Short Answer:

An autotransformer has only one single winding that acts as both the primary and the secondary, while a two-winding transformer has separate primary and secondary windings. In an autotransformer, part of the same winding is common to both input and output sides.

The main differences lie in construction, cost, efficiency, and electrical isolation. Autotransformers are lighter, cheaper, and more efficient but do not provide electrical isolation, unlike two-winding transformers, which fully isolate the input from the output for safety and protection.

Detailed Explanation:

Difference between autotransformer and two-winding transformer

Transformers are used to change voltage levels in electrical systems. Depending on the internal winding structure, they are categorized into autotransformers and two-winding transformers. Although both serve the purpose of voltage transformation, their construction, performance, and applications differ significantly.

Autotransformer:

An autotransformer uses a single continuous winding that serves both the input (primary) and the output (secondary). A part of the same winding is tapped to obtain the desired output voltage. Since the winding is shared, the input and output are electrically connected.

In this transformer:

• The power is transferred both conductively and inductively.
• Less copper and core material are used.
• It is suitable for small voltage changes, such as 230V to 200V.

Two-Winding Transformer:

In a two-winding transformer, there are two separate windings: one for the primary (input) and another for the secondary (output). These windings are wound on the same core but are electrically isolated from each other.

Here:

• Power transfer happens purely by induction.
• There is no direct electrical connection between the input and output.
• It is suitable for applications where isolation and high voltage transformation are necessary.

Key Differences:

1. Winding Structure:
   • Autotransformer: One winding with taps
   • Two-winding transformer: Two separate windings
2. Electrical Isolation:
   • Autotransformer: No isolation between input and output
   • Two-winding transformer: Complete isolation
3. Size and Cost:
   • Autotransformer: Smaller, lighter, and cheaper
   • Two-winding transformer: Larger and more expensive
4. Efficiency:
   • Autotransformer: Higher efficiency due to reduced losses
   • Two-winding transformer: Slightly lower efficiency
5. Applications:
   • Autotransformer: Used for voltage regulation, motor starting, and stabilizers
   • Two-winding transformer: Used in power systems, substations, and where isolation is essential

When to Use Each Type:

• Autotransformer is ideal when voltage change is minor and there is no requirement for electrical isolation. It is often used in voltage stabilizers, starting induction motors, and laboratory testing setups.
• Two-winding transformer is preferred for general power distribution, transmission, and where equipment or user safety is important due to the isolation it provides.

Conclusion:

An autotransformer differs from a two-winding transformer mainly in its construction and the way it transfers power. While an autotransformer has a single shared winding and offers better efficiency and lower cost, it lacks electrical isolation. A two-winding transformer, on the other hand, ensures complete isolation and is widely used for safer power delivery in most electrical systems. The choice depends on safety, voltage range, and cost considerations.