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. 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:. In core-type transformer, the windings are given to a considerable part of the core. 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. 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. In shell-type transformers, the core surrounds a considerable portion of the windings. The comparison is shown in the figure below. The coils are form-wound but are multi layer disc type usually wound in the form of pancakes. Paper is used to insulate the different layers of the multi-layer discs.
The whole winding consists of discs stacked with insulation spaces between the coils. These insulation spaces form the horizontal cooling and insulating ducts. Such a transformer may have the shape of a simple rectangle or may also have a distributed form. Both designs are shown in the figure below:. A strong rigid mechanical bracing must be given to the cores and coils of the transformers.
This will help in minimizing the movement of the device and also prevents the device from getting any insulation damage. A transformer with good bracing will not produce any humming noise during its working and will also reduce vibration. A special housing platform must be provided for transformers.
Usually, the device is placed in tightly-fitted sheet-metal tanks filled with special insulating oil. This oil is needed to circulate through the device and cool the coils.
It is also responsible for providing the additional insulation for the device when it is left in the air. There may be cases when the smooth tank surface will not be able to provide the needed cooling area. In such cases, the sides of the tank are corrugated or assembled with radiators on the sides of the device.
The oil used for cooling purpose must be absolutely free from alkalis, sulphur and most importantly moisture. Even a small amount of moistures in the oil will cause a significant change in the insulating property of the device, as it lessens the dielectric strength of the oil to a great extent. Mathematically speaking, the presence of about 8 parts of water in 1 million reduces the insulating quality of the oil to a value that is not considered standard for use.
Thus, the tanks are protected by sealing them air-tight in smaller units. When large transformers are used, the airtight method is practically difficult to implement. In such cases, chambers are provided for the oil to expand and contract as its temperature increases and decreases. These breathers form a barrier and resist the atmospheric moisture from contact with oil. Special care must also be taken to avoid sledging. Sledging occurs when oil decomposes due to overexposure to oxygen during heating.
It results in the formation of large deposits of dark and heavy matter that clogs the cooling ducts in the transformer.
The quality, durability and handling of these insulating materials decide the life of the transformer. All the transformer leads are brought out of their cases through suitable bushings. There are many designs of these, their size and construction depending on the voltage of the leads. Porcelain bushings may be used to insulate the leads, for transformers that are used in moderate voltages.
Oil-filled or capacitive-type bushings are used for high voltage transformers. The selection between the core and shell type is made by comparing the cost because similar characteristics can be obtained from both types.
Most manufacturers prefer to use shell-type transformers for high-voltage applications or for multi-winding design. When compared to a core type, the shell type has a longer mean length of coil turn. Other parameters that are compared for the selection of transformer type are voltage rating, kilo-volt ampere rating, weight, insulation stress, heat distribution and so on.
Transformers can also be classified according to the type of cooling employed. The different types according to these classifications are:. Oil filled self-cooled type uses small and medium-sized distribution transformers. The assembled windings and core of such transformers are mounted in a welded, oil-tight steel tanks provided with a steel cover. The tank is filled with purified, high quality insulating oil as soon as the core is put back at its proper place. The oil helps in transferring the heat from the core and the windings to the case from where it is radiated out to the surroundings.
For smaller sized transformers the tanks are usually smooth surfaced, but for large size transformers a greater heat radiation area is needed, and that too without disturbing the cubical capacity of the tank. This is achieved by frequently corrugating the cases. Still larger sizes are provided with radiation or pipes. This type is used for much more economic construction of large transformers, as the above-told self-cooled method is very expensive. Being one of the words best solutions means you can never go wrong with RALE.
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You can even create your custom core library with DadMatrac. Soft Bit Online gives you the power to modify core and conductor insulation, connection groups and flux density. By optimizing your design, you will get desired costing, average possible losses, performance, and more. Prolific Transformer Design Software is easy to use solution. It features a simple user interface, fast loading speed and it is the best tool for those who are looking for a simple tool to work with.
