Electric Transformers

Because there are so many contexts in which electronic transformation is necessary, there exist a wide variety of electric transformers to accommodate them. Auto transformers, step up and step down transformers, toroidal transformers, zig zag transformers and pulse transformers are just a few examples. By transferring electrical energy through two coil stages, transformers can increase, decrease, isolate, translate and pattern electrical currents to safely power electronic equipment of all voltage requirements. Electric transformer manufacturers configure transformers differently to meet all types of electric transformation applications and range in size from thumb-sized transformers in electric lamps or microphones to the enormous stationary transformers in power facilities. Low voltage transformers convert electrical currents into voltages that fit appliances such as dimmer lights and other small electronic devices, while high voltage transformers are used in the transmission of electricity between power generation facilities and its points of consumption. Most transformers are isolation transformers because they facilitate the transmission of electricity through induction, and many transformers are 3 phase transformers, capable of transforming electricity in 3 phases.

In addition to converting currents to a higher or lower voltage, electric transformers can serve to isolate parts of circuits from others. Auto transformers, however, have no isolation between the source and load circuit; they transmit electricity through conductors that are in contact with each other. An electric transformer can be as large as the fenced-in transformers for whole facilities, or they may be small enough to be tucked away in household appliances such as light fixtures. Electric transformers are necessary when there is a voltage difference between an electronic component or appliance and an electrical power supply. Safety is of the utmost concern in such situations, since using a voltage that is too high or too low to power a device can cause serious problems. Excessive voltage can cause device failure or destruction; in severe cases, over-voltage can cause fires and can expose users to powerful electric shocks. In the case of under-voltage, voltage deficiency can also cause device failure.

Instrument transformers, including current transformers, accurately measure and monitor power voltage as it is transmitted proportionally through the primary and secondary coils. Step down transformers convert higher voltages to lower voltages by having fewer secondary coil windings, while step up transformers' higher number of secondary coil windings allow them to convert lower voltages to higher voltages. Toroidal transformers are donut-shaped transformers that are highly space efficient and excellent for reducing electromagnetic interference; inductors limit the amount of AC flow to an appliance or transient application while suppressing high frequency noise, similar to toroids. Isolation transformers decouple two circuits, allowing AC power to move from one device to another without the two circuits connecting; this is achieved by having the primary and secondary coils not directly connected. Inverters are capable of converting direct current voltage (DC) to alternating current voltage (AC), while pulse transformers create the electrical surges that are used in telecommunication and detail logic applications such as camera flashes, radar equipment and particle acceleration. In addition, zig zag transformers are special-purpose 3-phase transformers that are intended for use in providing earthing for ungrounded electrical systems as well as filtering and controlling harmonic currents.
Electric transformers are comprised of two sets of coils or windings linked by a magnetic field. The core is iron or a ferrite compound or a laminated core wound with bare copper or enameled coils. The coils are primary and secondary and function as conductors. When the primary coil receives AC voltage, this produces a varying magnetic field of voltage surrounding the conductor; the magnetic field activates the secondary conductor coil. This results in the transformers changing the voltage and transferring electrical energy, ideally with the least amount of energy loss. The number of windings on each coil is important, as this determines the voltage that is conveyed from the primary to the secondary through the magnetic field. The ratio of turns (also called windings) in the primary coil to the number of turns in the secondary coil determines the magnitude of the voltage; for example, a step down transformer will have fewer turns in its secondary coil than the primary, while a step up transformer will have more secondary coil windings than primary. Once the voltage conversion is made, the energy is transferred to the load center and the electrical process continues from there. Both the size and expense of electric transformers increases in proportion to the number of primary windings.

Images Provided by Johnson Electric Coil Company

Image Provided by Lenco Electronics, Inc.

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Electric Transformer Types

• 3 phase transformers are tools used to change the voltage of 3 phase electrical transmission systems.
• Auto transformers are electrical transformers with one winding that is common between both circuits and does not have any isolation between the two circuits.
  
• Current transformers have a primary winding linked in with the circuit to make the current measurable; they are used to change electrical currents.
  
• Distribution transformers are rated between 3 and 500 KVA with 601 volts or more.
  
• Dry type transformers do not use liquid to cool or insulate.
  
• High resistance transformers have high leakage-to-reactance to limit the output current to a designated value in the event of a fault.
  
