Transformer Specifications

9 May 2023

If you are considering purchasing or using a transformer and feel that you do not have enough information about its specifications, this article we have prepared about transformer specifications will be beneficial for you. In this article, we have listed important transformer specifications that are commonly used in every country. These specifications are directly related to the applications and prices of transformers.

Types of Transformers

In the market, there are different types of transformers available depending on the need and the field of use. Depending on your requirements and project, you can choose between box-type transformers or oil-filled transformers.

If you prefer an oil-filled transformer, there are two options available for you to choose from. These are: expansion tank transformer and hermetic transformer.

The expansion tank transformer has an auxiliary oil tank and is sealed. If you prioritize aesthetics, it is more logical to choose a hermetic transformer instead of an expansion tank transformer. These types of transformers also provide environmental safety. Therefore, sealed transformers are generally suitable for use in areas where people are densely populated. For example, city centers, residential areas, urban areas can be preferred for the use of this transformer.

Winding Connection in Transformers

In three-phase transformers, windings can be connected in star, delta, or zigzag arrangements.

When connected in star, the three terminals are connected in a common point, and the other end is left empty, forming a delta connection. Then one end of one phase is connected to the other end. Each phase of the zigzag winding is divided into two halves and connected in series in the opposite direction.

Zigzag connection is a less commonly used type of connection. It is only used in rectifier transformers or measurement transformers to correct phase shift errors.

Nominal Power

The value of transformers is the amount of electrical energy they can convert for the load at the back. A transformer is not an energy conversion device like an electric motor. It only has the function of transmitting and distributing power. Therefore, the rating of the transformer is given in kVA units.

While transmitting power, a machine has two components of power: reactive power kVA and active power kW.

Secondary Voltage


The primary voltage, i.e., the primary voltage of the transformer, is the voltage applied to the ends of the primary winding of the transformer. The energy applied to the primary winding only creates a changing magnetic field in the secondary, resulting in current. The voltage shape applied to the primary winding is sinusoidal.

If the primary has fewer turns than the secondary, you have an elevated transformer, which increases the voltage. If the secondary has fewer turns than the primary, you have a step-down transformer, which reduces the voltage. The third possibility is that the primary and secondary have the same number of turns. This means that the output voltage is the same as the input voltage. This is the case with an isolation transformer.


The secondary voltage refers to the coil that provides the output voltage. The output voltage of a transformer varies depending on the load, even with a constant voltage input.

The degree of variation is influenced by several factors, including the mutual inductance degree between the primary and secondary windings, as well as the resistance of the windings.

Maintaining a constant secondary voltage is essential for applications where the transformer loads a constant voltage source and for differential load currents.

The variation degree is determined by the cooling method and winding size of the transformer. Adjusting the secondary voltage is mainly done to compensate for changes in incoming line voltage. The base secondary voltage is adjusted using an automatic device when the line voltage fluctuates. Usually, a voltage tolerance limit should be maintained to prevent variations in the stable voltage, typically between half a volt and a few volts.

Since a transformer consists of two or more windings connected to each other, applying voltage to the first coil results in current generation. As the magnitude of the applied current changes, the generated current also changes. This changing current establishes a connection between the primary and secondary, inducing a voltage across the secondary.

In general, we have discussed the important technical specifications of transformers. If you want to learn more about the well-known, common features of transformers, you can read our article titled “How Does a Transformer Work?”

Nano Medya