cooperation to build the capacity of both technical and functional staff would not have been possible without the endorsement and support of:

Electricité du Cambodge, Cambodia

Mr. Keo Rottanak, Managing Director

Mr. Chan Sodavath, Deputy Managing Director

Electricité du Laos, Lao People’s Democratic Republic

Mr. Khammany Inthirath, Managing Director Mr. Sisavath Thiravong, Deputy Managing Director Mr. Boun Oum Syvanpheng, Deputy Managing Director

Ho Chi Minh City Power Company, Vietnam

Mr. Le Van Phuoc, Director

Mr. Tran Khiem Tuan, Deputy Director

Hanoi Power Company, Vietnam

Mr. Tran Duc Hung, Director

Mr. Vu Quang Hung, Vice Director, Technical Mr. Nguyen Anh Tuan, Vice Director, Business

Metropolitan Electricity Authority, Thailand

Mr. Pornthape Thunyapongchai, Governor

Mr. Surapon Soponkanaporn, Director, Research & Development Department

International Copper Association Southeast Asia

Mr. Steven Sim, Chief Executive Officer

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Contents|

Chapter 1

Preparation of National Normative Technical Specification of Distribution Transformer

1. Introduction 2. Objective

3. Principle specification

4. Electricité du Cambodge - Additional Specification 5. Electricité du Laos - Additional Specifications

6. Ho Chi Minh City Power Company - Additional Specification 7. Hanoi Power Company - Additional Specification

8. References Chapter 2 Bidding Evaluation 1. Introduction 2. Objective 3. Formula Analysis

4. How to Evaluate The Best Choice 5. Excess Losses and Penalty 6. The Low Loss Limitation Table 7. Conclusion

8. Appendices Chapter 3

Transformer Production Inspection 1. Introduction

2. Objective

3. Inspection committee management 4. Inspection Process 5. Conclusion Chapter 4 Contract Acceptance 1. Introduction 2. Objective

3. Acceptance Committee Management 4. Acceptance Process

5. Conclusion Chapter 5

Installation and Operation 1. Introduction

2. Objective

3. Construction Standard 4. Loading Guide

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5. Conclusion Chapter 6

Maintenance and Asset Management 1. Introduction

2. Transformer Load Monitoring (TLM) 3. Maintenance and Inspection

4. Conclusion

Figures

Figure 1: Expenses generated by transformer price and cost of electricity losses Figure 2: Calculation of the present value of no-load loss

Figure 3: Calculation of the present value of no-load loss in actual costs Figure 4: Calculation of the present value of load loss

Figure 5: Calculation of the present value of load loss in actual costs Figure 6: Evaluation formula analysis

Figure 7: Production Process Flow Figure 8: Silicon Steel Core Loss Curve

Figure 9: Test circuit & Apparatus Configuration for No-load Loss Measurement Figure 10: Test Circuit & Apparatus Configuration for Load Loss Measurement Figure 11: Punch List Form

Figure 12: List of approval drawings

Figure 13: Sample Drawing of Technical and Guaranteed Data Figure 14: Supplier’s routine test report

Figure 15: Acceptance routine test report

Figure 16: Penalty Calculation without raising the Guarantee Value Figure 17: Penalty Calculation with Raising the Guarantee Values

Figure 18: Construction drawing for transformer installation (single concrete pole) Figure 19: Bill of material for transformer installation (single concrete pole) Figure 20: Construction drawing for transformer installation (platform) Figure 21: Bill of material for transformer installation (platform) Figure 22: Transformer load monitoring (TLM) system configuration

Tables

Table 1: The low loss limitation of no-load & load loss for each transformer rating Table 2: Table of power efficiency for low losses transformer

Table 3: Example of standard loss transformers Table 4: Temperature condition of transformer

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Chapter 1 Preparation of National Normative Technical

Specification of Distribution Transformer

1. Introduction

This is the first normative specification for distribution transformers. It is prepared for the Lower Mekong Sub-region (LMS) utilities which are: Electricité du Cambodge (EDC) Cambodia, Electricité du Laos (EDL), Lao People’s Democratic Republic, Hanoi Power Company (HNPC), Ho Chi Minh City Power Company (HCMCPC) Vietnam, and the Metropolitan Electricity Authority (MEA), Thailand.

The specifications refer to the latest edition of international and national standards. Single-phase, three-phase and oil-immersed transformers are covered in the discussion. The scope also includes transformers with maximum voltages of 36 kV, off-circuit tap changing, frequency of 50 Hz and those of neutral solidly grounded at the distribution substation and as well as outdoor application.

