According to a recent EPRI study, robotic inspection of generators without removing the rotor offers a cost-effective alternative to rotor removal and inspection
Companies that operate nuclear and fossil fuel power plants know well that it’s important to take good care of the turbine-generator. Failures can cost millions of dollars in direct repair expenses and lost generation revenue. Traditionally, detecting certain failure mechanisms has required shutting down the unit and removing the generator rotor for a thorough visual inspection. These inspections are expensive—up to $500,000 for large generators and less for smaller units. Generator rotor removal also has potential risks, such as dropping the rotor or bumping and damaging the stator.
According to a recent EPRI study, robotic inspection of generators without removing the rotor offers a cost-effective alternative to rotor removal and inspection. Based on a survey of more than 30 utilities as well as discussions with major manufacturers Siemens Energy and GE, EPRI found that robotic inspections provide reliable results and cost up to 75% less depending on the generator’s size.
“All indications are that robotic inspections yield results equivalent to rotor-out inspections,” said EPRI Technical Executive Bill Moore, who led the research. “Power industry acceptance of this approach should continue to trend upward.” More than 82% of respondents in the EPRI survey have conducted a robotic inspection on at least one unit in their fleet, and nearly two-thirds reported satisfaction with the results.
The EPRI study reported on attitudes toward robotic inspection among key electric power industry stakeholders. For example, insurance companies often pay for generator repairs and lost revenue associated with forced outages, thereby having a say in how generators are maintained. While they previously were reluctant to accept robotic inspections as equivalent to “rotor-out” inspections, many do now.
The EPRI research also provided an in-depth assessment of the state of the technology. In particular, “crawlers” are the most commonly deployed robot for generator inspections. They typically use “caterpillar” tracks (similar to those on military tanks) to move through a narrow space (known as an air gap) between the generator’s rotor and stator, carrying cameras, lights, and various sensors to conduct multiple inspections and tests. The robots connect to a power supply and control hardware through cables and transmit data for processing. To access smaller spaces, inspection technicians may use devices known as telescopic masts, which extend thin metal structures equipped with sensors.
Researchers found that robotic inspections on some units face challenges. For example, not all generator air gaps can be accessed by the larger robots, and some generators have additional obstructions that require precise maneuverability that not all robots can provide. Also, unlike rotor-out visual inspections that enable human inspectors to view defects directly at close range, robotic inspections require technicians to interpret camera images, which sometimes distort color and size.
There are nearly a dozen robot models available today. Manufacturers include Siemens Energy, GE, IRIS Power, Brush/Dekra, Mitsubishi-Hitachi, Ansaldo, Toshiba, ABB, and Nova Technology. When EPRI first researched this technology nearly 20 years ago, only three robots were available.
The EPRI study examined the technology’s current capabilities and latest advancements. Over the past few years, robotic inspection technology has advanced rapidly, driven by broader developments in robotics, computers, software, cameras, and lighting. One robot model carries four cameras, and image resolution for cameras on most models rivals the best television technology. Robots for generator inspections are getting smaller, thinner, and more maneuverable.
“The older models of crawler robots are up to 30 millimeters thick,” Moore said. “Now, smaller models are in the range of 12 millimeters. As robots get smaller, more of them can access generators with smaller air gaps. We’re still not able to perform a robotic inspection on 100% of operating generators, but the number we can’t inspect is getting smaller.”
“We make improvements with our robots multiple times a year as new technology becomes available,” said Colleen Crawford, who manages generator service research and development at Siemens Energy. “Each year, the robots can get into smaller spaces in the generators. Digitalization has enabled us to reduce the size of the inspection crew by one-third. We expect to develop even more automated systems.”
Moore predicts that the addition of artificial intelligence (AI) to robotic inspection will enhance results. For example, object recognition software could distinguish between acceptable conditions and anomalies, such as a foreign objects or obstructions.
“At EPRI, we believe AI can lead to further advances in robotic inspection development,” Moore said. “If these robots can automatically distinguish between acceptable and non-acceptable conditions, technicians may not have to continuously observe the robots as they inspect generators.”
Robotic inspection of generators is part of a broader trend of more automated generator monitoring and diagnostics. The ultimate objective for utility owners and technology developers is comprehensive knowledge of generator conditions without rotor removal, saving time and money.
Image at top of article is a crawler robot inspecting a generator. Photo courtesy of Iris Power.
Key EPRI Technical Experts:
Bill Moore
For more information, contact techexpert@eprijournal.com.
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