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6.1.
Background
93
authorised NAEEEC to develop and publish plans for MEPS for any industrial or
commercial equipment identified as a significant contributor to the growth in energy
demand or greenhouse gas emissions. These plans represent a transparent way for
government agencies to explore community and stakeholder support (for both mandatory
and voluntary measures) to reduce greenhouse gas emissions produced by these types of
equipment (NAEEP, 2001a). The MEPS development process includes feasibility
assessment (technical, economic cost-benefit analyses and available supervisory measures)
and wide public consultations before any final decision is made.
Distribution Transformers are being considered for MEPS due to the following:
there is a large number of distribution transformers and due to the fact that
almost all power generated in Australia passes through distribution transformers
means even small improvements in transformer efficiency can result in
significant savings of energy and in greenhouse gases reduction;
electricity distribution transformers have a very long life (estimates range from
average of 25 years to as much as 50 years for lightly loaded distribution
transformers);
the cost of transmission and distribution losses are passed on to consumers and
the electricity utilities who are responsible for purchasing most of the
transformers are not motivated to invest in more efficient distribution
transformers;
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mandating MEPS within relevant state and territory legislation commencing in July
2003 that match the relevant Canadian standards for distribution transformers
(CAN/CSA-C802.1 and CAN/CSA-C802.2, 2001);
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6.2.
96
A variation of this approach is used in this research, as this method has a number of
advantages over the statistical approach and its variants GWA (2002):
there is no need to consider the number of existing models which meet the criteria
found to be most cost-effective. This is not important provided the industry has a
capacity to produce complying models within a specified time, without
unacceptable adjustment costs (which are separately analysed);
the approach is less sensitive to time and place, since it concentrates on product
design and manufacture rather than market structure. However, it is still market
dependent to the extent that the baseline models selected for analysis are typical
of the market in question.
It should be noted, however, that this engineering method is time-consuming, resourceintensive and data-intensive and requires access to proprietary design information from
manufacturers and/or detailed knowledge of design and manufacturing principles).
Development of Australian MEPS levels for distribution transformers is based on global
Australian strategy for development of MEPS, which is endorsed by ANZMEC in 1999.
This strategy relies heavily on MEPS methodologies developed in other markets (based on
engineering and/or statistical approaches). This strategy is outlined in National Appliance
and Equipment Energy Efficiency Program: Future Directions 2002-04 NAEEEP
(2001):
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In 1999 ANZMEC agreed that Australia would match the best MEPS levels of our
trading partners after taking account of test method differences and other differences (eg
climate, marketing and consumer preference variations). This new policy represented a
radical change of direction from the previous Australian practice of debating the technical
possibilities of MEPS levels with all stakeholders. The new policy covered any product
regulated by mandatory labelling or MEPS programs in other developed countries.
In summary, this strategy defines the following steps in considering new MEPS, or
revisions to existing MEPS, for any given product GWA (2002):
establish what MEPS levels, if any, apply in the countries with which there is
significant Australian trade;
take account of test method differences and other differences (eg climate,
marketing and consumer preference variations), and adjust MEPS levels
accordingly;
subject the adjusted MEPS levels to cost-benefit, greenhouse reduction and other
appropriate analyses (working with key stakeholder representatives);
if the adjusted MEPS levels pass the appropriate tests, adopt them.
It should be noted, however, that ANZMEC approach does not limit application of
MEPS only to products, which were assessed in the other markets and it does not exclude
application of cost-effectiveness criteria GWA (2002).
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6.3.
The Council of Australian Governments (COAG) requires that the proposal such as
MEPS for distribution transformers must be subject to a Regulatory Impact Statement
(RIS). The RIS estimates the benefits, costs and other impacts of the proposal. It also
assesses the likelihood of the proposal meeting its major objectives: The purpose of
preparing a Regulatory Impact Statement is to draw conclusions on whether regulation is
necessary, and if so, on what would be the most efficient regulatory approach. Completion
of a RIS should ensure that new or amended regulatory proposals are subject to proper
analysis and scrutiny as to their necessity, efficiency and net impact on community welfare.
Governments should then be able to make well-based decisions. The process emphasises
the importance of identifying the effects on groups who will be affected by changes in the
regulatory environment, and consideration of alternatives to the proposed regulation.
Impact assessment is a two step process: first, identifying the need for regulation; and
second, quantifying the potential benefits and costs of different methods of regulation. In
demonstrating the need for the regulation, the RIS should show that an economic or social
problem exists, define an objective for regulatory intervention, and show that alternative
mechanisms for achieving the stated objective are not practicable or more efficient
COAG (1997).
The RIS for MEPS for distribution transformers GWA (2002) has considered the
following options:
the proposed regulation (mandatory MEPS) which adopts all the requirements
contained in Draft Australia Standard 2374;
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an alternative regulation which only adopts those parts of the Standard that are
essential to satisfy regulatory energy objectives (targeted regulatory MEPS);
100
Since Australian manufacturers can supply a wide range of high efficiency transformers,
MEPS should not unjustifiably disadvantage any single supplier. The MEPS itself is not a
trade barrier. There is, however, a capital cost premium for efficiency in transformers
reflecting increased material costs and, in some cases, handling costs. For example,
industry claim that the approximate cost difference between the low loss transformers
and the industrial range is in the region of 10 - 20%.
Without regulation, the increasing pressure on purchasers to reduce capital costs is likely
to result in a growth of inefficient transformers sold on a first-cost basis by importers.
This would have ramifications for Australian manufacturers as well as broader economic
and greenhouse impacts GWA (2002).
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The benefits from the MEPS for distribution transformers are calculated as the Net
Present Value (NPV) at 10% discount rate of the projected reduction in electricity losses.
Greenhouse gas emission savings have not been valued.
The cost arising from MEPS for distribution transformers is the NPV of the projected
increase in the price of transformers due to increased efficiency. The RIS states that
introduction of MEPS would not introduce any additional program costs, since
transformer energy efficiency testing is already common and the administrative
infrastructure for MEPS already exists GWA (2002).
In addition, the RIS concludes that the benefit/cost ratios range from 1.0 to 1.2 for
utility-owned transformers, where the value of losses is related to the wholesale price of
energy, and 3.3 to 4.0 for privately owned transformers, which face much higher marginal
electricity prices and for which the value of electricity saved is consequently higher. The
projections represent a price/efficiency ratio of 0.5. For private transformers, MEPS
remain cost effective up to ratios of 1.8, GWA (2002).
supplier and trade issues - distribution transformers are manufactured and freely
traded in all developed countries in the Asia Pacific region. Introduction of MEPS
levels is not likely to significantly change the number of suppliers, nor the price
competition between them;
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failure in the private 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 transformers to users would be lower
than otherwise;
product quality - MEPS are not expected to have any negative effect on product
quality or function. Actually, increase in transformer efficiency should lead to
lower heat gain in operation, and hence lower failure rates and higher overall
network reliability;
worlds best practice - Canada and Mexico have MEPS for transformers, and the
European Union and the USA are considering implementing them. The proposed
MEPS levels are based on and equivalent to, the most stringent currently in place
(those for Canada, which took effect in January 2002) and so are consistent with
the principle adopted by ANZMEC - matching but not exceeding the most
stringent MEPS levels in force elsewhere. The proposed criteria for designating
transformers as high efficiency are roughly equivalent to the MEPS levels under
consideration for the EU and the USA, and as such are an indicator of the likely
direction of worlds best practice.
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6.4.
From 1 October 2004, most distribution transformers rated between 10 and 2,500 kVA
that are designed for 11 and 22 kV networks are required to meet minimum energy
performance standards (MEPS) in order to be sold in Australia. Mandatory energy
performance levels are contained in the Australian Standard AS2374.1.2:2003 Power
Transformers - Minimum Energy Performance Standard (MEPS) Requirements For
Distribution Transformers, and apply to single and three phase, dry type and oil immersed
transformers. After 1 October 2004, distribution transformers that meet more stringent
performance levels than MEPS (also specified in AS2374.1.2) are allowed to be promoted
as High Efficiency Power Transformers. Appendix 2 provides more details about the
Australian Standard AS2374.1.2 and lists special distribution transformers, which are not
subject to MEPS. The values for MEPS are given in Appendix 3. These MEPS are
expressed as efficiency levels at 50% of nominal load. The test methods which should be
used to determine compliance with MEPS for distribution transformers are defined in
AS2374.1-1997 Power Transformers and AS2735-1984 Dry Type Power Transformers.
