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Seeing the writing on the wire
5/22/2013 12:00 AM
As measurements from the generator at Bonneville Dam stream through the homemade “black box,” electronics engineer Steve Yang keeps a close eye on the data.
Vigilant engineers crowd around a string of laptops set up on folding tables inside the cavernous Bonneville Dam. At the center of their makeshift office above the Columbia River is a homemade device they call “the black box,” crafted to collect measurements from one of the dam’s generators and send the data to their computers.
The engineers are alert because they are intentionally subjecting a 30-year-old generator to staged disturbances – sudden changes in voltage and frequency – to see how it responds. The tests sound invasive, but the engineers, working in partnership with the U.S. Army Corps of Engineers, know exactly how far to push the hydroelectric envelope.
“We’ll try not to make it too exciting – we don’t want any sparks to fly,” says BPA electrical engineer Dmitry Kosterev.
This is how engineers develop a baseline model of a generator’s behavior. The models help BPA understand the power system’s response to natural disturbances, such as lightning striking a transmission line, and set safe transmission operating limits. Inaccurate power plant models have contributed to catastrophic results, including the 1996 West Coast blackout that left millions of people in the dark.
Testing like this has allowed models to improve over the years, deepening BPA’s understanding of how the generators and the transmission system operate under unforeseen conditions. And now BPA engineers have found a way to make their models even more accurate and identify problems on the grid before they occur. The new method is cheaper, safer, more efficient and more accurate – and it can be done at any time in BPA’s synchrophasor lab, without taking the generator offline.
To create the innovative application, BPA coupled data from baseline tests, like the one at Bonneville Dam, with synchronized, high-speed measurements of the transmission system. The measurements come from synchrophasors – shoe-box-sized devices at substations that take precise snapshots of the grid’s behavior 60 times a second.
Getting the baseline
Electrical engineer Dmitry Kosterev, careful not to push the Bonneville Dam generator too far, monitors gauges on the control panel. He records measurements of the equipment’s behavior as it’s subjected to staged disturbances during a test.
Beneath the engineers’ steel-toed boots, the churning Columbia River is cranking a turbine. Experts from the U.S. Army Corps of Engineers and BPA work near a large control panel that tells the generator what to do. The control panel houses cartoonishly large versions of the breaker switches in a home’s electrical panel. But these switches control part of the mightiest river in North America. If one of them trips, the wicket gates below will close, blocking thousands of gallons of water from propelling the turbine.
The Bonneville Dam control panel was built in the late 1970s, but the presence of a small flat-panel touch screen is evidence of a recent upgrade. With a tap of a finger, one of the engineers makes a sudden voltage adjustment – something operators would expect to see during a system disturbance, such as a transmission line outage. Voltage is the force that keeps electrons flowing through transmission lines, and the generator’s reaction to a voltage change is critical.
Kosterev carefully watches the control panel, where the numbers – trending voltage, frequency and power output – are now moving in agitation as the generator reacts to the speed adjustments. “We’re pushing it to see how far it can go. Within limits,” he clarifies. “If we go too far, the unit can trip. That can damage the equipment.”
There’s a pop, followed by an intense, eerie groan. Onlookers dart their attention toward the generator.
Nancy Kroner hears a new note in the hum of the equipment she is monitoring. “That’s the governor saying ‘ouch’,” she calmly explains. “It’s trying to change the speed of the generator.”
Kroner runs Versalence LLC, a company that specializes in the equipment that controls the generator frequency, called the governor. All generators in interconnected power systems are synchronized and must maintain the same frequency, usually at 60 hertz. But in a disturbance, generators react by speeding up or slowing down. If generator controls aren’t set correctly, the unit can fall out of synchronization and off the grid.
Constant oscillations occur naturally in power systems. They are caused by small imbalances in power supply and demand, just as a drop of water creates ripples on a pond’s surface.
“What you want to see is that the oscillations are damped,” explains Steve Yang, BPA electronics engineer. “If our model shows them growing in time, we have to determine why. Something is either wrong with the generator, or with the model.”
Accurate models can prevent BPA from over- or under-investing in the transmission system. They can also help avoid operating the system in unsafe conditions. BPA – and much of the West Coast – experienced the fallout of inaccurate models in the 1996 blackout. A series of events, triggered by a transmission line that sagged into a tree, led to the unexpected loss of generation at McNary Dam. Within 73 seconds, power stopped flowing on the main artery to California, and seven million people lost power.
