Steam Generator Water Level Control via Valve Segmentation
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Solution Overview
Problem
Nuclear power plants face periodic water level fluctuations in steam generators due to stiction in main control valves, leading to instability and increased maintenance costs, especially during steady-state operations at high reactor power levels.
Innovation Solution
An integrated control logic device adjusts the positions of both the main and auxiliary control valves, using a hysteresis function to minimize the movement of the main control valve and compensate for its stiction effects, allowing the auxiliary valve to maintain stable water levels by applying a deadband to the main control valve's position demand signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the main control valve is used for water level control, then the water level control range and response speed are improved, but stiction causes periodic water level fluctuations and reduces control stability
Solution Approach 1:
The control function is segmented between two valves: the main control valve handles large flow capacity requirements and rapid response, while the auxiliary control valve handles precision control to eliminate stiction fluctuations. This division allows each valve to operate in its optimal range, with the auxiliary valve compensating for the main valve's stiction issues.
Solution Approach 2:
The auxiliary control valve acts as an intermediary that compensates for the stiction effects of the main control valve. By controlling the opening degree of the auxiliary valve based on detected stiction fluctuations, the system smooths out water level variations caused by the main valve's stick-slip behavior.
2Measurement precision
If the main control valve operates at high precision, then water level control accuracy is improved, but stiction increases causing periodic fluctuations
Solution Approach 1:
Precision control is separated from the main control valve and assigned to the auxiliary control valve. The main valve operates with larger movements for rapid response, while the auxiliary valve provides fine-adjustment precision control, eliminating the stiction-related precision issues of the main valve.
Solution Approach 2:
The auxiliary control valve serves as a precision intermediary that compensates for the main valve's stiction. By detecting water level deviations caused by stiction and adjusting the auxiliary valve accordingly, the system achieves high precision control without the instability caused by main valve stiction.
3Speed
If the main control valve position is frequently adjusted, then water level control responsiveness is improved, but valve wear increases reducing service life
Solution Approach 1:
The control adjustments are segmented between two valves: the main control valve makes infrequent, large adjustments for rapid response to major changes, while the auxiliary control valve handles frequent, small adjustments for continuous precision control. This segmentation significantly reduces the wear on the main valve.
Solution Approach 2:
The auxiliary control valve acts as a protective intermediary that absorbs the wear from frequent position adjustments. By handling the continuous fine-tuning operations, the auxiliary valve protects the main valve from excessive wear while maintaining control responsiveness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces water level fluctuations, extends the life of the main control valve, and decreases replacement costs by leveraging the auxiliary valve's precision to control water levels with five times the accuracy of the main control valve, while maintaining control performance during transient events.
Implementation Method 1
a hysteresis function unit to generate the second main control valve position demand signal by applying a hysteresis function with adjustable deadband to the first main control valve position opening demand signal
Data Source
AI summary
According to the disclosure, a position of a main control valve and a position of an auxiliary control valve are adjusted. In particular, a position of the auxiliary control valve is adjusted by determining whether a change in the position of the main control valve is in a preset deadband range, thereby preventing a periodic water level fluctuation of a steam generator.