Auto transformer 3507
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This document presents information about autotransformers. It discusses that an autotransformer has a single winding that acts as both the primary and secondary winding. The document then covers the theory of operation, types (step-up and step-down), advantages like reduced copper usage and size, disadvantages like lack of input-output isolation, applications like voltage regulation, and limitations such as safety issues if the winding insulation fails. The presentation aims to provide an overview of autotransformers.
Auto transformer 3507
- 2. Submitted by: Md. Atikul Islam Ashik 162-33-3507 Submitted to: Md. Nahid Reza Department of EEE Daffodil International University
- 4. CONTENTS 1. Autotransformers 2. Theory Of Autotransformers 3. Types Of Autotransformers 4. Step Up Autotransformers 5. Step Down Autotransformers 6. Advantages Of Autotransformers 7. Disadvantages Of Autotransformers 8. Applications Of Autotransformers 9. Limitations Of Autotransformers
- 5. AUTOTRANSFORMER An autotransformer (sometimes called auto step down transformer) is an electrical transformer with only one winding. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer.
- 6. THEORY OF AUTOTRANSFORMER N1=primary turn(1-3) N2=secondary turn(2-3) I1=primary current I2=secondary current V1=primary voltage V2=secondary voltage From Figure 1 we get:
- 7. OUTPUT The primary and secondary windings of an autotransformer are Connected magnetically as well as electrically. So the power transferred primary to secondary inductively as well as conductively.
- 8. TYPESOF AUTOTRANSFORMERS Step Up Auto-Transformer Step Down Auto-Transformer
- 9. STEP UP AUTO- TRANSFORMER An autotransformer in which Ns>Np is called a step up autotransformer. A step up autotransformer is a transformer which converts low alternated voltage to high alternated voltage.
- 10. STEP DOWN AUTO- TRANSFORMER An autotransformer in which Np>Ns is called a step down autotransformer. A step down autotransformer is a transformer which converts high alternating voltage to low alternating voltage.
- 11. ADVANTAGES OF AUTOTRANSFORMERS An autotransformer requires less Cu than a two-winding transformer of similar rating. An autotransformer operates at a higher efficiency than a two-winding transformer of similar rating. An autotransformer has better voltage regulation than a two-winding transformer of the same rating. An autotransformer has smaller size than a two-winding transformer of the same rating. An autotransformer requires smaller exciting current than a two-winding transformer of the same rating.
- 12. DISADVANTAGES OF AUTOTRANSFORMERS There is a direct connection between the primary and secondary. Therefore, the output is no longer D.C. isolated from the input. An autotransformer is not safe for stepping down a high voltage to a low voltage. If an open circuit develops in the common portion of the winding, then full-primary voltage will appear across the load. In such a case, any one coming in contact with the secondary is subjected to high voltage. This could be dangerous to both the persons and equipment. For this reason, autotransformers are prohibited for general use. The short-circuit current is much larger than for the two-winding transformer of the same rating. So that a short-circuited secondary causes part of the primary also to be short- circuited. This reduces the effective resistance and reactance.
- 13. APPLICATIONS OF AUTOTRANSFORMERS • Autotransformers are used to compensate for voltage drops in transmission and distribution lines. When used for this purpose, they are known as booster transformers. • Autotransformers are used for reducing the voltage supplied to a.c motors during the starting period • Autotransformers are used for continuously variable supply. • On long rural power distribution lines, special autotransformers with automatic tap-changing equipment are inserted as voltage regulators, so that customers at the far end of the line receive the same average voltage as those closer to the source. The variable ratio of the autotransformer compensates for the voltage drop along the line. • In control equipment for 1-phase and 3-phase electrical locomotives.
- 14. LIMITATIONS OF AUTOTRANSFORMERS • Because it requires both fewer windings and a smaller core, an autotransformer for power applications is typically lighter and less costly than a two-winding transformer, up to a voltage ratio of about 3:1; beyond that range, a two-winding transformer is usually more economical. • Like multiple-winding transformers, autotransformers operate on time- varying magnetic fields and so will not function with DC. • A failure of the insulation of the windings of an autotransformer can resultin full input voltage applied to the output. Also, a break in the part of the winding that is used as both primary and secondary will result in the transformer acting as an inductor in series with the load.
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