Harmonics Correction

When a non-linear load, such as a rectifier is connected to the system, it draws a current that is not necessarily sinusoidal.

Harmonics in power systems of are generated by non-linear loads. Semiconductor devices like transistors, IGBTs, MOSFETS, diodes etc are all non-linear loads. Further examples of non-linear loads include common office equipment such as computers and printers, Fluorescent lighting, battery chargers and also variable-speed drives. Electric motors do not normally contribute significantly to harmonic generation. Both motors and transformers will however create harmonics when they are over-fluxed or saturated.

Voltage distortion — a function of harmonic current and system impedance — is worse on ‘soft’ electrical systems with low available fault levels. So, users at the end of the utility distribution in remote locations or users who operate under generator power are more likely to experience issues relating to excessive voltage distortion.

Examples of non-linear loads include

• Fluorescent lighting
• Variable-speed drives
• Industrial Controls Systems
• Complicated Robotics Systems
• UPS Systems
• Common office equipment such as computers and printers

The other issue with voltage distortion is that it causes harmonics to propagate throughout the network to the linear loads as well.

Linear loads are just that — linear. If you apply a triangular voltage wave to a linear load, such as a full-voltage across-the-line motor, it will try to draw a triangular current waveform. Consequently, as voltage distortion increases, linear loads begin to draw harmonic current.