Electrical energy is passed through distribution
transformers to reduce high-distribution voltage levels down to end-use
levels. Nearly all energy used in the United States passes through at
least one distribution transformer before being consumed by an end-use
appliance, motor, or other piece of equipment. Transformers are found in
all sectors of the economy: residential, commercial, and industrial.
Distribution transformers are generally categorized in several ways:
type of insulation: liquid-immersed or dry-type
number of phases: single-phase or three-phase
voltage level (for dry-type): low or medium
General Purpose Distribution Transformers
They are generally
used for supply appliance, lighting, motorized machine and power loads
from electrical distribution systems. They are either ventilated or
totally enclosed, and are available with either aluminum or copper
windings in standard ratings from 50VA up to 750 kVA.
Non-Linear (K-Factor) Distribution Transformers
Theuse of electronic equipment has continued to
grow in both offices and industrial plants. Offices now include
computers, fax machines, copier, printers, cash registers, UPS's and
solid-state ballasts. They all contribute to the distortion of the
current waveform and the generation of Harmonics. The K-Factor
transformer are designed to tolerate the harmonic distortion associated
with these loads.
Energy Efficient Distribution Transformers
These distribution transformers are energy efficient,
dry type, general purpose transformers to meet NEMA TP-1 specifications.
In the past several years, there has been an accelerated rate of change
to introduce energy efficiency standards for transformers. Many products
have preceded the initiatives for transformers in an overall effort to
optimize manufactured goods for environmental concerns. Governments are
encouraging users to consider energy efficient products like dry type
transformers, in an effort to help reduce carbon dioxide emissions. In
addition to the benefits to the environment, energy efficient
transformers also can realize substantial savings in operating costs
thereby have a direct impact on the initial investment evaluated over a
period of time.
Distribution Transformer Basics
Copper or aluminum conductors are wound around a
magnetic core to transform current from one voltage to another. Liquid
insulation material or air (dry-type) surrounds the transformer core and
conductors to cool and electrically insulate the transformer.
Since small distribution transformers do not generate
much heat, a higher proportion of theses tend to be dry-type. Dry-types
are less flammable, and are therefore often selected for use when they
must be located in confined spaces on a customer's premises.
Distribution transformers are used in electric power
systems. The final part of the distribution system at medium voltage are
the distribution transformers. Due to the Iow impedance voltage, this
type of power distribution transformer will not substantially limit the
short circuit current in the case of a fault on its secondary side. It
is therefore common practice that power distribution transformers have
to be type tested to their ultimate short-circuit conditions. Power
distribution transformers may be oil filled or dry-filled.
Manufacturer offers a complete range of power distribution transformers,
which can be certified in one test access very efficiently.
You use a power distribution transformer when you have
no interest in what happens below the LV terminal of the power
distribution transformer. You use a power distribution transformer
element if you are interested in modeling loads or lines on the LV side
of the power distribution transformers. If you have a node with a power
distribution transformer, any loads on that node are assumed to be
applied at the LV side of the power distribution transformer. Modeling
the power distribution transformer give you the benefit of computer
values for secondary voltages, and transformer losses due to series (or
copper) losses and due to no load (or core energization losses.
Transformer Design Characteristics: Transformers consist of two primary components:
A core made of magnetically permeable material.
A conductor, or winding, typically made of a low
resistance material such as aluminum or copper.
Transformer Loss Basics
Core Losses are constant. Winding Losses increase
exponentially with the square of the load.
A Transformer uses the core's magnetic properties and
current in the primary winding (connected to the source of
electricity) to induce a current in the secondary winding (connected to
the output or load). Alternating current in the primary winding induces
a magnetic flux in the core, which in turn induces a voltage in the
secondary winding. A voltage step-down results from the exchange of
voltage to current, and its magnitude is determined by the ratio of
turns in the primary and secondary windings. A transformer with 50
primary turns and five secondary turns would step the voltage down by a
factor of 10, for example from 13,500 volts to 1,350 volts.
A given transformer's energy output is lower than the
level specified by the nameplate rating due to inefficiencies in both
the core and the windings. In general, transformer losses are less than
two percent of the total transformer load.
The magnitude of the losses is dependent upon the
loading of the transformer. Core losses remain constant while winding
losses increase with the square of the load. Thus, for a transformer
with an average load of 25 percent, the core losses may represent
approximately 75 percent of total energy losses. Conversely at 100
percent of rated load, the winding losses may represent more than 80
percent of total energy losses. Thus, core losses make-up a greater
share of total losses at lower transformer loads, while the winding
losses make-up a greater share of total losses at higher transformer
Many different distribution transformer designs are
available, depending on the loading patterns and needs of the end-user.
