Harmonics are unwanted electrical frequencies that distort the normal sine wave of voltage and current in a power system. They are caused by non-linear loads and can lead to serious power quality issues, including overheating, equipment failure, and reduced energy efficiency.
In an electrical system, harmonics are voltage or current waveforms that operate at multiples of the main power frequency—typically 50Hz in South Africa. For example, the 2nd harmonic is 100Hz, the 3rd is 150Hz, and so on.
These additional frequencies combine with the fundamental waveform, distorting its shape and affecting the performance of connected equipment.
Harmonics are caused by devices known as non-linear loads. These draw power in short bursts instead of a continuous flow, which creates distortion in the electrical waveform. Common sources include:
Variable Frequency Drives (VFDs)
LED lighting and dimmer switches
Uninterruptible Power Supplies (UPS)
Computers and office equipment
Welding machines and industrial chargers
Excessive harmonics can lead to a range of problems within an electrical network. These include:
Overheating of cables, motors, and transformers
Frequent tripping of circuit breakers
Increased energy consumption and reduced efficiency
Malfunction or damage to sensitive electronics
Poor power factor and voltage instability
Shortened equipment lifespan
If left unmanaged, harmonics can significantly increase maintenance costs and cause unexpected downtime.
Harmonic distortion is typically measured using a power quality analyser. The key measurement is Total Harmonic Distortion (THD), which indicates how much distortion is present.
Acceptable voltage THD: under 5%
Acceptable current THD: under 20%
If your system is above these levels, harmonic filtering may be necessary.
There are two main types of harmonic filters used to correct distortion in electrical systems:
These are tuned filters made of resistors, inductors, and capacitors. They are effective for reducing specific harmonic frequencies and are suitable for stable load environments.
These advanced filters use real-time monitoring to inject corrective currents into the system. They are ideal for dynamic, variable load conditions and can also improve power factor and voltage stability.
Controlling harmonics improves overall system performance and protects your electrical infrastructure. The benefits include:
Enhanced energy efficiency
Reduced risk of equipment failure
Lower maintenance and operating costs
Improved compliance with power quality standards
Longer lifespan for electrical components