What are harmonics in transformers?

In transformers, harmonics refer to the presence of frequencies that are multiples of the fundamental frequency in the electrical system. To understand harmonics in transformers, let's start with a real-life example.

Harmonics chart

Imagine a residential area with several houses connected to a common electrical grid. Each house has multiple appliances such as refrigerators, air conditioners, televisions, computers, etc., which are powered by electrical energy. When these appliances are operating, they consume electrical power from the grid.

Sample example.

Now, consider one specific appliance, let's say a computer, which has a power supply that converts the incoming alternating current (AC) from the grid into direct current (DC) for its internal components. The power supply of the computer is designed to draw a certain amount of power from the grid at a specific frequency, typically 50 or 60 Hertz (Hz).

However, due to various factors such as non-linear loads (appliances that do not draw current in a sinusoidal manner), electronic devices, and other disturbances, the current drawn by the computer may not be a perfect sinusoidal wave. Instead, it may have distortions and additional frequency components that are multiples of the fundamental frequency.

These additional frequency components are the harmonics. For example, if the fundamental frequency is 50 Hz, the harmonics would include frequencies such as 100 Hz (2nd harmonic), 150 Hz (3rd harmonic), 200 Hz (4th harmonic), and so on. These harmonics can distort the sinusoidal waveform of the current flowing through the transformers.

Problems caused by harmonics in transformer

When harmonics are present in the electrical system, they can cause several issues. One significant problem is increased heating in the transformers. Harmonic currents generate additional losses in the transformer's windings and core, leading to higher temperatures and potential degradation of the insulation materials. This can reduce the lifespan of the transformer and increase the risk of failure.

Harmonics can also cause voltage distortion, affecting the quality of power supplied to other appliances in the electrical system. This can lead to malfunctioning or reduced efficiency of sensitive electronic equipment.

How to avoid the harmonics?

To mitigate the negative effects of harmonics, transformers can be designed to handle harmonic currents more effectively. Special transformers, such as K-rated transformers or harmonic mitigating transformers, are designed to reduce losses and handle the increased heating caused by harmonics.

In summary, harmonics in transformers refer to the additional frequency components that are multiples of the fundamental frequency present in the electrical system. They can cause issues such as increased heating and voltage distortion, which can be mitigated through appropriate transformer design and the use of harmonic mitigating devices.

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