Being able to design your model on platforms other than the popular and commonly used Windows Operating System does make it possible for you to design the best object for your project irrespective of your type and version of your Operating System.
Here is a list of the additional software solutions that you will find useful. The software for Window is for electrical engineers who want to learn or teach how to design the best transformers on the Windows Operating System. It is easy to use and free to download. If the secondary output voltage is to be the same value as the input voltage on the primary winding, then the same number of coil turns must be wound onto the secondary core as there are on the primary core giving an even turns ratio of 1-to In other words, one coil turn on the secondary to one coil turn on the primary.
If the output secondary voltage is to be greater or higher than the input voltage, step-up transformer then there must be more turns on the secondary giving a turns ratio of 1:N 1-to-N , where N represents the turns ratio number. Transformer Action We have seen that the number of coil turns on the secondary winding compared to the primary winding, the turns ratio, affects the amount of voltage available from the secondary coil.
But if the two windings are electrically isolated from each other, how is this secondary voltage produced? We have said previously that a transformer basically consists of two coils wound around a common soft iron core. As the magnetic lines of force setup by this electromagnet expand outward from the coil the soft iron core forms a path for and concentrates the magnetic flux. This magnetic flux links the turns of both windings as it increases and decreases in opposite directions under the influence of the AC supply.
However, the strength of the magnetic field induced into the soft iron core depends upon the amount of current and the number of turns in the winding. When current is reduced, the magnetic field strength reduces. When the magnetic lines of flux flow around the core, they pass through the turns of the secondary winding, causing a voltage to be induced into the secondary coil. The amount of voltage induced will be determined by: N. Also this induced voltage has the same frequency as the primary winding voltage.
Then we can see that the same voltage is induced in each coil turn of both windings because the same magnetic flux links the turns of both the windings together. As a result, the total induced voltage in each winding is directly proportional to the number of turns in that winding.
If we want the primary coil to produce a stronger magnetic field to overcome the cores magnetic losses, we can either send a larger current through the coil, or keep the same current flowing, and instead increase the number of coil turns NP of the winding.
So assuming we have a transformer with a single turn in the primary, and only one turn in the secondary. If one volt is applied to the one turn of the primary coil, assuming no losses, enough current must flow and enough magnetic flux generated to induce one volt in the single turn of the secondary.
That is, each winding supports the same number of volts per turn. For the primary winding emf, N will be the number of primary turns, NP and for the secondary winding emf, N will be the number of secondary turns, NS.
Also please note that as transformers require an alternating magnetic flux to operate correctly, transformers cannot therefore be used to transform or supply DC voltages or currents, since the magnetic field must be changing to induce a voltage in the secondary winding. If a transformers primary winding was connected to a DC supply, the inductive reactance of the winding would be zero as DC has no frequency, so the effective impedance of the winding will therefore be very low and equal only to the resistance of the copper used.
Transformer Basics Example No3 A single phase transformer has turns on the primary winding and 90 turns on the secondary winding. The maximum value of the magnetic flux density is 1. Calculate: a. The maximum flux in the core. The cross-sectional area of the core. The secondary induced emf. Electrical Power in a Transformer Another one of the transformer basics parameters is its power rating. The power rating of a transformer is obtained by simply multiplying the current by the voltage to obtain a rating in Volt-amperes, VA.
Small single phase transformers may be rated in volt-amperes only, but much larger power transformers are rated in units of Kilo volt-amperes, kVA where 1 kilo volt-ampere is equal to 1, volt-amperes, and units of Mega volt- amperes, MVA where 1 mega volt-ampere is equal to 1 million volt- amperes. In an ideal transformer ignoring any losses , the power available in the secondary winding will be the same as the power in the primary winding, they are constant wattage devices and do not change the power only the voltage to current ratio.
Thus, in an ideal transformer the Power Ratio is equal to one unity as the voltage, V multiplied by the current, I will remain constant. Although the transformer can step-up or step-down voltage, it cannot step-up power.
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