Transcript Development of an IEC Standard - transformer

Transformer Materials Update
Impact; Cost; Environmental;
Energy Efficiency
Thursday – November 29, 2007
Omni La Mansion Del Rio Hotel
San Antonio, Texas
Technical losses in transformers

Transformers are very efficient electrical machines
reaching maximum efficiency at the level of 97.5% to
99.4%. Operating efficiency is smaller because
transformers do not operate at maximum efficiency all
the time. This maximum efficiency point is at the
point where load losses proportional to square of
transformer load are equal to the no load losses which
are constant and appear all the time when the
transformer is energized (usually between 40% and
50% loading).
No load losses

No-load losses are those losses required in
the excitation of the transformer load losses.
They include dielectric loss, conductor loss
due to excitation and circulating currents,
and core loss.
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The dominant no-load loss is core loss, which is
associated with the time-varying nature of the
magnetizing force and results from hysteresis and
eddy currents in the core materials.
Core losses are dependent upon the excitation
voltage and may increase sharply if the rated
voltage of the transformer is exceeded. There is
also some inverse dependence on core
temperature.

Hysteresis losses can be reduced by
selecting low core losses material, while
eddy currents by reducing lamination
thickness. During last fifty years the
improving technology of transformer sheets
rolling, with techniques to refine the
domains of the iron crystals, proper cut,
fabrication and assembling techniques
reduced unit losses from 3W/kg to less than
1 W/kg in traditional technologies.
Load losses

Unlike no-load losses, which are constant
and always present, load losses vary with
the square of the load current carried by the
transformer and include:
(1) the resistive heating losses in the windings
due to both load and eddy currents,
(2) stray loss due to leakage fluxes in the
windings, core clamps, and other parts,
(3) the loss due to circulating currents in
parallel windings and parallel winding
strands.

For transformers, the major source of load losses is the
I2R losses in the windings. Load losses can be reduced
by selecting lower-resistivity materials (such as
copper) for the windings, by reducing the total length
of the winding conductor, and by using a conductor
with a larger cross-sectional area. Eddy currents are
controlled by subdividing the conductor into strands
and insulating the conductor strands and by conductor
shape and orientation. Clearly, this involves a
combination of material and geometric options that
also depend upon the core dimensions
Non traditional solutions

Amorphous cores are relatively new technology widely
used in Japan but also in other Asia regions and in smaller
scale in North America . This technology originally
developed by Metglas® in the past was more appropriate
for single phase and rather small size transformers because
of technological difficulties in core assembly. Amorphous
metal materials have high electrical resistivity and very
little or no magnetic domain definition. Older designs
saturated at lower flux, approximately 75% of
conventional core flux density that resulted in bigger
transformer sizes.

The saturation level has been increased and
together with other technological
improvements amorphous cores can now be
applicable for three phase units at any size
of transformer. Efficiency gain is huge. No
load losses can be reduced by additional
70% to 80% compared to best silicon steel
reaching levels of 0,065W/kg

Superconducting transformer uses high temperature
superconducting materials (HTS) which need to be cooled
to the temperature of about minus 200°C. Prototypes and
single applications for non distribution business are
nothing new. China's Institute of Electrical Engineering
have lately demonstrated a three-phase, 630kVA
distribution transformer with voltage ratio of 10kV to
400V. It utilizes an amorphous alloy core to further reduce
electrical losses over that achieved by the superconductor
wires alone. The total energy efficiency of this first device
was 98,3%. It is expected that more mature designs will
achieve efficiencies as high as 99.9%

There are other solutions to increase
transformer efficiency even further like
replacing existing conductor material with
silver which is the best electrical conductor
or new insulation materials which enhance
heat transfer. These and other ideas are still
in very early R&D stage or simply not
practical and not ready for massive
deployment.

