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Ahmedabad Institute of Technology 1 SUB-DC MACHINES AND TRANSFORMER TOPIC-CONSTRUCTION OF SINGLE AND THREE PHASE TRANSFORMER GUIDED BY-PROF.MAYALAKSHMI PILLAI MADE BY-GROUP 3 SEM-3 Made by 2 140020109017 140020109019 140020109020 140020109021 140020109022 140020109023 140020109025 Makvana Mitesh Makvana shivam Urvish maru Dinesh matalani Parmeshwar meena Ronak mishra Nikhil pansuria Introduction 3 Transformer is an electrical device that transfers electrical power from one circuit to another by magnetic coupling. It does so without change of frequency and without any moving parts. Transformer works only with AC supply Construction of transformer 4 The transformer is very simple in construction It consists of magnetic circuit linking with two windings. Continue… 5 The simple element of transformer consist of two coil having mutual inductance and laminated steel core. The two coils insulated from each other and steel core. Other necessary parts are: A suitable container Suitable bushing suitable medium breathers Practical transformer 6 Continue… 7 In all types of transformer the core is constructed of transformer sheet steel lamination assembled to provide a continuous magnetic path within a minimum of air gap included. The steel used is of high silicon content. The eddy current loss is minimized by laminating the core. The lamination being insulated from each other by alight coat of varnish. Continue… 8 The thickness of lamination varies from 0.35 to 0.5 mm . Continue… 9 Constructional transformer are of two types: Core type Shell type Continue.. 10 The transformer called core type because the winding surrounds considerable part of core. The transformer called shell type because core surrounds a considerable part of winding. In diagram of core type transformers the primary and secondary winding are shown located on opposite legs of core but in actual these are interleaved to reduce leakage flux. Continue… 11 Core type transformer 12 The coil used are form wound and are of cylindrical types. But for large size transformers round coils are used. Circular cylindrical coils are used because of their mechanical strength these are wound in helical layers with different layer insulated from each other by paper. Since low voltage winding is easiest to insulate it is placed nearest to core. Continue… 13 Continue… 14 Because of lamination and insulation, the effective core area is reduced. For large size transformer it is wasteful to use rectangular cylindrical coils so circular cylindrical coils are preferred . A common improvement on square core is to employ cruciform core which demand at least two size of core stripes. Cruciform core 15 Shell type 16 In this the winding are put around the central limb& the flux path is completed through two side limbs. The coils are form wound but are multi layer disc type usually wound I the form of pancakes. Advantages of such construction. A relatively more rigid core Lesser weight and size per kVA rating Low iron losses at higher operating flux densities Low cost of manufacture. Shell type transformer 17 Three phase transformer 18 Three phase transformer 19 Large scale generation of electric power is usually 3- phase at generated voltage of 13.2kV or higher. For transmission purpose 3 phase transformer are necessary to step up generated voltage to transmission line. In olden days for this purpose 3 single-phase transformer are interconnected. But nowadays due to improvement in design 3 phase transformer are used. Continue… 20 Advantage of 3phase over single phase transformer It occupies less floor space for same rating. Weight less, cost about 15%less. Only one unit is to be handled and connected. Disadvantage: If any one phase become disabled then whole transformer has to be removed for service. Continue… 21 Cooling in transformer 22 Voltage below 25000V transformer are cooled by air blast no need of oil. For large transformer core and winding are immersed in insulating oil and conservative tank is placed above it. For very large transformer the oil is regulated by means of pump and heat is carried out by water which is flowing in pipes. Breathers 23 In large transformers where complete air tight construction is impossible, chambers are known as breathers are provided to permit thee oil inside the tank to expand and contracts temperature changes. The atmospheric moisture is entrapped in these breathers & is not allowed to pass in oil. Bushings 24 All transformer leads are carried out by suitable bushing. For moderate voltage porcelain bushing are used to insulate the leads as they come out of the tank. They are look like insulators on transmission lines. In high voltage installation oil filled type bushing are used. Conservator tank 25 It is the most important part of transformer for cooling purpose. Its size is depends on the type of transformer and power specification. Insulating mineral oil is filled in the conservative tank. The mineral is used for insulation purpose and for providing cooling in transformer References 26 1.A textbook of electrical technology, volume 2 AC and DC machine, B.L. theraja A.K. theraja, S.chand and company pvt.ltd. 2.DC machine and transformer , Dr J.G. Jamnani, Mahajan publishing house