Distribution transformers, as regulated products, offered for sale after 1 October 2004
must be registered with a State regulator. The distribution transformers, which were
registered with Australian Greenhouse Office (Energy Efficiency) by January 2005, are
presented in Appendix 1.
The Australian program and regulation for energy efficiency in distribution transformers is
being followed by New Zealand regulators.
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The RIS concluded that the mandatory MEPS option is likely to be effective in meeting
its stated objectives:
the mandatory MEPS option can deliver a better rate of improvement for energy
efficiency of transformers in Australia than market forces. MEPS can
demonstrably improve the energy efficiency of appliances and equipment,
particularly where the purchaser is able to pass on inefficient running costs to
third parties;
the projected monetary benefits of the mandatory MEPS option appear to exceed
the projected costs by a ratio of about 1.4 to 1, without assigning monetary value
to the reductions in CO2 emissions that are likely to occur (possibly as high as
870,000 tones CO2-e per annum by 2010);
6.5.
105
case studies, however, the findings are also relevant for distribution transformers MEPS.
The report also suggests improvements for the approach taken in Australia
The MEPS in Australia and USA are subject to distinctive and specific constraints as the
overall purposes of the programs are different:
Australia adopts the MEPS already in place elsewhere (i.e. Canadian Standards for
distribution transformers);
The approaches to determining the relationship of price to energy efficiency also differ:
106
similar (more details about these two methods are given in Chapter 5):
Australia uses average values, and this method could be improved if more data
were available.
the US approach uses statistical surveys that permit a more detailed analysis, based
on full distributions (rather than average values).
The methods for the national cost - benefits analyses methods are very similar, however
the methods would benefit by introduction of additional sensitivity analyses.
In addition, consideration should be given to lower discount rates, which could lead to
more stringent MEPS in some cases.
The technology and market assessments are similar and no changes are recommended for
either approach.
Both the Australian and the US analyses impacts on industry, competition, and trade are
quite detailed and the report does not recommend any changes.
In conclusion, Australias analysis approach could be expected to have less analytical
detail and still result in MEPS levels that are appropriate for their policy and market
context. In practice, the analysis required to meet these different objectives is quite similar.
To date, Australias cost-benefit analysis has served the goals and philosophies of the
program well and been highly effective in successfully identifying MEPS that are
significantly reducing greenhouse gas emissions while providing economic benefits to
consumers. In some cases, however, the experience of the USA - using more extensive
data sets and more detailed analysis - suggests possible improvements to Australias costbenefit analysis.
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It seems that recommended changes would increase the depth of analysis, require
additional data collection and analysis, and incur associated costs and time. The
recommended changes are likely to have incremental rather than dramatic impacts on the
substance and implications of the analysis as currently conducted McMahon (2004).
6.6.
LE (2005) analyses main barriers (and recommends possible remedial measures) for
electrical utilities investments into high efficiency equipment in a liberalized electricity
market:
discourages
companies
from
making
investments
for
efficiency
improvements, since cost reduction from the investment are shared with the
consumers. It would be advisable to allow some carryover of measurable
efficiency gains, so that investing in energy efficiency becomes more attractive for
the network companies;
the regulatory framework tends to concentrate on cost savings in the short term.
Such an approach does not encourage companies to take the life cycle costs of
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equipment into account. There should be incentive for network operators to take
LCC into account;
energy losses are calculated without consideration of external costs. The true cost
of network losses should be taken into account.
The following summary of efficiency standards and status of MEPS programs and
activities in different countries to address the tendency of both utilities and non-utilities to
purchase distribution transformers of lower efficiency than is cost-effective from a
lifecycle perspective is compiled from Ellis (2001) and LE (2005).
6.6.2. China
The mandatory minimum efficiency standards for power transformers (the S9 standard)
were introduced in 1999. This standard, approved by the State Bureau of Quality and
Technology Supervision, covers both distribution and power transformers. It limits the
maximum load losses and no-load losses for oil immersed types ranging from 30 to 31,500
kVA as well as for dry types in the range from 30to 10,000 kVA. Introduction of the S9
standard has significantly improved efficiency of power transformers in this market.
6.6.3. Europe
Distribution transformers in the European Union are covered by: world-wide standards
(e.g. ISO, IEC), European standards and regulations (e.g. EN, Harmonization
Documents) and various national standards (e.g. BSI, DIN, UNE, OTEL, etc).
CELEC has defined efficiency standards for three phase distribution transformers in the
range from 50 to 2,500 kVA, 50Hz and up to 36 kV. The standard HD428 defines three
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categories for load losses (C, A and B - value of losses in ascending order) and no-load
losses (C, B and A - value of losses in ascending order). A similar standard (HD538)
stipulates the load losses and no-load losses of dry type transformers. Distribution
transformers built to HD428 and HD538 have a limited number of preferred values for
rated power (50, 100, 160, 250, 400, 630, 1,000, 1,600 and 2,500 kVA), however, the
intermediate values are also allowed. A separate HD is under consideration for polemounted transformers. Loss values for transformers are usually declared as maximum
values with a specified tolerance. Higher losses may incur a financial compensation for
exceeding the loss limit and the losses lower than the guaranteed may be subject to a
bonus awarded to the manufacturer (this would normally apply for larger transformers).
HD428 therefore allows customers to choose between three levels of no-load losses and
three levels of load losses. In principle, there are 9 possible combinations, ranging from
the lowest efficiency, (BA) to the highest, (CC). These efficiency ranges are extremely
wide. The minimum efficiency in the highest category (CC) is still far below the efficiency
of the best in class and far below the 5-star transformer defined by the Indian standards.
CENELEC is currently defining new efficiency categories with lower losses. In 1999, a
Thermie project of the European Union assessed the total energy losses in distribution
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6.6.4. Taiwan
Since 1992, an eco-label program called GreenMark has been run by the Environmental
Protection Administration (EPA) and currently covers over 50 products. For
conforming products, the GreenMark logo label may be used on product packaging,
brochures or on the products themselves. It is intended that distribution transformers
will be covered by this program although the energy performance criteria have not yet
been determined Ellis (2001).
6.6.5. India
In India, the Bureau of Energy Efficiency (BEE) has developed a 5-star classification
scheme for distribution transformers in the range from 25 to 200 kVA. The scheme is a
co-operative venture between public and private organizations that issues rules and
recommendations under the statutory powers vested with it.
The 5-star program stipulates a lower and a higher limit for the total losses in
transformers, at 50% load. The scheme recommends replacing transformers with higher
star rated units. The 5-star unit represents world-class technology, while 3-star is
recommended as a minimum, and already followed by many utilities. India historically
has a rather poor performance in transformer energy efficiency, but this 5-star program
could become an important driver for change LE (2005).
6.6.6. Japan
In Japan, transformers are a part of the Toprunner Program, which either defines the
efficiency for various categories of a product type, or uses a formula to calculate
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6.6.7. Mexico
As in Australia, the Mexican standard includes voluntary and mandatory elements. The
Mexican standard, NOM-002-SEDE-1999 defines minimum energy performance
standards and maximum load losses and no-load losses for transformers in the range from
5 to 500 kVA. The standard also defines the compulsory test procedure for determining
efficiency performance. The efficiency levels are less stringent than those proposed for
Canada and the US. The regulation makes allowances for smaller manufacturers, who
may appeal for an exception during transitionary period before meeting the
requirements.
6.6.8. USA
The energy savings potential in the USA from switching to high efficient transformers
is high. In 1997, the National Laboratory of Oak Ridge estimated it to be 141 TWh.