Transformer engineers modify transformer design and vary material
depending upon circumstances. Transformer design includes variation of :
The material used for the core
The material used for the winding.
The material that insulates the core and the
The number of phases of the current that passes
through the transformer.
Mounting and the rated size.
The following describe these factor in more detail.
Transformer cores are usually made of either
grain-oriented silicon steel or amorphous metal. Silicon steel comes in
a variety of grades, each with its own conductive and efficiency
characteristics. Amorphous metal, a more costly but highly efficient
material, can significantly reduce core losses. Constructing the core of
laminated sheets, insulated from each other, also reduce losses, but
adds to the cost, weight and volume of the transformers.
The type of core material preferred by a utility is
usually dependent on the cost of its core losses and the expected
transformer loading levels. Since the marginal cost of energy for
electricity utilities is usually rather low, the financial incentive for
moving to high efficiency transformer materials may be limited.
Generally, copper and aluminum are used for transformer
windings. As with silicon steel, these materials are available in a
variety of grades and thicknesses, each with their own efficiency
characteristics. The types of windings chosen by the transformer
designer are also dependent on the cost of a specific utility's losses
and on assumed transformer loading levels.
The majority of utility distribution transformers are
liquid filled. The non-conducting liquid (mineral oil is
most commonly used) serves to electrically insulate and
cool the transformer. As the core temperature of the
transformer rises, the efficiency decreases, so an
efficient cooling method improves performance.
Typically, transformers perform best at temperatures
below 55 C above the ambient temperature.
Liquid-filled transformers transfer heat more
efficiently than dry-type transformers and are generally
preferred for larger applications. Most liquids used in
transformers now are non-flammable.
Transformers may be designed to step down a single
alternating current from one voltage to another, call
single-phase transformers, or contain three primary and
three secondary windings and therefore provide the
output in three-phases. Three-phase transformers induce
a more constant magnetic flux and output voltage
necessary for motors, heating, ventilating,
air-conditioning and other large equipment. Technically,
the three-phase transformer is equally efficient to the
In the US, over 95% of average annual transformer sales
comprise single-phase distribution units, mostly in the
15kVA to 25kVa range. Since the larger
transformers tend to be three-phase, these comprise 38%
of the total MVA sold each year.
Distribution transformers are either mounted on an
overhead pole or on a concrete pad at ground level.
There is some evidence to suggest that pole mounted
transformers dissipate heat more easily than pad mounted
units and may therefore be more fully loaded.
Properly sizing a transformer for a given application
has a significant impact on the overall transformer
efficiency and energy loss level. Oversized transformers
are lightly loaded, and consequently lose more energy
from excess core losses than optimally sized
transformers. Conversely, undersized transformers
operate at higher load levels and experience high load
Energy Losses from New Distribution
A new 50kVA single-phase utility
transformer will produce approximately 70 MWh in energy
losses. An average 1,500kVA liquid-filled three-phase
transformer will produce approximately 1.4GWh in losses
over its life time.
Studies in the US have shown that new,
efficient transformer designs could reduce energy losses
and associated air emissions by 10 percent to more than
40 percent, depending on materials used and the loading
pattern of the transformer.
Advance in transformer design have
produced substantial transformer efficiency improvements
over the past 20 years. The most significant
improvements have been made in core technologies with
the use of high-efficiency silicon-steel and amorphous
metal. Due to the large numbers of transformers in
service and the constant nature of energy losses, only
small increases in efficiency are need to produce
significant economic and environmental gains.
Sources of Transformer Efficiency
Transformer energy losses can be reduced
by improving the efficiency of the core or windings. The
relative importance of core and winding losses depends
on the loading on the transformer and the cost of each
type of loss to the utility.
Core Loss Reductions
Since the majority of transformer losses at low load
levels are due to core inefficiencies, much of the
research on reducing transformer losses has concentrated
on building more efficient cores. Core losses result
from cyclic changes in the magnetic state of iron, and
"eddy-current" losses caused by the flow of small
currents in the iron. Core losses can be reduced by
improving the magnetic permeability of the core material
or by using a core material that offers less magnetic
Considerable progress in reducing core
losses has been made over the past twenty years,
primarily through material improvements. In the early
1970's manufactures introduced more efficient
silicon-steels. The four main grades of silicon-steel
used in transformers are M2, M3, M4 and M6(decreasing in
efficiency). Differences are due mainly to the chemical
composition and the rolling techniques used in
manufacture of the core. The increased domestic
availability of higher grades of silicon-steel (M2 and
M3) and new manufacturing processes has led to the
improved efficiency of silicon-steel distribution
Amorhous metal, a highly efficient
material used in transformer cores, possesses good
magnetic properties, low inherent magnetic resistance
losses, and high resistively. Due to its ability to be
constructed into very thin sheets, "eddy-current" losses
are significantly reduced. Amorphous metals have been
found to reduce core losses by as much as 70 percent.
