B&R keeps the lights burning in Vienna.
A total outage of Viennese power is very improbable for structural reasons, but even a failure that only affects the street lights would be bad enough. To keep this highly sensitive area under tight control, the 40 Wienstrom power substations are equipped with transmitters that make it possible to switch electrical loads using an audio frequency ripple control system. The audio frequency ripple control transmitters control many different types of devices and are responsible for more than 70 000 recipients overall.
Although the principle of controlling the grid using audio frequency pulses in a high-voltage grid is considered antiquated from a technical point of view, the approach was deemed sufficient to cover normal ripple control transmitter tasks since the control commands in a single telegram allow for 144 switching variants. The transmitters are linked at Wienstrom headquarters via a special process control system that has been extensively modernised in the last few years to include state-of-the-art equipment.
“After several delays and increasing difficulties in getting the incumbent provider to implement our ideas adequately, we initiated contact with the Austrian manufacturer Bernecker & Rainer (B&R),” says, Gerhard Hafner, manager of the Service, Engineering, and Grid Safety department at Wienstrom. “Since we were only able to modernise the audio frequency ripple system in small steps, we asked B&R to build an initial prototype after preliminary consultations proved positive.”
System changeover
The most time-consuming process was the re-implementation of the audio frequency ripple control transmitters in the 40 substations. This work was carried out by Wienstrom over the course of several years. Only then could the changeover to the integrated control equipment in Wienstrom’s headquarters be implemented.
“This step in particular was an extremely tricky process since the changeover had to take place while systems were running and while preventing power failures,” says Hafner. “The excellent cooperation and high level of reliability exhibited by B&R engineers during this phase were all the encouragement we needed to select this provider to handle the entire project.”
While the old system was still running, the process control system implemented by B&R (APRO L) was put into trial run mode. The decision to use APRO L was not a difficult one for Wienstrom according to Hafner since “even the graphical user interface (GUI) by itself showed substantial advantages compared with other products and our employees were able to learn how the system operated during the trial run. Disconnecting the old system and changing over to the APRO L-based process control system was able to be carried out quickly and without delays.”
APRO L technology
The new master control system is one implementation of the APRO L technology developed by B&R. Advantages of this Linux-based process control system include a high degree of scalability as well as uniformity in an integrated solution that covers all areas of complex process automation – from the simplest electrical component to complex software implementation.
In the audio frequency ripple control system at Wienstrom, two redundant controllers at headquarters use Ethernet to communicate with a Visomat controller with over 128 digital I/O points, 10 redundant protocol converters, and the server application for the ripple control system database. The protocol converters have a very important function since they can communicate via modem with control points in the central substations, allowing them to reach the entire supply area. All in all, there are five control points equipped with I/O expansion modules. They are responsible for processing the ripple control signal data as well as returning messages from the addressed systems.
For more information contact Rob Snowball, Klare Technologies, +27 (0)41 503 9900, sob@klare.co.za, www.klaretech.com
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