Harmonics in Power Systems

What are harmonics?

Harmonics are frequency components in an electrical signal that are integral multiples of a fundamental frequency. Harmonic components distort the electrical signal as they are superimposed on the fundamental frequency component. These harmonic currents arise from non-linear loads in the distribution system, including rectifiers, discharge lighting, and magnetically saturated devices. A load is considered non-linear when the current it draws does not follow the waveform of the supply voltage. As these harmonic currents pass through system impedances, they generate voltage harmonics, further distorting the supply voltage. In power grids, harmonic frequencies are a frequent cause of power quality problems.

In Australia, the fundamental frequency is 50Hz. Harmonics occur at multiples of this frequency, including 100Hz, 150Hz, 200Hz and so on. The 150Hz component is known as the 'third' harmonic (3 × 50Hz).

What are the effects of harmonics?

Harmonics are undesirable within an electrical system and can have serious consequences if not properly managed:

Overheating and System Degradation

Harmonic distortion causes electrical components, including cables and transformers, to run hotter than normal. Over time, this heat stress degrades insulation, increases energy losses, and weakens the overall system integrity, leading to higher maintenance costs and unexpected failures. This can be managed by oversizing cables and transformers.

Reduced Equipment Lifespan

Harmonics put excessive stress on motors, drives, and other electrical components, accelerating wear and tear. Transformers are particularly vulnerable if they are not rated with the appropriate K factor. It is possible that the investment that you made in your motors and drives will not be realised.

Inefficient Power Usage

Harmonics distort the electrical waveform, reducing the efficiency of power delivery. While your facility will still be billed for the electricity supplied, a significant portion of that power may become unusable due to harmonic interference—resulting in higher energy costs without the full benefit of the power consumed.

Steps to Implement Harmonic Mitigation

Divergent Engineering can help you mitigate power quality issues by providing expert analysis, tailored mitigation strategies, and compliance support to ensure your electrical systems operate efficiently and reliably. The steps to implement harmonic mitigation are:

1. Analyse Harmonic Levels:

   Use power quality analysers such as ETAP and PowerFactory to measure THD (Total Harmonic Distortion), analyse individual harmonics, and identify problematic frequencies.

2. Evaluate Load Characteristics:

   Determine the types of non-linear loads in the network and their impact.

3. Select Mitigation Techniques:

   Choose between passive filters, active filters, or other methods based on budget, utility constraints and system requirements.

4. Follow Standards:

   Ensure compliance standards such as AS/NZS 61000.3.2, AS/NZS 6100-3-4, AS/NZS 61000.3.6, and IEEE 519 recommendations.

5. Monitor and Maintain:

   Continuously monitor the system for new harmonic sources.

Contact us to learn how we can enhance the performance and stability of your power infrastructure.