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Utilities purchase over 1 million new units each year, and it is estimated that if the average
efficiency of utility transformers was improved by one-tenth of one percent, greenhouse
emissions reductions of 1,800,000 tones CO2-e per annum would be achieved over a 30
year period. The US has currently has a number of voluntary initiatives designed to
increase the efficiency of distribution transformers USEPA (1998b).
minimum efficiency for dry and oil-filled type transformers in the range from 10
to 2,500 kVA and it is likely to become the mandatory minimum efficiency level
in the near future;
the third program in the US, set up by the Consortium for Energy Efficiency
(CEE), aims to increase the awareness of the potential of efficient transformers
in industry. It consists of a campaign to measure the efficiency of industrial
transformers and to stimulate year period. As a result, in the Energy Star
transformer program, participating utilities agree to perform an analysis of total
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6.6.9. Canada
In Canada the Office of Energy Efficiency (OEE) of Natural Resources Canada (NRCan) has amended Canadas Energy Efficiency Regulations (the Regulations) to require
Canadian dealers to comply with minimum energy performance standards for dry-type
transformers imported or shipped across state borders for sale or lease in Canada.
The standards are harmonized with NEMA TP-1 and TP-2 standards. Amendment 6 to
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Canadas Energy Efficiency Regulations was published in 2003. The regulation of drytype transformers is included in this amendment with a completion date of January 1,
2005. This requires all dry-type transformers manufactured after this date to meet the
minimum energy performance standards.
As far as oil transformers are concerned Canada has conducted analysis of MEPS
implementation potential and found that the great majority of Canadian oil distribution
transformers already comply with NEMA TP-1 so the standard would almost have no
influence on the market. The yearly MEPS standard impact would only be 0.98 GWh for
liquid filled transformers compared to saving potential at 132 GWh expected for drytype transformers. Also EnergyStar products are very actively promoted in Canada LE
(2005).
6.7.
It should be highlighted that under the incentive of the National Greenhouse Strategy
(NGS) and due to the strong support from all of the parties involved, the establishment of
the MEPS for Australian distribution transformers passed relatively smoothly. However,
there were some issues of concern which are listed below:
the MEPS development processes are relatively long and once the performance
levels are established (in a consultative environment) it will be very difficult to
review and change them. Carrying out a new consultation process requires
significant resources. Because of that, minimum efficiency standards are rarely
adjusted to the economics of the market or to new technology developments. This
inflexibility of MEPS regulation should be taken into account through
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there have been some arguments EEA (2003) that singling out of one small part
of a networks total asset base for an alternative regulatory energy performance
standard seems inconsistent and of very limited value given the level of savings
that could be achieved. According to EEA (2003) the electrical utilities take into
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discussions with some of key utilities in New Zealand indicate that the industry
already has higher efficiency levels for distribution transformers (through voluntary
self-regulation) than those proposed by the MEPS and to mandate a lesser
standard than what is being used would be a retrograde step;
the reports used as a basis for development of MEPS for distribution transformers
in Australia do not discuss rigorously data about the efficiency of the pre-MEPS
models. It seems that for a large part of distribution transformer population the
improvement in efficiency is measured in points of a percent. As the whole
concept is based on 50% loading (and not the actual load, which the distribution
transformer will experience), it is suggested that a substantial expansion of this
work would be required to rigorously demonstrate that the MEPS standard would
be appropriate EEA (2003);
the MEPS alternatives (presented in GWA (2002) and LE (2005)) include labelling
and voluntary schemes. Labelling is an effective way of bringing transparency to
the market. A clear definition of efficiency, a transparent measurement procedure
and a labelling system should be the start of every mandatory or voluntary
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it seems that the Australian market is generally comfortable with MEPS levels,
however, there were strong views (expressed during the consultation process) that
the method of calculating Australian MEPS was somewhat deficient. In particular,
strong reliance on Canadian MEPS and simple increase of Canadian MEPS to take
account of the different system frequency between North America (60 Hz) and
Australia (50 Hz) was too simplistic. In addition, it is not clear if the applied
methodology considered difference in definition of kVA rating between the two
standards. As the North American and Australian electrical distribution systems
are quite different (e.g. predominantly single phase supply and a large number of
smaller less efficient distribution transformers in North America versus mostly
three phase supply through larger more efficient distribution transformers in
Australia), the percentage of the lost energy due to distribution transformer
inefficiencies is much smaller in Australia;
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the MEPS does not take into account fact that some utilities require kiosk
transformers to be fully rated in the enclosure. Such units have much higher rating
outside of enclosure (and would be subject to higher efficiency requirements).
MEPS requires much more extensive testing regime. The cost of these additional
tests will have to be borne by the manufacturers who will no doubt pass it on in
the final product costs. The RIS GWA (2002) does not include these costs into
cost-benefit analysis. The costs for additional tests are estimated to be $2,000 3,000 per unit/model, and the customized small series product lines might be
significantly affected by these additional costs.
In conclusion, it is recommended that the MEPS for distribution transformers are refined
by including:
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Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
7.1.
Introduction
In the last 20 years the Australian market is showing an increasing demand for packaged
substations with three phase distribution power transformers. Unfortunately, the standards
and regulations do not cover this area very well and in the last few decades the electrical
supply authorities and transformer manufacturers have developed different designs based
on unique specifications and distinctive combination of construction features. Most
factory assembled packaged substations currently used in Australia utilize metallic
enclosures, which include various types of ventilation systems. Those products evolved
over the last 30-35 years from the transformer substations developed by electrical utilities
in Victoria and New South Wales. The recently developed substations were designed
around modern, compact Medium Voltage switchgear (11 - 36 kV), fully enclosed Low
Voltage switchboards and largely customized, purpose-built, unique Australian distribution
transformers. Highly restrictive local environmental and urban planning regulations have
resulted in development of very compact packaged substations with extremely arduous
service conditions for built-in distribution transformers. The limited footprints and ever
increasing transformer ratings have resulted in reducing the ratio between the physical
dimensions of the installed distribution transformer and its rated power. This research is
focused on Australian oil-immersed, ONAN cooled and hermetically sealed distribution
transformers rated 150 to 2,500 kVA, highlighting their distinctive features: unique design,
superior loading capability, high reliability performances and safety features. The
assessment techniques discussed in previous chapters are developed for distribution
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Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
transformers operating in free air and no allowance is made for built-in distribution
transformers. This chapter provides information necessary for better understanding of
physical phenomena of thermal processes taking place during the operation of distribution
transformers installed in metallic enclosures, without being heavily involved in design
investigations.
7.2.
121
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
development of uniform designs for kiosk substations based on such products is a logical
improvement path. The first IEC standard for pre-fabricated HV/LV substations was
published in 1995 (IEC 61330 Ed. 1.0 B, 1995). It specifies the service conditions, rated
characteristics, general structural requirements and test methods for High-voltage/low
voltage prefabricated substations, which include HV cable connections (up to 52 kV) and
distribution transformers up to 1,600 kVA.
Although the above standard has not become an Australian Standard yet, a number of
Australian electrical distribution companies have been discretely using this standard since
1997. Unfortunately, a strict application of the IEC recommendations for pre-fabricated
kiosk substations in Australia is not a straightforward exercise. The most complications are
due to highly customized Australian distribution transformers, which are designed for
specific users and conditions, resulting in extremely nonflexible solutions. In addition,
there is a range of differing requirements for loading of transformers installed in kiosk
substations. Most packaged kiosk substations are manufactured in very limited volumes,
they are not type-tested and very little technical data is publicly available.
7.3.
Applicable Standards
In addition to IEC 61330 and other standards and technical regulations which
independently deal with all major parts of kiosk substations, there are Wiring Rules (2000),
an Australian standard, which covers the general aspects of electrical installations at all
voltage levels and as such also includes some requirements for MV/LV substations.
The Australian standard Loading guide for oil-immersed power transformers AS 2374.71997, which is reproduced from an equivalent IEC standard - IEC 60354 Ed. 2.0 B (1991)
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Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
7.4.
123
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
where distribution transformers require a reduced level of attention. It has been widely
accepted that the loading evaluation, although necessary, has no factual relevance to the
expected service lifetime of a distribution transformer. Consequently, there is very limited
information on the loading of distribution transformers in Australia.
