磁感應(yīng)電機(jī)軟啟動外文翻譯-閱讀頁
2025-06-05 19:51本頁面
【正文】 r, in that they are turned on for a part of each cycle. The average voltage is controlled by varying the conduction angle of the switches. Increasing the conduction angle will increase the average output voltage. Controlling the average output voltage by means of solid state switches has a number of advantages, one of the major advantages being the vast improvement in efficiency relative to the primary resistance starter, due to the low on state voltage of the solid state switches. Typically, the power dissipation in the starter, during start, will be less than 1% of the power dissipated in a primary resistance starter during start. Another major advantage of the solid state starter is that the average voltage can be easily altered to suit the required starting conditions. By variation of the conduction angle, the output voltage can be increased or reduced, and this can be achieved automatically by the control electronics. The control electronics can be preprogrammed to provide a particular output voltage contour based on a timed sequence (open loop), or can dynamically control the output voltage to achieve an output profile based on measurements made of such characteristics as current and speed (closed loop). The switching elements must be able to control the current applied to the motor at line voltage. In order to maintain a high level of reliability on a real industrial type supply, the switching elements need to be rated at least 3 times the line voltage. On a 400 volt supply, this means that the requirement is for 1200 Volt devices, and 600 Volt devices on a 200 volt supply. It is also important that the switching elements have a good transient current overload Volt triacs with good current transient overload characteristics are not readily available, and so the choice is really between the SCRDiode and SCRSCR. There are some triacs which are suitable for this operation, but they are not easily attainable. The major differences between the SCRSCR and the SCRDiode options are price, and the harmonic content of the output voltage. The SCRSCR method provides a symmetrical output which is technically desirable from the point of supply disturbances and harmonics, while the SCRDiode method is inferior technically, it is mercially more effective and easier to implement. Harmonics awareness and paranoia has drastically reduced the number of SCRDiode type soft starters on tod
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