Transformers have primary and secondary windings that
are physically separated from each other. Sometimes
isolation transformers are referred to as "insulated".
To Order Isolation Transformers We
This is because the windings are insulated from each
other. In an isolation transformer the output winding
will be isolated, or floating from earth ground unless
bonded at the time of installation. Secondary neutral to
ground bonding virtually eliminates common mode noise,
providing an isolated neutral-ground reference for
sensitive equipment and an inexpensive alternative to
the installation of dedicated circuits and site
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
DC signals from one circuit to the
other, but allow AC signals to pass.
They also block interference caused by
ground loops. Isolation transformers
with electrostatic shields are used for
power supplies for sensitive equipment
such as computers or laboratory
instruments. Isolation transformers are
different from auto transformers in
which the primary and secondary share a
can accomplish a number of tasks:
primary and secondary windings may be
constructed to step-up or step-down the
output voltage. For example, the
transformer can accomplish voltage
matching between a 120 V load and an
electrical system that measures 208 V.
constructed with Faraday shields, will
improve power quality by attenuating
higher frequency noise currents.
Isolation transformers provide
better impendence matching of a critical
load to an electrical circuit . Internal
low-impedance isolation transformer component offers 100% isolation from
the input AC line.
Hospital Grade Isolation transformers is ideal
for the protection of sensitive electronic equipment in patient-care
Isolation transformer with Faraday shield reduces the cumulative
leakage current of the Isolator and connected equipment to levels below
Surge suppression components placed at the line input and
output combined with full line isolation offers continuous filtering of
a full range of power line noise in all modes. Active transformer
filtering offers continuous common-mode noise rejection with no wearable
parts, uniquely able to reduce surges in the worst of power environments
to harmless levels.
transformer provides a
"code-legal" method of re-bonding the
electrical system safety ground to the
neutral conductor on the transformer
secondary. Doing so eliminates
neutral-to-ground voltage and noise,
which is major cause of
reliability problems for
In electronics testing,
troubleshooting and servicing, an
isolation transformer is a 1:1 power
transformer which is used as a safety
precaution. Since the neutral wire of an
outlet is directly connected to ground,
grounded objects near the
device under test (desk, lamp,
concrete floor, oscilloscope ground
lead, etc.) may be at a hazardous
potential difference with respect to
that device. By using an isolation
transformer, the bonding is eliminated,
and the shock hazard is entirely
contained within the device.
Isolation transformers are commonly
designed with careful attention to
capacitive coupling between the two
windings. This is necessary because
excessive capacitance could also couple
AC current from the primary to the
secondary. A grounded shield is commonly
interposed between the primary and the
secondary. Any remaining capacitive
coupling between the secondary and
ground simply causes the secondary to
become balanced about the ground
All transformers provide isolation. They are
constructed with a primary and secondary
winding closely wrapped around the same ferrous core. Commercial transformers incorporate a
single Faraday shield between the primary and secondary
windings to divert noise, which would normally be
electrically coupled between the primary and secondary
windings to ground . The method through which this
electrical coupling of noise occurs is the capacitance
between the coils of the primary and secondary windings
of the transformer, which does not include a Faraday
shield. This same capacitance limits the upper frequency
band pass of the transformer in the same manner as
the mutual and self-inductances of the device determine
its low frequency cutoff. As the frequency of the
exciting currents increases, the reactance caused by the
capacitance between the windings, tends to
shunt these currents, thereby limiting high frequency
The single Faraday shield controls all manner of
evils which could be attributed to the electric coupling
of noise through a transformer. However, the problem
with a single shield arises when it is bonded to the
ground of either the primary or secondary side of the
transformer. The enclosure of a Faraday shield between
the primary and secondary windings eliminates
inter-capacitance, but it also establishes two new
capacitances between the shield and both windings. These
two capabilities allow high frequency currents to flow
in the grounding systems of both the primary and
secondary. Bonding the transformer shield to either the
primary or secondary ground establishes current paths
for high frequency noise in the reference conductor of
the circuit to be isolated. The particular choice of
ground for connection of the shield only provides
selection of the quieter of the primary and secondary
circuits. In many applications, this current path
defeats any isolating effect, which a transformer might
An isolation transformer is designed to
address the problems associated with referencing its
internal shields to ground. It is constructed with two
isolated Faraday shields between the primary and
secondary windings. When properly installed, the shield,
which is closest to the primary winding, is connected to
the common power supply ground and the shield closest to
the secondary winding is connected to the shield of the
circuit to be isolated. The use of two shields in the
construction of the isolation transformer diverts high
frequency noise, which would normally be coupled across
the transformer to the grounds of the circuit in which
they occur. The two shields provide more effective
isolation of the primary and secondary circuits by also
isolating their grounds. The isolation transformer adds
a third capacitance between the two Faraday shields,
which may allow coupling of high frequency noise between
the system grounds. However, increasing the separation
between the two Faraday shields normally minimizes this
third capacitance. Additionally, the dielectric effect
of the shields plus the increased separation of the
windings significantly reduce the inter-capacitance
between the windings.