2. Objective

The Primary goal is to help to reduce losses caused by the ineffective use of transformers, and minimize the need for new investment, through teaching the utilities' about loss reduction programs and minimizing negative environmental impact on our tomorrow.

The secondary goals are to: encourage greater energy efficiency in low loss energy consuming transformers, create new national standards, start cost effective savings programs in both utilities and customers, reduce losses from utility-owned transformers and minimize life cycle costs. In addition, this will provide not only more energy, but also decrease the investment cost of constructing new distribution substations, while meeting the customers demand.

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3. Principle Specification

Scope: This specification is created for power utility companies in LMS. Transformers shall be connected to the system with neutral solidly grounded at the distribution substations and fault level values in normal distribution status between 20kA and 25kA.

Site and Service Condition: LMS utilities operate in a tropical climate. The altitude ranges from 0 meters to 1,800 meters above sea level, ambient temperature ranges from 30°C to 45°C and relative humidity measures mostly 100%.

Reference Standard: International Electrotechnical Commission (IEC) is the common reference standard for all LMS utilities and a majority of countries around the world. For transformers, IEC 60076 series is the key reference. Some utilities also refer to their National standards which correspond to IEC except special requirements such as temperature, installation, etc.

Test, Inspection and Test Report: There will be two main test reports, specifically Type Test and Routine Test reports. Because the transformer is a very critical and expensive piece of equipment, the type test report is a key source of information for purchase assessment and decision.

Type Test contains data that validate factors such as design, raw material, workmanship and quality control during the manufacturing process are well within standard limits. The Routine Test certifies that all units pass limited values according to the reference standards before installation for service. The Utility reserves the right to send representatives to invigilate all required tests on the manufacturer’s site. Thus, sampling of the first batch of the transformers lies in the responsibility of the Utility’s representatives.

Drawings and Instructions: The supplier shall furnish six copies of all significant details of the transformer to the Utility for response in approval within a stipulated timeframe.

To protect mutual interest in cases of delayed or late submission, compensation terms shall be specified in the contract. Special installation instructions, characteristic curves, installation instructions and instruction manuals with the contract number marked thereon, in the metric system, shall be machine printed or typed and delivered prior to the first shipment.

Ratings and Features: The major characteristic of the transformer must be properly specified, such as suggested in the following:

Type Overhead, outdoor type, three phase, mineral-oil-filled

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Cooling method ONAN

kVA ratings To be specified during bid Temperature rise

(winding, Top oil) 60 degree (winding), 55 degree (oil) High-voltage rating 6 kV, 10 kV, 22 kV or 35 kV

Low-voltage rating 400 V

Tap ±2 x 2.5 % or +4x2.5%

Vector group Dyn11 or Dyn1 Insulation level

Voltage Rating 400V, 6kV, 10kV 15kV 22kV 35kV BIL Full Wave (kV

crest) N/A 50 70 125 170

Power Frequency

Test Voltage (kV) N/A 28 38 50 70

Impedance voltage

kVA Range from 50 to 3200

Nominal value Range from 4% to 7%

General Requirements

The transformer shall be self-cooled and/or designed with sealed-tank to ensure that forced cooling is not required. The transformer installation methods such as single concrete pole or platform concrete pole shall also be included. To protect the transformer from damage caused by lightning, it will be the most efficient and practical to install three lightning arresters on the transformer tank cover.

The lightning arrester shall be of the distribution class with a ground lead disconnector, gapless or gapped with metal oxide as main elements.

The gaskets shall be specified to withstand hot oil of extremely high temperatures and have a life span of more than 20 years.

One of the plans included to reduce system losses, is to up-rate the distribution voltage; the dual voltage switch type shall be required such as 12/24 kV,

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The kVA rating value should be visibly specified and easy to locate for field workers. The information regarding the centre of gravity (CG) of the transformer is essential for the installation and to improve safety for the field workers.

The concrete poles need to be designed to withstand the bending moment which is calculated by accounting for the weight of the transformer, associated equipment, cables, and wind speed. Hence, all transformers are recommended to have weight limits. Transformers installed in close proximity to public facilities such as hospitals, schools, etc shall also be designed to keep noise level within 58 to 68 decibels. Transformers installed near hospitals, schools and important places should also be designed to generate audible noise within the limit of 58 to 68 decibels. Tank and Cover

The material for fabricating the tank side walls and bottom shall be corrosion resistant. Rust-preventive finishing shall be strongly recommended for units with more than 20 years of service life. The paint coat shall depend on utilities’ requirement in preferred colours.

