Harmonic Mitigation
(Concept of Harmonics)
Power harmonics refer to the components with frequencies that are integer multiples of the fundamental frequency, obtained by decomposing a periodic non-sinusoidal alternating current quantity using the Fourier series. In simple terms, on the basis of the normal and regular sinusoidal AC waveform, some other waveform components whose frequencies are multiples of the fundamental frequency are mixed in, causing the waveform to be distorted and no longer in the standard sinusoidal form.
(Reference Standard)
According to GB/T 14549-1993, the limit values of harmonic voltage (phase voltage) in the public power grid are as follows:
(Typical Harmonic Sources)
◎ Rectifying equipment:◎ Variable frequency speed control devices:◎ Arc furnaces:◎ Issues such as equipment magnetic saturation and uneven magnetic fields;
(Harmonic Hazards)
◎ Increased equipment heating and power loss◎ Enhanced vibration and elevated noise levels◎ Capacitor resonance and inaccurate metering◎ Raised field strength and shortened service life◎ Malfunction of relay protection systems and interference with communication
(Harmonic Mitigation)
● Passive filtering: Its essence lies in impedance shunting. A filter capacitor and a filter reactor are connected in series to form a circuit, which is tuned to a specific harmonic frequency. For harmonics of this frequency in the circuit, the circuit exhibits low impedance, acting as a “trap” for such harmonics and thereby achieving the filtering effect.Characteristics: Simple structure, relatively low cost, high reliability, no need for additional power supply, and easy installation and maintenance.
● Active Power Filter (APF): It detects the harmonic conditions in the line in real time and injects harmonics with equal magnitude but opposite direction to the harmonic current in the line. This realizes real-time dynamic compensation and ensures high power quality.
Its characteristics are good filtering effect and fast response speed, and it is often used in occasions where high power quality is required.
