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Hydro Governors and Controls: A Perspective

From the earliest mechanical governors to today’s microprocessor-controlled integrated control systems, much has changed in the way hydroelectric powerplants are controlled, yet much remains the same. In The Beginning
Amos Woodward did not invent the water wheel governor, but he had an inventor’s heart and saw much that needed to be improved in the governors in use in the 1860’s. He received a patent in 1870 for “Improvement in Water-Governor”1 that marked the beginning of a small company that would have a profound effect on hydro turbine controls over the next century. Thirty years later, Woodward Governor Company had become one of the preeminent suppliers of governors to the emerging hydroelectric industry. The industry itself was undergoing profound change. Old-fashioned water wheels driving mechanical loads gave way to full-fledged hydro turbines coupled to a new device produced by Edison and Westinghouse: the AC generator. By 1911, Amos’ son Elmer had become Chief Engineer and rolled out his masterwork: the Oil Pressure Governor, which evolved into what is now known as the Gateshaft governor. Perhaps the most common hydro governor in the world today, the Woodward Gateshaft governor is now as it was then: “a simple, strong and durable” device capable of “accuracy and smoothness in the control of load changes.” 1 Designed to last a hundred years, thousands of Gateshaft governors remain in use today, still functioning and largely unchanged (aside from normal wearing components) after nearly a century of service. The fact that there are far fewer operating examples of competitors’ offerings is a testament to the Woodward’s mechanical design abilities, ingenuity, and attention to quality and customer service. Even some of Amos’ original mechanical governors are still in use today. Gateshaft governors - and the larger mechanical and analog governors that followed - share the same fundamental features found in the most advanced computerized control systems today. They sense speed quickly and precisely, control gate position exactly via a closed-loop feedback system, and provide a means (droop) for operating multiple generators in parallel with stability. Although many advances in hydro control theory were made in later years, these fundamental qualities that separate a governor from a simple speed control remain today. The Boom Years
The demand for electricity in the United States during the first half of the twentieth century grew explosively. Since hydro provided not only power generation, but flood control and irrigation as well, Congress approved and funded the construction of many large dams throughout the Western US: Hoover, Bonneville, and the largest undertaking of all, Grand Coulee. As hydro turbines grew larger, so did the size of the hydraulic servomotors controlling the opening and closing of the massive turbine wicket gates. This required greater amounts of governor force and oil flow, which required larger governors and oil pressure systems. Whereas early mechanical governors could fit in the trunk of a car, governors powerful enough to control these new turbines required large Cabinet Actuators the size of small garages, delivered on rail cars, with pressure vessels large enough to climb into parked nearby. Plants had also grown considerably in the number of units per powerhouse. Where once there were only a few units, now there were five, ten, as many as twenty-seven in a single powerhouse. Remote control mechanisms were added to the governors, enabling them to be controlled from a central control room. Likewise, the central control room concept required auxiliary systems, like cooling water and turbine lubricating oil, to be automated. The use of relay logic was implemented, permitting semi-automatic starting of units. Early Automation
Governor manufacturers were tasked to support plant automation, and they responded in creative ways. DC motors were added to mechanical governors to allow the Speed Adjust and Gate Limit controls to be driven by remote Raise and Lower signals. Multiple speed and gate position switches, driven by mechanical cams connected to governor restoring shafts, provided discrete signaling of turbine status during starting and stopping. Generator air brake valves became standard equipment on large cabinet actuators. Selsyn transmitters and receivers were provided to relay vital unit operational data up to the control room. By the 1950’s it was no longer good enough to precisely control speed/frequency; automation required direct megawatt control to simplify the remote setting of power output. By the 70’s, even this wasn’t good enough. To effectively control power flow in their transmission systems, utilities needed remote control of entire powerplants from Dispatch Centers located hundreds of miles away. Thus, the Supervisory Control and Data Acquisition (SCADA) industry was born. Governor manufacturers responded in kind with the introduction of the analog electronic governor. Endowed with multiple fail-safe operating modes and capable of receiving direct setpoints instead of (slowly) responding to the rotation of a gear element, the analog electric governor quickly gained favor. Nevertheless, most new advances were layered upon the old. Typically, a SCADA Master Station sent signals to a Slave Remote Terminal Unit in the plant, which interacted with the existing plant relay logic that sent Raise/Lower pulses to the governor (there were still hundreds of mechanical governors still in service, as now). Fully-automatic plants from this period used more than 40 discrete relays to control governor, exciter and turbine/generator auxiliary equipment. Impressive when it worked, difficult to troubleshoot when it didn’t. At the heart of it all remained, for most plants, a mechanical governor, which was seen as a benefit to most plant personnel. They knew that if automation failed, they could go down to the governors and operate them manually. The Digital Age
