Understanding Electrical Harmonics in Building Power Systems

Modern buildings rely heavily on electronic equipment. While this equipment improves efficiency and functionality, it also introduces a common power quality issue known as harmonics.

What Are Harmonics?

According to the Fourier series, any waveform can be represented as a series of sine waveform. For example, a rectangular shaped waveform can be broken up into a series of sine waveforms of fundamental frequency and harmonic multiples of the fundamental frequency.

In an ideal electrical system, voltage and current waveforms are perfect sinewaves made up of just the fundamental frequency.

What Causes Harmonics?

Harmonics are caused by non-linear electrical loads — equipment that does not draw current evenly. These loads switch off and on the sinewave, chopping it in essence and thus creating a different shaped waveform. This waveform as discussed can be represented by the original waveform and a series of harmonics at multiple of the frequnecy of the fundamental.

Type loads which intoduce harmonics are:

• Variable speed drives (VSDs)

• Uninterruptible power supplies (UPS)

• LED lighting

• IT equipment and data centre servers

  
  

As buildings become more technology-driven, harmonic levels tend to increase.

Why Harmonics Matter

Harmonics can have serious effects on building electrical systems.

Overheating of Equipment

Harmonic currents increase heating in:

• Transformers

• Cables

• Switchgear

• 
  

This can shorten equipment life and reduce reliability.

Neutral Conductor Overloading

In three-phase systems, triplen harmonic currents combine in the neutral conductor rather than cancelling out which may lead to the neutral requiring to be oversized, increasing costs.

Reduced System Efficiency

Harmonics increase losses within the electrical system, leading to:

• Higher energy consumption

• Reduced capacity of electrical infrastructure or unnecessary oversizing

Interference and Malfunctions

Excessive harmonics can:

• Disrupt sensitive electronic equipment

• Cause nuisance tripping of protective devices

• Interfere with monitoring and control systems

How Harmonics Are Managed

Electrical harmonics can be controlled through good system design and appropriate mitigation measures, including:

• Harmonic-rated or K-rated transformers

• Oversized or separate neutral conductors

• Passive or active harmonic filters

• Power quality monitoring and assessment