Leading UK energy supplier, SSE needed to address the obsolescence of its existing DCS and to provide an expandable solution to extend the working life of its Keadby power station. Invensys Operations Management delivered a total upgrade solution in time for a planned major shutdown and in parallel with other plant projects with minimal commissioning time

Keadby Power Station in Scunthorpe, North Lincs, is operated by SSE, one of the largest energy companies in the UK. The Keadby plant, which began commercial operation in 1996, is a 720-megawatt combined-cycle gas turbine generating facility. SSE also owns the UK’s largest onshore gas storage facility at Hornsea in East Yorkshire and is currently building a larger one at Aldbrough.

The Keadby power-generating plant includes two General Electric frame 9FA gas turbines, one Alstom steam turbine, two Babcock three-pressure waste heat recovery boilers and a Siemens GT10B auxiliary gas turbine. It is maintained and operated by a staff of 53 including managers, engineers and technicians. When SSE management realised the facility’s distributed control system (DCS) was approaching plant-wide obsolescence, the company chose Invensys Operations Management to upgrade the plant to a more flexible, scalable, and supportable solution.

SSE is a vertically integrated energy utility, and is involved in the generation, transmission, distribution and supply of electricity as well as the storage, distribution and supply of natural gas, telecommunication, contracting and energy services. SSE has more than 10 million customer accounts in the UK, supplying natural gas and electricity to more than 3.5 million homes and businesses.

The company has a total of more than 11,300 megawatts of capacity, 2,000 megawatts of which is installed renewable capacity. As such, SSE is the UK’s second largest generation business overall, and the largest generator of electricity from renewable sources. SSE, formed with the merger of Scottish Hydro Electric and Southern Electric, also has an ownership interest in more than 100 thermal and renewable power stations.

New infrastructure approach

Before the upgrade, the majority of the plant was operated by a site-wide Emerson WDPF (Westinghouse Distributed Process Family) DCS system. A moderate-sized control system, this included 26 fault-tolerant controllers; 12 HMI workstations, including one historian and comprising 6,046 hardwired I/O, eight control level data links (Modbus, Allen-Bradley DH+, GE-GSM); three supervisory level data links (Modbus-TCP, ODBC, OSI-PI); and 190 process screens, including approximately 130 overlays and 48 sequences.

SSE engineers initially identified seven key criteria for the DCS upgrade project at Keadby Power Station. Top of the list was that the upgrade had to be completed in time for a scheduled major plant outage and the system migrated with minimal site commissioning time. In addition, the new DCS system had to address the pressing obsolescence issues and remain current for the remainder of the plant’s expected service life. Sufficient expandability in terms of controller memory, I/O capacity and network bandwidth together with simplified online configuration was also considered a key requirement. Because of the potential impact on operating procedures and other human

factors, engineers also specified that the new plant solution should maintain the existing control strategies and HMI interface standards.

Harmonised upgrade

As planning progressed, it became clear that the DCS upgrade had to be conducted in parallel with essential major maintenance activities as well as other expansion projects. Furthermore, site works needed to take place with minimal disruption to the outage programme. A risk assessment of the project requirement identified two key areas of concern: the I/O upgrade, plant engineers at Keadby cited challenges such as faded conductor identification labels, incomplete loop drawings, human error risks and the potential impact on the outage programme associated with on-site rewiring and testing of approximately 6,000 loops.

“Although the existing system had been reliable in the past, problems were emerging,” says Hugh Ferguson, C&I engineer at Keadby Power Station and project manager for the DCS upgrade project. “An increasing number of components were either no longer available or no longer repairable. Plus, controller memory was near capacity and most of the data highway bandwidth was already utilised.”

Migration of the application software was also considered a potential problem area. Documentation was limited and there were no control narratives available. This meant that the application software itself had to be used as the source of the migration process raising concerns over the potential for human error, the skill-sets required, and the functional acceptance test criteria.

Based on the potential obstacles, it was not clear whether there was an alternative to upgrading to Ovation, the next generation of the WDPF platform. However, because of concerns over software acceptance testing and continued support for the existing I/O hardware, SSE decided to go out to tender for the project.

Six DCS vendors pre-qualified for the proposed migration project, with four vendors asked to present formal technical evaluations of their proposed solutions. Invensys Operations Management was ultimately selected by SSE because of its proven plug-in I/O card migration solution for WDPF, WDPF migration expertise, in-house simulation capabilities and the incorporation of a model-based plant simulator for application software testing and operator training.