Core

It is necessary to mention the quality of the core material, such as high permeability silicon steel, because no-load loss is mainly caused by the core material. The core construction shall be firmly fixed in the tank and designed to avoid the occurrence of loosened core strips due to vibration from road traffic. Adequate cooling facilities shall also be provided at the oil ducts.

The magnetic circuit shall be grounded in accordance with practices mentioned in the specification. The different maximum flux density is designed to meet 1.55 to 1.65 Tesla to prevent harmonic behaviour.

Windings

The winding or coil shall be made of copper for better performance based on technical and economic comparisons. To cater to the physical characteristic, the winding shall be designed to withstand thermal and mechanical effects caused by external short circuits. The coil clamping arrangement and clamping rings shall be designed to withstand force due to short circuit. To cater to the electrical characteristic, the winding shall be designed and assembled to handle temperature increase specified in the tender specification. The insulation of winding and connections shall not be likely to soften, loose, shrink or collapse during service. Insulating Oil

As mineral oil is used as the insulation and cooling mechanism; it should be well filtered and tested to meet the dielectric strength (which is not less than 30kV) before filling in the transformer tank. The insulating oil dielectric taken from a new transformer shall not be less than 26 kV as tested by the method specified by ASTM D877.

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Bushings and Terminals

The requirements for bushings and terminals should be specified for different applications such as platform transformer or pole mounted transformer to facilitate installation, monitoring and maintenance. To maintain the current integrity throughout the equipment’s useful lifecycle, the connectors shall be made with solderless tin-plated copper; two belleville spring washer, coned-disk types shall be supplied to provide adequate pressure on the conductor during thermal-cycling. The size of the terminals or connectors, both high voltage and low voltage, shall be subjected to the transformer capacity. The bushing cover shall be made of ultra-violet radiation resistant and track resistant plastic or rubber to protect equipment from impairments caused by animals such as birds, squirrels and snakes, etc. Accessory Equipment

The transformers will be equipped with standard accessories, at least with lifting lugs, tap changer, manual pressure relief fitting, nameplate, tank grounding pad or stud, etc. Other accessories will be also specified depending on the size and application.

3.1. Transformer Evaluated Cost

Typically, the transformer price depends on core and winding loss i.e. high loss transformers have a lower cost, and the low loss transformer a higher one. Thus, Utilities work out an “evaluation formula” which takes into consideration many factors such as: transformer service life, load factor, operation and maintenance cost, interest rate and inflation rate, etc. Each utility should compute the cost estimate based on updated data. This shall eventually be used in the bid comparison for the evaluation of unit costs and losses. The following is an example of cost evaluation.

A = B + XC + YD

Where

A = Evaluated cost of transformer in any currency

B = Unit cost of transformer converted into US Dollars according to the evaluation clause specified in the bid condition

C = No-load loss at room temperature not more than 30°C in kW D = Load loss in kW

X = Constant value for No-load condition Y = Constant value for Loading condition

Excess Losses and Penalty

The excess loss and penalty will concentrate on transformer losses which are higher than guaranteed no-load and load losses including allowable tolerances stated in the reference standards. It will be divided into the following two cases:

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a. The individual transformer loss is higher than tolerance: Individual transformer with losses beyond the limits will be rejected unless the supplier agrees to increase the guaranteed value of average losses of all transformers, compensated at 1.5 times (arbitrary value) of the evaluation formula.

b. The total number of transformers: In the event that the supplier’s report shows that the no-load and load loss values conform to the guaranteed values within the tolerance limit, the utility shall conduct sampling on the transformers for their individual loss measurement (i.e. the number of transformers depends on utilities’ facility, but normally 5% of the contracted quantity or at least one unit for small quantity order).

If the average values of no-load loss and load losses are higher than average losses from the manufacturer test report by 2.5% (arbitrary value), the manufacturer measured value will be adjusted by the ratio of difference between both sets of measurements, and use the adjusted losses for the calculation of loss compensation. Otherwise the losses from the manufacturer’s report will be used.

Additional Requirements for Marking and Packing

Consideration shall be given to facilitate convenient clearing from the port customs. The transformers shall be shipped oil-ed with the serial number properly indicated in the invoice. All spare parts shall be delivered with the first shipment to ensure that spares are available in the event of need. . Equipment or instruments packed in the cartons shall be firmly attached on pallets for easy handling.