In the early 80’s, nearly all of the original governor manufacturers were long gone: Leffel, Pelton, Lombard, I.P. Morris. All gone. Even Allis-Chalmers, a large American turbine manufacturer who had made a fair amount of their own governors (until they switched to using Woodward exclusively), was out of business, having been sold to Voith. It was in this period that a totally new form of control blazed on the scene and turned the governor market on it’s ear: digital computers. This was truly a paradigm shift, but Woodward was slow to notice it. Small upstart companies, using their own microprocessor designs or buying off-the-shelf industrial controllers, leaped into the market and quickly gained a foothold in the burgeoning small hydro market. Small, privately-owned hydro was encouraged by PURPA legislation and tax credits for renewable energy. Developers of small hydro projects had small budgets and couldn’t afford to pay the salaries of the large Operations & Maintenance (O&M) staff found at large hydro powerplants. This financial reality coincided nicely with the digital controllers virtues. With an integrated digital control system, you could not only govern a unit, but control its generator voltage, automatically synchronize it, and then control pond level while on-line (most small plants were strictly run-of-river). All for half the cost of a cabinet actuator. Digital controls monitored the myriad alarms and safety systems in the plant, and communicated with headquarters in real-time, allowing one operator to remotely operate multiple plants safely. Embracing this new technology, consulting engineers began designing unattended hydro plants. At first, utilities scoffed at the notion of replacing their tried-and-true governors with a small computer. Computers at that time were better known for billing foul-ups, frequent operating system crashes, and simple games. Why trust them in a mission-critical application like controlling a massive hydroelectric turbine? As in many fields, though, Early Adopters paved the way for what is now commonplace. Now, all new powerplants use digital controllers for everything from governing to river management, linked directly to utility SCADA systems, Information Technology (IT) Systems, and even the Internet (monitoring only, if you please). With the advent of deregulation, 15-minute generation commitments, and scaled-back O&M staffs, computers have become an integral and indispensable part of hydro powerplants. Changing O&M Concepts
The US had been accustomed to utility regulation, which turned out to be a double-edged sword. Utilities had operated their powerplants with an almost fiduciary duty. Their job was to keep the lights on for the nation, and they took preventive maintenance very seriously. Minor overhauls were performed annually, with major overhauls occurring every five years (or sooner, if the situation warranted it). Regional utilities operated collegially, coordinating with each other and helping each other out during forced outages. They bought and sold power to each other like one neighbor sharing a cup of sugar with another in a pinch. There was not much motivation to economize on maintenance because, at the end of the year, utilities took their expenses, added a ‘reasonable return for the shareholders’, and submitted that to the regulating agencies as part of the justification for their rate request. They did their job so well, in fact, that everyone took electricity for granted, which brings us to the other edge of the sword. Deregulation – even the threat of it – changed everything in the utility world. When proponents dangled the chimerical concept that deregulation would reduce everyone’s electricity rates, customers demanded the break-up of the utility monopolies. The utilities, fearing younger and nimbler competitors, began slashing O&M staff to reduce their cost-of-generation. Some utilities switched overnight from preventative maintenance to a new concept called Reliability-Centered Maintenance, which, loosely corresponds to the old adage: “If it ain’t broke, don’t fix it.” Trouble was, nobody knew how to predict when it would break. What does any of this have to do with the governor? In hundreds of plants throughout the US, mechanical and analog governors had been operating with few problems for decades. Unlike digital controls, these governors can still limp along even when they are extremely worn or out of adjustment. Plus, their primary gate control mechanisms are so robust as to be virtually immune from failure. So, even if a governor is sloppy and can’t even control speed, the operator can always just walk up to it, operate it manually to get the unit on-line, and