The problem of power conversion (rectification and inverter) resulting in power distribution system pollution, lighting control system, switching power supply and other non-linear electrical equipment generated harmonics, can cause the distribution system itself or connected to the system of equipment failure.
Hazard of Harmonics
The harm of harmonics to power system mainly includes:
(1) Additional power loss and heat may be generated on the rotating motor, and may cause vibration.
(2) the reactive compensation capacitor bank causes resonance or harmonic current amplification, resulting in capacitor damage due to overload or overvoltage; Overload or overvoltage breakdown can also be caused to power cables.
(3) Increase the loss of the power grid. The loss can reach considerable extent when resonance or amplification occurs.
(4) to relay protection, automatic control device, information machine caused by the wrong action and interference.
(5) Harmonics increase the error of the watt-hour meter itself, and users absorb both fundamental reactive power and harmonic power.
With the rapid development of power electronic technology, the application of switching power supply is more and more extensive. On the one hand, switching power supply is developing towards high reliability and miniaturization. On the other hand, the power capacity and power density of the power electronic devices themselves are also increasing, and the high-power switches in the switching power supply will inevitably produce high-order harmonics and electromagnetic interference when running at high frequency, which will inject into the power grid and endanger the stability of the power grid and the system itself. At present, the methods of harmonic suppression at home and abroad are mainly passive filtering and active filtering.
At present, harmonic has become one of the main obstacles for switching power supply and electronic system to operate normally and reliably in the application field. European and American countries in 1996 has formulated the relevant standards and compulsory strict implementation, do not meet its standards of electrical products are not allowed to enter the market. Our country also formulated the corresponding standard in 2003, and in a few cities carried out a certain punishment system for the harmonic content of users exceeding the standard, so the research on the harmonic of switching power supply is particularly important at present.
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