The cause of harmonic generation in the intermediate frequency melting furnace and how to manage it.

The intermediate frequency electric furnace is the intermediate frequency of the power frequency power supply, and generates a large number of harmful high-order harmonics to the power grid during the working process, which is one of the largest harmonic sources in the grid load. Harmonics can seriously affect the safe operation of the power grid. For example, harmonic current is generated in the transformer, generating additional high-frequency eddy current iron loss, overheating the transformer, reducing the output capacity of the transformer, increasing the noise of the transformer, and seriously affecting the life of the transformer; The convergence effect of harmonic current makes the cross section of the wire smaller, which increases the loss of the line; the harmonic voltage affects other various electrical equipments on the power grid, which can not work normally, resulting in malfunction of the automatic control device, inaccurate meter measurement; harmonic voltage and current Interference occurs in the normal operation of nearby communication equipment; temporary overvoltage and transient overvoltage generated by harmonics cause insulation damage of the equipment, causing three-phase short circuit and burning transformer; harmonic voltage and current will cause parallel resonance and series connection locally in the public power grid. Resonance, causing a serious accident. In the inverter process, the square wave power supply is first obtained by direct current, and the square wave is equivalent to the superposition of sine waves containing a large number of higher harmonics.Although the latter circuit is filtered, the higher harmonics are not completely filtered out, which is why harmonics are generated.

We designed 5 , 7 , 11 , and 13 single-tuned filters. Before the filter compensation, the power factor of the user's intermediate frequency melting furnace melting stage is 0.91. After the filter compensation device is put into operation , the maximum over-compensation to the capacitance is 0.98 . After the filter compensation device is put into operation , the total voltage distortion rate (THD value ) is : 2.02% . It meets the standard of power quality GB/T 14549-1993 voltage harmonic ( 10KV ) value below 4.0% . After filtering the 5th , 7th , 11th and13th harmonic currents, the filtering rate is about 82 ∽ 84% , which is the allowable value of the national standard. The compensation filtering effect is better. The use of thyristor rectifiers is the root cause of harmonic generation in intermediate frequency melting furnaces . Passive filters can be used, the effect can reach 70-80% , and the effect load is required by national standards. Active filters should not be considered, and the price is high. It is recommended to contact a professional manufacturer to order .

http://www.firstfurnace.com/BdwlkjNews.asp?id=1514