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Harmonics in Electrical System: Mitigation (2nd Series)
Harmonics in Electrical System: Mitigation (2nd Series)

September 11, 2024

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Having understood the various causes and the impacts of the Harmonics in the previous article, this article offers various avenues for its mitigation.


In an alternating current (AC) system, the voltage potential and the current through load circuit is described in terms of frequency and amplitude. The frequency of the current will be identical to the frequency of the voltage as long as the load resistance/impedance does not change.  In a linear load, like a resistor, capacitor or inductor, current and voltage will have the same frequency. As long as the characteristics of the load components do not change, the frequency component of the current will not change. When we deal with non-linear loads such as switching power supplies, transformers which saturate, capacitors which charge to the peak of the supply voltage, and converters used in drives, the characteristics of the load are dynamic. As the amplitude of the voltage changes and the load impedance changes, the frequency of the current will change. That changing current and resulting complex waveform is a result of these load changes. In short, a linear load would have a uniform waveform and a non-linear load would have a non-uniform or disturbed waveform deciding the health of the system.

Having understood the various causes and the impacts of the Harmonics in the previous article, this article offers various avenues for its mitigation. 

Reduction of Harmonics Effects:

Harmonic problems is best resolved through prevention. This involves selecting equipment and installation practices that minimize harmonics in circuits or facility sections. Often, power quality issues arise when new equipment is added to older systems without proper consideration.

Even within existing facilities, simple solutions can address problems related to harmonics. These include improving grounding or earthing for individual equipment or the entire facility, redistributing loads across branch circuits, or adding new circuits to isolate sensitive equipment from the source of harmonic distortion.

If these straightforward measures don’t cater to the solution, there are two main options:

Strengthening the Distribution System: Install double-size neutral cables or separate neutral cables for each phase. Consider oversized or harmonically protected and rated transformers to enhance heat dissipation. Note that this option is more suitable for new facilities due to retrofitting costs.

- Installing Harmonic-Resistant Devices: Use harmonic-rated circuit breakers and panels to prevent overheating caused by harmonics. Explore passive harmonic filters, isolation transformers, and active filters (which vary in cost).

Operations of Harmonic Filters

The functions of recommended harmonic filters are described below which would reduce the overall impact of the harmonic effect:

Types of Filters

Here’s a look at some of the most effective filters:

 

Criterion for Selection of Harmonic Filter:
The selection of harmonic filter must be based on the following criteria
1. kVA requirements of the load 
2. Harmonic profile of the load current 
3. Harmonic factor of the neutral current
4. Configuration of existing or proposed system

In this article, we have explained the fundamentals of harmonic effects and strategies to mitigate their impact. Specifically, the use of specific harmonic filters available in the market. These filters should align with the guidance provided by electrical consultants to ensure the right filters are selected for the required electrical system.

 

Before implementing any filters, conducting a thorough power quality check using Power Analyzer tests is essential. This step helps us understand the exact harmonics effect and its existing levels.

 

Also Read: Colliers | Harmonics in Electrical System: Sources and Effects (1st Series)

About the Author:

Imran Khan| Director | Real Estate Management Services


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