Types of Single-Phase Transformers

What Are the Three Types of Single-Phase Transformers?

Single-phase transformers are commonly used in residential, commercial, and light industrial power distribution. Based on structure and insulation medium, they are generally classified into three types: dry-type transformers, oil-immersed transformers, and autotransformers.

Dry-Type Single-Phase Transformer

Dry-type transformers do not use oil for insulation; instead, they are cooled by air or resin. These transformers are ideal for indoor environments such as hospitals, schools, and buildings where fire safety is critical. Key benefits include:

• Environmentally friendly and pollution-free

• Low maintenance costs

• High safety performance

However, dry-type transformers are more sensitive to ambient temperature and are typically used in applications below 2000 kVA.

Oil-Immersed Single-Phase Transformer

Oil-immersed transformers use insulating oil for cooling and insulation. They are widely applied in outdoor electrical distribution systems. Features include:

• Excellent heat dissipation and stable performance

• Suitable for long-term heavy load operation

• Generally lower in price than dry-type models

These units require regular maintenance and oil testing, and they are not ideal for indoor areas with strict fire protection standards.

Autotransformer

An autotransformer has a single winding acting as both the primary and secondary. This design is compact and efficient, making it popular in applications such as testing equipment and motor startup. Advantages include:

• Lower cost and smaller size

• Minimal energy loss

• Easy to install

However, it lacks electrical isolation between input and output, so it is not suitable for protective applications.

Summary

Dry-type, oil-immersed, and autotransformers represent the three major types of single-phase transformers, each suited to specific environments and performance needs. Choosing the right type involves evaluating safety, cost, space, and application requirements.

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