Understanding Power Transformers

Transformers convert an AC system’s electrical power at one current or voltage into electrical power at a different current or voltage without using rotating parts. power transformers provide this critical function as components of electrical and electronic circuits. Besides the common application of stepping voltages up
or down, these magnetic components can also be used to provide isolation for impedance mismatch and other applications.

How Power Transformers Work

Understanding how power transformers work is key to understanding what transformers do. Transformers use magnetic coupling to transfer electrical power between AC circuits—they do not create their own electrical power. The transformer’s core offers a controlled path for the magnetic flux the transformer generates due to the current flowing across the coils.

A basic transformer’s primary components include the input and output connections, the coils, and the core.

Input and Output Connections

A transformer’s input side is known as the primary side as the primary electrical power which needs to be changed is connected on this side. The output side is commonly referred to as the power transformer’s secondary side. On this side, electrical power is transferred to the load. This incoming transferred electric power may be either decreased or increased depending on the load’s requirement.



Transformers have more than two coils, or windings. These are known as the primary and secondary windings. The primary coil draws power from the power source. The secondary coil delivers the energy at the altered voltage and current to the load. These transformer windings are normally subdivided into many coils to minimize the creation of flux.

What the coils are made of depends entirely on the application of the transformer. Small power and signal transformers use insulated solid copper wire, while large power transformers use aluminum or copper strip or rectangular conductors.


The core of the transformer provides a controlled path for the magnetic flux that the transformer creates. Rarely, the core may be a solid bar of silicon steel. More commonly, the core often comprises several layers of thin laminated silicon steel sheets. This construction significantly minimizes heating by lowering the eddy current effect.

Transformers usually have one of two types of cores—the core type and the shell type. How the primary and secondary windings are placed around the steel core distinguishes these two types of cores. With a core type, the coils surround the laminated core. With a shell type, the laminated core surrounds the coils.

Know the Transformer Lingo

Once you get a good grasp on a power transformer’s overall design and how it works, you can better understand some critical terms that professionals commonly use when talking about transformers.

Inrush Current

The inrush current refers to the instant high-input current that a transformer draws from electrical equipment or a power supply when it turns on. This occurs because of the high initial current that is needed to charge the transformers or inductors and capacitors.

Magnetizing Current

Magnetizing current refers to the current that flows into the primary side of a transformer while a particular frequency and voltage is energizing the transformer with open-circuited secondaries. Magnetizing current is a slight misnomer as it is, in fact, the sum of the current necessary to supply the losses in the winding and the amount of current necessary to magnetize the core.

Short Circuit Impedance

Short circuit impedance is the same impedance at reference temperature and rated frequency across the terminals of one coil of a pair while the terminals of the one coil has short-circuited and the other coil is open-circuited.

Request Your Power Transformer Today

MPS offers many varieties of power transformers which we can customize to meet the needs of any application. Examples of transformer types we provide include:

  • Balun transformers
  • Flyback transformers
  • Planar transformers
  • Toroidal transformers

MPS Industries, Inc., manufactures a wide array of custom magnetic components for industries such as automotive, aerospace, defense, medical, and OEM. For more information on power transformers, request a quote or contact us today.

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