Does an EMC filter reduce harmonics?

In the world of power electronics and industrial automation, understanding power quality is essential. One of the most common questions engineers and system integrators ask is: “Does an EMC filter reduce harmonics?” The answer is more nuanced than a simple yes or no.

Understanding Harmonics

Harmonics are unwanted frequencies that distort the ideal AC sine wave. They are integer multiples of the fundamental frequency. For example, if the supply frequency is 50Hz (as in Australia), the harmonics would be at 100Hz, 150Hz, 200Hz, etc. The third harmonic is at 150Hz, the fifth at 250Hz, and so on.

These distortions are typically introduced by non-linear loads such as Variable Speed Drives (VSDs), computers, LED lighting, and inverters.

Signs You May Have Harmonics in Your System

• Flickering lights

• Unexpected tripping of MCBs, RCDs, or MCCBs

• Unexplained alarms

• Overheating of cables, switchboards, or motors

• Frequent failure of automation systems or insulation

• Premature wear on motor bearings

These symptoms can indicate harmonic distortion affecting your electrical infrastructure.

Why Harmonics Are Dangerous

Harmonics do more than just distort voltage and current waveforms:

• Cause overheating of components and cables

• Reduce equipment lifespan, especially for motors, PLCs, and inverters

• Decrease power system efficiency

• Lead to costly downtime and repairs

• Result in paying for unusable power

To counter these problems, the industry turns to harmonic mitigation techniques.

What Is Harmonic Mitigation?

Harmonic mitigation refers to strategies and technologies used to reduce or eliminate harmonic distortion in electrical systems. The aim is to restore clean sine waveforms and ensure system longevity and energy efficiency.

There are multiple devices used for harmonic mitigation, depending on the location and source of the distortion.

Harmonic Mitigation Devices

On the Input (Line) Side of a VSD

Line Reactors

• Also called inductors or chokes

• Reduce harmonic distortion

• Protect semiconductors

• Improve power factor

• Minimize surge currents

Passive Harmonic Filters

• Designed to attenuate harmonics generated by VSDs and inverters

• Can reduce THD (Total Harmonic Distortion) to 5–6%

• Improve voltage and current waveforms

• Reduce cable heating and system losses

• Help comply with IEEE 519 and AS/NZS 61000.3.6 standards

Active Harmonic Filters

• Monitor and dynamically correct harmonic currents

• Can bring THD to below 5%

• Address multiple loads simultaneously at the main distribution board

• Improve efficiency, reduce maintenance

• Provide reactive power compensation

On the Output (Load) Side of a VSD

Load Reactors

• Protect motors from reflected wave damage

• Reduce harmonic distortion on the motor side

• Lower audible noise and surge currents

dV/dT Filters

• Protect motor windings from steep voltage spikes

• Improve insulation life

• Reduce peak voltages and EMI

Sine Wave Filters

• Convert PWM waveform into a true sine wave

• Greatly reduce motor heating and noise

• Allow use of unshielded motor cables

• Eliminate voltage reflections and common-mode currents

Where Does an EMC Filter Fit In?

What Is an EMC Filter?

An EMC (Electromagnetic Compatibility) filter, also known as an EMI (Electromagnetic Interference) filter, is primarily used to:

• Suppress high-frequency noise

• Ensure compliance with EMC regulations

• Prevent line-conducted interference, typically between 150 kHz and 30 MHz

It works by introducing impedance mismatches and filtering components (inductors and capacitors) to block unwanted frequencies in both directions—network to equipment and equipment to network.

EMC Filter vs Harmonic Filter

Conclusion? While an EMC filter is crucial for EMC compliance, it does not significantly reduce harmonics. For that, you need dedicated harmonic mitigation equipment such as passive or active harmonic filters.

Advanced Filter Solutions That Combine EMC and Harmonic Mitigation

Some manufacturers, like Noordin Etech, offer filter combinations—for example, a three-phase line choke combined with an EMC filter. These hybrid solutions can:

• Reduce harmonic reactive power

• Minimize both EMI and harmonics

• Lower energy costs by up to 20%

Other advanced filters such as REOWAVEpassive also target THD and improve system efficiency while reducing component stress.

For more information, please refer to our article <What are the components of EMC filter?> to explore real-world applications and product comparisons.