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Integrated drive solution boosts reliability at power station

31 May 2017

Marchwood Power Station, a combined cycle gas turbine (CCGT) site has operated efficiently since its commercial operations began in December 2009. When its three main water cooling pump systems started having reliability issues, Siemens provided a solution

CCGT power stations use a combination of both gas turbine and steam turbine technology, whereby the steam turbine is driven by virtue of the heat produced via the gas turbines. Typically, this can produce an overall efficiency in the region of 60%. Further improvement remains a quest for all energy users, and Marchwood has used Siemens control systems (CS) and integrated drive systems (IDS) to create a total engineered technology solution to upgrade to a more efficient and reliable electricity generator.

Now capable of generating in excess of 900MW of electricity, Marchwood plays a key role as one of Britain’s best-performing power stations.  

In 2010 it started having problems with its three main water cooling pump systems, responsible for providing cooling water through the steam turbine condenser and ancillary cooling system sections of the plant. Reliability was becoming compromised as the swirl regulators used to regulate the flow of water were sticking, due to the associated mechanical linkage, which led to difficulties regulating flow. Additionally, gearboxes linking motor outputs to cooling pumps were a significant weakness due to oil leaks, leading to premature wear, excessive noise and heat issues.  

The water cooling pumps are at the heart of the operating system at Marchwood. The water flow at the site was controlled by a fixed speed pump package, comprising AC induction motor, gearbox, oil cooling system and pump. Water flow was regulated by a swirl regulator (controllable valve) on the inlet side of the pump. Marchwood has three pumps, two of which are required to operate to maintain maximum output of the station, with one on standby, due to the critical nature of the application. The power station has to be available to respond to grid requirements at all times, so it was critical to remove any potential points of failure.

Siemens provided an integrated drive systems (IDS) total engineered solution, which incorporated:

•  Distributed control system (DCS) modification

•  Three 2.5MW 6.6kV Perfect Harmony variable speed drives (VSDs) with component failure bypass (cell bypass)

• Three 2.1MW 10-pole 6.6kV vertically mounted AC induction motors with mechanical adaption bedplates

•  An electrical equipment module (EEM), ie. a mobile switchroom to house all three VSDs

•  All electrical power and control cabling requirements for the improvement upgrade

•   Removal from site of existing motors, gearboxes, oil cooling system and pumps

•  Improved couplings for supporting reduced mechanical stress on the infrastructure during start-up 

•  Installation and commissioning of each of the new drive trains

• Full project management.

The pumps at Marchwood were removed and given a five-year overhaul.

This was a CS IDS total engineered solution, with the associated benefits of greater reliability, extended availability and significant improvement to operational efficiency. For Marchwood this meant lower running costs, better plant efficiency and a reduction in CO2 emissions, lowering the plant’s carbon footprint by more than 2000t per year. Fundamentally, there was now less stress during start-up on the whole mechanical and electrical infrastructure.

Scott Curtis at Marchwood Power was the lead engineer on the project. He says: “We had a number of ongoing reliability issues associated with the pumps, motors and gearboxes of the main cooling water system. These posed a significant risk to the commercial operation of our station. Through a collaborative effort with Siemens DF and PD, we have engineered out the problems that we were encountering and drastically improved the control and reliability of our cooling water system."

Gary Palmer, Siemens DF and PD application specialist for large drives customer services, comments: “Using our Perfect Harmony VSDs in conjunction with our induction motors meant we were able to provide a truly integrated drive solution, from design through delivery of the installation and commisssioning; all from a single source of supply."

The system has been operating since October 2015 and figures have already shown improvements on the predicted energy savings. Actual energy savings will be in excess of £150,000 per year. CO2 reduction has been predicted to drop by 2100t over the next year, leading to additional cost savings