Additional Requirements for Responsibility

In the event of breakdown within the period of warranty, the manufacturer shall promptly investigate, repair or replace the unit. All replacement shall be made with 60 days from the first notice, or risk forfeiting equipment performance and security.

4. Electricité du Cambodge - Additional

Specification

This section discusses about the additional specifications specially collated for Electricité du Cambodge of Cambodia (EDC).

4.1. For Reliable Performance of the Transformer

EDC should consider adding technical information as follows:

a. Short circuit test reports that prove that the design, raw materials and workmanship of the manufactures are adequate, and that they possess a high level of quality control management.

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b. The lightning arresters should be specified to be installed on the transformer tank’s cover to effectively protect the transformer itself. The lightning arrester ground lead isolator operation test is required to be submitted with the quotation.

c. The transformers shall not produce audible noise exceeding the specified limits due to environmental disturbance, especially when installed near hospitals, temples and schools, etc.

4.2. For Loss Reduction:

It has been reported that the EDC’s total losses are approximately of 10% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. EDC plans to reduce the loss to 7% by the year 2012. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in EDC’s system.

It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, the EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation.

a. In the basic loss evaluation process, three transformer figures are: purchase price, no-load loss and load loss. For the purposes of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer’s cost according to the formula below: A = B +7,121C +2,939D

Where

A = Evaluated cost of transformer in US Dollars.

B = Unit cost of transformer converted into US Dollars according to the evaluation clause specified in the bid condition.

C = No-load loss at room temperature not more than 30°C in kW. b. No-load Loss: Typically, it is called core loss or iron loss. The no-load

loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not.

There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has since advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching.

Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited

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number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

c. Load Loss: When the load is connected, the transformer will supply the power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. The designer must keep in mind, however, how it will affect flux density and core losses.

Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component with a magnetizing

circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

4.3. Transformer Loss Reduction Benefits

Transformer losses are one of the main losses in the distribution system. However, more research is necessary to predict and design a typical model that takes into account items such as: the detailed loading patterns, types of transformer, operation, and loading guides. When achieved, this will aid in achieving: energy cost savings, greenhouse gas reduction, CO2 reduction and increased ability for emissions trading. Nowadays, the trend of both the

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manufacturers and the utilities is to try to meet high efficiency transformer performance while maximizing production capability and minimizing investment costs.

• Reduce total energy loss:

Eloss[kWh] = (P0 + Pk * I ² ) * 8,760

Where:

Eloss is total energy loss P0 is the no-load loss [kW]. Pk is the load loss [kW].

I is the rms-average load of the transformer. 8,760 is the number of hours in a year

• Increase power efficiency of a transformer: 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

• Increase life cycle cost

TCCloss = Eloss * C * (1 + r) ⁿ - 1/ r * (1 + r) ⁿ

Where:

TCCloss = Total Capitalized Cost of the losses C = the estimated average electricity cost per kWh r = the cost of capital

n = the life time of the transformer in years ELoss = Total energy loss

• Environmental and Health Costs

These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show a positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

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5. Electricité du Laos - Additional Specifications

This section discusses about the additional specifications specially collated for Electricité du Laos of Lao PDR (EDL).

5.1. For Reliable Performance of the Transformer:

EDL should consider adding technical information as follows:

• Short circuit test reports to prove that the design, raw material and workmanship of the manufactures are adequate experienced and represent high level of quality control management.

• The lightning arresters should be specified to be installed on the transformer tank’s cover to effectively protect the transformer itself. The lightning arrester ground lead isolator operation test is required to be submitted with the quotation.

• The transformers shall not produce audible noise exceeding the specified limits due to environment disturbance especially, when installed near hospitals, temples and schools, etc.

It has been reported that the EDL’s total losses are approximately 17.5% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. EDL plans to reduce the total system losses. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in EDL’s system.

It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation.

a. In the basic loss evaluation process, three transformer figures are: purchase price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer cost according to the formula below: A = B +5,000C +3,500D

Where

A = Evaluated cost of transformer in US Dollars.

B = Unit cost of transformer converted to US Dollars according to the evaluation clause specified in the bid condition.

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b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not.

There are two types of core losses: hysteresis loss and eddy current loss. The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

c. Load Loss: When the load is connected, the transformer will supply the power to that load and produce resistive losses in windings as well as eddy current losses in windings, structural steelwork and tank. These load losses increase proportionally to the square of the load current. To reduce the load losses, the designer may increase the cross section of the windings. He must keep in mind, however, how it will affect flux density and core losses.

Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy savings. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

d. Extra losses due to harmonics: Harmonics can be caused by the source and the loads. The transformer is a component of the magnetizing

circuit which is sensitive to the harmonic distortion when it is designed to perform near to the yield point of the steel characteristics. Some components of the transformer’s non-linear loads are: TV sets, computers, UPS systems, variable speed drives, inverters and other instruments which convert alternating current (AC) to direct current (DC) supply. Harmonics not only present an extra load loss, but also de-rate the transformer capacity and affect the transformers’ service life. To prevent this

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harmonic effect, the utility must set harmonic restrictions both voltage and current generated to the industries which are the major contributors to power distortion in the distribution system.

Transformer losses are one of the main losses in the distribution system. However, more research is necessary to predict and design a typical model that takes into account items such as: the detailed loading patterns, types of transformer, operation, and loading guides. When obtained, this will aid in achieving: energy cost savings, greenhouse gas reduction, CO2 reduction and increased ability for emissions trading. Nowadays, the trend of both the manufacturers and the utilities is to try to meet high efficiency transformer performance while maximizing production capability and minimizing investment costs.

Eloss[kWh] = (P0 + Pk * I ² ) * 8,760

Where:

I is the rms-average load of the transformer 8,760 is the number of hours in a year

• Increase power efficiency of a transformer: EP = Load power/ [Load power + Power loss] = PL / [PL + PC + PW]

Where:

TCCloss = Total Capitalized Cost of the losses C = the estimated average cost per kWh r = the cost of capital

These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2,

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the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

6. Ho Chi Minh City Power Company - Additional

Specification

This section discusses about the additional specifications specially collated for Ho Chi Minh City Power Company (HCMCPC).

6.1. For Reliable Performance of the Transformer

HCMC PC should consider adding the following technical information: • Short circuit test reports to prove that the design, raw material and

workmanship of the manufactures are adequate and represent a high level of quality control management.

• The transformers shall not produce audible noise exceeding the specified limits due to environment disturbance especially, when installed near hospitals, temples and schools, etc.

It has been reported that the HCMC PC’s total losses are approximately 7.07% of those in 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. HCMCPC plans to reduce the total system losses. One of the programs suggested in this Handbook is to acquire and/or increase the use of low loss transformers in HCMC PC’s system.

It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, EDC will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation.

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purchase price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to obtain the evaluated transformer cost according to the formula below:

A = B +4,080C +2,220D

Where

B = Unit cost of transformer converted in US Dollars according to the evaluation clause specified in the bid condition.

C = No-load loss at room temperature not more than 30°C in kW.

b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss.

The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%.

Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to

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a number of technical obstacles and high construction cost.

Transformer losses are one of the main losses in the distribution system. However, more cases or research to predict and design a typical model taking into account the detailed loading patterns, types of transformer, operation, and loading guides are needed. This will result in energy cost savings, greenhouse gas reduction, CO2 reduction and emission trading. Nowadays, the trend of both the manufacturer and the utility is to try to meet high efficiency transformer performance while maximizing production capability and the minimizing the investment cost.

Eloss[kWh] = (P0 + Pk * I ² ) * 8,760

Where:

• Increase power efficiency of a transformer EP = Load power/ [Load power + Power loss] = PL / [PL + PC + PW]

Where:

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These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

7. Hanoi Power Company - Additional

Specification

This section discusses the additional specifications specially collated for Hanoi Power Company, Vietnam (HNPC).

7.1. For reliable performance of the transformer:

HNPC should consider adding technical information as follows:

• Short circuit test reports to prove that the design, raw materials and workmanship of the manufactures are adequate and they have a high level of quality control management.

• The transformers shall not produce audible noise exceeding the specified limits due to environmental disturbance, especially when installed near hospitals, temples and schools, etc.

It has been reported that the HNPC’s total losses are approximately of 8.85% of those in the year 2007. The utility has begun many activities to aid in reducing losses, including hosting conferences which invited papers and research from different experienced utilities. HNPC plans to reduce the loss to 7% by the year 2012. One of the programs suggested in this Handbook is to

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acquire and/or increase the use of low loss transformers in HNPC’s s system. It is better to start by using an evaluation formula for a specific time period, for example 5 years. After this period, the HNPC’s will have learned about the advanced transformer technology efficiency improvement by compiling records of the best values of no-load loss and load loss for each rating and applying it to the guaranteed low loss transformer table, included in the transformer specification for implementation

a. In the basic loss evaluation process, three transformer figures are purchase price, no-load loss and load loss. For the purpose of bid comparison, the transformer unit cost and losses shall be evaluated to get the transformer evaluated cost according to the formula below:

A = B +6,300C +1,300D

Where

B = Unit cost of transformer converted in US Dollars according to the evaluation clause specified in the bid condition.