then just ‘block load’ the unit. Digital governors, on the other hand, do not come with a mechanical manual control. They require the CPU, the I/O modules and most of the sensors functional in order to start and run a unit, even in manual. If specified, they can be provided with redundant sensors and I/O modules, enhanced logic to automatically detect failed or failing sensors, can even redundant hydraulic control valves. All these features must be specified clearly or chances are they will not be included in the delivered system. Without these, when some part of the digital control system has a serious problem, somebody’s going to have to go up to the plant – quickly – to replace parts and attempt to restart the system. In the deregulated world, a missed start when a unit is needed (e.g. when it’s power has been committed) can have dire financial consequences. Likewise, a missed start at a remote powerplant that has mechanical or analog governors is a big problem, too, but the solution is different. The main culprits of missed starts are more humble: worn governor components, dirty oil, lack of calibration, or a combination of all three over time. These can be easily addressed by performing routine maintenance. The problem is: whereas governors used to get annual maintenance, now they are required to run for many years without significant (or any) maintenance. There are fewer annual outages, and the ones that are taken are much shorter in duration. Often, the governor is overlooked. Pacific Gas and Electric has a large number of mechanical and analog governors, spread throughout the Sierra Nevada mountains, and struggled with this problem. Many of their plants were unattended, and access to them was difficult and time-consuming, even in good weather. Due to retirements and downsizing, even finding qualified governor mechanics to send up was a challenge. Yet, upgrading to digital was expensive. PG&E, in conjunction with Stevens Point Consulting, developed a creative solution. They implemented an Annual Calibration and On-Line Tune-Up program that allowed PG&E to test governor health and analyze performance on-line, without taking an outage. If a governor passed the test, it was Good-To-Go for another year. If it failed the test, procedures were employed to isolate the cause of the problem while the unit remained on-line. If needed, a short outage could be scheduled to replace a worn-out part, but many times the governor just needed to be calibrated and tuned for optimal performance. Three years later, Mike Mato of PG&E is very pleased: “It’s worked so well, we’re doing it on all our hydros. We’re also bringing in governor experts to teach our newer mechanics how to test, troubleshoot, repair, and optimize these old governors. You know, they work really well when they’re adjusted right and the oil is kept clean!” The Future: Old Things Made New Again
Despite the trend toward digital control, mechanical and analog governors will continue to be used for many years. Plant owners with these types of governors need to develop plans for how they will service their old governors. In spite of pressure from vendors to upgrade to digital, many plant mechanics understand these governors and want to work on them. Yet, getting parts from large OEM vendors can be frustrating: parts take too long to get (when you can get them) and cost too much. Luckily, small companies comprised of former OEM employees are rising to the occasion, providing new and reconditioned governor parts, field service, training and calibration services. Even mechanical governors that have had minimal maintenance for twenty years can be brought back to life and ‘made new again’ by a simple overhaul and calibration. They can be every bit as responsive as the newest digital governor, albeit without all the bells and whistles. Digital controls, on the other hand, have support problems of their own. The ‘shelf life’ of a digital controller is typically between five and ten years. Computer technology is simply moving too fast for any vendor to support a particular platform longer than this. When a control platform is retired, getting replacement parts for these units can rapidly become impossible. Unless you want to replace the ‘digital brain’ every five to ten years, you will need to invest in a healthy stock of spare parts right from the beginning. You may also want the application source code for your project, just in case you need to support the system software on your own. In the end, it’s your choice. As far as fundamental features go, all governors do the same thing: control speed precisely off-line and respond to minute frequency deviations to provide grid stability on-line. If your needs have changed, perhaps due to new requirements demanded by FERC relicensing, you may need to replace your existing governor and relay logic system with a new digital control system. If your existing mechanical or analog governors work well and serves your needs, there are people and organizations that can keep it operational for years to come. Just search the web with keywords like “gateshaft governor”, “mechanical cabinet” or “analog cabinet”. Bibliography
The Woodward Way by Woodward Governor Company, 1997, Tan Books & Publishers Inc., Rockford, IL
Gerald Runyan's picture

Thank Gerald for the Post!

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