Electrical Power transformer, definitions and its types
A transformer, a static machine used in converting power from one circuit to another without any need to change in frequency. This defines the work of a transformer. It is a static device where there is no rotation or moving part. Transformer works on ac supply. The basic principle of a transformer is mutual induction.
History of Transformer
If you are interested in knowing about the history of transformer we have to rewind back to 1880s. In 1830 property of induction, the working principle of transformer was found. Later the transformer design was enhanced leading to more performance and smaller size. Progressively the huge capacity of transformers with several KVA range, MVA was introduced. During 1950, 400KV electric power transformer was found in high voltage electrical power system. At the start of 1970s, a 1100 MVA unit rating was generated followed by 800KV and even higher KV class transformers were built during the year of 1980.
Applications of Power Transformer
Electrical energy generation at lower voltage level is very much affordable. Actually the receiving end receives the transmitted low voltage power. But if this is transmitted then it will lead to greater line current that will lead to more losses. And if you increase the voltage power, there is a reduction in the power of the current which causes reduction in ohmic or I2R losses in the system, decrease in capital cost due to reduction of the cross sectional area of the conductor and it also enhances the voltage regulation the system.
Therefore low-level power must be stepped up for effective electric power transmission. Step up transformer completed this work at the receiving end of the electrical power system. And now the Step down transformer comes into the picture because the high power voltage cannot be directly distributed to the customers. This shows the importance of transformer in electrical power transmission.
The reason behind the usage of the two winding transformers are usually where the ratio of high voltage and low voltage is greater than 2. In such cases one can use an auto transformer where the ratio between the higher and the lower voltage is less than 2.
Comparatively, a single unit three phase transformer is affordable when compared to a bank of three single phase transformers. The only draw back is a single three phase transformer is difficult to maintain because even if one of the phases breaks down then you need to discard the entire device.
Types of Transformer
Transformers can be classified in different ways, based upon upon their objective, use, construction
etc. The types of transformer are as follows,
1) Step Up Transformer and Step Down Transformer – This is actually used for stepping up and down the voltage levels of power in transmission and distribution power system network.
2) Three Phase Transformer and Single Phase Transformer – Three phase is mostly used in three phase power system as it is affordable than later. But when size comes into the picture, it is more suitable to use a bank of three single phase transformer as it is convenient to transport than one single phase transformer unit.
3) Electrical Power Transformer, Distribution Transformer and Instrument Transformer – For stepping up or down the voltage levels in the transmission network, power transformers are used. It works mainly during high or peak loads and has the highest possible performance at or near full load. Distribution transformer steps down the voltage for distribution to domestic or commercial customers. It has good voltage reputation and works all the day with the highest possible performance at 50% of full load. Instrument transformers include C.T and P.T are mainly for reducing high voltages and current to lesser values which can be read by conventional instruments.
4)Two Winding Transformer and Auto Transformer –
When the ratio between high voltage and low voltage is greater than 2 then you can use two winding transformer. Auto transformer is used when the ratio is lesser than 2 and it is easily affordable.
5) Outdoor Transformer and Indoor Transformer – Transformers used for setting up at the outdoors is called Outdoor Transformer and the one used for indoor purpose is called indoor transformer.
6) Oil Cooled and Dry Type Transformer – Oil is used as a medium for cooling in the oil cooled transformer and air is the medium used for cooling in the dry cooled transformer.
7) Core type, Shell type and Berry type transformer – Core type transformer consists of two vertical legs or divisions with two horizontal sections known as yoke. Core is rectangle-shaped common magnetic circuit. The limb contains cylindrical coils (HV and LV).
Shell type transformer: It contains a central limb and two external limbs. The central limb contains both HV, LV coils. It contains a double magnetic circuit.
Berry type transformer: It contains wheel like spokes at its core. Metal sheet tanks are welded and are used for sheltering this type of transformer with transformer oil filled inside.
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