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How Does Winding Metal Type Change Transformer Properties?

The wire used is generally magnet wire. Magnet wire is a copper wire with a coating of varnish or some other synthetic coating. Transformers for years have used Formvar wire, which is a varnished type of magnet wire.

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The conducting material used for the winding depends upon the application. Small power and signal transformers are wound with solid copper wire, insulated usually with enamel, and sometimes additional insulation. Larger power transformers may be wound with wire, copper, or aluminum rectangular conductors. Strip conductors are used for very heavy currents. High frequency transformers operating in the tens to hundreds of kilohertz will have windings made of Litz wire to minimize the skin effect losses in the conductors. Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings. Each strand is insulated from the other, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. This "transposition" equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size is.

For signal transformers, the windings may be arranged in a way to minimize leakage inductance and stray capacitance to improve high-frequency response. This can be done by splitting up each coil into sections, and those sections placed in layers between the sections of the other winding. This is known as a stacked type or interleaved winding.

Windings on both the primary and secondary of power transformers may have external connections (called taps) to intermediate points on the winding to allow adjustment of the voltage ratio. Taps may be connected to an automatic, on-load tap changer type of switchgear for voltage regulation of distribution circuits. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull type circuit. Modulation transformers in AM transmitters are very similar. Tapped transformers are also used as components of amplifiers, oscillators, and for feedback linearization of amplifier circuits.

To make the basic single-phase transformer more versatile, both the primary and secondary windings can be made in two equal parts. The two parts can be reconnected either in a series or in parallel. This provides added versatility as the primary winding can be connected for either 480 volts or 240 volts and the secondary winding can likewise be divided into two equal parts providing either 120 or 240 volts. (note: there will be four leads per winding brought out to the terminal compartment rather than two). either arrangement will not affect the capacity of the transformer. Secondary windings are rated with a slant such as 120/240 and can be connected in a series for 240V or in a parallel for 120V or 240/120V (for 3-wire operation). Primary windings rated with an X such as 240X480 can operate in series or parallel but are not designed for 3-wire operation. A transformer rated 240x480V primary, 120/240V secondary could be operated in 6 different combinations.

Enameled wire is a thin wire coated insulation and used in electric motor coils. It is placed in the motor slots in order to create magnetic flux when electricity flows through it. It is also used in the construction of electromagnets, transformers and inductors. The core material is copper, coated with a thin layer of enamel. For ease of manufacturing inductive components like transformers and inductors, most of these wires can be soldered. This means that the electrical connections at the ends can be made without stripping off the insulation as for normal insulated wires. Enameled wires are classified by their diameter (AWG number or millimetres), temperature class and isolation class. Class 2 wire has thicker insulation layer resulting in a higher breakdown voltage than class 1 wire. The temperature class indicates the temperature of the wire where it has 20,000 hours service life. At lower temperatures the service life of the wire is longer (about a factor 2 for every 10 °C lower temperature). Common temperature classes are 120, 155 and 180 °C.

Copper is a superior electrical conductor. Aluminum's conductivity is about 62% that of copper when measured on a volume basis. Aluminum does offer lighter weight, because of the metal’s large density difference. That’s why it is often chosen for such applications as pole-top distribution transformers, where light weight can sometimes be beneficial. On the other hand, copper-wound transformers are smaller, and that can be very important too, as we'll explain in a minute.

First cost certainly plays a role. Aluminum-wound transformers are sometimes less expensive initially, but the difference is relatively small for medium-to-large transformers. In that size range, the cost of the windings has surprisingly little to do with the cost of the finished transformer.

Size is the overriding practical reason for using copper. Utility transformers are designed with very large short circuit tolerances, because of the size of the grid and the magnitude of the current flow in the event of a fault. The windings have to be both large enough to handle those currents and strong enough to withstand the mechanical loads they impose. Aluminum's (volumetric) conductivity and its strength are much lower than copper’s, so an aluminum transformer that matched the kVA rating of, say, a 400-MVA copper unit would be huge! It would be too large to transport, and utility or substation transformers are not items that can be assembled on site. All of the transformers make with copper-wound larger transformer are ship by rail. Size can also be important in transformers installed in high-rise buildings, where space is often at a premium.

Another technical issue has to do with what are called continuously transposed cables. These are specially twisted winding conductors that help optimize flux control and reduce losses.  

