17.07.2018 Projects

ECOTAP® VPD® stabilizes secondary voltage in open-pit lignite mining

The world´s smallest high-speed resistor-type tap-changer from Maschinenfabrik Reinhausen in industrial use: ECOTAP® VPD® has been stabilizing the secondary voltage for two 630 kVA transformers with downstream frequency inverters in an open-pit lignite mine for the last year.

In mid-March 2017, two regulated three-winding transformers for pumps fed by inverters were commissioned together with Maschinenfabrik Reinhausen (MR) at an open-pit mine operated by RWE Power AG. The transformers are outfitted with the ECOTAP® VPD®, providing a regulated low voltage of 690 V.

The ECOTAP® VPD® is primarily used in public distribution grids, where regulated local grid transformers have been providing stable voltage for years as the amount of energy fed in by renewable energies increases. But the ECOTAP® VPD® can do even more, as demonstrated by its use in the open-pit lignite mine in Hambach, Germany.

This mine is located west of Cologne between the towns of Jülich and Elsdorf in the heart of the Rhine valley coalfield. It opened in 1978 and currently reaches a depth of about 400 meters. Approximately 40 million metric tons of lignite are extracted each year. Of that coal, 70% is used to generate electricity, covering almost 15% of the power needs for the German state of North Rhine-Westphalia. That equates to about 5% for Germany as a whole. The remaining pit coal is used in refining operations and is processed into products such as coal dust, briquettes and coke.

Safe extraction of coal in an open-pit mine requires lowering the water table. The process of lowering the ground water level entails drilling wells, installing pumps and laying pipes. Drainage is achieved using pump shafts. Electricity is supplied to the shafts by compact stations or directly from medium voltage.
A compact station contains a distribution transformer, a medium-voltage system and a low-voltage system. The pump in the shaft has a rated output of 400 kW and is powered by a frequency inverter.

Due to the lengths of lines in the 6 kV network, switching operations or load changes can cause voltage fluctuations in the network. These can, in turn, cause faults in the frequency inverter's intermediate circuit. Together with the power quality experts from MR, RWE employees were able to solve this problem. They quickly found the ECOTAP® VPD® to be the best technical solution.

Fitted in the transformer, the ECOTAP® VPD® ensures that consumers are supplied with a stable voltage under all circumstances. This is done by compensating for deviation in the medium voltage from the nominal voltage by changing the transmission ratio, which would otherwise remain constant. This compensates for fluctuations in voltage (both increases and decreases), enabling stable operation of industrial processes without interruptions. This saves precious production time and money.

In addition, the distribution transformer's footprint remains the same thanks to the compact design of the on-load tap-changer. No structural changes are needed. This compact design philosophy also extends to the control system, which supports space-saving installation on the busbar in the grid dimension of a single fuse strip through the use of an adapter. All parameters can be set with ease on the controller, so no laptop is needed.

The electro-mechanical operating principle of the proven MR vacuum technology with 500,000 maintenance-free tap-change operations ensures stable, reliable operation for decades without the need to service the primary equipment Even today, it already meets the requirements of the EU Ecodesign Directive for 2021. Important points for consideration by the decision-makers at RWE. The ECOTAP® VPD® continues to facilitate safe and cost-effective operation in the outlined application.