C = No-load loss at room temperature not more than 30°C in kW.

b. No-load Loss: Typically, it is called core loss or iron loss. The no-load loss is a constant value varying for each designed transformer rating and is present no matter if the load is connected or not. There are two types of core losses: hysteresis loss and eddy current loss.

The core material development progressed from hot-rolled steel to the cold-rolled grain oriented silicon steels (CGO) to reduce the core losses. It has advanced to the new technology of high permeability grain oriented steel (HiB) that controls the domains of the iron crystals by laser etching. Finally, another technology of amorphous iron has been gradually applied in some countries. Its deployment is limited because of the limited number of manufacturers and sophisticated production lines which need highly skilled workers and non-typical instruments. Nowadays, the low loss transformers are more often used in the capital or large cities in order to reduce the total system losses and to avoid construction of new substations in expensive locations in attractive city centres. HiB grain oriented steels together with experienced design, advanced core cutting and slitting machine, high skilled fabrication and assembly, may exhibit transformer efficiencies of up to 99.7%

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Most of the transformer windings will be made of copper due to its high conductivity and subsequent effect on energy efficiency, size reduction and energy saving. The technology of the copper windings is remarkably developed to withstand the short circuit strength, to prolong the service life and safety by using copper foil instead of windings which can also reduce eddy current loss from non-linear loads. There is another solution to improve the load loss reduction by upgrading the copper windings to super-conducting windings, but unfortunately, this new technology of super-conducting transformers is not ready for market deployment due to a number of technical obstacles and high construction cost.

Transformer losses are one of the main losses in the distribution system. However, more cases or research to predict and design a typical model taking into account the detailed loading patterns, types of transformer, operation, and loading guides are needed. This will result in energy cost savings, greenhouse gas reduction, CO2 reduction and emission trading. Nowadays, the trend of both the manufacturer and the utility is to try to meet high efficiency transformer performance while maximizing production capability and the minimizing the investment cost.

Eloss[kWh] = (P0 + Pk * I ² ) * 8,760

Where:

• Increase power efficiency of a transformer: EP = Load power/ [Load power + Power loss]

= PL / [PL + PC + PW]

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Where:

These environmental and health costs originate from the various types of emissions resulting from the combustion of fossil fuels. Apart from CO2, the main offenders are SO2 and NOx which contribute to the acidification of the environment. According to the Kyoto Protocol, the use of low loss energy transformers can show positive effect on carbon credits and can balance the global warming effect. This will support the country’s policy of the installation of more clean energy systems such as solar energy, wind turbines, energy from waste energy, etc.

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8. References

• Energy saving in industrial distribution transformers transformer losses, May 2002, W.T.J. Hulshorst and J.F. Groeman (KEMA) • The Potential for Global Energy Savings from High Efficiency

Distribution Transformers, February, 2005, (Roman Targosz, editor ; Main authors and reviewers: Ronnie Belmans, Jan Declercq, Hans de Keulenaer, Katsuaki Furuya, Mayur Karmarkar, Manuel Martinez, Mike McDermott, Ivo Pinkiewicz)

• Technical Report, Distribution Transformers : Proposal to Increase MEPS Levels, October 2007, T R Blackburn

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Chapter 2 Bidding Evaluation

1. Introduction

This chapter is to guide and assist the utility to learn about the solution, and from what criteria it is derived. Only distribution transformers will be discussed in this handbook. Therefore, there will three factors: purchase price of the transformer, load losses and no-load losses which shall be considered.

The lowest evaluated cost including losses will be the criteria utilized to choose the initial proposal that the utility will study before making a contract. It will affect the utility investment cost, paying a little more for low loss transformers, but in return it can save more money than the cumulated value of losses during transformer operation. The penalty values should be specified as well in the bid documents.

2. Objective

The trade off between the transformer’s price and the losses of the transformer is simplified in the tender specification. It is accomplished by adding the evaluation formula where the purchase cost minus the loss, which reflects the utilities’ true investment cost.

The manufacturers should offer their best design capability and highest quality of raw materials and workmanship in order to convince the utilities to invest in energy efficient transformers.