• High voltage transformers are designed to handle electrical energy in high voltage levels.
• Instrument transformers accurately measure and monitor power voltage as it is transmitted proportionally through the primary and secondary coils.
• Inverters convert between AC and DC power.
• Isolation Transformers are transformers that insulate the primary circuit from the secondary circuit.
  
• Low voltage transformers convert into lower voltages.
• Power transformers are devices that convert voltage to lower levels.
• Pulse transformers are wide-band devices that are mainly intended for waveform transmission. They transmit rectangular electrical pulses, meaning that the pulses have fast rise and fall times with a fairly constant amplitude.
• Step down transformers have the power to convert higher voltages to lower voltages by means of transferring electrical energy through two coil stages, the second coil stage having fewer coil windings.
• Step up transformers are transformers that have a high voltage winding connected to the output load and a low voltage winding connected to the power source.
  
• Toroidal transformers have copper wire around a cylindrical core so the magnetic flux is contained.
  
• Transformers are a static piece of apparatus that transfers electrical energy from one circuit to another circuit by electro-magnetic induction, often with altered values of voltage and current.
• Zig Zag Transformers are special-purpose three-phase transformers that are intended for use in providing earthing for ungrounded electrical systems as well as filtering and controlling harmonic currents.

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Electric Transformer Terms Air Cooled - A transformer that uses air to cool by use of fans or normal ventilation. Auto Transformer - A transformer with one winding per phase. Banked - Describes multiple single phase transformers connected together to provide power to a three phase load. Core - The transformer's central part or inductor that enhances the power of the magnetic field.   Core Saturation - A condition that results from a transformer or inductor reaching highest magnetic strength. Delta - In a three phase connection the windings all connect to form a loop. Duty Cycle - proportion of time for a transformer to provide full rated power to the load. This measurement greatly affects the actual size of the transformer.   Electrostatic Shielding - A component that sits between windings - typically the primary and secondary - to supply the most isolation; more of these can be placed between secondary windings as needed. It is normal to connect the shielding to the core. Encapsulated - A dry transformer with an enclosed core and coil assembly. Exciting Current - The amount of current a transformer draws at nominal voltage input in an unloaded state.   Ferroresonance - Resonance results from the saturation of a ferrous core of an inductive component, which increases the inductive reactance relative to the capacitance reactance.   Filter - A complex system within the transformer that consists of capacitors, inductors and a resistor; it provides a relative small opposition to specific frequencies or direct current, as it blocks or attenuates other frequencies. Flexible Connector - A conductor that can handle thermal expansion and contraction as well as reduce noise. Impedance - That the forces that resist the flow of current in AC circuits like resistance or inductive or capacitive reactance.   Inductance - The capability of a coil for storing energy and resisting changes in the flow of current; it is a function of the core material, amount of turns of the coil and the cross section.   Inrush Current - This is when the transformer has a short current surge through it from residual flux, occurring at the moment energy is applied to the transformer.   Isolation Transformer - This transformer has physical separation from the primary and secondary windings in order to allow magnetic coupling between isolated circuits and minimize electrostatic coupling. KVA - Kilovolt Ampere rating that is a measurement of the output of a transformer without exceeding a certain temperature. Load - The quantity of electric power supplied or necessitated at any particular spot in the system. Also a requirement of the KVA or VA from the transformer; light bulbs are loads.   Magnetic Shielding - This conductive material attenuates stray magnetic fields by its positioning around a transformer's coils. Polarity - The direction of the current between two leads. If the directions are the same, the leads have the same polarity. In electric transformers the polarity is classified as either additive or subtractive. Power Factor - Watts divided by volt amps, KW divided by KVA - the leading and lagging of voltage versus current caused by inductive or capacitive loads. Harmonic power factor relates to nonlinear current.   Rated Power - The total of the Volts and Amps derived from all the secondary windings.   Reactance - The opposition to variations of alternating current; capacitive reactance relates to capacitors, and inductive reactance is the opposition to change from an inductor or coils.   Resonance - A condition of an AC circuit in which capacitive and inductive reactances interact, resulting in a maximum or minimum circuit impedance. Secondary Winding - On the load or output side, the connected transformer winding. Sudden Pressure Relay - Pressure switch device that detaches the transformer from the line. Voltage - The measurement of the amount of force on a unit charge because of the surrounding charges. Voltage Regulation - The change, in percentages, of the output voltage from no load to full load.   Voltage Taps - Supplemental connections to a winding that permit varying voltages from the same winding; typically utilized on the primary winding to permit the transformer to be used in different countries with varying line voltages.

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