Along the Jinsha River, as spring gives way to summer, a new technological partner has joined the maintenance team at the Baihetan HPP. The Quantum Non-Destructive Testing (NDT) Robot, which began its service last year, is now deployed at the maintenance site of the plant's 1,000 MW hydro-generating unit.

This robot is engineered to closely conform to the curved surfaces of critical unit components including runner blades, runner crown and runner band. It effectively overcomes numerous challenging conditions at the maintenance site, such as confined spaces, humid and enclosed environments, and complex electromagnetic interference, thereby performing comprehensive and precise NDT operations on the equipment.

At the site of the non-destructive testing (NDT) on the runner blades of Unit 16, the nearly 20-meter-high maintenance platform previously required for manual inspections is no longer needed. In its place stands this new, agile partner. Two maintenance personnel place the approximately 10-kilogram inspection robot onto the surface of a runner blade, where it adheres firmly, much like a gecko. By manipulating a control handle, operators can guide the robot to move smoothly across the runner blade's surface to perform intricate tasks. This process not only enables NDT within the confined spaces of the runner blades but also significantly mitigates the risks to personnel.

Leveraging quantum measurement technology, this robot can detect weak magnetic signals imperceptible to conventional instruments, thereby performing a comprehensive "health check" of the runner blades. WANG Dong, a Senior Technician in the Mechanical and Hydraulic Maintenance Department of Baihetan HPP, said: "This robot can pinpoint minuscule defects as small as 10 micrometers wide and 50 micrometers deep in metallic components. Its detection accuracy and probability of detection (POD) both reach an impressive 99%, successfully overcoming the technical limitations of conventional testing equipment."

The critical components of large hydropower unit runners, including runner crowns, runner bands and runner blades, are all cast steel components. Their large volume and weight, combined with the complex geometry of their flow passages, make them susceptible to issues such as fatigue cracks and cavitation erosion after prolonged operation under high water heads and variable operating conditions. These issues, often caused by imbalanced fluid forces, pose a potential threat to the safe and stable operation of the generating unit.

So, how can these hidden defects be detected in a timely manner? The conventional approach involves utilizing standard Non-Destructive Testing (NDT) methods such as Magnetic Particle Testing (MT), Penetrant Testing (PT), Radiographic Testing (RT), Ultrasonic Testing (UT), and Eddy Current Testing (ET). However, these methods have inherent limitations. MT and PT can only reveal the length and shape of surface-level flaws but cannot determine their depth. Meanwhile, RT, UT, and ET demand highly skilled operators and often yield results that are not intuitively clear.

The application of solid-state quantum precision measurement technology effectively addresses the shortcomings of these five conventional NDT techniques. This robot, equipped with a diamond probe and quantum detection technology, offers distinct advantages, including intuitive result visualization and highly accurate defect localization. Its operating principle is based on the countless NV (Nitrogen-Vacancy) color centers embedded in the diamond—often described as "microscopic compasses" thousands of times smaller than a human hair. These are unique particles capable of sensing the most minute changes in their environment. With extraordinary sensitivity, they react instantaneously to even the faintest variations in surrounding magnetic fields and temperature. By illuminating the diamond with a laser to read these changes, the precise magnitude of the magnetic field can be calculated. Its detection sensitivity and accuracy far surpass those of current conventional equipment, making it a prime example of emerging technology being successfully applied in the engineering sector.

In recent years, China Three Gorges Corporation ("CTG") has been actively implementing national science and technology major projects to reinforce the operational safety barriers of core equipment in its power plants. By adopting a "quantum sensor + application scenario" strategy, CTG is proactively investing in quantum technology, reserving key NDT expertise, and advancing the practical application of quantum precision measurement technology in the industrial sector.

By deeply integrating advanced solid-state quantum precision measurement technology into the field of equipment NDT, the Baihetan HPP operated by CYPC, a subsidiary of CTG, has successfully developed a novel NDT robot. This robot is distinguished by its high sensitivity, superior measurement accuracy, and compact design, while also enabling damage imaging and quantitative assessment. It has been successfully deployed in practical unit maintenance. "Previously, setting up the maintenance platform for traditional methods alone took three to four days," said WANG Dong. "In contrast, the quantum robot requires no such platform. This not only effectively reduces maintenance costs and significantly shortens the maintenance period but also boosts operational efficiency to three times that of conventional methods."

To date, this newly deployed quantum NDT robot has successfully completed the NDTs on the runners of three 1,000-MW units at Baihetan HPP. It is now scheduled to be dispatched to the Xiangjiaba HPP for a new round of equipment maintenance.

ZHANG Ge, Plant Manager of Baihetan HPP, commented that the application of the quantum NDT robot at the front lines of unit maintenance allows for the early detection of minor equipment degradation. This supports the implementation of refined O&M management for critical components, effectively reducing the risk of safety incidents and manual inspection costs. It further propels the maintenance of large-scale hydropower plants towards greater intelligence and precision.