Generally, a conductive foil completely enclosing the
windings will provide a ground path for primary circuit
noise and has the advantage that a very much smaller
capacitance exists between primary and secondary coils
than in the case of a simple Faraday shield. The Faraday
shield is simply a grounded single turn of conductive
nonferrous foil placed between coils to divert primary
noise to ground. The enclosing shield, if grounded
properly, will not re-radiate the noise signal, and will
provide effective electromagnetic noise reduction.
Typically, according to Topaz at a distance of 18
inches from a transformer's geometric center, the field
strength will be less than 0.1 gauss, and will roughly
follow inverse cube laws.
Since inter-winding capacitances are the primary path
by which significant power line and transient related
noise couples to the system, more information is needed
to describe what occurs. During the time power is being
transferred between transformer windings, noise
potentials between the primary circuits and ground is
similarly coupled to the secondary through both
capacitive and resistive paths. This noise appears in
three forms normally in a transformer circuit:
common-mode, transverse mode, and electromagnetic.
Common - Mode Noise
This noise appears between both sides of a power line
and ground. Since this noise is
referenced to the power system ground, the most obvious
method of eliminating this noise is by grounding the
transformer center tap to the system ground via the
lowest impedance path possible. Internal transformer
designs, which separate the coils to reduce capacitive
coupling, have some advantage, but it also increases
leakage inductance and reduces the power transfer.
Transverse - Mode
Transverse-mode noise is much more difficult to
eliminate than common-mode noise. The key here is to
differentiate between power and noise, and then reduce
Noise and power are separated by the difference in
their frequencies. The most effective transformer would
be a design exactly opposite to a
audio transformer. The purpose is to transfer the power
required by the load at the fundamental power frequency
and to eliminate all higher and lower frequencies.
Sub-harmonic frequencies are attenuated by operating the
transformer at relatively high flux density, which is
effective in reducing or eliminating them. Above the
fundamental frequency, noise is reduced by introducing
as much leakage inductance as possible, consistent with
good power transfer to the secondary.
Transverse-mode noise appears as a voltage across
both the primary and secondary windings of an isolation
transformer. It occurs when a common-mode noise signal
causes current to flow in the primary winding (or
secondary winding), and from there to ground via
capacitance to a grounded shield. Common-mode noise can
also be transformed into 'transverse-mode noise, and
thereby, through magnetic coupling, contaminate the
secondary of an isolation transformer. Normally, by the
proper selection of core loss verses primary winding
inductance, a well-designed isolation transformer will
eliminate the majority of this type of noise. Here
again, grounding the transformer shield to the lowest
impedance path available, will result in noise currents
using this return path rather than some other higher
impedance path to the noise source ground.
Electromagnetic noise does not constitute a major
problem in most applications, but is sometimes critical
in some recording or digital data systems, and in making
electromagnetic interference measurements.
Box Level Applications
transformers are often used to protect high gain
circuits, or prevent noisy ground paths in
instrumentation. Shielding at the instrument level is
difficult and often ineffective. Since most commercial
instrumentation has single shielding in its power
transformer, designers sometimes hope that by adding a
isolation transformer ground problems can be eliminated. This approach
often results in no benefits to the system unless all
other ground paths in the instrument can be totally
isolated. An isolation transformer is not a substitute
for the proper shielding or grounding of individual
. The amount of ground isolation
provided by the transformer at the box level is limited
by the use of a single chassis shield enclosing the box.
High frequency noise currents generated by the box
circuitry can be coupled onto the circuit reference
conductors through the connection of both transformers'
shields to the circuit reference. Additionally, any
potential difference between the power system ground at
the isolation transformer primary input and the power
system ground at the equipment and the power system
ground at the equipment chassis willcause
currents to flow in the reference conductor of
Rack Level Applications
The most effective application of isolation
transformers is with racks of equipment. A rack acts as
an outer shield for internal instruments, while serving
as the zero-signal reference for system output signals.
Isolation transformers are used to control shield
currents, and to break up the mutual capacitance between
rack instrumentation and an unknown power ground.
The main benefit of using an
isolation transformer with a rack of equipment is the
enhanced control of currents in the equipment shields.