However, the cost of transformers with more efficient
cores increases due to the following factors:
Increasing core efficiency requires
the use of more core material.
The larger core size associated with
the energy-efficient transformer necessitates the use of additional
winding material, generally resulting in lower winding efficiencies
and other cost.
The thin lamination of amorphous
metal tends to make the core material more difficult to handle.
Certain types of efficient
transformers may encounter specific problems, such as the
difficulties associated with larger and heavier transformer design.
Winding Loss Reductions
Winding losses, or load-losses, arise
from the conducting material's inherent resistance to the flow of
electrical current. Winding losses increase with the square of the
transformer load. Efficiency gains can be achieved by using materials
with lower resistively or greater diameters. For example, distribution
transformer coils made with low resistively conductors, such as copper,
can have considerable lower load losses than those made with other
materials. However, low resistively conductors often cost more than
other conducting material.
Importance of Sizing
Overall transformer efficiency depends
critically on the percent of time that the transformer is heavily or
lightly loaded. the load factor.
Transformers need to be sized to cope
with expected peak loads, rather that average loads, and therefore where
there is a large disparity between these two, the load factor will be
For example, distribution transformers serving primarily
residential loads regularly carry average loads that are only 15 percent
to 20 percent of the transformer's rated capacity but also must be
designed to support peak morning and evening loads. Because of the wide
gap between peak and non-peak loads, and the relatively limited amount
of time that the transformer is peak-loaded, average transformer loading
tends to be fairly low. In this case, total losses may be mainly
attributed to core losses.
Larger distribution transformers, used
more often in transforming power for commercial or industrial customers,
tend to be loaded at higher average levels over the course of the year.
Transformers that serve businesses operating from 9:00 am to 5:00 pm,
for example, typically experience a consistent and relatively higher
load throughout the day. In this circumstance, it is likely that load
losses will make the major contribution to total losses.
Correctly sizing a transformer is
therefore critical to the quantity and source of losses, and optimizing
transformer design for efficiency remains a complex task.
To complicate matters, the marginal cost
of energy varies dramatically throughout the day,
altering the cost of energy losses and the cost-benefit
of installing more efficient transformers from the
In addition, transformer loading patterns
tend to change over time. Homeowners may accumulate more
appliances and equipment (or new houses built in the
area), or businesses may expand and consequently
increase the load on the transformer. Generally,
utilities estimate load growth when sizing and
purchasing transformers. In the Us it has been
calculated that, on average, utilities size single-phase
transformers so that transformer peak load at
installation is approximately 88 percent of its
capacity, and 157 percent of capacity at the end of its
In an effort to improve transformer
sizing practices, the U.S. Environmental
Protection Agency as part of the Energy Star Transformer
Program, has developed technical tools to enable
utilities to enter utility-specific loading information
in order to optimize transformer size and total owning
cost which providing reliability and energy-efficiency.
allows signal or power to be taken from one device and fed into
another without electrically connecting the two.
are devices that transfer electrical energy from one electric
circuit to another, without changing the frequency, by
are designed to meet certain performance specifications and size
requirement that you require. There is a wide range of custom
Buck Boost Transformers
is a ideal solution for changing line voltage by small amounts.
Often used to buck (lower), or boost (raise) the voltage from 208v
to 240v for lighting applications.
Pole Mounted Transformers
are mounted to poles for overhead electrical lines. Used in various applications.
Are available in single phase or three phase transformers.
Medium Voltage Transformers
are used with a medium range of voltages. They come in a full
range from liquid-filled, convention dry type as well as cast coil.
Pad Mounted Transformers
are a excellent choice for commercial and industrial such as
manufacturing facilities, refineries, office buildings, schools,
hospitals, restaurants, and retail stores. They come in various
sizes and can be used underground as well.
typically these voltage transformers are used in power transmission
applications. High voltage transformers are also used in microwave.
Transformers - With Acme Electric being in
business over 80 years, they have always believed in
offering there customers superior service, quality
and technical expertise in the transformer market.
Transformers - AMVECO designs and
manufactures toroids transformers, current
transformers, and auto transformers. Most AMVECO
products are custom designed utilizing their
state-of-art proprietary CAD programs. The AMVECO
engineers can quickly generate designs in a matter
of hours, if needed.