Magnetic components designers are always
looking for improved soft ferromagnetic core
materials to increase the efficiency, temperature
rating and power density of transformers, motors,
generators and alternators, and energy density of
inductors. The primary means to increase the
transformer’s efficiency is to decrease the loss in
the magnetic core material and the I2R or Joulean
loss in the windings. The primary means to
increase the transformer’s power density is to
increase the frequency.

But increasing the frequency without a decrease in
the magnetic flux density will increase the core
loss. So in most instances, the trade-off between
power density, efficiency, and temperature rise
comes down to a trade between operating
frequency and magnetic flux density of the
magnetic core material and current density in the
windings. It should be noted that increasing the
frequency will also increase the AC I2R loss in the
windings.
 Energy
Efficiency of
Amorphous Metal Based
Transformers
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FUNDAMENTALS - CASTING
To achieve an amorphous structure in a
metallic solid, one has to solidify the molten
metal before constituent atoms take their
positions in a crystalline atomic structure. The
required rate for molten-metal cooling is about
one million degrees Celsius per second for most
of the amorphous metal we are interested in.
Therefore mass-produce amorphous metal is in
the early stages of development.

Why amorphous versus crystalline soft
magnets? Amorphous Metals exhibit:

easier magnetization (low coercivity and high
permeability)
lower magnetic loss (low coercivity, high permeability
and high resistivity)
faster flux reversal (as a result of low magnetic loss)
versatile magnetic properties resulting from postfabrication
heat-treatments and a wide range of adjustable
chemical compositions
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TRANSFORMER LOSS
Amorphous
vs.
SiFe Steel Transformers
NO LOAD LOSSES
Amorphous vs. SiFe Steel
Transformers
Core Loss (W)
 75 to 80% reduction

New amorphous transformer core materials
with improved performance are being
invented.
Transformer standards & regulations

There are different regulations and standards for
distribution transformers around the world.
NEMA TP-1 is American standard which is still
under US rule making process. This standard is
perceived as not tough enough by major US
utilities! Top runner is Japanese scheme based on
the principle that today’s technology which is
most advanced in efficiency challenge becomes
market average in certain period.
EN-50464 is new European standard which classifies
transformer no load and load losses.
Existing policy measures

European debate on security of supply has
indicated large EU energy dependency and the
need for seeking measures to reduce it. Increasing
energy efficiency and promotion of renewables are
today’s answer. These energy policy directions
have certain impacts on distribution transformers
purchasing decisions;
DOE outlined the procedural and analytical
approaches for the manufacturer impact
analysis.
 Phase 1, “Industry Profile,” consisted of
preparing an industry characterization,
including data on market shares, sales
volumes and trends, pricing, employment,
and financial structure.


Phase 2, “Industry Cash Flow,” focuses on
the industry as a whole. Using publicly
available information developed in Phase 1,
the Department adapted a generic structure
to perform an analysis of the impact of
transformer energy conservation standards
on the industry cash flow.

Phase 3, the “Sub-Group Impact Analysis,”
DOE conducted interviews with several
manufacturers. DOE interviewed included
small, medium, and large manufacturers
providing a representative cross-section of
the U.S. distribution
 Climate
change threat led to practical
measures in Europe such as
introduction of Emission Trading
Scheme (ETS).
 CO2 savings in transformers are the
component of ETS. Increasing
efficiency of transformers can produce
environmental benefits.
 Adopted
in March 2006, by European
Council, The Energy End-Use
Efficiency and Energy Services
Directive can be a new challenge to
improve energy efficiency also in
transformers.

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Ecodesign directive is another policy measure to
improve environmental picture of energy using
products.
Transformers are not yet subject to this directive
but if they were, operation phase of environmental
performance (operation phase is responsible for
more than 90% of the total of typical transformer
environmental impact including production,
operation and utilization phases) would justify
efforts to make the transformers more efficient.
Conclusion & Strategy
 TTA monitor and provide input
 TTA could drive energy efficiency
standards instead of waiting for the
government to tell them what is practical.
This is similar to automotive companies
developing fuel efficiency standards with or
without government intervention.
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