Although the above principles are somewhat valid for smaller pole-mounted distribution
transformers (up to 500 kVA), the larger distribution transformers, as well as those
installed in kiosk substations require much more rigorous analysis of their service
conditions and respective loading capabilities. Firstly, there is a very emaciated possibility
of using non-optimal (increased) rating of those transformers due to material limits
imposed by the enclosure. Secondly, degradation of insulating materials caused by
increased ambient temperature due to restricted air flow around the transformer is
considered to be much more critical for its lifetime than the external influences. Finally,
the large distribution transformers in most cases supply loads which request very high
reliability of supply (e.g. hospitals, large residential blocks, commercial and industrial sites).
Reliability analysis of such transformers is much more complex than simply relying on a
quick replacement of a failed transformer.
The maximum intermittent loading of distribution transformers for normal cycling, longterm and short-term loading is vaguely defined in Australian Standard AS 2374.7-1997 as
1.5, 1.8 and 2.0 p.u. of the rated current respectively. Although, it is well known that
smaller transformers have generally better overloading capabilities, there is no
confirmation of that fact in Australian Standard AS 2374.7-1997, which recommends the
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Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
same loading limits for all power transformers below 2,500 kVA (defined as distribution
transformers).
The author of this thesis has tested a large number of distribution transformers and the
tests have shown that relative differences in thermal performances of distribution
transformers are due to designation to operate in free air or enclosed and due to
transformer size. The tests suggested that in addition to free air or enclosed
classification, distribution transformers should be further classified into four categories:
Both standards series, Australian Standards 2374 and IEC Standards 60076, deal with oilimmersed power transformers, which are installed in free air. If different service
conditions apply, such as restricted airflow around transformers cooling system when
transformer is enclosed, then transformer rating (and respective continuous and
intermittent loading limits) should be reduced to allow for departure from the prescribed
service conditions. The requirements in Australia are somewhat different, as the full nameplate rating for distribution transformers is required for each application (in free air and in
an enclosure), forcing manufacturers to develop two completely different electrical designs
for the same nominal transformer rating.
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Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
The thermal deterioration of the transformer insulation (as the most important factor for
loading considerations) is the function of the hot spot temperature and the top oil
temperature, which are dependant on ambient temperature.
The actual ambient temperature varies as function of the climate, the season, the time of
the day, etc. Table 13 from AS 2374.1 shows the maximum ambient temperatures defined
for standard oil-immersed distribution transformers in free-air operation:
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
126
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
400C
300C
200C
Australian kiosks employ both, the hermetically sealed and the free-breathing distribution
transformers. However, the users have given preferences to hermetically sealed
transformers due to their superior performances and very low maintenance requirements.
Those transformers are designed for top-oil temperature rise 60K (Kelvin) and average
winding temperature rise 65K.
Temperature limits for sealed distribution transformers with A thermal class of the
insulation system, assuming normal cyclic loading are presented in Table 14.
TABLE 14 - TEMPERATURE LIMITS FOR OIL-IMMERSED DISTRIBUTION TRANSFORMERS
Insulation system (top-oil temperature)
1050C
980C
1400C
The above values do apply even if ambient temperatures are different to those in Table 13
(in Australian conditions demands for the maximum ambient temperature of 450C are not
rare) or if an operation inside the kiosk substation or building is required.
7.5.
The IEC standard IEC 61330 compares transformer top-oil temperature rise in an
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
127
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
enclosure and in free-air (for the same load) and the difference between those two values is
defined as the temperature class of the enclosure. It recommends three temperature
classes for the enclosure: 10K, 20K and 30K. In addition to its temperature class, the
enclosure is defined by its rated maximum power, i.e. the free-air rating of the largest
transformer, which fits into that enclosure. It is clearly stated that the maximum power,
expected to be delivered from the kiosk, is lower than the free-air rating of the
transformer. The correlation of the temperature class of the enclosure and the ambient
temperature is given in this example: a 20K class enclosure could release the full rating of
the transformer only at an ambient temperature of 00C (i.e. average yearly ambient
temperature 200C 20K=00C). The Australian Standard AS 2374.7 recommends two
methods in assessing the impact of the enclosure on the transformer hot spot temperature
and the top oil temperature. The preferred (but not always feasible) method is to conduct
the factory temperature rise tests on the transformer installed in the enclosures. The
alternative method assesses the additional temperature rises experienced by the
transformer operating in the enclosure by measuring the temperature rise of air inside the
enclosure. It is suggested that half of the temperature rise of air inside the enclosure should
be added to the transformer top-oil temperature rise obtained by testing in free-air
operation. For example, an extra air-temperature rise in the kiosk-substation of 200C will
increase top oil temperature rise of the transformer by 100C. A variation of this method is
to correct transformer temperature rise by applying values for the temperature rise of air
inside the enclosure recommended in AS 2374.7.
Some of those recommended corrections are presented in Table 15.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
128
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
Temperature increase in
ambient due to enclosure
250
500
750
1,000
10 C
15 C
20 C
The author has thoroughly investigated both variations of the second method and it
appears that Table 3 in AS 2374.7, which provides recommendations for correction for
increase in ambient temperature due to the enclosure, should be extended by considering
the following:
losses in transformer and switchgear; with a large number of transformerswitchgear arrangements the range of losses released in the kiosk-substation could
be very wide. For example, a kiosk with a non-standard high-loss 750 kVA
transformer (AS 2374.1.2-2003) and a fully enclosed LV switchboard could have
higher total losses than a kiosk with an efficient low-loss 1,000 kVA transformer
and a low-loss switchgear;
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
129
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
Application of the second method by assessing impact of the enclosure on the extra
transformer top-oil temperature as 50% of the air temperature rise inside the enclosure is
very difficult, simply because it is not clear how and where to measure temperature inside
the enclosure. The analysis has also shown that the thermal classes for enclosures 10K,
20K and 30K, as recommended in IEC 61330 would not be the best solution for
Australian conditions. 30K class substations, where the top-oil temperature rise inside
enclosure is 300C higher than the top-oil temperature rise in free-air, would require very
expensive distribution transformers.
The authors suggest that the thermal classes for Australian conditions should be limited to
10K, 15K and 20K as the same output could be achieved more efficiently with an effective
ventilation system than with an over-designed transformer (AS 4388-1996). It seems that
most Australian users prefer the 15K temperature class enclosure. Incidentally, designs for
kiosk transformer for this type of enclosure appear to be the most economical under the
current set of technical specifications in Australia (AS 4388-1996).
7.6.
Case Study
The author has thoroughly investigated features of a range of kiosk substations (300 kVA 2,000 kVA) locally developed and installed in Australia.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
130
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
7.6.1. Enclosure
Most Australian manufacturers claim that their prototype enclosures have been
successfully subjected to the full set of normal type tests. Some manufacturers offer a
special type test to assess the effects of arcing due to an internal fault. The constructions
features related to internal-arc tests have not been taken into account when assessing
thermal performances of distribution transformers, as at present time, there is no big
interest in the Australian market for kiosks with internal-arc containment features.
The kiosk-substations installed in Australia are very compact and fully outdoor-operated.
The kiosk contains of a metallic enclosure with transformer and switchgear compartments
and a base. Typically, the enclosure and compartments are made of 2.5 mm thick
galvanized mild steel sheets. Some versions utilize aluminium or stainless steel sheets. The
kiosk base is made of a reinforced concrete or hot-dip galvanized steel channels. The
transformer compartment is in the middle, completely segregated from the LV and the
MV switchgear compartments. Some kiosks include extensive ventilation and anticondensation systems, lift-off enclosure facilities and oil-containments.
The ventilation system include air baffles, air ducts, prefabricated air grilles, holes punched
in side-walls, outlet air openings above access doors in both switchgear compartments and
air-grilles in transformer compartment walls as shown in Figure 14.
Most manufacturers offer enclosures in three to four different sizes, covering transformer
sizes 300 to 2,500 kVA. Number of switching functions in MV compartment has
considerable impact on size of the enclosure, as most transformers have already been
optimised for kiosk application (i.e. significantly reduced in size comparing with ordinary
outdoor type distribution transformers).
