Bosch High-frequency production tools professional blue Strana 46
Nabídka komerčních zákazníků **Nejlépe prodávané z Bosch Blau
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46 | High-frequency technology | Guide High-frequency technology A guide for the user Layout of a system for high-frequency tools: A frequency converter that is to be operated on a 400 V network with a star-delta switch absolutely must be designed for 400 V in a delta. If this kind of converter Frequency converters with synchronous generator is only designed for 230 V in a delta, it can only be The best solution technically for frequency converters switched on directly in a star on a 400 V network, i.e. is achieved by the combination of asynchronous motor without star-delta switch. This absolutely must be tak- and synchronous generator. The converters are single- en into consideration when designing a new system. shaft units with an asynchronous motor as drive motor and a brushless internal pole generator with fitted Parallel operation of frequency converters current generator. Frequency converters can be connected in parallel to increase the economic efficiency of the overall sys- The voltage difference between no-load and full-load tem and to compensate load peaks. In this way, you with a small converter and a power factor of cos φ = achieve optimum adaptation to the tools used. When 0.6–0.9 is only approx. 3%; with large converters it is using frequency converters with synchronous genera- approx. 4%. tor, different power grades can be operated in parallel without special precautions. The synchronous converters are independent of voltage fluctuations in the primary three-phase supply Wattless current compensation network and are secured against short circuits. The Each inductive consumer is subject to an inductive rated voltage can be aligned using a potentiometer. wattless current that does not perform any effective They are also maintenance-free up to 20,000 hours of work, instead it only burdens the cables. Frequency operation. converters and high-frequency tools are also inductive consumers. The formula for calculating the secondary frequency is as follows: f2 = f1 · p2/p1 f1 = Primary frequency of the three-phase supply network f2 = Secondary frequency for high-frequency tools p1 = Number of pole pairs of the drive motor p2 = Number of pole pairs of the generator Compensation of the wattless current on the secondary side of the converter requires considerable effort because each tool has to be compensated individually. Depending on the quantity and power of the individual high-frequency tools, a total power factor cos φ of 0.5–0.85 has to be expected. On the primary side of the frequency converter, the power factor cos φ can be improved considerably As a rule, frequency converters with a power output if the magnetising current from the drive motor and of over 4 kVA should not be connected directly to the generator is compensated. By connecting correspond- network, instead they should be connected by means ingly rated capacitors, it is possible to compensate of star delta switches. During direct activation, a brief the primary-side wattless power of the converter at surge of current occurs, which could overload the no-load practically completely and under load to such feed cables on converters over 4 kVA and trigger the an extent that a power factor greater than cos φ = 0.9 upstream fuses. is achieved. Using star-delta switching reduces the surge of current because, as opposed to direct switching, only a third of the current flows. The star-delta switch is used to switch the winding of the drive motor via star (switchon process) to delta (operating position).
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