New turbine control for Qinshan II13 February 2018
A turbine control upgrade at China National Nuclear Corporation’s Qinshan Phase II is boosting reliability. Dylan Boby gives an overview of the project.
Westinghouse Electric Company completed the turbine control upgrade at Qinshan Phase II unit 2 on 4 September 2017. It is the first of four such upgrades the company is implementing on indigenous design CNP-600 pressurised water reactors at Qinshan Phase II In Zhejiang province, and the first such upgrade Westinghouse has completed in China.
The upgrade at Qinshan Phase II unit 2 replaced the plant’s original Westinghouse Distributed Process Family based turbine control system with a robust OvationTM based turbine control and protection system. The project also included mechanical scope, which involved Westinghouse replacing the mechanical overspeed bolt turbine trip system with an electro-hydraulic system and added redundant linear variable differential transformers for valve position indication on the main governor valves.
The existing turbine control and protection system was once the state of the art both electronically and mechanically – but that was more than 30 years ago. It had become obsolete both electrically and mechanically.
Coupling the Ovation-based digital platform with the electro-hydraulic trip system presents potential savings of $78,000 per outage, and additional power production revenues ranging from $70,000 to $150,000 annually. Such monetary gains are made possible through maintenance cost reduction; provision of system diagnostics, which reduces average repair time; automatic valve calibration; and online testing. Having a control system common to both fossil and nuclear plants in the fleet also facilitates support of the system by utility personnel at multiple utility sites.
In addition, Westinghouse works to contain total installed cost by using a low-risk field implementation strategy, making maximum use of closed loop models and performing extensive validation and testing before the system ships to site.
Westinghouse’s electronic scope for the project included removing and replacing four control system cabinets and one network infrastructure cabinet, including turbine control, turbine protection, automatic turbine control and rotor stress and moisture separator reheater cabinets, as well as their associated computer system and manual controls in the main control room. The new cabinets were custom built to fit in exactly the same locations as the original cabinets, including using identical bolt patterns to mount the cabinets to the floor. This level of attention to detail reduces the time and cost of installing equipment in the plant. Westinghouse also provided pressure transmitters that were direct replacements of older pressure switches used in the turbine protection system. Providing the pressure transmitters and using them as inputs to special software algorithms in Ovation achieves increased reliability and provides better information to both operators and maintenance personnel.
The more modern computer system and control panels in the main control room provide the turbine control operator with updated screens and functionality for alarms, trending and troubleshooting. They also allow valve tests and protection system tests to be more easily performed by the operator. The modern computer system is also more intuitive, easier to operate and maintain and allows a new generation of operators to quickly learn the system.
Westinghouse’s mechanical scope was to remove the mechanical overspeed bolt protection system and replace it with an electro-hydraulic overspeed protection system. The new system utilises a 2 out of 3 solenoid valve scheme to allow online testing of the protection system while the turbine-generator is producing power. The new system is more reliable than the older mechanical system and allows overspeed tests to be performed at reduced speeds, which eliminates stresses to the turbine. Additionally, the new system has multiple redundancies to protect the turbine and plant personnel from turbine overspeed conditions.
With the goal of building local turbine control and protection system experience in China, Westinghouse China- based engineers were provided with training on software-in-loop testing and then presented and demonstrated all turbine software functions to the Qinshan customer in the USA. Such comprehensive hands-on training continued throughout the project in China during verification and validation, factory acceptance testing, site installation, site acceptance testing and commissioning, and finally power ascension testing at the plant site. Westinghouse is also expanding training in China on its instrumentation and control systems and has recently begun planning for that training, as well as hiring instructors at the company’s offices in Shanghai, Pudong District.
Westinghouse will be completing turbine control and protection system upgrades at Qinshan Phase II units 1, 3 and 4 in 2018.
A more detailed case study is published in the January 2018 issue of Modern Power Systems magazine.