10 things to consider when buying a transformer

10 things to consider when buying a transformer

Buying a transformer

Our transformer manufacturing team are here to help you get the transformer specification you are looking for ranging from design, build and installation requirements. However, there are a number of essential principles regarding electrical transformers which are important to know before buying.

Here is a list of points which are important to understand about transformer design.

How many phases are required?

Before choosing a transformer, you need to determine if you require a single phase or a three phase transformer. This will be determined by the equipment you are using.

For example, most households in the UK use single phase as this is ample for most small machines, whereas three phase transformers are more common in large businesses, as well as certain industries.

What voltage?

When designing a transformer you must know the input (primary) voltage and output (secondary) voltage. This is determined by the power supply and the voltage of the equipment you are using.

For example, input (primary) and output (secondary) voltages vary depending on the incoming power supply and output required. Most Military ships require an input voltage of 440v and output voltage of 118v.

What frequency?

The frequency of a transformer is normally determined by your power supply. Sometimes the incoming frequency varies from the output frequency required. This is normally done by using a frequency converter on the output of the transformer.

For example, most UK incoming suppliers run at 50Hz however if a piece of equipment is imported from the US the frequency will be 60Hz. This is where you would require a frequency converter as well as a transformer.

What kVA rating is required?

An important factor of transformer design is determining the load size and nature of the load. Transformer kVA sizing is calculated from the primary or secondary winding voltage and amperage (current) information. Once you have determined the maximum load which is required, you can select the transformer based on that.

What is the purpose of the transformer?

You must also consider the purpose for the transformer, such as; isolation, K-factor or an auto-transformer. This is determined by how the transformer is to be used and what is required.

What environment will the transformer be used in?

It is critical to know where the transformer is going to be used, indoor or outdoor, in a hazardous area or an offshore location which all require different specifications. Most transformers that are used outdoor, are liquid-filled to protect the winding from the elements.

Temperature also plays an important role in transformer design; understanding the working ambient temperatures will ensure operating temperatures are taken into consideration in the design process.

For example, transformers which are used within a hazardous area often need to meet ATEX approval along with other regulations depending on specific requirements.

What are the space requirements?

It is important to take note of what physical sizes are required. Often transformers are designed around standard core sizes, however when required it is possible to design transformers to meet tight space requirements.

For example, on marine vessels or submarines it is hard to lift heavy transformers into place. This is when special design features can be added to the transformer to ensure safe lifting or even reassemble when the transformer is in place.

What standards and approvals are required?

Another critical area to understand is what standards and approvals are required for the specific industry you are operating in.

For example, often for offshore equipment special approvals are required; this may include Lloyds Register, DNV or Atkins depending on the specific use.

What wire configuration is needed?

Transformers can be connected in different configurations to meet almost any requirement. In the case of three-phase transformer windings, three forms of connection are possible; star, delta and interconnected-star.

The combinations of the three windings may be with the primary delta-connected and the secondary star-connected, or star-delta, star-star or delta-delta, depending on the transformers use

For example, standard lighting transformers are often connected delta/star; however when a neutral is required throughout the system a different form of connection is required.

What other things to think about?

  • Power factor
  • Efficiency
  • Impedance
  • Cooling methods


By choosing the right transformer for your application, you can increase the efficiency and the life of the transformer.

If you have any questions regarding the items above or have a special requirement you would like to discuss with us please contact us on 0151 486 6760 or email Eleanor on eleanor@rbaker.co.uk. Our transformer manufacturing team are here to help you understand and guide you to ensure you purchase the transformer which is best equipped for your job.

To see our full transformer range please click here.