“Utilities did try aluminum back in the 1970s. Interest rates and inflation were high then, and first-cost considerations got in the way of conventional wisdom. Some utilities bought aluminum-wound transformers because they were initially less costly. They ended up having many more failures than with copper transformers, and, as a result, utilities won't touch aluminum today for transformers .

But what about cost? In a typical large transformer, 50% of the cost is in materials. Of that, about 15% to 20% is for copper and an equal percentage is for steel — structural members and core laminations — with the remainder in oil, insulation and the rest. So we're talking about between 6% and 10% of the total cost of the unit being in the winding material and conductors. The price difference between copper and aluminum wire might vary quite a bit, but its overall effect on total cost is relatively small. Besides, copper offers other savings.

Copper allows us to use less lamination steel because the core is smaller. The low-loss silicon steel we use in some of our transformers is expensive, so using less means more savings. And, because the core and windings are smaller, they need less insulation, less structural steel for the oil tank, less oil to fill it, smaller heat exchangers and pumps to cool it, and so on. Also their a saving on paint. Copper has a favorable multiplying effect on transformer economics.

Copper is also a lot easier to work with. It is said it has better manufacturability than aluminum. Its smaller-diameter conductors are easier to wrap and assemble; also they can use smaller winding equipment, and in-house materials handling is simpler. Also, if you use aluminum, you eventually have to connect to copper somewhere, and dissimilar-metal connections invite problems with corrosion and connectivity. Given all that, copper is prefer.

Utilities also recognize the advantages of all-copper transformers. One regional utility insists on 100% copper for its substation transformers. The company expects a 40- to 50-year life cycle in medium and large transformers, and reliability is very important. So is low maintenance. Utilities conduct periodic oil analyses to check on the condition of internal connections. Any sign that a connection is loose or corroded requires draining the tank and disassembling the unit, taking it off line. Copper’s higher strength and corrosion resistance compared with aluminum means connections stay tight longer, thus reducing life-cycle costs. The utility concluded that, with lower maintenance costs and higher reliability,  the difference in initial cost between copper and aluminum is not a big factor.

Summing Up

Copper is the logical choice for medium-to-large transformers. It keeps the size of completed units small enough to transport easily.

The smaller size of copper transformers saves core steel, as well as structural elements including the tank, oil, cooling equipment and other accessories.

Manufacturing savings and the fact that coils and conductors comprise less than 10% of the cost of the finished transformer minimize the effect of price differences between copper and aluminum.

Copper is stronger than aluminum and, therefore, withstands stresses imposed by fault currents better than aluminum. Because the coil is stronger and less likely to deform, transformer life is extended and lifecycle maintenance costs are reduced.

Copper's better connectivity means that connections inside the unit stay tight, reducing maintenance and prolonging life.
 The initial cost difference between copper and aluminum transformers in this size range is not significant, and lower maintenance and higher reliability make copper the lower-cost material over the life of the transformer.

Copper: preferred by PTTI for better manufacturability.


Great Power Transformer Articles

1. Top 20 Things to Know before Selecting a Power Transformer  - This is a great article to help educate and inform you on how to select the right transformer before you buy. It will help you make an informed decision and covers questions including, what voltage power output do you need?, will it be single phase or three phase?, etc. We answer the 20 most asked questions so you can be well informed and choose the right transformer for the job. Choosing the right transformer can be a daunting task for the inexperienced. This section takes the first step toward becoming a confident, knowledgeable consumer. This article addresses the process of choosing these transformers at its most fundamental level.

2. How Does Transformer Manufacturer Company Brand Affect Power Transformer Quality? - For manufacturers of large power transformers, product design and features seem fairly standard. But different manufacturers offer unique features. there are several standards such as ASTM D 3487 and IEEE Standard C57.12.90. Quality transformers can have a significant impact on cost. Did you know that some transformers brands improved materials, design and quality can save you 30%, or more, in energy cost? Understanding the differences can play a key role in making an informed selection.

3. How Does Winding Metal Type Change a Transformers Properties? - gain knowledge on how the winding and types of metal used can change transformer properties. The conducting material used for the winding depends upon the application. Small power and signal transformers are often wound with solid copper wire. Larger power transformers may be wound with copper wire, or aluminum and may include rectangular conducts. When copper wiring is used it will increase the efficiency of the transformer and will generally generate a lot less heat. Read more to learn about the many other efficiencies gained by choosing a transformer with a metal composition that is fit for your needs

4. Understanding Power Transformer "K-Factor Rating" - A great information article on what "K-Factor Rating" is and the effects they have on transformer choice. The K-Factor rating assigned to a transformer and marked on the transformer case in accordance with the listing of Underwriter Laboratories. It is an index of the transformer's ability to supply harmonic content in its load current while remaining within its operating temperature limits.