Federal Pacific Transformers - Federal
Pacific is a division of Electro- Mechanical
Corporation, a privately held, American owned
company founded in 1958. Federal pacific offers
dry-type transformers from .050 KVA through 10,000
KVA single and three phase, up to 34.5 KV, 150 KV
BIL with UL approval through 15 KV.
Transformer - Ever since they opened their
doors for business a half a century ago, they have
been a leader in innovative transformer design. As a
family-owned company they are proud of the
reputation they have earned for making quality-built
transformers that deliver exceptional performance
Transformers - Hammond Manufacturing was
founded in 1917 in Guelph, Ontario, Canada. In the
last 3 decades it has expanded to the US and the
international markets offering many types of power
Transformers - TEMCo a family-owned
business has been manufacturing and distributing
electrical products since 1968. They focus on
transformers that significantly reduce power
consumption over 30 percent compared to competitive
- GE has been a key player in the energy
industry for more than a century. Since the
installation of their first steam turbine in 1901.
They have become number one provider of
high-technology power generation equipment.
Jefferson Electric Transformers - Jefferson
Electric has been a pioneer and innovator of
magnetic products since 1915. Jefferson broad line
of dry-type transformers are backed by quality
assurance systems so stringent that each and every
unit gets thoroughly tested before it goes out there
Distribution Transformers - Distribution
Transformers are generally used in electrical power
distribution and transmission power. This class of
transformer has the highest power, or volt-ampere
ratings. and the highest continuous voltage rating.
Substation Transformers - Substation
transformers are large devices which usually weigh
tens of thousands of pounds. They are filled with
tens of thousands of gallons of heat transfer
fluid. Although they are typically 99.8% efficient
in the transforming of electricity from one voltage
to another, processing hundreds of Mega Volts-Amps
of electricity force the liberation of hundreds of
BTUs per second.
Medical Grade Isolation
Transformer - Medical Grade Transformers
generally refer to the transformers used in medical
devices as well as hospital, biomedical and patient
care equipment. There are a number of strict safety
rules, guidelines and laws governing the design,
construction and the test of these transformers.
Drive Isolation Transformer - They are used
to adjust the speed of induction motors by varying
the frequency. They are becoming more popular
because of their impact on energy saving, and they
are easy to control.
Transformers - Toroidal transformers are
more efficient than the cheaper laminated EI types
of similar power level. Some of the advantages are
smaller size, lower weight, less mechanical hum,
(making them superior in audio amplifier),
Transformers - A Step-Up Transformer is one
whose secondary voltage is greater than its primary
voltage. This kind of transformer "steps up" the
voltage applied to it. -
Transformers - A Step-Down Transformer is
designed to reduce voltage from primary to
secondary. They can range from sizes from .05 KVA
to 500 KVA
Transformers - An Isolation Transformer is a
device that transfers energy from the alternating
current (AC) supply to an electrical or electronic
load. It isolates the windings to prevent
transmitting certain types of harmonics.
Boost Transformers - Buck Boost Transformers
make small adjustments to the incoming voltage. They
are often used to change voltage from 208v to 240v
for lighting applications. Major advantages of Buck
boost transformers include; low cost, compact size
and light weight.
Voltage Transformer - There are many
different types of voltage transformers. A High
Voltage Transformer operates with high voltages.
Typically, these voltage transformers are used in
power transmission applications, where voltages are
high enough to present a safety hazard.
Medium Voltage Transformers - A Medium
Voltage Transformer can be connected directly to a
primary distribution circuit and generally has the
most load diversity. These voltage transformers have
installation practices that are generally in
accordance with application recommendations from the
Institute of Electrical and Electronic Engineers
Voltage Transformers - A Low Voltage
Transformer is an electrical device that transforms
120 volts (line voltage) into 12 volts or 24 volts
(low voltage). Some uses for low voltage transformer
are in landscaping lighting.
Phase Transformers - In electrical
engineering, single-phase electric power refers to
the distribution of electric power using a system in
which all the voltages of the supply vary in unison.
Single-phase distribution is used when loads are
mostly lighting and heating, with few large electric
Phase Transformers - Three Phase
Transformers must have 3 coils or windings connected
in the proper sequence in order to match the
incoming power and therefore transform the power
company voltage to the level of voltage needed while
maintaining the proper phasing or polarity.
Transformers - Custom Transformers are
designed for a certain performance specifications
and size requirements. The company works with your
Industrial Control Transformers - Industrial
Control Transformers are used to convert the
available supply voltage to the required voltage to
supply industrial control circuits and motor control
Mounted Transformers - Pad Mounted
Transformers are usually single phase, or three
phase, and used where safety is a main concern.
