On the job
Hydro dispatchers help make every drop of water count
Somewhere deep in the basement of TVA’s Power System Operations Center in Chattanooga, an alarm bell rings.
It’s a distinctive sound that Michael Richards has heard many times before. That resonant r-r-ring signals a deviation of 500 megawatts or more in TVA’s generating output — a sure sign that something significant has happened somewhere on the power system.
Richards is in the middle of a 12-hour shift at TVA’s Hydro Dispatch Control Center (HDCC), sort of a high-tech “command post” where trained technicians known as Production Coordinators monitor the fully automated hydroelectric system. From this location, they can send operating instructions to hydro plants hundreds of miles away — starting units up or shutting units down and decreasing or increasing generating output.
He and the other individuals who keep the HDCC staffed on a round-the-clock basis are obliged to keep a close eye on a bank of 21 computer monitors, checking to make sure that things are running according to a previously-programmed generation schedule. It’s a technically advanced electronic system that reduces the need for on-site operation.
Richards acknowledges that it would be hard to overstate the value of hydro in terms of recovering generating capacity. “If a large generating unit somewhere in the TVA system trips and suddenly goes off line, hydropower is always the first generating source to be pressed into service because it’s inexpensive and can be brought online almost instantly. We start scrambling to see what can be done to make up the shortfall. Typically, we can use our hydro plants to address this kind of issue within a matter of five to 10 minutes.”
That fact places the HDCC squarely on the front lines of TVA’s efforts to recover temporarily lost generation. “Other generating sources may be needed if a significant shortfall occurs,” says Richards, “but we’re there to respond quickly as other assets are being brought online.”
But generation isn’t the only factor considered in hydro dispatch. Richards is clear on that point: “We’re proud of the role we play in the cost-effective production of electricity — no question. But there are times when that takes a back seat.”
He cites the need to operate the river system in a way that minimizes flood damage as an example. “When a major weather system moves into the region, we may need to shut down hydro generation on the tributary reservoir system in order to hold the water back until it can be released at a controlled rate. On the main river, on the other hand, we typically run all available hydro generating units at “maximum sustainable load.’ Main-river reservoirs have very little storage space. So, in a storm situation, we run flat-out with every bit of capacity that we can muster to move water through the system as quickly as possible until we’re able to recover sufficient flood storage space.”
If the water can’t be released fast enough through the turbines to recover the needed storage space, it has to be spilled, says Richards. “Since spilled water doesn’t generate any hydroelectric power, it isn’t something we like to do, but sometimes there’s simply no choice. Protecting the lives and property of Valley residents comes first.”
Spilled water is water released through the dam via pipes or channels instead of through the powerhouse.
Richards emphasizes that the HDCC plays an important role in many other river system operations — from protecting the environment to providing recreational opportunities. “We have to be ready to make adjustments to keep our fossil and nuclear plants within the water temperature discharge limits specified in their permits. We adhere to a schedule for providing minimum flows to prevent riverbed dry-out and enhance aquatic habitat. And we cooperate in efforts to manage reservoir levels for recreation.” Those efforts include holding levels steady for the spring fish spawn, managing flows to maintain TVA’s targeted summer pool levels, providing scheduled releases for whitewater recreation, and going to ‘zero flow’ at certain times for anglers who fish the tailwaters.
TVA’s hydroelectric system is one of the largest automated systems in the world. The transition from a manual to a fully automated system took seven years to complete. The last plant (Ocoee No. 2) was brought online as a fully automated plant in 2005.
HDCC manager Mike Holt is a firm believer in the benefits of automation. “From our vantage point here in TVA’s System Operations Center, the folks who staff the HDCC are able to see the big picture and can act accordingly. We have the tools and capability, for example, to make judgment calls about the advisability of taking a particular generating unit out of service for maintenance. Automation also has distinct advantages over the old system of communicating with individual operators at each hydro plant.”
Richards echoes that sentiment: “Automation allows me to be able to send instructions electronically to start multiple units simultaneously — something that formerly would have meant a dozen phone calls to as many different plants in several states. Plus, the system is capable of instantly and continuously determining what we refer to as the ‘most efficient load’ — the precise generation set-point for each individual unit that ensures maximum output. Due to constantly changing variables that affect that optimal set-point, that’s something even the most experienced operators would never be able to do.”
This improved efficiency benefits ratepayers since every bit of electricity that can be produced by hydropower means just that much less need for relying on other generating assets which have higher operating costs — or for turning to power purchased from outside sources. If hydro were suddenly out of the mix, for example, TVA would be forced to turn to gas- or oil-fueled combustion turbines for a quick response to a generation shortfall — at a cost that is considerably more expensive than hydro generation.
Automation also enables TVA to maximize the value of the available water for Valley citizens in other ways, says Holt.
“Production Coordinators like Michael Richards may be many miles away when they are monitoring the computerized system that sends instructions to generating units at the hydro plants. But whether we’re trying to make up for a shortfall in generating capacity or allowing the reservoirs to fill in time for the Memorial Day holiday, we are always mindful that our decisions impact people’s lives — their work and their play.”