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Engländer & Beyer, Wuppertal (Germany) / KES, Wuppertal (Germany) Current protection in machine tools It is common practice in modern machine tools to supply all electronic components from a common power supply unit. No matter how reliably the power supply unit works – as soon as faults occur on the primary or secondary side, failures of the whole machine are inevitable. It is absolutely essential to provide all-round protection here to prevent the often serious consequences for the machine. The Sitop power supply range offers exactly the right solutions. Measurements made on machines in North America have shown that in the event of a failure of three mains periods, i.e. 60 milliseconds, the input voltage drops to about 70 percent. That is too much for conventional power supplies. The 24 Volt supply drops by half after only 16 milliseconds. Such mains failures have since become common in Europe too. The cause is the continuing liberalization of the electricity market in which more and more cheap providers are supplying electricity from unstable networks. There are often interruptions in the millisecond range which can have serious consequences without a buffering of the 24 Volt side. The power supplies of Sitop power offer a supplementary module based on maintenance-free electrolytic capacitors for buffering in such cases which can bridge power failures up to three seconds. A DC-UPS module offers reliable protection in the range of minutes and even hours against longer power failures – depending on the current requirement and on with which Sitop accumulator modules the UPS is supplemented. Selective fusing at every output Of course faults can also occur on the 24-Volt side which activates the electronic current limiting of the power supply. This can also lead to a total breakdown in the 24-Volt supply. To avoid this exactly this circuit must be switched off selectively beforehand by a protective element. "Engländer & Beyer" is a trademark for robust and uncomplicated grinding machines. KES in Wuppertal and the E&B Retrofit GmbH in Remscheid designed a low-cost concept for their modernization in which the automation and drive tasks are taken over completely by Siemens components. In the 24-Volt power supply the power supplies of Sitop power in combination with the new Sitop select diagnostic module were relied on. Up till now line circuit breakers have been used for secondary fusing which require a low overcurrent for tripping. However, there was a danger in the modernization that these switches would respond as soon as the various components were switched on due to their current peaks. On the other hand no slow blow circuit breakers could be used because the multiple rated current required for tripping in the event of a fault cannot be supplied by the power supply unit. With Sitop select the necessary selectivity in 24-Volt supply circuits is now achieved at which the interference-free connection of loads with a high inrush current requirement is possible at the same time. The module is also ideal for retrofitting an existing machine. Defective consumers can be identified easily by telediagnosis via a sum signal contact and display by one two-colored LED per channel which also reduces the standstill times to a minimum. Conclusion: The flexibility demanded by the customer for worldwide application in all networks – and thus the high availability of the system – was achieved without any problem. motion world 1 / 2002 |
