Dynamic Modeling Of Pressurized Water Reactor And Its Interaction With The Grid

As a kind of clean energy,nuclear energy has become the main force in China's energy structure adjustment with its high energy density,low pollution and zero emission.In recent years,the installed nuclear power capacity of China has been increasing and the proportion of nuclear power generation has been rising,which indicates that the nuclear power industry in China has been developing rapidly.At present,some nuclear power units not only run with base load,but also have certain capability of load tracking.With the increasing proportion of nuclear power,it is imperative for nuclear power units to participate in peak regulation like conventional thermal power units.Due to higher requirements on safety and stability of the nuclear reactors,it is necessary to understand dynamic characteristics of nuclear power units and take specific protective measures when designing,operating and maintaining nuclear power units.In this paper,the model of PWR nuclear power unit is built based on ADPSS(Advanced Digital Power System Simulator)platform,and the parameters are checked and adjusted by comparing with the recorded curve of actual nuclear power plant.The simulation research of the nuclear power plant is carried out from three aspects of dynamic characteristics,network-related protection and characteristic comparison,1.The nuclear power unit is connected to the power grid,and its primary frequency modulation,three-phase short-circuit fault response,load rejection and excitation characteristics are simulated.The simulation results show that,the nuclear power unit has certain power adjustment ability and can keep the internal parameters safe and stable when participating in primary frequency modulation.The internal time constant of the unit is relatively large,resulting in the slow response to external faults and disturbances.So short time faults and disturbances will not cause instability of the internal parameters.As a medium and long-term fault,load rejection will cause the internal state of the nuclear power unit to deviate greatly.The higher the power level of the unit,the greater the internal deviation amplitude will be.Complete loss of excitation will cause the nuclear power unit out of sync and even lead to power grid collapse.Therefore,the complete loss of excitation must be avoided,and it is necessary to repair the fault as soon as possible or cut off the nuclear power unit decisively when the loss of excitation occurs.2.Protection measures are put forward corresponding different working conditions.Since rotor overspeed is easy to occur in short circuit and load rejection of nuclear power units.An optimized overspeed protection control strategy is proposed to improve the overspeed inhibition of nuclear power units.The valve closing system and bypass system are adopted to protect nuclear power units from load rejection.The simulation results shows that the valve closing system can suppress the overspeed of the unit directly,while the bypass system and the valve fast closing system can reduce the internal parameter fluctuation of the nuclear power unit.In actual operation specific protection strategies can be adopted according to different needs.Forced excitation,over excitation and low excitation have little effect on the internal parameters of the nuclear reactor.The protection measures against forced excitation,over excitation and low excitation can protect the excitation system of the nuclear power plant and the reactive power balance of the system,which is conducive to the stable operation of the nuclear power unit.3.Through the comprehensive comparison of nuclear power and thermal power,the similarities and differences between nuclear power and thermal power are obtained.They are similar in general,so in the overall simulation analysis of the power grid,thermal power units can be used to replace nuclear power units to avoid high-order modeling and complex calculation.The difference between nuclear power plant and thermal power plant is mainly the difference in response speed to external disturbance,because the changeable main steam pressure of nuclear power plant is equivalent to a certain amount of damping added to the regulation system.In addition,the operating range of nuclear power plant is smaller than that of the thermal power plant due to the strict operating requirement of internal parameters.