High fidelity at lower cost

11 July 2016

Southern Company and Emerson have implemented a first-of-a-kind high-fidelity simulator for the Daniel unit 3 combined cycle plant in which simulator process models are embedded in the simulator control system platform, rather than having separate platforms. This results in reduced maintenance costs and improved future proofing. It also permits a “mixed fidelity” approach to be adopted in which process models of differing levels of fidelity can be combined – eg, high-fidelity for turbine and certain BOP equipment, lower-fidelity for condensate and lube system – enabling fidelity to be balanced with budget.

The benefits of high-fidelity power plant simulators are well recognised, not just for operator training but also for event replay and analysis, engineering development and ‘what if’ analysis. But there are challenges, for example finding the expertise and resources needed to develop and maintain customised plant models and also the need, with conventional simulators, to maintain not just one but two simulator software platforms – the simulated process models platform and the simulated control system platform – with the complexity that brings.

To address these issues Southern Company and Emerson Process Management have installed a first-of-a- kind high-fidelity simulator at the 530 MW Daniel unit 3 combined cycle facility (GE FA gas turbines in 2-on-1 configuration, with Emerson Ovation plant control system plus GE MkV control system for the turbines).

This novel simulator makes use of process models embedded in the simulator control system platform and has been found to deliver all the advantages of a traditional full-scope simulator, but with significantly reduced maintenance burden and improved future proofing.

As is common at US power plants, high staff turnover has been driving the need for effective training of control room personnel at Daniel. In addition, reduced cycling and load following due to market conditions (which contrast markedly with those in Europe, for example) have greatly reduced opportunities for on-the-job training. To address the risks posed by these circumstances it was decided to procure a high-fidelity simulator for Daniel (which is owned and operated by Mississippi Power, part of Southern Company).

Southern Company says it has a good deal of experience with simulators supplied by various simulation companies and, being familiar with technical challenges associated with their existing simulators, they wanted a simulator that better served the needs of both the operations and engineering staff.

Southern came to the project with clear goals, including: quick implementation of the operator training functions, 12 months or less; high-fidelity plant equipment models to provide realistic dynamic response to operator actions and simulated abnormal conditions; effective duplication/emulation of third party control system graphics and hard-panel control stations; controls and plant models to be easily updatable and kept in step with the plant configuration; and ability to provide a test bed as an engineering tool for modelling proposed control and plant equipment changes, without affecting operations.

‘High-fidelity’ requires that the behaviour and dynamic response of the simulated plant equipment and systems should be based as much as possible on first-principles engineering/physical process models. Recognising that the OEM-supplied turbine control systems were already predominantly black-box in nature, the action and response of those control systems were permitted to be ‘emulated’.

It was also required that all of the modelling and control logic of the simulator should be open and available for modification by Southern Company, with even the emulated empirical models of ‘black-box’ systems made accessible for tuning and adjustment. This is expected to help future-proof the simulator, making it easy to modify plant equipment operating characteristics as the plant ages, equipment is repaired/replaced, etc.

Benefits of a single platform

One of the challenges of building high-fidelity simulators has been that the first-principles process models of the plant equipment

used in the simulator and the simulator plant control systems have generally been provided by different companies on different platforms. This has exacerbated the difficulties of producing realistic plant responses to control system actions and to unexpected events (eg, equipment failures).

Also, having two systems on two platforms means that changes have to be accommodated on both platforms by two different sets of experts, and the dynamic response of the changed system has to be re-tuned to restore the realism.

Combining the first-principles process models and the control system on one platform in the simulator overcomes this problem. Southern therefore opted for the Emerson Ovation Simulator, which uses embedded-model simulation. Embedded- model simulation means that the first- principles process models of plant equipment are embedded in the Ovation control system computing platform used for the simulator.

The Ovation Simulator includes a complete suite of plant equipment process models (algorithms) that are connected together in a flow-diagram-type structure, modelling plant systems in a hierarchical manner and ensuring continuous adherence to the laws of thermodynamics, heat transfer and fluid mechanics, ultimately resulting in a high- fidelity model of the plant. 

