Step-Down Transformers

See also;   TEMCo Step-Down Transformers

A Step-down transformer is one whose secondary voltage is less than its primary voltage. The step down transformer is designed to reduce the voltage from the primary winding to the secondary winding.

This kind of transformer "step down" the voltage applied to it. They often range in voltage sizes from 0.5 kva to 500 kva.

There is many uses for step-down transformer and the larger devices are used in electric power systems, and small units in electronic devices.  Industrial and residential power transformers that operate at the line frequency (60 Hz in the U.S.), may be single phase or three-phase, are designed to handle high voltages and currents.  Efficient power transmission requires a step-up transformer at the power-generating station to raise voltages, with a corresponding decrease in current.  Line power losses are proportional to the square of the current times the resistance of the power line, so that very high voltages and low currents are used for long-distance transmission lines to reduce losses. At the receiving end, step-down transformers reduce the voltage, and increase the current, to the residential or industrial voltage levels, usually 115 to 600 V.

In electronic equipment, transformers with capacities in the order of 1 kw are largely used ahead of a rectifier, which in turn supplies direct current (DC) to the equipment.  Such electronic power transformers are usually made of stacks of steel alloy sheets, called laminations, on which copper wire coils are wound. Transformers in the 1-to100-W power level are used principally as step-down transformers to couple electronic circuits to loudspeakers in radios, television sets, and high-fidelity equipment.  Known as audio transformers, these devices use only a small fraction of their power rating to deliver program material in the audible ranges, with minimum distortion.  The transformers are judged on their ability to reproduce sound-wave frequencies (from 20 Hz to 25 kHz) with minimal distortion over the full sound power level.

How does a step-down transformer work?

A transformer is a electrical device with one winding of wire placed close to one or more other windings, used to couple two or more alternating-current circuits together by employing the induction between the windings. A transformer in which the secondary voltage is higher than the primary is call a step-up transformer, if the secondary voltage is less than the primary, then its a step-down transformer. The product of current times voltage is constant in each set of windings, so that in a step-up transformer, the voltage increase in the secondary is accompanied by a corresponding decrease in the current.

 Factors in choosing a step-down transformer:

Transformers must be efficient and should dissipate as little power as possible in the form of heat during the transformation process. Efficiencies are normally above 99 percent and are obtained by using special steel alloys to couple the induced magnetic fields between the primary and secondary windings.  To increase transformer efficiency and reducing heat one of the most important considerations is choosing the metal type of the windings. Copper windings is more efficient than aluminum and other winding metal choices.  Transformers with copper windings cost more initially, but can save on electrical cost and maintenance over time and more than makes up for the initial cost. The dissipation of even 0.5 percent on the power transmitted in a large transformer generates a large amount of heat, which requires special cooling. Typical power transformers are installed in sealed containers that have oil or another substance circulating through the windings to transfer the heat to external radiator-like surfaces, where it can be discharged to the surroundings.

Information on a typical step-down transformer:

A transformer is a device for stepping-up or stepping-down electric signal. Without efficient transformers, the transmission and distribution of ac electric power over long distances would be impossible.

 Typical transformer

There are two circuits; the primary circuit, and the secondary circuit. There is no direct electrical connection between the two circuits, but each circuit contains a winding which links it inductively to the other circuit. In transformers, the two windings are wound onto the same iron core. The purpose of the iron core is to channel the magnetic flux generated by the current flowing around the primary windings, so that as much of it as possible also links the secondary winding. The common magnetic flux linking the two windings is conventionally denoted in circuit diagrams by a number of parallel straight lines drawn between the windings. In other words, the ratio of the peak voltages and peak currents in the primary and secondary circuits is determined by a the ratio of the number of turns in the primary and secondary windings; this latter ratio is usually called the turns ratio of the transformer. If the secondary winding contains more turns than the primary winding then the peak voltage in the secondary circuit exceeds that in the primary circuit. This type of transformer is called a step-up transformer, because it step us the voltage of an ac signal. Note that the peak current in the secondary circuit is less than the peak current in the primary circuit in  a step-up transformer (as must be the case if energy is to be conserved). Thus, a step-up transformer actually steps down the current. Likewise, if the secondary winding contains less turns than the primary winding then the peak voltage in the secondary circuit is less than that in the primary circuit. This type of transformer is called a step-down transformer. Note that a step-down transformer actually steps up the current (i.e., the peak current in the secondary circuit exceeds that in the primary circuit).

The use of step-up and step-down transformers in power distribution stations:

Electricity is generated in power stations at a fairly low peak voltage (sometime like 440V), and is consumed at a peak voltage of 110V to 220V for households and businesses in the U.S.  AC electricity is transmitted from the power station to the location where it is consumed at a very high peak voltage (typically 50,000V). As soon as a ac signal comes out of the generator in a power station it is fed into a step-up transformer and fed into a high tension transmission line, and transports the electricity over many miles, and once the electricity has reached its point of consumption, it is fed through a series of step-down transformers until its peak voltage is often reduced down to 110V.

If Electricity is both generated and consumed  at low peak voltages, why go to the trouble of stepping up the peak voltage to a very high value at the power station and then stepping down the voltage again once the electricity has reached its point of consummation? Why not generate, transmit, and distribute the electricity at a voltage of 110V? Consider an electric power line which transmits a peak electric power between a power station and a city. We can think of the number of consumers in the city and the nature of the electrical devices which they operate, as essentially a fixed number. Suppose that the peak voltage and peak current of the ac signal are transmitted along the line. We can think of these numbers as being variable, since we can change them using a transformer. However, since, the product of the peak voltage and the peak current must remain constant. The resistance of the line causes power loses that are greater at lower voltages over distance. The peak rate at which electrical energy is lost due to ohmic heating in the line is high.

If the power transmitted down the line is a fixed quantity, as is the resistance of the line, then the power lost in the line due to ohmic heating varies like the inverse square of the peak voltage in the line. It turns out that even at very high voltages, such as 50,000 V, the ohmic power losses in transmission lines which run over ten kilometers can amount to up to 20% of the transmitted power. It can readily be appreciated that if an attempt were made to transmit ac electric power at a peak voltage of 110V then the ohmic losses would be so severe that virtually none of the power would reach it destination.  It is only possible to generate electric power at a central location, transmit it over large distances, and then distribute it at its point of consumption, if the transmission is performed at a very high peak voltage (the higher, the better). Transformers play a vital role in this process because they allow us to step-up and step-down the voltage of a ac electric signal very efficiently. A well designed transformer typically has a power loss which is only a few percent of the total power flowing through it.

Power Transformer Sources: Power Transformer * Step Up Transformer * Step Down Transformer * Electrical Transformer * Isolation Transformer * Toroidal Transformer * Acme Transformer * High Voltage Transformer * Distribution Transformer * Transformer Manufacturer * Three Phase Transformer * Dry Type Transformer * 3 Phase Transformer * Cast Transformer * Voltage Transformers * Variac * Voltage Stabilizer * Voltage Regulators

 Power Transformer Information:

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 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 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.

• Starting Capacitor For use with single phase motors and gearmotor applications.
• Run Capacitor For use with 1 and 3 phase motors.
• Start Cap TEMCo offers a wide selection of start caps.
• Air Conditioner Capacitor For use with air conditioners.
• Replacement Capacitor Learn when you need to replace a capacitor and how to pick a new one.
• Motor Capacitor Need help with motor capacitor facts? Check out our FAQ here.
• Test Capacitor Need help with testing a capacitor? Check out our tutorial here.

 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.