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
131
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
The standard required degree of protection for switchgear and transformer compartments
is IP24D. The safety margin is achieved by designing standard enclosure in such a way that
it is able to dissipate all heat generated inside and accumulated on its outside surfaces, for a
slightly higher level of protection (e.g. IP25D, which has a higher level of protection
against ingress of water). Ventilation openings are arranged to prevent any undesired
condensation on electrical equipment and inner wall surfaces. The optimum airflow is
achieved when the minimum quantity of heat dissipated by the transformer is discharged
in switchgear compartments. A simplified air temperature diagram along the sidewall for a
1,000 kVA kiosk-substation is shown in Figure 15. The measurements taken during the
temperature rise test show that the air temperature inside the enclosure is a mixture of
different temperatures and a complex function of the position (distances from the heatsource, ventilation openings and air-flow barriers inside the enclosure). It is very difficult
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
132
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
to talk about average temperature inside the enclosure because of large temperature
divergences in all directions.
Temperature
0
( C)
60
45
30
15
0
2
1.5
Height (m)
TX
TX 1 1.5
1
0.5
LV
0.5
MV
MV 3
TX 2 2.5
Length (m)
18.80C)
The author adopted temperatures at two heights as relevant for transformer loading
assessment:
Midheight (approximately half of the internal height of the kiosk and 50 mm from
the sidewalls).
Typical temperature rises in a 1,000 kVA kiosk are shown in Figure 16. A simple
methodology to calculate air-temperature around the transformer inside enclosure based
on AS 4388-1996 has been developed. The calculated values are approximately 20C above
the measured values and as such provide a small safety factor in transformer loading
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
133
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
calculations.
Temperature
Topheight
rise ( C)
50
Midheight
40
30
20
10
0
0
0.5
LV
1
TX
1.5
TX
2
TX
2.5
MV
3
MV
Length (m)
The fact that the increase in transformer top oil temperature rise by 60C halves its life (AS
1078-1984) emphasizes importance of an accurate forecast of air temperatures inside the
enclosure.
7.6.2. Transformer
Selection criteria for a distribution transformer are out of scope of this paper, and it has
been assumed that all factors, such as network performance, specific load requirements
and environmental considerations have been taken into account by selecting an
appropriate rating and suitable design. Table 16 presents data for a typical Australian oilimmersed, ONAN distribution transformer designed for installation in kiosk substations.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
134
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
Transformer data
kVA
1,000
8,950
hours
3.7
580
300
W/m2
980
Ventilation (inlets)
m2
1.08
Ventilation (outlets)
m2
1.20
59
63
14
40
35
27
75
Ambient temperature
30
hours
145
103
133
150
C
C
C
C
C
Pre-overload conditions
Overloading
Overload duration
112
103
90
82
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
135
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
Limiting the peak load to the transformer nameplate rating would result in an
uneconomical use of the transformer overload capability. Short-time peak overloads,
without significantly decreasing the life expectancy, are permitted (and very often
requested) from distribution transformers installed in kiosk substations.
While the loading of the transformer, during the overload, can increase rapidly, the oil
temperature increases more gradually with a time constant in the order of a few hours. The
temperature gradient between windings and oil reaches its ultimate value quickly, but the
slow rising temperature of cooler oil suppresses quick winding temperature rise. Hot-spot
temperatures considerably above 980C can be carried for short periods of time without
decreasing normal life expectancy, if this is offset by extended operation below 980C.
Table 17 compares overload requirements defined in AS 2374.7-1997 and capabilities of a
typical Australian kiosk transformer (24 hours cyclic loading, maximum ambient
temperature is 300C, duration of overload is 2 hours and preceding loading is 75% of the
rated power). The kiosk transformer is thermally optimised and has a low temperature
gradient and an increased thermal time constant. The difference between performances of
the average transformer and the transformer designed for kiosk application is obvious.
TABLE 17 - OVERLOAD CAPABILITIES IN % OF RATED POWER
Rating
AS2374.7
Kiosk transformer
Requirements
1,000 kVA
130 %
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
145 %
136
Chapter Seven: Performances of Distribution Transformers Installed in metallic enclosures an Australian experience
7.7.
CONCLUSION
The reliability of the entire LV network and thus most activities in residential, industrial
and commercial areas depends on the reliability of kiosk substations and their most
important part the distribution transformer. Designing such an important part of
distribution network requires knowledge and control not only of the functioning of its
components, but also of the external influences to which they are subjected.
Most large distribution transformers in Australia are installed inside very compact metallic
enclosures. Those transformers are specially designed for such an application and have
thermal performances, which well exceed standard requirements. Classification of kiosk
enclosures as proposed by IEC 61330 has been reviewed and a narrower range of
temperature classes for enclosures has been suggested.
Loading of distribution transformers in kiosk-substations is not properly covered by the
Australian Standards. Recommendations given by IEC 61330 are not fully applicable for
Australian conditions. A design investigation was formulated to show the performance of
optimised distribution transformer designs when installed in kiosk-substations. Simple
methodology was developed to forecast temperature rises in transformer compartments at
two different levels: midheight and topheight of the transformer compartment. Heat run
tests confirmed calculated temperature rises under different overload conditions.
Comparison between data for average transformers given in AS 2374.7-1997 and thermally
optimised kiosk transformers confirmed the need to further investigate this topic. Future
analysis should also include assessment of improved designs and the total operating costs
for distribution transformers in kiosk substations.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
137
8.1.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
138
This refined methodology highlights importance of design and costing stages in the
assessment process. Further, it recommends moving from simple capitalisation of
transformer losses by extending evaluation of the total operating costs through
introduction of new evaluation factors based on life cycle cost concepts and on expected
service and loading conditions. The fact that Australian distribution transformers are
highly customized (designed for specific users and conditions) introduces additional
complexities into assessment process. The presented case study on pad-mounted
distribution transformers highlights importance of selecting proper kVA rating as well
inclusion of expected service and loading conditions into total assessment process.
8.2.
This research project did not include the following design and technology options:
The aim of this research is assess only technologies incorporated in commercially available
distribution transformers products, which are practical to manufacture, install, operate and
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
139
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
140
Consequently, at this stage these transformers built on superconducting technology are not
considered to be technologically feasible and practicable to manufacture.
141
An emerging technology that may improve future designs for distribution transformers is
the use of carbon fibre composite materials for heat removal. In addition to excellent
electrical insulation performances, these materials are very good heat conductors. The first
prototype suggests possibility of reducing size and core losses by 35% DOE Screening
Analysis (2001). Unfortunately, this technology is not feasible for larger distribution
transformers. It seems that this technology is still be several years away from
commercialisation.
The application of power electronics technology for power transformers is in the early
stages of development. A small transformer was built at Purdue University DOE Screening
Analysis (2001), however no distribution transformer prototype has ever been
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
142
8.3.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
143
9. PUBLICATIONS
No
Authors
Title
Conference /
Proceedings
1.
2.
M. All-
DISTRIBUTION NETWORK
AUPEC96
Dabbagh
Melbourne 1996
S. Corhodzic
GROUNDING CONDITIONS
S. Corhodzic
THERMAL CHARACTERISTICS OF
AUPEC98
OIL-IMMERSED DISTRIBUTION
Hobart
TRANSFORMERS INSTALLED IN
1998
PADMOUNTED SUBSTATIONS
3.
A. Kalam
LOADING OF OIL-IMMERSED
INT-PEC99
S. Corhodzic
DISTRIBUTION TRANSFORMERS
Churchill, Vic
INSTALLED IN PADMOUNTED
1999
KIOSK SUBSTATIONS
4.
A. Kalam
ASSESSMENT OF DISTRIBUTION
AUPEC
S. Corhodzic
/EECON99
CAPITALISATION FORMULAE
Darwin
1999
5.
A. Kalam
ASSESSMENT OF DISTRIBUTION
Journal of
S. Corhodzic
Electrical and
CAPITALISATION FORMULAE
Electronic
Engineering
Australia,
Issue May 2000
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
144
6.
A. Kalam
ANALYSIS OF LOSS
IEEE/PowerCon
S. Corhodzic
CAPITALISATION FORMULAE
2000
Perth
AUSTRALIAN DISTRIBUTION
2000
TRANSFORMERS
7.