Ease of maintenance and mixed fidelity

With embedded simulation, standard control system engineering tools are used to construct the simulator plant system models in exactly the same way they are used to construct simulator control systems. Modifications to plant equipment or controls are accounted for in one place using one set of tools, making updating and maintenance of the simulator much more straightforward than was possible with traditional simulator architectures.

This supports Daniel plant management’s goals of simplified maintenance, performable by Southern Company engineers, providing a lower total cost of ownership over the life of the simulator.

With the simulator control system and process models being programmed in the same environment, it is possible to combine models of differing levels of fidelity, eg, a high-fidelity model for the turbine and some BOP equipment, combined with an empirical model for the condensate system, and an even more simplified model for the turbine lube oil system.

This provides the ability to balance fidelity with budget and allows a simulator buyer/owner to start with a relatively small investment/low-fidelity then piecewise upgrade the fidelity as budget and/or engineering time becomes available.

HMI and instructor station

One of Southern Company’s project goals was to ensure that the simulator HMI (human machine interface) be as realistic as possible, so that student operators can seamlessly transfer their experience from simulator training sessions to the plant control room.

At Daniel, simulator workstation arrangements mimic the actual plant control room, so that operators are more likely to internalise the actions necessary to perform control functions located in different areas of the control room.

Hard panel control stations are emulated on the simulator’s computer screens via digital photographs of the actual panel stations, with embedded active components such as push buttons, pistol grip switches, analog gauges, etc.

Instructor station screens and tools were designed with significant input from Southern Company, making the instructor’s efforts much more effective and significantly increasing the ease with which abnormal operating scenarios can be simulated.

Project execution

A key imperative for project execution was to address Daniel unit 3’s urgent need for an operator training simulator. At the outset of the project, Emerson had not yet developed models that accurately simulated the operation of the combustion turbines (CTs) and the selective catalytic reduction (SCR) unit, or the interplay between them. Therefore, it was agreed that the strategy would be to execute the project in two phases. Phase 1, completed in Spring 2015, included: final high-fidelity models for all the plant equipment and systems, except the CTs and the SCR; empirical models for the CTs and SCR; final control logic for the Ovation control system and emulations of the third-party-supplied controls; software emulated hard panels and third-party control graphics; and all required simulator hardware.

To compress the project schedule, simulator software configuration was performed in an environment with remote connectivity, concurrent with engineering, ordering and assembling the project hardware and configuring the software platform on that hardware.

Southern Company’s engineers and operators were able to remotely participate in system testing and tuning through a virtual private network (VPN) connection, ensuring the accuracy and realism of the simulation while drastically cutting travel time and costs.

Phase 1 results provided proof of concept for mixed-fidelity simulation, where high- fidelity and empirical simulation of major plant systems are combined seamlessly on the same simulator. The mixed-fidelity approach can be used to control costs and compress project schedule while achieving desired functionality.

Phase 2, completed in autumn 2015, included upgrading the Daniel 3 empirical models for the CTs and SCR to high-fidelity models.

Realistic and pragmatic training tool

Southern Company used the Phase 1 mixed- fidelity simulator for approximately six months, and was very satisfied with its utility as a training simulator, both from a student and instructor perspective. The mixed-fidelity capability of embedded-model simulation was successfully leveraged to support a phased implementation schedule. This allowed expedited delivery of a realistic and pragmatic operator training tool, covering normal operations, startups and upset conditions. With the delivery of the Phase 2 CT and SCR models, Southern Company is now using a full-scope, high- fidelity simulator.

The physical models embedded in the simulator control system platform make every physical model and control algorithm accessible to Southern Company engineers via the standard control system engineering tools. This facilitates upkeep and gives them expanded flexibility to perform maintenance via in-house personnel. They also have cross-functional use of the simulator as anengineeringtestbed,enablingtrialsof changes to both plant equipment parameters and control techniques to be carried out in a harmless virtual environment prior to implementing them on the actual plant.  

Simulator Modifications to plant equipment or controls are carried out in one place using one set of tools, making updating and maintenance of the simulator much more straightforward than was possible with traditional simulator architectures. This screenshot shows building of a pump model from standard Ovation engineering tools (pump curve in centre, model sheet above it, and pump parameters on left)
Simulator Section of screenshot from typical instructor station display

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