Read Addition Power Transformer Articles - Additional informal helpful articles about power transformers.

 Power Transformer Information:

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Power Transformer Types

Step Up and Step Down Transformers Step Up and Step Down Transformers to Power transformers to step-up ( raise) or step-down (lower) the electrical voltage.
Isolation Transformers Isolation Transformers allows signal or power to be taken from one device and fed into another without electrically connecting the two.
Toroidal Transformers Toroidal Transformers are devices that transfer electrical energy from one electric circuit to another, without changing the frequency, by electromagnetic induction.
Custom Transformers
Custom Transformers are designed to meet certain performance specifications and size requirement that you require. There is a wide range of custom transformer types.
Buck Boost Transformers
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
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
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 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.
High Voltage Transformers High Voltage Transformers typically these voltage transformers are used in power transmission applications. High voltage transformers are also used in microwave.

 Power Transformer Manufacturer

  • ACME 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.
  • 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 TransformersFederal 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 TransformersHammond 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 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.
  • GE 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 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 door.
  • More power transformer brands - Check out more companies by clinking this link.

 Power Transformer Types

  • 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 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.

 Power Transformer Types

  • 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. -
  • Step-Down 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
  • 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 electric motors.
  • 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.
  • More power transformer types - Read further about additional transformer types and their uses.

Power Transformer Term Definitions

  • 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 household.
  • Isolating 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 pass. 
  • 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 electromagnetic or acoustic waves as well as electric power transmission. Components of transmission lines include wires, coaxial cables,  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 Phase - Most transformer are either single phase or three phase.
  • 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 electrical equipment.
  • Primary Voltage - The coil winding that is directly connected to the input power.
  • Secondary Voltage - The coil winding  supplying the output voltage.
  • 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.
  • Weatherproof - Enclosed transformers come with a weatherproof standard set by NEMA.
  • 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 conditions.
  • More power transformer terms - Such as inductor, ground fault, core saturation, current transformer, faraday shield, etc.

Related Transformer Products

  • 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 power supply.
  • 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.

For an additional resource the Best of Industry Web Directory : Electrical Power Transformer Directory section is quite useful.

Additional Useful Resources:
Transformer Selection Guide • Custom Transformers • Dry-Type Transformers • Auto Transformers • Control Transformers • Step-Up Transformers • Step-Down Transformers • Harmonic Cancellation • Isolation Transformers • K-Factor Rated Transformers • 3-Phase Transformers • European Voltage Transformers • Drive Isolation Transformers • High Voltage Transformers • Epoxy Encapsulated NEMA 4 Transformers • Weatherproof NEMA 3R Transformers • Transformers • AC Transformer • Voltage Transformer • Buy Transformer • New Transformer • Output Transformer • Transformer KVA • Converter Transformer • Line Transformer • Toroidal Transformer • Oil Filled Transformers • Voltage Regulator • Automatic Voltage Regulator • DC Power Supply • PDU • Rack PDU • Power Conditioner • Power Line Conditioner • Load Center • Switchgear • Voltage Converter • Transformer Wiring • Transformer Circuit • Variable Transformer • Pole Transformer • Transformer Pad • VA Transformer • WYE Transformer • Potential Transformer • Transformer Protection • Variac • Transformer Rating • Sunbelt Transformer • Pacific Transformer • Jefferson Transformer • Electric Transformer • Power Transformer • Transformer Sizing • Transformer Rectifier • Center Tap Transformer • Power Distribution • Industrial Transformer • Replacement Transformer • Insulation Transformer • Micron Transformers • Westinghouse Transformer • Power Supply Transformer • Instrument Transformer • Pulse Transformer • Substation Transformer • Furnace Transformer • Pad Mounted Transformers • Transformer Manufacturer • Distribution Transformers • GE Transformers • Step Up Transformers • Step Down Transformers • Buck Boost Transformers • High Voltage Transformers • Isolation Transformer • Single Phase Transformer • Hammond Transformers • Buck Boost Transformers • Diesel Generators • Diesel Power Generators • Diesel Generator Sets • Power Generators • Onan Diesel Generators • Kipor Diesel Generator • Kubota Diesel Generator • Cummins Diesel Generator • Yanmar Diesel Generator • Variable Frequency Drive • Soft Start Drives • Motor Control • Baldor Motors • Weg Motors