9 Different Types of Power Transformers

The 9 Different Types of Power Transformers

9 Different Types of Power Transformers

Power transformers are essential parts of our electric infrastructure, but they serve different purposes and come in different shapes and sizes. What are transformers used for, and where can we find them?

Transformers are machines with no moving parts that convert electrical energy from one circuit to another. Transformers keep frequency constant but can modify voltage and current levels depending on their configuration. 

Voltage and current are inversely related. If voltage is increased, the current goes down, and vice versa. Depending on the need, a transformer can optimize one or the other of these metrics. There are various reasons we may want to do this. It can be changed again later down the line using another transformer. 

There are several different types of power transformers designed for various purposes and situations. Here are a few broad classifications of commonly used transformers on the power grid. Some of these descriptors refer to the function, while others describe different configurations or how they are mounted. So a particular unit may fit into several of these categories.

How does it affect the voltage?

This is the most important aspect of how transformers differ from each other. By far, most transformers are used to either raise or lower voltage levels. Sometimes this is done for efficiency, other times for safety. 

Step Up Transformers

A step up transformer converts low-voltage, high-current power to high-voltage, low-current power. 

These units are most commonly used at the source of the power generation before it’s loaded onto the power grid. Generating electricity is most efficient at a low voltage. But transmitting electricity at low voltage results in a great deal of loss. Step up transformers are used to change the power to a high voltage, which is much less prone to loss.

Step Down Transformers

Step down units do the opposite of step up transformers. They convert high-voltage, low-current power to lower-voltage, higher-current power.
These transformers are used at various steps between long-distance energy transmission systems and other parts of the grid where voltage is reduced for use in multiple applications. These units can be large enough to take all the power needed for a whole community or very small, such as the one in your cell phone charger.

There are different types of step down transformers:

  • Substation transformers – These are large units that take power off the grid at 46k to 161k volts and convert it to lower voltages for distribution – typically between 2.4k and 35k.
  • Distribution transformers – These are relatively small transformers used to bring power to individual homes from distribution lines. In some industrial applications, they may actually be used to step up power.

How is it cooled?

As you might guess, as electricity passes through a power transformer, it generates a lot of heat. This heat needs to be dissipated to prevent damage to the components and even fire. Typically, we cool transformers by circulating some fluid through the system to carry the heat outward. The most common fluids used for this purpose are air and oil.

Dry Type Transformers

Dry type systems circulate air to cool their cores. Smaller systems are often set up so that natural convection moves the heated air out and cool air in so they’re constantly being cooled without mechanical intervention. 

For larger units, it’s sometimes necessary to use forced air if the natural flow isn’t enough to keep things cool. At a certain temperature, fans will turn on, blowing cool air directly into the core and cooling it rapidly. 

Oil Cooled Transformers

In oil-cooled transformers, the core is immersed in oil. Like air, oil rises when heated. When the heated oil comes into contact with air, it transfers the heat by convection into the atmosphere. Like with dry type transformers, oil-cooled types can be cooled faster by using fans to circulate the air around the oil tank more quickly. Some even use pumps to circulate the oil. 

How many windings?

This classification gets into the nuts and bolts of how power transformers work. Transformers have a primary side (where the electric current originates from) and a secondary side (the output). These two sides can consist of two separately wound wires or one wire that acts as both. 

Two Winding transformers

This configuration is also known as a conventional transformer. It consists of two windings that are magnetically coupled but electrically insulated from each other. This is the standard type of transformer for most applications as it is more efficient where the change in voltage, either up or down, is greater than doubled.

Auto Transformers

In this type of transformer, one winding is used: one part as primary and another part as secondary. This means the two sides are connected magnetically through the core and electrically through the wire. Auto transformers are useful in applications where the change in voltage is less than double.

How is it mounted?

How a transformer is mounted for service is the next question. You’ve most likely seen both pole-mounted and pad-mounted distribution transformers. You may not have seen mobile transformers.

Pole-Mounted Transformers

This refers to distribution transformers mounted on powerlines as they go into individual homes and businesses. They are typically drum-shaped devices near the top of powerlines and are often oil-cooled. 

Pad-Mounted Transformers

These distribution transformers have been mounted to concrete pads on the ground. These are common in more urban areas and are fed from underground wires. These are the green metal casings you’ve seen around residential and commercial buildings and are typically oil-cooled. 

Mobile transformers

These units are less common and typically only used for large substation transformers. They are used in situations where transformers or entire substations are needed temporarily in a particular location. They are typically mounted on semi-trailers. 

UTB Transformers has the right unit for your applications

Whether you’re looking for power transformers for a new project or replacing older transformers, UTB can help. We have a wide variety of options to fit different industrial and residential needs. We have the knowledge to provide guidance and install your equipment properly. Contact us today to get a quote.