3. Formula Analysis

There are many factors to be taken into account in the evaluation formula which are: no-load loss, load loss, interest rate, inflation rate, electricity unit cost, operation & maintenance cost and transformer service life. All these values differ due to fluctuations in the economy and government policies which each utility operates in.

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3.1. Interest Rate

Interest rates are an important part of a loan; they help determine its total cost. Each utility has to apply for a loan in both local and foreign countries. It is typical that the local loan will be less advantageous in terms of interest rate, grace period and repayment terms than a foreign one. It is recommended that one ask for all of this information, from the Finance Department or the Department which responds to the loan application.

3.2. Inflation Rate

The purpose of this factor is to show the effect of the inflation rate on the real value of the money. In fact, a substantial increase in the price of transformers is related to an increase in the inflation rate which means a decrease in the value of money. As inflation rate increases, the price of goods increases. As with the interest rate analysis, the finance department will analyze and provide the real figures. These figures will differ from country to country.

3.3. Electricity Price Purchased

Some countries have divided the generation utility and distribution utility; in this case it is common for distribution utility to get the average electricity unit purchased from the generation utility. But some countries have an organization who owns both power generation and distribution. In this case, the electricity unit purchase will be calculated on the basis of the investment cost of electricity unit production at the point of the terminal station where electricity is sold to customers.

3.4. Operation and Maintenance (O&M) Expenses in Distribution System

This cost (USD/kW/Year) must be calculated from the accumulated actual expenses as follows:

- Transformer and distribution cost - Customs accounting and collections cost - Administrative and general costs - Depreciation cost

As shown, this figure is obtained and calculated from information from many disparate groups and/or different departments, the more realistic the expenses, the more accurate the operating & maintenance costs.

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This is understood as the average service life of the transformer in number of years. Some transformers may still be in service after 25 years, while others may only reach the age of 15. After discussions with reputable transformer manufacturers, all confirm that the recommend service life of the transformers is typically to be 20 years for regular loading according to the international standards.

The evaluation formula analysis starts from the no-load loss calculation. Once the transformer is energized, the utility has to pay both the transformer cost and the cost of electricity losses or energy losses consists of no-load loss (core loss) and load loss (winding loss) throughout the life of the transformer as shown in Figure 1.

Price of Transformer

Cost of Electricity Losses

Year 0 Year 1 Year 2 Year 3 Year 4 Year N

Figure 1: Expenses generated by transformer price and cost of electricity losses a. Criteria for calculation of no-load loss used in this case

• Distribution transformer life = 20 years • Interest rate = 6.26%

• Inflation rate = 1.56%

• Electricity unit purchased = 0.0597 $/kWh

• O&M expenses in distribution system = 29.29 $/kW/Year

The cost of no-load loss will be generated by the transformer core which means that once the transformer is energized, this loss is present throughout the transformers life and calculated back to present value as shown in Figure 2.

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Cost of No-Load Losses

Year 1 Year 2 Year 3 Year 4 Year N

Year 0

Computation of Present Value

Figure 2: Calculation of the present value of no-load loss

The result is calculated from the values of criteria as shown in clause a., using the formula of present value and is shown in Figure 3.

No-load expenses = (0.0597 x 8,760) + 29.29 = 552.3 $/kW/Year Present Value calculation result

= 552.3 (1-(1.0156/1.0626)20)(1.0156) / (1+0.0626) (1-(1.0156/1.0626))

= 7,109.29 $/kW (see Figure 3)

$552.30/kW/year

Year 0

Computation of Present Value $7,109.29/kW

Figure 3: Calculation of the present value of no-load loss in actual costs b. Criteria for calculation of load loss used in this case.

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• Interest rate = 6.26% • Inflation rate = 1.56%

• Electricity unit purchased = 0.0597 $/kWh

• O&M expenses in distribution system = 29.29 $/kW/Year • Loss factor 0.3803 (see more detailed below)

Loss factor = 0.84(Load factor)2 + 0.16(Load factor) = 0.84(0.5843)2 + 0.16(0.5843)

= 0.3803

Remark: Load factor (distribution system) = 0.5843 (Formula from REA Bulletin 160-1)

The cost of load loss will reflect resistive losses in the windings and leads, and losses generated by eddy currents in the windings, the structural steelwork, and the tank, throughout the transformer life and calculated back to present value as shown in Figure 4.

Cost of Load Losses

Year 0

Computation of Present Value

Figure 4: Calculation of the present value of load loss

The result is calculated from the values of criteria as shown in clause b., using the formula of present value and is shown in Figure 5.