A. Kalam
DEVELOPMENT OF UNIVERSAL
DISTRIBUTION
S. Corhodzic
2003
Adelaide
2003
8.
A. Kalam
PERFORMANCES OF
IEEE
S. Corhodzic
DISTRIBUTION TRANSFORMERS
Transactions on
INSTALLED IN METALLIC
Power Delivery
ENCLOSURES AN AUSTRALIAN
July, 2005
EXPERIENCE
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
145
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GWA (2004, A preliminary cost benefit study of the transition to the GAEEEP, George
Wilkenfeld and Associates for SEAV, February 2004.
GWA (2004a), National Appliance and Equipment Energy Efficiency Program (NAEEEP):
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(CLASP) Asia Regional Symposium on Energy Efficiency Standards and Labelling, May
2001.
Howe, B. (1993), Distribution Transformers: A Growing Energy Savings Opportunity,
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ICF (1998), Transforming Dollars in Sense, ICF Inc., Report prepared for EPA, 68-D40088, 1998.
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IEC Standard IEC 60529 Ed 2.1:2001, Degrees of protection provided by enclosures (IP Code),
February 2001.
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December 1995.
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Appliance and Equipment Energy Efficiency Committee, Canberra, 1999.
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combined impacts from an extended and enhanced program, National Appliance and Equipment
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NAEEEP (2002a), A Review of the Stringency Levels for the Mandatory Minimum Efficiency of
Three-Phase Cage Induction Motors in Australia. September 2002.
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NAEEEP (2003), When you can measure it, you know something about it: Projected Impacts 2000
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A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
154
Appendices
APPENDICES
APPENDIX 1 - DISTRIBUTION TRANSFORMERS TYPICAL PRODUCT
DATA
Table A1-1 Single Phase Distribution Transformers Registered with Australian Greenhouse
Office (Energy Efficiency) Status: January 2005
Manufacturer
ETEL
ABB
Transformers
Tyree
Transformers
Aust. Pty Ltd
Model
D217
D240
D241
D216
D218
D242
D253
D252
D254
D255
X015NGS3F
X030NGS3G
X050NGS3G
50kVA, LW,LS
10kVA, LW,LS
16kVA, LW,LS
25kVA, LW,LS
50M2A-B
25M2A-B
25M7A-A
16M1A-C
Network
Voltage kV
22
11
11
22
22
22
11
22
11
11
11
11
11
11
11
11
11
22
22
22
11
Rated Output
kVA
25
15
30
16
25
50
10
10
25
50
15
30
50
50
10
16
25
50
25
25
16
High
Efficiency
-
155
Appendices
Table A1-2 Three Phase Distribution Transformers Registered with Australian Greenhouse
Office (Energy Efficiency) Status: January 2005
Manufacturer
Schneider
Electric
(Australia) Pty
Limited
Tyree
Transformers
Aust. Pty Ltd
Wilson
Transformers
Co. Pty Ltd
ABB
Transformers
Model
MG2000
MG400
MG500
MG600
MG750
MG800
MG1000
MG300
MG1500
MG200
MG2500
MG1250
MG315
MG100
MG160
500M4B
200M5B-C
100M4A
25M4A-C
315M5B-B
63M5A-B
400M4B-C
100KVA
1500KVA
750KVA
500KVA
315KVA
200KVA
2000KVA
100KVA
X300PHM3B
XK10NHM3F
X030NHW3F
X050NHW3G
X075NHW3G
X100NHW3H
X150NHW3B
X200NHW3F
X300NHM3M
X750NHM3F
Network
Voltage kV
11
11
11
11
11
11
11
22
11
22
11
11
22
22
22
11
22
11
11
22
22
11
11
11
11
11
11
22
11
11
22
11
11
11
11
11
11
11
11
11
Rated
Output kVA
2000
400
500
600
750
800
1,000
300
1,500
200
2,500
1,250
315
100
160
500
200
100
25
315
63
400
1,000
1,500
750
500
315
200
2,000
100
300
1,000
30
50
75
100
150
200
300
750
High
Efficiency
YES
YES
YES
YES
YES
YES
YES
YES
YES
-
156
Appendices
ABB
Transformers
ETEL
X500PHM3A
HK15NKM2A
X050PHW3C
X075PHW3B
X150PHW3A
X200PHM3B
X500NHM3N
25KVA, LW,LS
63KVA, LW,LS
100KVA, LW,LS
200KVA, LW,LS
315KVA, LW,LS
500KVA, LW,LS
750KVA, LW,LS
1000KVA, LW,LS
1500KVA, LW,LS
2000KVA, LW,LS
XK10PHM3B
XK20NHM3E
D221
D222
D250
22
11
22
22
22
22
11
11
11
11
11
11
11
11
11
11
11
22
11
22
22
22
500
1,500
50
75
150
200
500
25
63
100
200
315
500
750
1,000
1,500
2000
1,000
2,000
63
100
200
D232
22
315
D224
22
200
D243
11
15
D214
11
750
D098
11
500
D215
11
1,000
D206
11
30
D207
11
50
D208
11
75
D209
11
100
D210
11
150
D211
11
200
D212
11
300
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
157
Appendices
1,600 kVA
2,000 kVA
2,300 kVA
Rated voltage kV
20
20
20
No Load Losses kW
2.0
2.4
2.5
13,000
18,000
19,000
Length (l) mm
1,992
2,110
2,245
Width (w) mm
770
770
770
Height (h) mm
1,676
2,040
2,125
Total weight kg
3,430
4,400
5,580
Description
There are increasing requirements for a distribution transformer that can fit into compact
volumes such as inside wind turbine towers. Until recently, the solutions available came
with a significant compromise: a rising winding temperature. This resulted in reduced life
expectancy and overheated environment for the surrounding power electronics and lowvoltage equipment. Areva has developed an innovative, highly technically advanced
solution, SILTRIM distribution transformer. That patented design allows to retain low
winding temperature despite transformers extremely compact size. SILTRIM is specifically
built for complex mechanical & electrical environments and is installable in the harshest
environmental locations, meeting the demand for up to 2.3 MVA and 20 kV.
Advantages
158
Appendices
It is test-proven for extremely high level of over-voltage and is equipped with a pressurerelief device as additional safety measure against explosion. It offers lower winding
hotspot temperatures resulting to longer working life with high availability and reliability.
SILTRIM handles high harmonics environment and overload conditions. It is designed
to provide protection against over- fluxing, through its correct application of operating
flux density and use of magnetic core material.
Performances and Application Field
The high level of SILTRIMs performance (higher efficiency, low temperature rise, fire
resistance) combined with its compactness is obtained by using excellent heat dissipation
dielectric such as silicon oil or Midel.
The SILTRIM transformer is ideally suited for installation in wind turbines towers,
compact sub-stations, on-and off-shore platforms. Extremely compact, it fits into
reduced spaces and remains cool. It offers lower winding hotspot temperatures
resulting to longer working life with high availability and reliability.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
159
Appendices
TPC liquid filled distribution transformer Typical modern European distribution transformer
Table A1-4 Technical Data
Type
Pole-mounted
Ground-mounted
Rated
power
kVA
Rated
primary
voltage
kV
15 or 20
Operating
volts/Test
volts/BI L
kV
50
100
160
100
160
250
250
20
24 / 50
/125
Off load
410 off load between phases,
secondary
V
237 between phases and neutral
voltage
Vector group
Yzn11 Dyn11 Dyn11 Dyn11 Dyn11 Dyn11
symbol
No Load Losses (W) 125
210
375
210
375
530
Load Losses
(W) - (75C)
Ground
mounted
reduced
noise level
Dyn11
460
1,350
2,150
3,100
2,150
3,100
4,200
4,000
Impedance
voltage
Ucc
%
No-load
current
Io%
1.5
1.5
2.1
Acoustic
power
LWA
dB(A)
49
57
49
57
60
44
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
160
Appendices
Type
Pole-mounted
Ground-mounted
Ground
mounted
reduced
noise
level
Rated power
kVA
50
100
160
100
160
250
250
Length
mm
935
1,125
115
914
894
1,200
1,174
Width
mm
730
730
780
730
770
800
779
Height
mm
1,044
1,140
1,193
1,027
1,083
1,300
1,410
Total weight
kg
390
476
549
515
615
974
1,095
Mineral oil
weight
kg
129
132
117
133
148
270
274
Product Description
Pole-mounted: 50, 100, 160 kVA; ground-mounted: 100, 160 and 250 kVA;
Frequency 50 Hz;
161
Appendices
2 HVA fuses;
1 pressure detector;
in addition, the connections and coils insulation have been reinforced to avoid the
risks of electrical earth faults.