Following the blackout, BPA analyzed data from the preceding days and saw voltage changes that its models weren’t sophisticated enough to predict. That meant dispatchers didn’t have the information they needed to see the catastrophe coming. After 1996, the Western Electricity Coordinating Council (WECC) started requiring baseline tests at generators west-wide at least every five years. BPA funds the tests at plants owned by the Corps and Bureau of Reclamation. The tests have helped the models evolve and restored confidence.
“The benefits are indisputable,” Kosterev says. “Our model data has improved significantly.” But the simulations aren’t perfect. “Even after we establish a baseline,” he says, “we need to keep monitoring generators.”
They can always use more data.
BPA turns to satellites
BPA began installing experimental phasor measurement units in the 1980s. The devices helped move the art of monitoring the grid into a new era by collecting data at a much higher rate of 60 measurements per second and by using Global Positioning System satellites to time-synchronize the measurements. “They gave us an unprecedented view of the dynamic state of the power grid,” Kosterev says.
Initially, a PMU was a stand-alone device that collected data at a substation. After the 1996 outages, the value of having real-time, synchronized measurements taken over a wide area available in control centers became obvious. BPA was the first to network PMUs from substations to the control center. The agency also developed the first phasor data concentrator, a device that time-aligns multiple PMU data streams. That allows operators to compare measurements taken from any point in the Western Interconnection, a transmission system that spans Alberta, Canada, to Baja, Mexico. Today, synchronized phasor measurements, and often the PMUs themselves, are referred to as synchrophasors.
Since the 1996 blackout, BPA has increased PMU coverage and started streaming real-time data into its control center, giving operators better information on which to base decisions. With 120 synchrophasors in its grid, BPA is leading the nation in the use of these methods.
Kosterev and Yang used the data to develop the Power Plant Model Validation application, funded through BPA’s Technology Innovation program. It’s a game-changer in the world of generation modeling.
Back at the lab
At his BPA office in Vancouver, Wash., Yang skims a list of computer files and opens one with data from Chief Joseph Dam. The information, collected by synchrophasors, tells Yang how the generator responded to a recent system disturbance – a large, sudden change in voltage and frequency.
On another screen, he accesses a simulation of the disturbance, showing how BPA would expect the dam to react. With a few more clicks of his mouse, a graph appears. It compares the actual and simulated events, telling Yang how accurate the prediction was.
The information was compiled in a lab at BPA’s Ross Complex in Vancouver, Wash., where the synchrophasor data is archived. When a dispatcher sees an event on the system, the engineers are notified, and they can easily find the data of the disturbance, “because it’s time-stamped,” Yang says. “That’s the beauty of synchrophasors.” And then they run a calculation to test the existing model.
BPA is working to further automate the process of model verification. “In the future, it will be a seamless process,” Yang says. “I’ll be able to click one button, go for coffee, come back and see the report.” The report compares the megawatts and megavars that the dam produced in the actual and simulated events.
Yang explains, “When frequency (on the grid) drops, we expect all generators to pick up the slack. Generators control frequency by absorbing or supplying megawatts.” Similarly, when there is a voltage change, the generator reacts by producing or absorbing megavars, the measurement of reactive power. In the simplest of terms, reactive power doesn’t do any work, but it does provide a necessary ingredient of a healthy grid, called voltage support.
“Reactive power doesn’t turn a motor or light a room. But it’s necessary because it transmits the power across a transmission line,” Yang says.
So far, BPA is using this computer application to test six hydroelectric plants. The agency is also helping thermal generators validate their models.
“It gives them an alternative,” Yang says. “It’s cheaper than doing the test at the generator, and it gives us a more reliable system.”
Test saves time, money
Initially, the validation test was pass/fail. If a model failed, the generator would have to be subjected to another baseline test.
“It’s easy to test a hydro unit that way, but it’s a challenge to test a thermal plant,” Kosterev explains. At Bonneville Dam, for example, engineers were able to shut down one generator at a time. But at the region’s only nuclear plant, the Columbia Generating Station, the testing is much more challenging. The actual test only takes a few hours, “but there’s no such thing as a four-hour shutdown at a nuclear plant,” he says. CGS takes three to four days to return to service, meaning each test costs between $100,000 and $700,000, depending on the timing of the outage.
