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.

1. WELCOME TO MY
PRESENTATION

2. Submitted by:
Md. Atikul Islam Ashik
162-33-3507
Submitted to:
Md. Nahid Reza
Department of EEE
Daffodil International University

3. TOPIC
Auto Transformer

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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