The numbers are tough to defeat. During the five-year period 2000-2004, around 200,000 MW of gas-fired capacity was installed in the US. The expected life of the control systems for those facilities is far less than the physical components-the steam turbine, for example-considering the dizzying progress with digital technology and general obsolescence characteristics of digital hardware. This explains why so many combined cycles and peaking gas turbine/generator plants have been undergoing control system retrofits in recent years.
This issue offers case histories involving control upgrades/replacements on LM5000, LM2500, Frame 6B, and FT4 engines. In the recent past, CCJ has published several articles focused on control system improvements-including upgrade of overspeed protection on legacy Westinghouse (Siemens) and GE machines, alarm management specs for replacement control systems, link-up of disparate legacy control systems at a cogen plant, etc. It's easy to access other articles on the subject of interest using the search bar at the top of this page.
It's no secret that Emerson Process Management's Ovation platform is involved in a significant volume of this retrofit activity. A key reason is that the distributed control system (DCS) is morphing into a plant knowledge system, with enhancements focused on adding functionality and organizing the user experience (Fig 1). At the most recent meeting of the Ovation Users' Group conference, Emerson's Glen Wagner discussed the expanded role of the main automation contractor (MAC) for a project, as distinct from a DCS supplier.
Whereas the traditional vendor retrofit services might be proposal, hardware, engineering, training, and field support, MAC additionally includes scope definition, installation design and drawings, full-scope installation and commissioning, high-performance control room, and integration of plant drawings into Ovation. It's a variation on the single-source supplier model: A turnkey controls and knowledge platform supplier, or a lifecycle partner, rather than vendor type of relationship.
User group conferences are valuable for keeping up with industry trends, best practices, lessons learned, system/equipment improvements, etc. Make note that the next meeting of the Ovation Users' Group will be July 26-30, 2015 at the Westin Convention Center in Pittsburgh.
Retrofits often have multiple motivations. Emerson's Laurence O'Toole and David Cicconi opened their presentation showing how many fossil units have changed operating profiles. In many areas, a small coal-fired unit (Fig 2) will be "filling in" around must-take renewable assets and less-expensive gas-fired assets. Meanwhile, many gas-fired combined cycles have dramatically increased their capacity factors over the last few years. Plant control systems have to provide a new level of flexibility to meet these challenges.
O'Toole and Cicconi illustrated four broad themes for gas-turbine (GT) retrofits: (1) a retrofit experience base that now includes most, if not all, control system OEMs one might find in a gas-fired plant today; (2) partnerships with independent GT service providers to offer enhanced solutions and more flexible service agreements; (3) product enhancements for overspeed protection, vibration, and overall turbine health monitoring; and (4) nine GT controls-retrofit project briefs.
One of those projects, the subject of a separate presentation with Dan Jones, Kansas City Power & Light Co, recaps Ovation retrofits for 19 turbine control and excitation systems, with a focus on replacing two 7EA DLN-1 Mark V control systems at KCP&L's Hawthorn Generating Station.
More and more today, controls retrofits include a makeover for the operator graphics, or the human-machine interface (HMI). Clint Vanderford, NV Energy, illustrated in his presentation the high-performance control room for the Ft Churchill station retrofit. Although not a gas-turbine-based plant, the characteristics, objectives, and lessons learned of the HMI would likely be similar, namely:
- Reduce alarm overload and operator alarm fatigue.
- Adopt a graphical hierarchy for different operator skill levels, such as clear summaries for veterans and P&ID graphics for step-up operators.
- Use gray scales rather than color to avoid distractions and improve situational awareness and response.
- Work from a written alarm philosophy (one version of the truth) and focus on alarms during logic review.
- Design graphics from the beginning; they drive important logic details.
- Don't neglect ergonomics, such as furniture details and selection.
- Involve the operators early in the process and expect to resolve conflicting opinions and preferences.
Plant simulators are another way Emerson differentiates its Ovation product line. Today, simulators provide benefits far beyond offline operator training. According to the company's Billy Moore, simulators can identify and diagnose fault conditions; improve operational techniques to optimize startup times; reinforce cause and effect relationships; dynamically verify equipment design, controls, and graphics; troubleshoot process issues and identify root cause; and develop and test advanced control schemes and strategies.
