AI Fame Rush

How to Select the Perfect Size for the Transformers?


How to Select the Perfect Size for the Transformers?

Share this article
high voltage electrical transformers electricity distribution power plant high voltage power lines life power supply close up scaled
High voltage electrical transformers in an electricity distribution power plant. High voltage power lines, life power supply. Close-up

Transformers are one of the key components when it comes to power distribution. This critical electrical component helps determine the power reaching the load from the source. It impacts the performance of electrical systems during operation or in case of malfunction. Intelligent engineers, therefore, ensure that transformers are properly selected for their specific purpose, are perfectly sized, and can deliver sufficient power to electrical loads under specific conditions and regulations. In this article, learn how to choose and size low-voltage transformers.

How can one choose the best transformer for an application?

Transformers are available in various voltages. Capacitance (volt-amps) determines how much current a particular device can handle before it becomes overloaded. The application plays an important role in choosing the right transformer. When selecting a particular transformer, consideration should be given to cases where typical loads may spike.

Parameters to consider when dimensioning a transformer

● Primary & Secondary Voltage

Primary voltage is all voltage provided at the input side of the transformer. Secondary voltage is the voltage output from the transformer. If the available supply voltage is 414V three-phase and the required output is 240V single-phase, select a transformer with 415V input and 240V output.

● Winding connection

For single-phase transformers, winding connections are not a problem, but for three-phase transformers, it is important. In addition, other parameters such as power factor, transformer type, cooling equipment, operating temperature, surge resistance, voltage regulation, and mounting equipment are also considered when selecting a transformer, with a special focus on cutting-edge current transformers for enhanced electrical safety.

● KVA rating

Calculating KVA is very important when choosing and sizing a transformer. It represents the maximum apparent power that the transformer can handle. KVA depends on power factor, voltage, and current.

● Operating frequency

A low-voltage transformer operates at a specific frequency. Solenoid current, rated current, kVA is directly proportional to transformer frequency. Therefore, transformers must operate at their rated frequency. The rated frequency of the transformer should always equal the operating frequency of the input source and load.

New system transformer dimensions

One must size transformers properly due to their critical role in power distribution systems. Sizing makes them fit all application loads. If it is bigger, problems such as load loss can occur in the power distribution system. In general, the sizing of Transformers can be done based on the following two methods.

• Connected load

• Operating load

In both cases, load increases, future plant changes, and other factors such as ambient temperature and altitude must be considered. Growth factors are typically based on each system design and may vary.

The difference between these two methods is determining the total kilovolt-ampere load connected. There are several considerations in deciding which method to use. Some of these are required design margins, project specifications, costs, space availability, and impact on voltage drop and available fault current.


Do not overload the transformer beyond its wattage or amperage rating. It can cause overheating and fire hazards. Select the right size of the low-voltage transformer based on the parameters discussed. Finally, ensure that all strands of copper wire are securely fastened to the terminal block. If unsafe, arcing may occur, causing overheating and potentially a fire hazard