Load loss expenses = (0.0597 x 8,760 x 0.3803) + 29.29 = 228.18 $/kW/Year

Present value of Load loss expense = 2,936.95 $/kW (20 years) (see Figure 5)

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$228.18/kW/year

Year 0

Computation of Present Value $2,936.95/kW

Figure 5: Calculation of the present value of load loss in actual costs

A = B + 7,109C + 2,936D (see Figure 6)

Where

A = Evaluated cost in USD B = Transformer price in USD C = No-load loss of transformer in kW D = Load loss of transformer in kW

The evaluation formula analysis is shown in Figure 6 consisting of the components: the price of transformer, the no-load loss and the load loss at the present values calculated for the entire 20 year service life of transformer.

Price of Transformer ($)

Year 0 Year 1 Year 2

2,936D 7,109C

Figure 6: Evaluation formula analysis

4. How to Evaluate The Best Choice

Often, engineers are asked to choose the best transformer with a suitable price (as low as possible). Best choice means utilizing many factors from which to decide upon the best transformer for the money. As discussed, engineers will not only analyze the price or cost of the transformer, but will also consider quality which

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leads to loss issues as well. In this case that typically means total losses of the transformer. Of course, its characteristics must conform to the reference standards. The following example will show the Least Cost Analysis for the two transformers having ratings of 24 kV 3-phase 500 kVA capacity and conform to the same reference standards or specification, but the transformer price, no load loss and load loss are different as shown below.

After applying the evaluation formula A = B + 7,109C + 2,936D, it can be seen that in this case, the transformer with the price of UDS 24,533.- will be selected because its evaluated cost is cheaper which means it will return more profit in the future within 20 years. In fact, it can be less than 20 years if there is an increase in the cost of raw materials, workmanship, interest rates and/or cost of living. The benefit will be realized earlier than shown in the formula.

Transformer X [Low Loss] Transformer Y [Standard Loss] kVA 500 500 Price($) 24,533 15,758 No load(kW) 0.67 0.97 Load loss(kW) 3.030 5.500 Evaluated cost($) 38,192 38,801 Preferred Selection

5. Excess Losses and Penalty

Transformers will always have losses. It cannot be avoided. The amount of the loss depends on the quality of workmanship of each crew and the factory’s experience. Therefore, international standards limit the tolerances which the utilities will refer to in accepting a transformer. The process to deal with the acceptance of the transformers which are in excess of the guaranteed values will be explained, including a discussion of the penalty clause which has been used for over twenty years.

After the supplier delivers the transformers to the utility together with the routine test report, all units of the transformers technical information will be reported, according to the contract. The testing values of no-load loss and load loss will be calculated and declared for each unit with its separate serial number. The acceptance process is explained as follows:

a. Limits of tolerance:-

No-load loss: not more than +10%

No-load loss + Load loss: not more than +6%

b. The individual transformer having losses beyond the limits of tolerance will be rejected immediately

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c. If average losses of all transformers of the same kVA rating exceeds the guaranteed value but remains within the limits of tolerance, the penalty will be:

No-load loss at USD 10,697 / kW x N. Load loss at USD 4,424 / kW x N. Where N = Number of transformers.

In the event of negotiation and/or dispute over loss tolerance, the maximum value of the transformer shall be used to compute tolerance limits relating to higher guaranteed values. In this case, the supplier shall bear all penalties rightful of total purchase made.

6. The Low Loss Limitation Table

Some utilities have applied the evaluation formula for more than 20 years. Finally, the low loss values of the transformer will be reached to maximize profits to the utility. These low loss values will be adjusted and arranged in the table for each rating. The transformers losses in the table are the lowest losses that most of the reputable manufacturers can design and keep to meet the contract values which all transformers shall not exceed.

Transformer Rating Transformer Loss (Watt)

(kVA) No Load Loss Load Loss

15 70 160 45 160 360 75 220 580 112.5 255 840 150 300 1,000 225 420 1,530 300 480 1,860 500 670 3,030 750 840 4,370 1,000 1,000 6,400 1,500 1,200 10,000

Table 1: The low loss limitation of no-load & load loss for each transformer rating

• All transformer losses shall be within the limits without any tolerance. For each transformer rating, and each lot of shipment, the utility will sample the transformers for their own loss measurement purposes, at quantity specified by the contract. The transformers will be accepted if the measured losses for the sample are within the limits.