Variable transformers are components that allow the precise control of electrical current, voltage, and power. They are used in conjunction with a variety of other technologies and have applications across many industries, including voltage correction, electrical testing, and heating control. 

As a type of autotransformer, variable transformers do not have a dual-coil core design, meaning that they differ significantly from other types of transformers. There is no separation between the load and voltage source, making it unsuitable for functions aiming to protect operators or devices from high-voltage surges. 

Finding the right variable transformer for your intended application depends on a variety of factors, however, you must do your research beforehand to achieve the intended function. When selecting your variable transformer for your project, here are the basic parameters that you need to consider: 

Voltage Range 

Starting from the basics, the necessary input and output voltage range will vary from application to application. The number of windings in a transformer determines how much voltage a load receives, and these windings may be located at different points along the coil, allowing the voltage to be varied.

Industry applications such as in high-power machinery will require a much higher voltage range than devices used in residential settings. 

Current Capacity 

The current limit of the transformer and the requirements needed for your project will influence your choice. There are significant safety risks when connecting a load that exceeds the maximum current limit, including long-term damage to the transformer and mechanical hazards. 

It’s important to select a transformer with a kVA rating to accommodate the intended load, especially if it is expected to grow in the future. 

Control Mechanisms 

Depending on the type of variable transformer you choose, you will find different control mechanisms available. These typically include manual adjustment, motorized control, or digital interfaces. 

Manual adjustment and motorized control mechanisms are most commonly found in single-phase and three-phase transformers. While still efficient, this means they vary in function compared to digitally controlled devices. 

Different Types of Variable Transformers 

There are two primary types of variable transformers available that offer efficient and hassle-free methods of varying AC voltages. These include: 


Single-phase variable transformers rely on primary and secondary windings that transport the input voltage, typically crafted from copper or aluminum. This type of transformer is better suited to domestic settings and is used in air conditioning, heating systems, and lighting within residential homes. 


Power is generated in three-phase variable transformers using three pairs of windings that are rotated through a magnetic field. This transformer is more efficient, so is used more often in large-scale, industrial settings and heavy-duty machinery. They are often utilized in electrical power systems, including the electrical grid. 

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