What is the difference between transformer and autotransformer

zhengxi
30 November, 2024
Transformers knowledge

Autotransformers and traditional transformers are both common electrical equipment in power systems. They both use the principle of electromagnetic induction to adjust the voltage, but they are very different in structure, working principle and application occasions. The following is a comparison between the two:

Autotransformer vs. Traditional Transformer Comparison Chart

Feature	Autotransformer	Traditional Transformer
Structure¹	Primary and secondary share part of the winding	Primary and secondary have separate windings
Voltage Conversion Principle	Partial shared windings, voltage changes according to winding ratio	Complete isolation, voltage change based on turns ratio
Voltage Ratio Range	Suitable for voltage ratios of up to 2-3 times	Can handle larger voltage ratios
Efficiency	High efficiency, low loss	Slightly lower efficiency due to more windings and losses
Size & Weight	Compact, lightweight	Bulkier, heavier
Cost	Lower cost	Higher cost
Electrical Isolation	No complete electrical isolation, lower safety	Complete electrical isolation, higher safety
Applications	Motor starting, voltage regulation	High voltage transmission, applications requiring electrical isolation
Safety	May cause over-voltage issues, requires additional protection	High safety, suitable for high-risk environments

What are the advantages and disadvantages of autotransformer?

Advantages

1) Higher efficiency:
Because the windings of the autotransformer are shared, the energy transfer loss is smaller and it is more efficient than traditional transformers. It is particularly suitable for applications that require high efficiency and low power.
2) Smaller size and weight:
Because there are fewer windings and less material required, the autotransformer is small and light. This saves space and is particularly suitable for applications with limited space.

208 to 120 control power transformer — Traditional Transformer

Disadvantages

(1) Limited voltage conversion range
The voltage conversion of the autotransformer is achieved through the turns ratio of the windings, but because their windings are shared, the voltage conversion range is usually small. Generally speaking, it is suitable for applications where the voltage ratio does not exceed 2-3 times. If a larger range of voltage conversion is required, a traditional transformer is more suitable.
(2) Poor electrical isolation
The primary and secondary windings of the autotransformer share part of the winding, which means that there is no complete electrical isolation between them. In some situations where strict electrical isolation is required, such as high voltage or sensitive equipment, it may not be safe to use an autotransformer.

Summary

The main difference between transformer and autotransformer

Autotransformer is suitable for occasions with small voltage ratio change, high efficiency and energy saving, and low requirements for electrical isolation, such as motor starting, voltage regulation, etc.

Traditional transformers are more suitable for occasions that require high electrical isolation and large voltage ratio, such as high-voltage power transmission, protection of power networks and isolation of electrical equipment.

In general, autotransformers have the advantages of high efficiency, energy saving, small size and low cost, and are widely used in industry, transportation and new energy fields. However, in occasions that require high safety, voltage isolation or large voltage conversion, traditional transformers are still a better choice.

How many windings are normally found in an autotransformer
The biggest difference between an autotransformer and a traditional transformer is the number of windings. A traditional transformer has two completely independent windings, one primary and one secondary. An autotransformer has only one winding, which is used as both the primary and secondary windings. The primary and secondary achieve voltage conversion by sharing part of the winding. ↩︎