TYPES OF TRANSFORMERS PDF
PDF | Transformers may be classified according to dielectric insulation material as follows: • Oil-filled transformers• Dry type transformers. identify the common types of transformers from their schematic diagrams. size overcurrent protection for dry-type transformers operating at V or less. TRANSFORMER TYPES. Instrument transformers. Instrument transformers comprise a large category of current and potential transformers for various voltage.
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latively common point of view on most of those transformers types. Keywords: classification, distribution transformers, power transformers, reactors, transfor-. There are various types of transformer used in the electrical power system for different purposes, like generation, distribution and transmission and utilization of . This article discusses different types of transformers and their applications. step- up, step-down, air core, iron core, power transformer, indoor& outdoor.
The energy is drawn out from the second coil and thus can be called as the secondary winding. In short, a transformer carries the operations shown below: Transfer of electric power from one circuit to another.
Transfer with the principle of electromagnetic induction.
The two electrical circuits are linked by mutual induction. The two coils are insulated from each other and from the steel core.
The device will also need some suitable container for the assembled core and windings, a medium with which the core and its windings from its container can be insulated. In order to insulate and to bring out the terminals of the winding from the tank, apt bushings that are made from either porcelain or capacitor type must be used.
In all transformers that are used commercially, the core is made out of transformer sheet steel laminations assembled to provide a continuous magnetic path with minimum of air-gap included.
The steel should have high permeability and low hysteresis loss. For this to happen, the steel should be made of high silicon content and must also be heat treated.
By effectively laminating the core, the eddy-current losses can be reduced. The lamination can be done with the help of a light coat of core plate varnish or lay an oxide layer on the surface. For a frequency of 50 Hertz, the thickness of the lamination varies from 0. Types of Transformers Types by Design The types of transformers differ in the manner in which the primary and secondary coils are provided around the laminated steel core.
According to the design, transformers can be classified into two: 1. The coils used for this transformer are form-wound and are of cylindrical type. Such a type of transformer can be applicable for small sized and large sized transformers. In the small sized type, the core will be rectangular in shape and the coils used are cylindrical. The figure below shows the large sized type. You can see that the round or cylindrical coils are wound in such a way as to fit over a cruciform core section.
In the case of circular cylindrical coils, they have a fair advantage of having good mechanical strength. The cylindrical coils will have different layers and each layer will be insulated from the other with the help of materials like paper, cloth, micarta board and so on. The general arrangement of the core-type transformer with respect to the core is shown below. Both low-voltage LV and high voltage HV windings are shown. Core Type Transformer Cruciform Section Core Type Transformers The low voltage windings are placed nearer to the core as it is the easiest to insulate.
The effective core area of the transformer can be reduced with the use of laminations and insulation. The comparison is shown in the figure below.
Core Type and Shell Type Transformer Winding The coils are form-wound but are multi layer disc type usually wound in the form of pancakes. In power plant, this transformer is used as connecting transformer of the generator to the grid.
It used to step down the voltage level from lower to higher level at secondary side as shown below so that it is called as a step-down transformer. The winding turns more on the primary side than the secondary side.
In distribution networks, the step-down transformer is commonly used to convert the high grid voltage to low voltage that can be used for home appliances. Based on the medium placed between the primary and secondary winding the transformers are classified as Air core and Iron core.
Types of Transformer
Both the primary and secondary windings are wound on a non-magnetic strip where the flux linkage between primary and secondary windings is through the air. Compared to iron core the mutual inductance is less in air core, i. But the hysteresis and eddy current losses are completely eliminated in air-core type transformer. Both the primary and secondary windings are wound on multiple iron plate bunch which provide a perfect linkage path to the generated flux.
It offers less reluctance to the linkage flux due to the conductive and magnetic property of the iron. These are widely used transformers in which the efficiency is high compared to the air core type transformer. Standard transformers have primary and secondary windings placed in two different directions, but in autotransformer windings, the primary and the secondary windings are connected to each other in series both physically and magnetically as shown in the figure below.
On a single common coil which forms both primary and secondary winding in which voltage is varied according to the position of secondary tapping on the body of the coil windings.
According to the necessity, these are classified as the power transformer, distribution transformer measuring transformer, and protection transformer. The power transformers are big in size. They are suitable for high voltage greater than 33KV power transfer applications.
It used in power generation stations and Transmission substation. It has high insulation level.
In order to distribute the power generated from the power generation plant to remote locations, these transformers are used. This applies to both types of instrument transformers. Correct identification of terminals and wiring is essential for proper operation of metering and protective relay instrumentation.
Main article: Current transformer Current transformers used in metering equipment for three-phase ampere electricity supply A current transformer CT is a series connected measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary. Current transformers are commonly used in metering and protective relays in the electrical power industry.
Current transformers are often constructed by passing a single primary turn either an insulated cable or an uninsulated bus bar through a well-insulated toroidal core wrapped with many turns of wire.