Typical applications; restaurant, commercial
building, shopping mall, institutional.
Mounted Transformers - Pole Mounted
Transformers are used for distribution in areas with
overhead primary lines. Outside a typical house one
can see one of these devices mounted on the top of
an electrical pole.
Filled Transformers - Oil Filled
Transformers are transformers that use insulating
oil as insulating materials. The oil helps cool the
transformer. Because it also provides part of the
electrical insulation between internal live parts,
transformer oil must remain stable at high
temperatures over an extended period.
Transformers - Dry-Type Transformers are
available for voltages up through 34.5 kV (although
the most common upper limit is 15) and KVA ratings
up through 10,000 (with 5000 as the usual limit).
Dry-type use air as a coolant, lowering health and
Transformers - An Autotransformer is an
electrical transformer with only one winding. The
winding has at least three electrical connection
points called taps. Autotransformers are frequently
used in power applications to interconnect systems
operating at different voltage classes, for example
138 kV to 66 kV for transmission. Another
application is in industry to adapt machinery built
for 480 V supplies to operate on the local 600 V
Electrical Transformers - Electrical
Transformers are devices used to raise or lower the
voltage of alternating current. For instance, power
is transported over long distance in high voltage
power lines and then transformers lower the voltage
so that the power can be used by a business or
Transformers - An Isolating Transformer is a
transformer, often with symmetrical windings, which
is used to decouple two circuits. An Isolation
transformer allows an AC signal or power to be taken
from one device and fed into another without
electrically connecting the two circuits. Isolation
transformers block transmission of DC signals from
one circuit to the other, but allow AC signals to
Transmission Power Lines - A Transmission
Line is the material medium or structure that forms
all or part of a path from one place to another for
directing the transmission of energy, such as
electromagneticor acoustic waves as well as electric
power transmission. Components of transmission lines
include wires, coaxialcables, dielectric slabs, option fibers,electric power lines, and waveguides.
Voltage - The measure of the amount of force
on a unit charge because of the surrounding charge.
Transformer Frequency - The transformer
cannot change the frequency of the supply. If the
supply is 60 hertz, the output will also be 60
K Factor - Some transformers are now being
offered with a k-factor rating. This measure the
transformer's ability to withstand the heating
effects of non-sinusoidal harmonic currents produced
by much of today's electronic equipment and certain
- The coil winding that is directly connected to
the input power.
Cancellation - Harmonic cancellation is
performed with harmonic canceling transformers also
known as phase-shifting transformers. A harmonic
canceling transformer is a relatively new power
quality product for mitigating harmonic problems in
electrical distribution systems. This type of
transformer has patented built-in electromagnetic
technology designed to remove high neutral current
and the most harmful harmonics from the 3rd through
Enclosed transformers come with a weatherproof
standard set by NEMA.
Encapsulated - A process in which a
transformer or one of its components is completely
sealed with epoxy or a similar material. This
process is normally preferred when a unit might
encounter harsh environmental conditions.
Regulators - A Voltage Regulator is an
electrical regulator designed to automatically
maintain a constant voltage level. It may use an
electromechanical mechanism, or passive or active
electronic components. Depending on the design, it
may be used to regulate one or more AC or DC
AC Line Reactor
- AC Line Reactors is a three phase transformer
used in conjunction with AC variable frequency and
DC motor drive. They are a bi-directional protective
Power Conditioners - Power or Line
Conditioners regulate, filter, and suppress noise in
AC power for sensitive computer and other solid
Supplies - Conversion of one form of
electrical power to another desired form and
voltage. This typically involves converting 120 or
240 volt AC supplied by a utility company to a
well-regulated lower voltage DC for electronic
Phase Converters - Rotary Phase Converters
are commonly used in home or small commercial or
industrial settings. Rotary phase converters convert
single-phase power into three-phase power. This is a
very cost-effective way to power three-phase
electric motors and other three phase equipment.
Converters - A Frequency Changer or
Frequency Converter is an electronic device that
converts alternating current (AC) of one frequency
to alternating current of another frequency.
Converters - A Voltage Converter changes the
voltage of an electrical power source and is usually
combined with other components to create a power
Motor Starters - Magnetic Motor Starters are
essentially heavy duty relays mounted in boxes,
often equipped with heater/thermal overloads matched
to the motor they start.
Motor Starting Auto Transformers - An Auto
Transformer starter uses an auto transformer to
reduce the voltage applied to a motor during start.
The auto transformer may have a number of output
taps and be set-up to provide a single stage
starter, or a multistage starter.