Project Focus: Optimising the Wessex Grid
Optimiser software using a sophisticated closed loop control system has been central to enabling efficient water transfers to take place as part of Wessex Water's flagship supply project
Julian Welbank, Wessex Water Head of Asset Strategy: “The system provides a leading example of the System Operator model that is discussed nationally as a way forward for the optimium management of regions."
Drummond Modley, Grid Programme Manager: “The development of the Optimiser software has been very successful. It brings a cultural change: the operational side of the business moves from central monitoring and local control, to central monitoring and control”.
by Steve Bilton, Senior Engineer, Infrastructure, Atkins, and Drummond Modley, Programme Manager, Wessex Water
Wessex Water’s integrated water supply grid is its largest ever and most complex project. The grid, which will be completed in 2018, includes the construction of 200km of new pipelines, 24 new or refurbished pumping stations, and 12 new storage tanks ranging in capacity from 2 to 8 million litres.
The grid includes more than 50 individual projects designed to combat resilience issues within the water supply network, costing a total of £228M over 8 years and two AMP cycles.
It provides the first opportunity to transfer water between Wessex Water’s northern and southern supply zone. On completion, it will meet future water supply demand for the next 25 years; improve the security of supply for customers by ensuring that customers are no longer supplied by a single source of water; help to meet reductions in abstraction licences required by the Environment Agency to improve flows in some rivers and protect their ecology; and deal with seasonal or occasional deteriorating raw water quality, particularly increasing concentrations of nitrates at some groundwater sources.
Wessex Water’s internal engineering and construction services business, Wessex Engineering and Construction Services (WECS) has managed the overall delivery programme, with both WECS and Atkins providing engineering design, planning and environmental services.
Atkins were involved in scoping the route of the new trunk main and assisting WECS to receive buy-in to the preferred route.
Innovation and the Optimiser
One of the most innovative aspects of the scheme was the development of the ‘Optimiser’ which will manage and optimise the transfer of water along the trunk main.
The Optimiser is a sophisticated closed loop central control system, which is designed to manage network operation efficiently and effectively. Atkins’ role was Project Manager on behalf of WECS, to develop the conceptual design, prepare the initial business case for the Optimiser, and assistance with the implementation of the Optimiser to the network.
Alongside the development of the Optimiser, Atkins also developed an overall control philosophy for the trunk main. This was based around 4 levels of Control:
1) Local Manual Control – the basic level of control with no automation and pumps/reservoir levels controlled manually.
2) Local Automatic Control – this is historically the normal method of control, with operating instructions issued to individual assets at each site.
3) Co-ordinated Control – two sub-systems are being integrated into the supply grid. Under this level, the local automatic controls receive commands/set points over communication links from a centralised system. These can override locally held level set points and pump on/off commands. If the communication links fail, then the system should revert to automatic local control.
4) Optimiser Control - This will ultimately be the normal and preferred method of overall system control for the grid trunkmain. The Optimiser will control all strategic assets considering the whole strategic network and determine the optimum operation taking account of constraints, including the need to meet conditioning and sweetening flows. It will monitor system operation compared with the optimum schedule and issue updated instructions regularly. Typically, where changes are required, these instructions will be issued every 30 minutes and will be implemented by the Level 2 (or Level 3) control system.
The Optimiser will enable Wessex Water to respond more effectively to incidents and planned outages, ensuring that supplies to customers are maintained as well as minimising operating costs.
In order to understand and establish Wessex Water’s particular requirements for the Optimiser, Atkins arranged a series of internal stakeholder workshops incorporating staff from operations, water resources, IT and water quality. The output from these workshops was the production of a comprehensive user requirement specification (URS). The team also consulted suppliers and other users of optimising solutions to gain a good understanding of the scope of technologies available.
In order to select a supplier for the technology, Atkins undertook a closed loop pilot trial in the spring of 2012, which sought to test the pumps, replace and amend the telemetry, and install new assets in the reservoir.
In 2012, Servelec Technologies was appointed as the preferred supplier of the Optimiser software.
Atkins, with Servelec Technologies, worked with many parts of Wessex Water on the development of Phase 1 of the Optimiser. This was to be developed and tested on an existing section of Wessex Water’s water distribution network where the operating regime and constraints were previously understood.
This development work identified enabling works required to provide the necessary feedback from the system regarding metered flows and reservoir levels. A programme of enabling works was managed to install new level transducers and flow meters and GSM telemetry loggers.
System constraint information was also required to understand abstraction licences, treatment works outputs and pump operations allowable.
Rigorous end-to-end testing of the communications network was undertaken to ensure that control signals were passed through various systems between the optimiser and the site control systems.
Phase 1 went live in September 2014, controlling 28 individual pumps and 2 flow control valves successfully.
The knowledge gained and difficulties overcome during Phase 1 have allowed Wessex Water’s Supply Optimisation Team to build the Optimiser model for Phase 2 which is extending the network under Optimiser control to include the integrated grid assets as they become operational.
The Optimiser allows an holistic view to be taken over the supply network and 72 hours ahead – rather than decisions being based on only the current water level in the adjacent reservoir. This gives many benefits, including improved security of supply and contingency planning; efficient transfer of flows in a complex supply system; efficient management of assets in a complex transfer and distribution system; savings made in avoiding Triads and Duos periods; optimal outage planning; optimal blending ratios for nitrate sources; and reduced call outs out-of-hours, as forecast provides more confidence in network flexibility.
In conclusion, the water supply grid will ensure that Wessex Water can meet its customer demands for the next 25 years, will provide security of supply through its ability to redistribute surplus water to areas in deficit and will allow blending of sources to maintain water quality.
The Optimiser provides an effective, reliable, repeatable and auditable solution to the challenge of managing a large and diverse water supply network.
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