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| STEAG AG, Lünen (Germany) | | Less Maintenance Effort with a New Drive Technology | Sinamics G150 used in a coal power station
Sinamics G150 frequency converters regulate the air stream of the suction draught fan in the Steag power station in Lünen. They ensure a high regulating accuracy, operation which is kind on the system, low maintenance and low energy requirement. In order to comply with the regulations for power stations, series connected line harmonics filters in these 6-pulse devices reduce the low frequency mains feedback to a level which can otherwise only be achieved by 12-pulse devices.
The Lünen coal power station of the Steag AG, a wholly-owned subsidiary of the RAG with its headquarters in Essen, generates approximately 500 MW of electrical power, part of this goes to the German Railways AG. The power station has also been producing district heating since 2003. In the course of a modernization project, the owners decided to replace the aging drive systems of the two suction draught fans of a boiler - each of them conveying up to 360,000 m3/h of flue gas. The existing drive system dating from 1962 was a so-called three-phase current asynchronous collector motors system with additional regulator knobs in cascade circuit. The motor could be set from 250 to 1080 rpm with these regulators.Steag AG therefore relied early on a variable-speed drive technology. However, this turned out to be very maintenance-intensive in comparison with the latest state of the art. The collectors had to be serviced approximately every 12 weeks and the motor cooler had to be cleaned once a year. For this reason these systems are no longer used today and were to be replaced by another modern, variable-speed drive solution.Reasons for variable-speed drivesA variable-speed operation has many advantages over fixed speed motors with mechanical control concepts such as fan flaps for blowers. On the one hand, the conveyed volume, here of flue gas, can be set much more accurately and adapted more quickly to the current operating requirements. The necessary conveyed volume fluctuates continuously depending on the momentary combustion intensity. In addition the gentle start-up and run-down processes of the machine with variable speed are kind on the mechanics of the entire powertrain.The are also major advantages on the energy side. Unlike fixed speed motors which always run at full speed and therefore always have a higher power consumption, the performance of variable speed drive systems with frequency converters can be continuously adapted exactly to the current operating requirements. Especially in applications with square load torque, i.e. in flow machines such as fans, blowers or pumps, the variable-speed operation saves up to 50 % energy in comparison with fixed speed engines. A modern, low-maintenance drive system of three-phase asynchronous short-circuit rotor motors and frequency converters has proven useful in the modernization.Low maintenance, reliable and easy to handleRobust low-voltage N-compact motors with 710 kW and Sinamics G150 frequency converters with the appropriate power for regulating the motor speed, both from Siemens, were chosen. As a member of a new drive generation, Sinamics G150 benefits from the common technological basis for all versions, that is for all power and voltage classes as well as performance stages and applications. They all have a uniform and simple configuration and operation in common. Sinamics G150 is the device for drive tasks without mains feedback, for example fans, blowers, pumps, extruders, mixers or mills. Due to a wide range of available components and options the device can be adapted in detail to suit different application-specific requirements. Its uncomplicated structure makes Sinamics G 150 robust and reliable. Modules can be changed with a few actions when servicing. Pre-configured for the drive tasks at the factory, the converters are also very easy to commission and operate. The sophisticated, clear operating philosophy means that the user only has to concern himself with functions that he really needs. Sinamics G150 can be operated by a graphic display with clear text or a central control computer. In the Steag power station the frequency converter is connected to the central control system. The necessary Profibus interface is standard in Sinamics. As network-friendly as the 12-pulse technologyThe Sinamics G150 converters are all designed in 6-pulse technology. The VDEW regulations for power stations demand harmonic values as they are normally only achievable with 12-pulse technology. To meet this strict standard, the Sinamics G150 converters are preceded byline harmonics filters. These line harmonics filters then reduce the low-frequency mains feedback to the level of a 12-pulse converter and even below these values. They considerably reduce the 5th and 7th current harmonics in particular. The mains current consumed by the line harmonics filter is very close to the sinusoidal shape and therefore fully meets the requirements of the VDEW. In comparison with conventional 12-pulse feeds, no triple-wound transformer with 30° offset secondary windings is necessary in concepts with 6-pulse converters plus line harmonics filters. Because of the low current root mean square value, smaller cross sections of the mains supply cable are possible and the losses in the transformer are lower. Because no second rectifier is necessary the entire system is more compact on the whole. Line harmonics filters are installed as independent components in a robust housing between Sinamics G150 and the low voltage distributor. They are assembled without a fan and operate with internal convection cooling. This eliminates the necessity for both an auxiliary power supply and all maintenance.Sinamics G150 which are already in operation can also be retrofitted quickly and simply with a line harmonics filter. By pre-circuiting a line harmonics filter, the Sinamics G150s are independent of the network operator's requirements - the ideal solution for all low-voltage drive tasks of high power which require no feedback - whether in energy generation or elsewhere.
Advance 3/06 | |
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