Main Components
1 locking system of the short-circuiting switch (to be used during transport and
handling);
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
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Appendices
1 filling hole;
1 rating plate;
2 lifting lugs;
4 LV busbars for 250 kVA fitted with 4 individual flexible PVC sheaths (IP2X
IK07 that allow connection of 1 or 2 cables);
4 rollers.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
163
Appendices
single-phase transformers with rated power less than 1 kVA and three-phase
transformers less than 5 kVA;
instrument transformers;
starting transformers;
testing transformers;
welding transformers.
When IEC standards do not exist for such categories of transformers, this part of IEC
76 may still be applicable either as a whole or in part. For those categories of power
transformers and reactors which have their own IEC standards, this part is applicable
only to the extent in which it is specifically called up by cross-reference in the other
standard. At several places in this part it is specified or recommended that an 'agreement'
shall be reached concerning alternative or additional technical solutions or procedures.
Such agreement is to be made between the manufacturer and the purchaser. The matters
should preferably be raised at an early stage and the agreements included in the contract
specification.
Abstract
Specifies the technical requirements for single and three-phase power transformers,
including auto transformers, but excludes single-phase transformers rated at less than 1
kVA, three-phase transformers rated at less than 5 kVA, and certain special transformers
such as instrument, starting, testing and welding transformers, transformers for static
converters and those mounted on rolling stock. Based on but not equivalent to and has
A New Approach to Assessment and Utilisation of Distribution Power Transformers
164
Appendices
been reproduced from IEC 76-1:1993. Includes Australian variations such as commonly
used power ratings and preferred methods of cooling, connections in general use, and
details regarding connection designation.
History
This standard applies to dry-type and oil-immersed type, three-phase and single-phase
power transformers with power ratings from 10 kVA to 2,500 kVA and system highest
voltage up to 24 kV. This standard does not apply to certain categories of special
transformers such as
instrument transformers;
auto transformers;
starting transformers;
testing transformers;
welding transformers;
arc-furnace transformers;
earthing transformers;
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
165
Appendices
flame-proof transformers.
Abstract
Specifies minimum power efficiency levels and high power efficiency levels for oilimmersed and dry-type distribution transformers, with power ratings from 10 kVA to
2500 kVA, intended to be used on 11 kV and 22 kV networks. It is expected that this
Standard will be called into legislation by individual States and Territories mandating
these requirements under Minimum Energy Performance Standard (MEPS) regulations.
History
Specifies temperature-rise limits and methods of test for measuring temperature rise.
Based on but not equivalent to, and has been reproduced from IEC 76-2:1993.
Includes Australian variations.
History
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166
Appendices
This standard specifies the insulation levels and dielectric tests for power transformers.
Abstract
Specifies the insulation levels and dielectric tests for power transformers as defined in
AS 2374.1. Based on IEC 76-3.
AS 2374.3.0-1982/AMDT 1-1992: POWER TRANSFORMERS - INSULATION
LEVELS AND DIELECTRIC TESTS
AS 2374.3.1-1992: POWER TRANSFORMERS - INSULATION LEVELS AND
DIELECTRIC TESTS - EXTERNAL CLEARANCES IN AIR
Abstract
Sets out minimum clearances in air between live parts of bushings on oil-immersed
power transformers and objects at earth potential. The text has been reproduced from
IEC 76-3-1:1987 and the tabulated minimum clearances have been modified.
History
This standard specifies the design of power transformers as defined in AS 2374, Part 1,
and the requirements necessary both in regard to their ability to withstand short-circuit
and the means of demonstrating that ability.
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Appendices
NOTES:
1. Pending the publication of a standard that applies to dry-type transformers, the
requirements of this standard may be applied to dry-type transformers subject to
agreement between the purchaser and the manufacturer and taking into account the
principles established in Sections 2 and 3.
2. A reduced schedule of short-circuit tests may be applied to Category I transformers by
agreement between purchaser, manufacturer and testing authority. Guidance on the
reduced schedule is given in Appendix A.
Abstract
OF
Scope
This standard defines the methods by which the sound levels of transformers, reactors
and their associated cooling equipment shall be determined so that compliance with any
specification requirements may be confirmed and the characteristics of the noise emitted
in service determined.
This standard is intended to apply to measurements made in the manufacturer's works
since conditions may be very different when measurements are made on site because of
the proximity of other objects, background extraneous noises, etc. Nevertheless, the
same general rules as are given herein may be followed when on-site measurements are
made.
In those cases where sufficient power is available in the factory to permit full
energisation of reactors, the methods to be followed are the same as for transformers.
Such measurements shall be made by agreement between the manufacturer and the
purchaser. Alternatively, measurements may be made on site where conditions are
suitable.
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168
Appendices
The methods are applicable to transformers and reactors covered by IEC Publications
76, 726 and 289, without further limitation as regards size or voltage and when fitted
with their normal auxiliary equipment, inasmuch as it may influence the measurement
result. Although the following text refers only to transformers, it is equally applicable to
reactors provided that it is recognized that the current taken by a reactor is dependent on
the voltage applied and, consequently, that a reactor cannot be tested at no-load.
This standard provides a basis for calculation of sound power levels.
The methods of measurement and the environmental qualification procedure given in
Appendix A are in accordance with ISO Standard 3746. Measurements made in
conformity with this IEC standard tend to result in standard deviations which are equal
to or less than 3 dB.
Abstract
Defines sound power versus sound pressure and sets out the methods by which the
sound power levels of transformers, reactors, and their associated cooling equipment
shall be determined. Standard and reduced sound power level limits for transformers
only have been added in an Australian Appendix. Technically equivalent to IEC
551:1987, with the addition of Appendix AA.
History
169
Appendices
Scope
This Standard applies to power transformers complying with the series of publications
IEC 60076.
It is intended to provide information to users about:
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170
Appendices
selection of rated quantities and tapping quantities at the time of purchase, based
on prospective loading cases;
Part of the information is of a general nature and applicable to all sizes of power
transformers. Several chapters, however, deal with aspects and problems which are of
the interest only for the specification and utilization of large high-voltage units. The
recommendations are not mandatory and do not in themselves constitute specification
requirements. Information concerning loadability of power transformers is given in IEC
60354, for oil-immersed transformers, and IEC 60905, for dry-type transformers.
Guidance for impulse testing of power transformers is given in IEC 60722.
Abstract
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171
Appendices
http://www.energyrating.gov.au/considered.html#transformers
NAEEEC introduced MEPS for certain distribution transformers on 1 October 2004.
Details are contained in the MEPS profile and Regulatory Impact Statement (see below)
and in AS 2374.1.2-2003. The following reports have been released for distribution
transformers:
Prepared for the Australian Greenhouse Office by Mark Ellis & Associates with the
assistance of Professor Trevor Blackburn (UNSW). Final Report, March 8th, 2000.
Gives data on market, overseas programs, emissions, test procedures and program
options. Concentrates on MEPS for distribution transformers, which operate on 11 kV
and 22 kV systems from 10 kVA to 2,500 kVA; includes liquid filled and dry type.
MEPS Profile Distribution Transformers
Author: NAEEEC, March 2001
Location: http://www.energyrating.gov.au/library/detailsprofile-transform2001.html
Proposes MEPS levels for a range of distribution transformers, which operate on 11k
and 22kV systems from 10kVA to 2500 kVA; includes liquid filled and dry type. Sets out
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
172
Appendices
the timetable for public consultation in the development of the new MEPS levels.