Working Principle of Transformer
The CT is typically described by its current ratio from primary to secondary. Standard secondary current ratings are 5 amperes or 1 ampere, compatible with standard measuring instruments. The secondary winding can be single ratio or have several tap points to provide a range of ratios. Care must be taken to make sure the secondary winding is not disconnected from its low-impedance load while current flows in the primary, as this may produce a dangerously high voltage across the open secondary and may permanently affect the accuracy of the transformer.
Specially constructed wideband CTs are also used, usually with an oscilloscope , to measure high frequency waveforms or pulsed currents within pulsed power systems. One type provides a voltage output that is proportional to the measured current.
Another, called a Rogowski coil , requires an external integrator in order to provide a proportional output. A current clamp uses a current transformer with a split core that can be easily wrapped around a conductor in a circuit.
This is a common method used in portable current measuring instruments but permanent installations use more economical types of current transformer. Voltage transformer or potential transformer[ edit ] Voltage transformers VT , also called potential transformers PT , are a parallel connected type of instrument transformer, used for metering and protection in high-voltage circuits or phasor phase shift isolation.
They are designed to present negligible load to the supply being measured and to have an accurate voltage ratio to enable accurate metering. A potential transformer may have several secondary windings on the same core as a primary winding, for use in different metering or protection circuits.
The primary may be connected phase to ground or phase to phase. The secondary is usually grounded on one terminal. There are three primary types of voltage transformers VT : electromagnetic, capacitor, and optical.
The electromagnetic voltage transformer is a wire-wound transformer. The capacitor voltage transformer uses a capacitance potential divider and is used at higher voltages due to a lower cost than an electromagnetic VT.
An optical voltage transformer exploits the electrical properties of optical materials. An optical voltage transformer is not strictly a transformer, but a sensor similar to a Hall effect sensor.
Combined instrument transformer[ edit ] Combined instrument transformer A combined instrument transformer encloses a current transformer and a voltage transformer in the same transformer.
There are two main combined current and voltage transformer designs: oil-paper insulated and SF6 insulated. Small versions called signal types are used in digital logic and telecommunications circuits, often for matching logic drivers to transmission lines. Medium-sized power versions are used in power-control circuits such as camera flash controllers. Larger power versions are used in the electrical power distribution industry to interface low-voltage control circuitry to the high-voltage gates of power semiconductors.
Special high voltage pulse transformers are also used to generate high power pulses for radar , particle accelerators , or other high energy pulsed power applications.
In power-type pulse transformers, a low coupling capacitance between the primary and secondary is important to protect the circuitry on the primary side from high-powered transients created by the load. For the same reason, high insulation resistance and high breakdown voltage are required.
A good transient response is necessary to maintain the rectangular pulse shape at the secondary, because a pulse with slow edges would create switching losses in the power semiconductors. The product of the peak pulse voltage and the duration of the pulse or more accurately, the voltage-time integral is often used to characterise pulse transformers. Generally speaking, the larger this product, the larger and more expensive the transformer. Pulse transformers by definition have a duty cycle of less than 0.
RF transformer[ edit ] There are several types of transformer used in radio frequency RF work. Laminated steel is not suitable for RF.
Air-core transformer[ edit ] These are used for high frequency work. The lack of a core means very low inductance. All current excites current and induces secondary voltage which is proportional to the mutual inductance. Ferrite-core transformer[ edit ] Ferrite-core transformers are widely used in impedance matching transformers for RF, especially for baluns see below for TV and radio antennas.
Many only have one or two turns. Transmission-line transformer[ edit ] For radio frequency use, transformers are sometimes made from configurations of transmission line, sometimes bifilar or coaxial cable, wound around ferrite or other types of core.
This style of transformer gives an extremely wide bandwidth but only a limited number of ratios such as , or can be achieved with this technique. The core material increases the inductance dramatically, thereby raising its Q factor.
The cores of such transformers help improve performance at the lower frequency end of the band. RF transformers sometimes used a third coil called a tickler winding to inject feedback into an earlier detector stage in antique regenerative radio receivers. In RF and microwave systems, a quarter-wave impedance transformer provides a way of matching impedances between circuits over a limited range of frequencies, using only a length of transmission line.
The line may be coaxial cable, waveguide, stripline , or microstrip. Main article: Balun Baluns are transformers designed specifically to connect between balanced non-grounded and unbalanced grounded circuits. These are sometimes made from configurations of transmission line and sometimes bifilar or coaxial cable and are similar to transmission line transformers in construction and operation.The rectangular cores are made up of stampings, often in E-I shape pairs, but other shapes are sometimes used.
What is Wave Propagation? Electric transformers.
Types of Transformer
This article needs additional citations for verification. Instrument transformer is an electrical device used to transform current as well as voltage level. Institution of Electrical Engineers. There are several types of transformer used in radio frequency RF work. Share This Post: To minimize distortion of the pulse shape, a pulse transformer needs to have low values of leakage inductance and distributed capacitance , and a high open-circuit inductance.
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