Steam Turbine Valve Control for Power System Accident Response
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Solution Overview
Problem
Existing valve control methods for steam turbines in power plants, such as Early Valve Actuation and those disclosed in JP H10-252416 A, suffer from delays in responding to electric power system accidents, leading to decreased effective power output and instability in reactor pressure control during and after such events.
Innovation Solution
A valve control system comprising a normal control circuit and a high-speed valve control circuit, which includes a first selection unit for rapid closure of control valves and a second selection unit for rapid opening of turbine bypass valves, along with an opening position correction unit and an opening speed hold unit, to manage steam flow and maintain reactor pressure stability during power system accidents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Early Valve Actuation is used to rapidly close all control valves or intercept valves to prevent turbine overspeed, then turbine rotation speed control is improved, but the recovery time of mechanical torque output is delayed and effective power to the electric power system significantly decreases
Solution Approach 1:
The invention divides the valve control into two independent systems: a high-speed valve control circuit that rapidly closes only the necessary control valves to prevent overspeed, and a normal control circuit that manages the remaining valves to maintain power output. This segmentation allows selective valve closure rather than closing all valves, thus preventing turbine overspeed while minimizing impact on effective power output.
Solution Approach 2:
The high-speed valve control circuit is pre-configured with solenoid valves and control logic to immediately actuate upon detecting power system accidents. This preliminary setup enables rapid response without waiting for normal control systems, suppressing turbine overspeed before it occurs while the normal control circuit continues managing power output.
2Ease of operation
If valve opening position is adjusted through servo actions to control steam flow rate, then steam flow control is achieved, but time delay occurs before actual valve position follows control demand signal
Solution Approach 1:
The invention introduces solenoid valves as intermediary devices between the control system and the steam flow path. These solenoid valves can rapidly change position in response to electrical signals, bypassing the slower servo action mechanism for emergency control. This allows the system to achieve both precise steam flow control through normal servo actions and rapid response through solenoid valve actuation.
3Reliability
If control valves are rapidly closed to block steam flow and prevent overspeed, then turbine rotation speed stability is improved, but reactor pressure control stability deteriorates due to sudden steam flow reduction
Solution Approach 1:
The invention segments the valve control function into emergency overspeed protection (handled by high-speed circuit closing specific valves) and normal steam flow management (handled by normal control circuit). This allows the system to maintain reactor pressure stability through the normal control circuit while the high-speed circuit provides targeted valve closure for overspeed protection, preventing the destabilizing effect of sudden complete steam flow blockage.
Solution Approach 2:
The invention changes the control parameters by introducing a dual-control architecture where the high-speed circuit modifies valve position rapidly for emergency protection while the normal control circuit adjusts steam flow rate gradually to maintain reactor pressure stability. This parameter separation allows independent optimization of both turbine speed protection and reactor pressure control.
Data Source
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AI summary
A valve control system for a steam turbine that decrease in effective power as well as secure control stability in the event of an electric power system accident is provided. A valve control system for a steam turbine includes an accident detection unit 44 which detects an occurrence of an electric power system accident, a first selection unit 45 which selects, from a plurality of control valves 13 (13a~13d) which adjust a volume of steam flowing into a steam turbine, control valves 13 to be rapidly closed according to a scale of the accident detected, and a normal control circuit 11 which continues normal pressure or speed control by the control valves 13 which are not selected.