BPA and the Department of Energy wanted to find a way to avoid taking plants off line and instead calibrate the models using synchrophasor data. DOE funded work, mostly at the University of Wisconsin, to figure it out. Then, after finding that the CGS model was inaccurate, BPA and the university tested new methods. The engineers were able to calibrate the nuclear plant model using synchrophasor data from a series of disturbances.
“CGS now has the most accurate model in the BPA area,” Yang says. “Without synchrophasors, we would have had to go back to the plant to test it. Now when there’s a disturbance, we can immediately run a test, see how our model looks and calibrate it if we need to.”
Vickie VanZandt, former BPA chief engineer and senior vice president of Transmission Services, highlighted another benefit of the new method. “The fact that they can meet testing requirements without taking the generating units offline led to the installation of additional PMUs, with the added benefit of greater observability of the grid.”
VanZandt, who was chief engineer during the 1996 blackout, has a keen interest in system visibility and modeling. Today she leads an effort called the
Western Interconnection Synchrophasor Program
(WISP) to install more than 400 new or upgraded PMUs.
BPA is working with WECC and WISP to help other generator owners and operators use this method to improve and validate their models, increasing the simulation accuracy of the Western Interconnection overall.
Model spots equipment failure
The tests can also tell engineers when a generator’s behavior is amiss. One test revealed an equipment failure at Grand Coulee Dam.
“We were watching the model for Grand Coulee, and it had been matching for some time,” Yang says. “Then we had an event where the simulation did not match the generator’s reaction.” BPA contacted operators at Grand Coulee and asked if the power system stabilizer, which damps oscillations, was operating. “They said it was working, but we still saw this difference in our model.”
Later an engineer at Grand Coulee looked into it further. He found an internal failure in the stabilizer.
“The green light indicated it was working, but it wasn’t,” Yang says. “We wouldn’t have found that failure without the ability to run these tests. If this happened at several units at the same time and you didn’t know it, you could be operating in unstable conditions.”
BPA is also seeing benefits of installing synchrophasors at wind plants. All generators play a role in power system stability. And with nearly 5,000 MW of wind generation connected to BPA’s transmission system, wind generators are playing an increasingly greater role. System planners and operators need to ensure that wind power plants have accurate and predictable models. BPA has installed nine synchrophasors at wind plants and is partnering with DOE and the Utility Wind Integration Group in data analysis.
The new testing methods have helped BPA identify control problems that could have damaged wind turbines. In one case, turbine blades had been continually tilting back and forth for six hours, causing unnecessary wear and tear and diminishing their efficiency.
Where synchrophasors are taking us
When PMU installation on BPA’s grid is complete, they will be collecting a combined 150,000 measurements per second, and the agency is only just beginning to unlock the benefits.
“It’s an information overload,” Kosterev says. “We’re still developing the intelligence to sift through it and analyze it. This project was about helping us make better decisions. But eventually, synchrophasors will help us take better actions.”
VanZandt set a mission for BPA before her retirement in 2009: “It is time to move forward from wide-area monitoring [using PMUs] to wide-area controls.”
Through WISP – a $107.8 million investment by Western utilities and the Department of Energy – the participants will build a wide-area synchrophasor infrastructure and deploy monitoring and control applications. WISP will enable reliable real-time data exchange among multiple operators. The need for better data exchange was cited as a contributing factor in the evaluation of the Sept. 8, 2011, Pacific Southwest outage, in which Kosterev participated.
BPA is one of the largest WISP cost-share participants, along with WECC, Pacific Gas and Electric, Southern California Edison, Idaho Power Co., NV Energy, PacifiCorp, Salt River Project and California ISO. Ten additional participants have agreed to install synchrophasors on their systems to complete visibility on the interconnection.
Linking synchrophasors to Smart Grid
The synchrophasor project is a part of the larger Smart Grid initiative to develop technologies that can improve reliability, enhance efficiencies and give consumers choices about when, how and at what price to use energy.
Kosterev explains the link: “Just like in your life, you get information, make decisions, and then you take actions. Synchrophasors provide better visibility of the power grid, which will lead to better decisions. But ultimately, you need to take an action to realize the benefit of your decision.”
BPA is looking into the benefits of direct load control using Smart Grid technologies. For example, in a system disturbance today, dispatchers might need to cut power to a city block. In the future, BPA could take more exacting actions.
Kosterev describes something called selective end-use drop. “If they want to, dispatchers will be able to shut off just the air conditioners in that area for several minutes,” he says. “Most people wouldn’t even know there was a problem.”
Or that operators just averted a blackout.
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