The effect of harmonic on mechanical and electrical equipment

The effect of harmonic on mechanical and electrical equipment

  What are harmonics?

  Harmonics refer to the components resulting from the Fourier series expansion of a periodic, non-sinusoidal electrical quantity that are integer multiples of the fundamental frequency; these are commonly referred to as higher-order harmonics. Simply put, harmonics are components whose frequencies are integer multiples of the power frequency (50 Hz).

  In power systems, the fundamental frequency is typically 50 Hz or 60 Hz; therefore, the frequencies of harmonic voltages or currents can be 100 Hz, 150 Hz, 200 Hz, and so on. Harmonics are primarily caused by nonlinear loads, such as arc furnaces, electric motors, UPS systems, switching power supplies, rectifiers, and variable-frequency drives. These loads cause current waveforms to distort, generating harmonic currents, which in turn distort the voltage waveforms, resulting in harmonic voltages.

  The hazards posed by harmonics in power supply and distribution systems are primarily manifested in the following aspects:

  Under the influence of high-frequency components, power supply equipment experiences increased skin effect, eddy currents, and hysteresis, leading to abnormal overheating and a significant increase in losses. Harmonic components cause distortion in current and voltage waveforms, and distortion at the zero-crossing points of these waveforms directly causes interference and malfunctions in measurement and control components or equipment.

  Major Equipment Affected by Harmonics

•   Transformers, Rotating Motors

  Increased magnetic induction loop currents in the core significantly increase heat generation and power consumption in electrical equipment; they also accelerate insulation aging and shorten the equipment’s service life.

•   Wires and Cables

  The skin effect increases, leading to higher heat generation; this also accelerates insulation aging and shortens the service life.

•   Power Capacitor Banks

  Harmonic voltages accelerate aging, increase the loss factor of capacitors, and raise additional losses, thereby increasing the likelihood of failures and shortening the service life of the capacitors. On the other hand, when the resonant frequency of a resonant circuit approaches the frequency of a specific harmonic, harmonic currents are amplified, and resonance may even occur.

•   Power Supply and Consumption Equipment

  The speed of rotating motors becomes unstable, mechanical vibrations in power supply and consumption equipment increase, and resonance may even occur.

•   Measurement and Control Components or Equipment

  Harmonic interference can cause errors or malfunctions. For example, load switches may trip erroneously, leading to loss of control or instability in measurement and control equipment.