Line filter, RF filter In terms of electromagnetic compatibility (EMC), any electrical equipment must withstand the interference of external electromagnetic phenomena and have a certain degree of immunity, and do not send interference to other electrical equipment. Produce electricity hazards. The frequency converter is no exception, the frequency of interference can be divided into low frequency and high frequency, its demarcation line is set as 9kHz in IEC1800) 3 standard (some standards are set as 10kHz). In addition, there are wide spectrum interferences such as air discharge and contact discharge. This refers to high frequencies and is actually aimed at radio frequency RF.
Many power transmission systems (PDS) do not operate properly in industrial environments without filters, and do not interfere with other electrical appliances and equipment. Filters that reduce the amount of PDS emissions also reduce the efficiency of the PDS and increase the overall size and cost of the device. In most cases, there is no interference with this device, but in RF receivers or sensitive appliances (for very low voltage measurements, for example), interference reduction methods (such as high-frequency filtering) need to be considered. Few measurements indicate the presence of radiated emissions because there are no complaints in this regard. It can be seen that practice has shown that it is not necessary to set the filter to reduce the high-frequency interference conducted by the power supply in most industrial environments. As for the residential building environment (it has a large number of radios, televisions, etc.), in addition to the higher requirements of the inverter on EMC standards, the installation of RF filters is also considered.
According to IEC standards, manufacturers should provide the harmonic content of the inverter's incoming current. Inverter sets with built-in line reactors are an appropriate way to reduce harmonics. Several manufacturers such as ABB, Schneider, and Finland's VassaControl have such products and hope that other manufacturers can follow suit and gradually promote them.
Harmonic filtering and reactive power compensation devices are centrally installed on low-voltage busbars with many frequency converter applications, which is a complicated and labor-intensive engineering problem. It also requires low costs and occupies space. Inverter built-in reactor is simple and easy, harmonic suppression in place is not distributed, in addition to suppressing the harmonics, it also brings some other benefits, so it is a good program to promote and promote. When the power of the transformer and the inverter is equivalent, the transformer has 4% short-circuit impedance. At this time, the inverter no longer needs to add a line reactor. Therefore, when the inverter power is large, whether it is built-in or a peripheral device. For reactors, their reactance values â€‹â€‹should be classified into grades such as 3%, 2%, 1%, etc., to accommodate different transformer impedances and to reduce the size and cost of the device.
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