RWE Westfalen power station – Overhaul for Block E

Preventive maintenance and refit for protected power supply in order to achieve optimum plant availability

You need to have a high degree of know-how about complex plant when it comes to replacing electrical components such as IGBT driver cards or intermediate circuit capacitors.

Fuel is brought to the power station primarily via the Datteln-Hamm canal. From that point the coal is conveyed by belt to the coal bunkers for the steam generator. The rail network also offers an alternative supply route.

It was in 1963 that the Westfalen power station, which is located in the municipality of Hamm-Uentrop, was commissioned. Nowadays, power is generated exclusively from Block E, which was completed in 2014. This coal-fired power station, with 46% net efficiency, has reduced its CO₂ emissions by approximately 20%, relative to the older-type plants. Accordingly, a saving of approximately 1.3 million tonnes of CO₂ per annum is achieved.

The most modern procedures for desulphurisation and denitrification of flue gases are used. Thanks to these highly efficient filtering and purification systems, the result is not only reliable compliance with the legally permissible limit values for atmospheric pollutants such as sulphur dioxide, nitric oxide and dust, but compliance with a clearly creditable margin. The maximum output, 800 MW, can be selected on a very versatile basis. Accordingly, there is the option for responding at short notice to fluctuations on the grid as they arise.

These are ideal prerequisites for interactive operation with production of power from regenerative energy sources in the medium load range.

Maximising availability

After the costs of initial investment, it’s primarily the fuelling and operating costs that determine a power station’s profitability. Availability represents a crucial factor. It determines the plant’s capability for converting energy and placing it in store. It determines a power station’s potential output: both technically and according to economic criteria.

Requirements concerning maintenance planning, preparation and implementation are correspondingly high. This is also especially applicable to the power supply systems that are deployed for operation, and likewise applicable to the issue of protection for process-critical consumers. For example, these include the electrical switchgear, the power station’s extensive controls and the standby power supply for the oil pumps, for flue gas cleaning, for water processing and for the water-steam circuit.

Thermal imaging has an important part to play in the servicing process. Thermal imaging is used as the means of enhancing operational safety, since this technology makes it possible to detect hotspots, loose terminal connections or excessively high contact resistance levels.

Fans employed in forced ventilation systems are subject to mechanical wear. Accordingly, they constitute a wear and tear part which needs to be replaced on a regular basis.

Late in the summer of 2018, RWE AG started work on the detail planning for the extensive overhaul for Block E. The aim being to secure uninterrupted, fault-free operation for the next 4 years.

The operation was planned for completion within the period from 27-04-2019 to 07-06-2019.

Co-ordinating and reconciling the closely inter-related tasks would prove to be a particular challenge. Consequently, the companies to be entrusted with servicing had to exhibit the maximum of flexibility and reliability.

Plant servicing as such has to wait for the refit to be completed. In this process, the system is checked over for performance data and tolerances. Values as measured must match up to those delivered by a brand-new plant.

Retrofitting as a preventive measure

In essence, there have to be two independent channels for supply to the consumers that are crucial to operation – and this applies to all large power stations in general. Consequently, all power-supply systems need to be fully-redundant.

For the power station’s Block E, in 2010 BENNING supplied a wide range of equipment that was specifically tailored to the levels of reliability and quality that are associated with industrial operating conditions. This includes not only static rectifier and UPS equipment but also modular inverters and DC/DC converter systems.

In conjunction with high battery capacities, these systems guarantee a protected supply of 220 V/24 V direct current and 400 V alternating current. Overall, the total power output installed on-site is in excess of 1.6 MW DC and 1 MW AC.

The installed systems combine the maximum of availability with low operating costs.

In order to assure this in the long term, BENNING recommends not only regular servicing but also the precaution of preventively replacing all electrical and mechanical components that have a limited service life.

Accordingly, servicing plans work on the assumption of various replacement intervals for components such as fans, input capacitors, output capacitors and intermediate-circuit capacitors, because they are subject to a certain degree of ageing and/or wear.

Various system topologies

A wide range of topologies in power supply systems had to be taken into account when configuring the servicing tasks to be completed in the process of overhauling the power station.

Monoblock systems tend to be very heavy, due to the transformers that are normally used. Consequently, these static power supply systems were overhauled exclusively on site.

This task comprised a detailed analysis of assemblies and the replacement of various parts at component level. Only in the power-off state could such tasks be completed – given the level of complexity in the employed power circuits.

Servicing of modular systems

Servicing tasks on modular systems are conducted in quite a varied range of ways. Should it be necessary to minimise the degree of servicing time or shutdown time whilst power station operation is ongoing, then there is the option of rapidly replacing on-site installed modules, and this approach is described as a revolving exchange. Alternatively, recourse can be had to retrofit modules from BENNING’s stores.

In this instance, the modules were overhauled in the repair shop at BENNING’s Bocholt works. The various components and circuit boards were replaced in accordance with an extensive test/inspection procedure.

By this means it was made certain that all of the parameters of a new system were fulfilled in their entirety.

By 29-05-2019, all of the maintenance and servicing tasks on the BENNING power supply systems had been completed on time. Accordingly, BENNING’s power supply solutions have, once again, contributed to the maximum possible power station availability, making the process, an important contribution to its safe, legally compliant and trouble-free operation.

Daniel Becker, RWE Generation SE, Westfalen power station

“Our collaboration with BENNING was characterised by openness, fairness and absolute dependability.

We hope to maintain this high level of constructive co-operation into the future.”

There are considerable advantages to modular UPS topology: after all, there’s the option of swiftly replacing your modules that are installed on-site – however complicated the planned steps may be. This is an area where systems with hot-swap capability are decisively advantageous.