Emerson is developing models and algorithms which will be embedded in Ovation, so a single platform and integrated database can be used for controls and simulation-the ultimate vision being one in which the Ovation simulator and DCS controls are always in synch with real-time data so that operators can simulate actions in real time. As an example of outsourced services, Emerson can also host the simulator and ensure it is updated continuously. Moore's presentation concludes with several examples of simulator projects at US powerplants.
Automatic voltage regulation (AVR) is one dimension of today's need for operating flexibility. Grid operators require faster response and/or have pricing models for powerplants that can respond faster to deliver ancillary services.
Emerson now offers a digital generator controller (DGC) as part of Ovation that builds on its experience with exciter control retrofits. This eliminates separate systems and third-party protocols, offers enhanced alarms and graphics, adds historical data trending for the generator to the DCS, and, in general, reduces hardware and spare parts by integrating once separate systems.
The Ovation I/O is configured to act like hard controls and the existing cabinets can even be reused, if desired. The presentation by Emerson's Joe Rossi reviews other important considerations such as standards met by the DGC product, conversion from rotating to static exciters, redundancy, HMI graphics, and exciter and generator modeling.
The recent release of Ovation 3.5.1 offers more capabilities. If you are a serious control system and software engineer, request a copy of the Tom Weigand/Diane McMaster presentation, "What's New in Ovation 3.5.1." Otherwise, just know that the controllers have been hardened, they meet new certifications (Wurldtech Achilles®, for example), feature advanced algorithms and enhanced diagnostics, and include special features important for aeroderivative GT control. Several new and redesigned I/O modules-RTD, thermocouple, sequence-of-events and others-offer increased channel capacities.
Wireless electric actuators can solve specific problems for combined-cycle plant operators, according to Emerson's Tom Johnson and Mike Rooney. A good illustration is an HRSG repeatedly tripping because of a sticking feedwater isolation valve upstream of the control valve.
If the hardwired electric actuator does not have torque monitoring capability, an operator has to go to the top of the HRSG to determine if there is a valve or actuator problem and open the actuator compartment to adjust the torque switch. Fig 3 shows some possibilities for greater intelligence from valves and actuators in the cooling-tower system.
Greater intelligence afforded by wireless and electric actuators is, of course, possible for all the critical valves in the gas-fired plant-including those for main-steam stop/isolation, boiler-feed pumps, makeup water, boiler drains, cooling-tower pump discharge, and HRSG sky vents. Diagnostics are now available to detect loss of power phase, continuous position indication, remote enabling, valve opening and closing, torque switch trips, motor overload, loss of internal control voltage, stalled or jammed valves, and increasing force to operate caused by such issues as accumulation of deposits, seat and disc damage, packing gland problems, and bushing wear and lubrication.
Cybersecurity continues to concern plant operators. Two presentations complemented each other in this area. Adam Boeckmann's "Security Essentials" gave the system designer perspective, while Xcel Energy's Dave McMullan, Grant County PUD's Jeff Reams, and Emerson's Jaime Foose delivered more of an owner/operator perspective in the case study "Cybersecurity in Real Life."
The first presentation addresses what cybersecurity looks like inside the control system in terms of system architecture, firewalls and routers, secure access and management, ports and services documentation, network intrusion, encryption, and compliance with NERC Critical Infrastructure Protection Standards (CIPS).
McMullan and his co-presenters offer an interesting comparison between a facility identified as a critical asset under NERC CIPS v.3, and one with no compliance obligations under NERC CIPS v.3. The differences in products, processes and procedures are shown in Fig 4.
The authors stress that compliance does not guarantee security, as is now widely recognized in the industry. The presentation concludes with lessons learned from implementing a cybersecurity program whether it be compliance-focused or best practice-focused, along with a list of what Emerson considers cybersecurity best practices (Fig 5).
Finally, backing up your Ovation system should follow the old saying about voting in Chicago: Do it early and often! Emerson's Brian Delancey outlined a holistic approach to backing up your system that goes beyond "traditional" approaches.