Regulatory Impact Statement: Minimum Energy Performance Standards and
Alternative Strategies for Electricity Distribution Transformers
Authors: George Wilkenfeld and Associates, January 2002
Location: http://www.energyrating.gov.au/library/details200218-transformers.html
Electricity distribution transformers are essential for the operation of the electricity
system. Their function is to step the supply voltage down from transmission voltages of
33,000 volts and above to the 415 volt three-phase supply which most electricity users
receive (a single phase of this supply is 240 volts). Industry sources estimate that there
are about 577,000 utility-owned distribution transformers in use in Australia, and their
number is increasing at about 1.5% per annum.
The proposal is to introduce mandatory minimum energy performance standards for all
electricity distribution transformers of up to 2500 kVA capacity, falling within the scope
of a proposed new part of Australia Standard AS2374-1-2 2001: Power Transformers:
minimum energy performance standards for distribution transformers. They are
expressed in terms of minimum efficiency levels at half rated load. It is recommended
that: States and Territories implement the proposed mandatory minimum energy
performance standards. The mode of implementation should be through amendment of
the existing regulations governing appliance energy labelling and MEPS in each State and
Territory. The amendments should:
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
173
Appendices
instrument transformers;
auto transformers;
starting transformers;
testing transformers;
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174
Appendices
welding transformers;
arc-furnace transformers;
earthing transformers;
flame-proof transformers.
MEPS Levels
MEPS levels, set out as minimum power efficiency levels at 50% of rated load for various
transformer types, are set out below. Reference should be made to AS 2374.1.2-2003 for
detailed conditions and test methods.
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175
Appendices
Type
Three phase
kVA
10
98.30
16
98.52
25
98.70
50
98.90
25
98.28
63
98.62
100
98.76
200
98.94
315
99.04
500
99.13
750
99.21
1,000
99.27
1,500
99.35
2,000
99.39
2,500
99.40
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
176
Appendices
Type
Three phase
kVA
Um=24 kV
10
97.29
97.01
16
97.60
97.27
25
97.89
97.53
50
98.31
97.91
25
97.17
97.17
63
97.78
97.78
100
98.07
98.07
200
98.46
98.42
315
98.67
98.59
500
98.84
98.74
750
98.96
98.85
1,000
99.03
98.92
1,500
99.12
99.01
2,000
99.16
99.06
2,500
99.19
99.09
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
177
Appendices
Type
Three phase
kVA
10
98.42
16
98.64
25
98.80
50
99.00
25
98.50
63
98.82
100
99.00
200
99.11
315
99.19
500
99.26
750
99.32
1,000
99.37
1,500
99.44
2,000
99.49
2,500
99.50
Minimum efficiency levels for High Power Efficiency Transformers, set out as minimum
power efficiency levels at 50% of rated load for various transformer types, are set out in
Table A3-3. Reference should be made to AS 2374.1.2-2003 for detailed conditions and
test methods.
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Appendices
Table A3-4 Table High Power Efficiency Levels for Dry-Type Transformers
Type
Three phase
kVA
Um=24 kV
10
97.53
97.32
16
97.83
97.55
25
98.11
97.78
50
98.50
98.10
25
97.42
97.42
63
98.01
98.01
100
98.28
98.28
200
98.64
98.60
315
98.82
98.74
500
98.97
98.87
750
99.08
98.98
1,000
99.14
98.04
1,500
99.21
99.12
2,000
99.24
99.17
2,500
99.27
99.20
Note: For intermediate power ratings the power efficiency level shall be calculated by
linear interpolation.
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179
Appendices
The certain fundamental relations between distribution transformers ratings and their
physical size and performance have been well known (Feinberg, 1979; CIGR, 2001 and
McConnell, 2001).
Figure 4-1 presents a simplified cross sectional area of a basic three-leg core type
distribution transformer (including windings in one of the windows).
The rating per phase of the transformer S (MVA), could be expressed as a function of
frequency f (Hz), flux density Bm (T), the cross sectional area of the magnetic core AFe (m2),
number of turns N1 and current I1 (A) in winding 1.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
180
Appendices
[4-1]
[4-2]
assuming that the current density is the same in both windings and that ACon is the overall
cross sectional area of both windings (m2), or
S = 1.11 fBm gA Fe kw Aw
[4-3]
where g is the current density (A/mm2) in both windings, Aw is the core window area (m2)
and kw is window space factor (e.g. 0.3-0.4 for 11 kV transformers). It should be noted that
for constant MVA rating, flux density and current density, the product of conductor cross
sectional area ACon and core cross-sectional AFe is constant.
Equation [4-2] could be rewritten as:
A Fe =
2.22 fB m gACon A Fe
A Fe
S2
= S
= S
2
(2.22 fBm gACon )
2.22 fB m gACon
(2.22 fBm gACon )
[4-4]
or
A Fe = K AS S
[4-5]
Factor KAS is defined as the output coefficient for distribution transformers and it is
constant over a relatively wide MVA rating range. For three phase oil immersed
distribution transformers KAS is in the range of 0.04 0.05 (a nominal median value is
0.044). From Equations [4-1] and [4-5], it is also possible to express the volt/turn ratio
V/N as:
V
= 4.44 fB m A Fe =
N
(4.44 fBm )2 K AS 2 S
[4-6]
or
V
= K VS S
N
[4-7]
where KVS , the winding coefficient, is also constant for a wide range of MVA ratings.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
181
Appendices
These two coefficients, the output coefficient and the winding coefficient are related as
follows:
K VS = 4.44 fBm K AS
[4-8]
The typical design values for three phase distribution transformers used in the above
Equations are presented in Table 4-1.
Table A4-1 Typical Design Values for Three Phase Oil-Immersed Distribution Transformers
Design Parameter
Range
Typical Value
1.55 1.80
1.72
1.5 3.0
2.4
AFe/ACon
1.4 2.8
1.6
KAS
0.04 0.05
0.044
KVS
14 20
17
Flux B (T)
Equations [4-5] and [4-7] are used in scaling performances of distribution transformers.
The mean turn length s is a function of AFe0.5 and bw/4, where bw is the width of the core
window (Fig. 4-1). Consequently, s is a function of S 0.25 :
s A Fe 0.5 + b w / 4 S 0.25
[4-9]
As an example for scaling factors, the load losses could be expressed as:
PLL =
K S 2 N 2s
S 2 S 0.25
S 2R
= 1
=
= K 3 S 0.75
K
2
2
0.5
1000V
SS
AConV
[4-10]
The other scaling factors could be derived in a similar way. Some of them are graphically
presented in Figure 4-2. Table 4-2 presents comparison of theoretical values and calculated
scaling factors for three-phase oil immersed distribution transformers developed for
Australian market.
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
182
Appendices
Scaling Factors
2.0
1.5
Linear
Dimensions:
1/4 power
1.0
% Losses,
% Resistance:
-1/4 power
0.5
0.0
0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5
kVA Rating Ratio
Quantity
Weight
Cost
Length
Width
Height
Total Losses
No-load losses
Exciting Current
% Total loss
% No-load loss
% Exciting Current
% Resistance
% Reactance
Volts/turn
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
183
Appendices
The loss evaluation factors for distribution transformers defined in the non-binding
industry
standard
Specification
for
Polemounting
Distribution
Transformers
Table A5-1 Calculation of Net Present Value of Transformer Losses based on AEEMA/ESAA,
(1998) GWA (2002)
Item
Unit
Rating
Efficiency
kVA
1,500
1,500
kW
1,500
1,500
Core loss
kW
4.5
3.0
kW
4.5
3.0
98.8%
99.2%
$/W
6.30
6.30
28,350
18,900
$/W
1.80
1.80
36,450
24,300
Purchase price
$/kVA
40
40
Purchase price
60,000
60,000
96,450
84,300
37.8%
28.8%
Lifetime
years
30
30
kWh
6,570,000
6,570,000
kWh
78,840
52,560
0.049
0.049
0.055
0.055
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
184
Appendices
A New Approach to Assessment and Utilisation of Distribution Power Transformers S. Corhodzic PhD Thesis
185
Appendices
Electrical utilities should assign a value to distribution transformer energy losses, which is
equal to the value of the revenue from selling that energy to the customer. In addition,
there should be additional component related to the value of the postponement of the
capital cost of distribution network augmentation. This additional component is highly
variable (as described in Chapter 5).
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