Types of Electrical Harmonics in Power Systems

After understanding what harmonics are, the next important step is to understand the types of electrical harmonics that appear in power systems.

Electrical harmonics are additional frequency components that exist along with the fundamental frequency of 50 Hz in India. These harmonics distort the waveform of voltage and current and can affect the performance of electrical equipment.

In this blog, we will explore the Types of Electrical Harmonics and understand how they appear in electrical systems.

Types of Electrical Harmonics

Electrical harmonics are generally classified based on the order of the harmonic frequency relative to the fundamental frequency.

If the fundamental frequency is 50 Hz, the harmonic frequencies will be:

• 3rd harmonic → 150 Hz

• 5th harmonic → 250 Hz

• 7th harmonic → 350 Hz

• 9th harmonic → 450 Hz

These harmonics are called harmonic orders.

Harmonics are broadly classified into the following types.

Odd Harmonics

Odd harmonics are the most common harmonics found in electrical power systems.

They occur at odd multiples of the fundamental frequency.

Examples include:

• 3rd harmonic

• 5th harmonic

• 7th harmonic

• 9th harmonic

Odd harmonics are mainly generated by non-linear loads, such as:

• Variable Frequency Drives (VFDs)

• UPS systems

• Rectifiers

• LED drivers

• SMPS power supplies

Among these, the 3rd and 5th harmonics are usually the most dominant in many electrical installations.

Even Harmonics

Even harmonics occur at even multiples of the fundamental frequency, such as:

• 2nd harmonic

• 4th harmonic

• 6th harmonic

In most well-designed electrical systems, even harmonics are very small or negligible.

The presence of significant even harmonics usually indicates:

• equipment malfunction

• asymmetric operation

• faults in power electronic devices

Therefore, engineers often treat large even harmonics as an indication of abnormal system behavior.

Triplen Harmonics

Triplen harmonics are a special category of harmonics that occur at multiples of three.

Examples include:

• 3rd harmonic

• 9th harmonic

• 15th harmonic

Triplen harmonics have a unique behavior in three-phase systems.

Instead of canceling each other, they add together in the neutral conductor. This can lead to:

• overheating of neutral cables

• excessive neutral currents

• increased losses in distribution systems

This problem is particularly common in commercial buildings and IT facilities with many computers and electronic loads.

Interharmonics

Interharmonics are frequencies that do not follow exact integer multiples of the fundamental frequency.

They appear between the standard harmonic frequencies.

Interharmonics are typically generated by:

• variable speed drives

• arc furnaces

• cycloconverters

• power electronic converters

These harmonics can cause:

• flicker in lighting systems

• interference in communication systems

• instability in power systems

Total Harmonic Distortion (THD)

To measure the overall impact of harmonics, engineers use a parameter called Total Harmonic Distortion (THD).

THD represents the percentage distortion of the waveform caused by harmonics.

There are two common types:

Voltage THD

Measures distortion in the voltage waveform.

Current THD

Measures distortion in the current waveform.

International standards such as IEEE 519 provide guidelines for acceptable harmonic limits in electrical systems.

Why Understanding Harmonic Types Is Important

Understanding the types of electrical harmonics helps engineers:

• identify the source of harmonic distortion

• design proper electrical systems

• select appropriate mitigation methods

• prevent equipment damage

Different harmonic orders affect equipment in different ways, which is why harmonic analysis is an important part of modern power system design.

Wrapping Up

Electrical harmonics can be classified into odd harmonics, even harmonics, triplen harmonics, and interharmonics. Each type behaves differently in electrical systems and can affect equipment performance in different ways.

As modern electrical systems increasingly use power electronic devices, understanding these harmonics becomes essential for maintaining power quality and system reliability.

In the next blog, we will explore how harmonics are generated in different electrical equipment such as chargers, LED drivers, computers, rectifiers, and drives.