Mastering the migration process

Invensys WDPF migration-style FBMs are a plug-in replacement for WDPF Q-Line I/O cards which allow the existing WDPR I/O racks, power-supplies, and field wiring to be retained and re-used by the new Foxboro IA system. From an IA system perspective, these modules appear identical to standard Foxboro 200-series FBMs.

Semi-automated tools were offered to migrate the Westinghouse application to the Invensys InFusion environment. InFusion is the Invensys delivery mechanism for enterprise control, and consists of the hardware and software components necessary to provide a true aggregated view of information across an organisation, enabling a robust foundation for collaboration between people, processes and systems.

The SimSci-Esscor Dynamic Simulation Suite provides both model-based plant simulation and a platform for enabling a complete Operator Training Simulator (OTS) solution comprising virtualised DCS control processors, interfaces to third-party virtual controllers and a feature-rich training environment. The SimSci-Esscor solution provides the full power of rigorous dynamic simulation and control system emulation for process engineers, plant engineers, operators and managers to improve plant design, check out controls, train operators and improve plant performance. It also offers a modern alternative to dated, fragmented, empirical and hard-to-use products with which many engineering firms and plants currently struggle.

Invensys also demonstrated an extensive track record for supporting the Foxboro IA Series Distributed Control System, a key component of the Invensys InFusion Enterprise Control System, and were able to offer a number of products to further enhancement the system including Sequential Function Charts for DCS sequences and the ROMeo Online Performance Suite for plant performance metrics.

ROMeo is an advanced, unified modelling environment delivering online optimisation applications to help users obtain peak performance from their operating units. ROMeo offers process optimisation across an entire enterprise with online modelling and equation-based optimisation capabilities providing more accurate, current operating information to better manage changing market pressures, product values, energy costs and equipment performance.

“The migration approach offered by Invensys Operations Management showed that an alternative to the existing system was a viable option,” says Ferguson. “Simulation is also proving particularly useful at resolving hard-to-replicate problems, and was invaluable in leveraging the experience of plant operators during migration of the application software.”

Initially, migration of the DCS application software and development of the OTS plant model were undertaken as separate, parallel activities by separate Invensys project teams. Once competed, these two elements were then combined to allow functional testing in the factory, prior to installation at site.

Once the system architecture and hardware had been specified, the Invensys DCS team began by developing migration tools and carrying out code analyses; breaking the application down into HMI components, interlock/protection logic, sequences, unique strategies, and typicals. Migrated DCS components were then tested on a modular basis via a combination of code reviews and basic I/A Series functional testing.

The OTS team’s first task was

to mark-up plant Piping and Instrumentation Diagrams (P&IDs) in order to clarify the required scope and topology of the SimSci-Esscor DYNSIM process model. Once the model had been constructed, this was followed by model acceptance testing to demonstrate the validity of the resulting process simulation. The DCS and OTS teams joined together for the integration and testing phase.

“Plant simulation greatly assisted the software migration process and allowed us to catch a number of software integration issues before the system was accepted for installation on site. I am therefore convinced that without it the plant would not have returned-to-service as smoothly as it did, and would certainly have required much more commissioning time,” says Ferguson.

Virtual plant commissioning was implemented on a plant area-by-area basis. Virtual plant commissioning on the simulator mimicked that which would have occurred on the real plant and included plant pre-start, start-up, steady-state operation and shutdown by an experienced Keadby operator. Once it had been demonstrated that it was possible to operate the plant in accordance with existing operating procedures, SSE gave the ‘green light’ to progress with the site installation phase of the DCS upgrade.

Well-executed plan

The project was delivered in time for Keadby’s planned shutdown and within SSE budget parameters. The equipment upgrade was completed in less than 13 days, compared with the 18 days that was scheduled. In addition, the expandability issue has been resolved as the new DCS now supports up to 2,000 nodes and the central processor loading is less than 25 percent of capacity. Keadby also enjoys simplified online configuration.

Invensys also successfully delivered a model based OTS system, DCS sequence enhancements, process interlock diagnostics/overrides, an online heat balance reconciled performance package via the Automated Rigorous Performance Monitoring product that is part of the ROMeo suite, and alarm performance analysis via the third-party PAS PlantState Suite.

Invensys Operations Management

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