Any potential differences between the utility power
ground and the rack's ground will cause currents to flow
in the loop. The isolation transformer allows these
"ground" currents to be directed through a portion of
the rack's shielding which will not effect the operation
of sensitive circuits and completely isolates these
currents from the internal equipment reference
Room Level Applications
It is often necessary to isolate EMC test enclosures
from noisy building grounds. Not only can isolation
transformers be used to effectively decouple building
power, but also since they also act as tuned circuits;
they reduce the differential noise from external
equipment, which reaches your screen room. While it is
recognized as a second isolation transformer inside the
test room will greatly reduce power line ambient, this
section will only consider using transformers on the
power lines to a typical screen room.
As with any transformer, isolation transformers
radiate magnetic fields. Physically locating the
transformer adjacent to, or connected to, a screen room
may increase rather than decrease ambient noise. Since
the physical case of a transformer, as well as the
primary winding shield, are normally connected to the
third-wire power ground of the supplied power, the
secondary winding shield must be isolated from the
transformer case and connected only to the conduit
shield going to the shielded room to achieve proper
ground isolation. The conduit acts as an RF shield for
the room's power and completes the connection between
the shielded room and the secondary winding shield in
If the transformer is three phase and supplies more
than one room, the best application for isolation
between rooms is to use only one phase for each room,
with a limit of three rooms per transformer. With this
approach, power line filters will effectively isolate
the room while providing practical noise attenuation.
Proper transformer design, wiring, and, above all,
grounding, are the only effective means of reducing the
three types of noise problems. Grounding should be
controlled and use the lowest impedance path possible
(i.e., bonding) to the central reference ground system
to insure maximum attenuation of noise sources. To
achieve the maximum protection from a transformer, not
only must it be applied properly, but also the
transformer should be one specially designed for
Three Phase Isolation Transformers
Three phase Isolation transformers are used for many applications
ranging from grain dryer, saw mills, conveyer belt systems,
refrigeration and air conditioning. Three phase have 3 primary and 3
secondary windings that are physically separated from each other. Each
of these windings are insulated from each other. The output windings
will be isolated, or floating from earth ground unless bonded at the
time of installation .
The Shielded three phase isolation transformers have all the feature of
the standard 3 phase plus they also incorporate a full metallic shield
(usually copper or aluminum) between the 3 phase primary and 3 phase
secondary windings. This electrostatic shield or Faraday
Shield, is connected to earth ground and performs two functions:
Its attenuates (filters) voltage transients (voltage
spikes). These shielded 3 phase isolation transformers have an
attenuation ratio of 100 to 1.
It filters common mode noise, Attenuation of
approximately 30 decibels.
The shield three phase isolation transformer is
preferred over the standard three phase isolation transformer because it
provides protection to sensitive and critical equipment. When more that
one shielded 3 phase isolation transformer is used between the source
and the load, it is referred to as a " cascading" and greatly improves
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.
- 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.
AMVECO 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.
Marcus 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 and savings.
Hammond 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 Transformer, a family-owned business which has been
manufacturing and distributing electrical products since 1968.
They focus on transformers that significantly reduce power
consumption over 30 percent compared to competitive makes.
Transformers - 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 and distribution
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 door.
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
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
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 isolate a drive from a main power line to
prevent the transmission of harmonics that the drives produce back
into the power line. They stop drive harmonics from disrupting
computers and other sensitive equipment.
Toroidal 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), low-off-load loss.
Step-Up 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. -
- A Step-Down Transformer is designed to reduce voltage from primary to
They can range from sizes from .05 KVA to 500 KVA
Isolation 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.
Buck 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.
High 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 (IEEE).
Low 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.
Single 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
Three 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.
Custom Transformers -
Custom Transformers are designed for a certain performance
specifications and size requirements. The company works with
your engineering specification.
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 loads.
Pad 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.
Pole 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.
Oil 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.
Dry Type 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 environmentally concerns.
Auto 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 supply.
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 household.
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 pass.
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.
Transformer 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 hertz.
Transformer 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
Primary Voltage - The coil winding that is directly connected
to the input power.
Harmonic 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 21st.
Enclosed transformers come with a weatherproof standard set by
Epoxy 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
Voltage 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 voltages.
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 filtering device.
Line Power Conditioners -
Power or Line Conditioners regulate, filter, and suppress noise in
AC power for sensitive computer and other solid state equipment.
DC Power 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 devices.
Rotary 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.
Frequency 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.
Voltage Converters -
A Voltage Converter changes the voltage of an electrical power
source and is usually combined with other components to create a
Magnetic 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.