Analysis And Research On Primary Frequency Modulation Performance Of Regional Power Grid

With the rapid development of the power industry,the requirements for primary frequency modulation of power systems are getting higher and higher.Frequency anomaly or frequency collapse will bring extremely serious consequences to the safe and stable operation of the power system.Based on the composition of the power grid and the factors affecting the frequency stability in Xinjiang,the influence of heating extraction,sliding pressure operation and power change in regional grid power tie-line on the primary frequency modulation capability of the heating unit is studied.China's thermal power units have low utilization hours and long-term low-load operation.Power generation companies often use sliding pressure to reduce the unit's throttling losses and improve economy.At the same time,heating units account for about30%of the total installed capacity of thermal power units and these units are in the operation of steam extraction in winter.These two operating conditions greatly affect and restrict the primary frequency modulation capability of the steam turbine,which brings hidden dangers to the safe operation of the power grid.In order to study the response characteristics of the unit to the frequency under large steam extraction conditions,primary frequency regulation test was carried out to record the performance parameters of the unit under different main steam pressures and different extraction conditions.According to the principle and control process of primary frequency modulation,the Matlab/Simulink software platform is used to establish the prime mover and control model of the heating unit with primary frequency modulation capability,and relevant model of generator unit connecting to the grid.According to the test results,the parameters of the primary frequency modulation simulation model were determined.The power output characteristics of steam turbine are analyzed.By adding the response coefficient of low-pressure cylinder Q_R to the simulation model,the time constant T_COO of the connecting pipes of medium and low pressure is modified for the heating unit,and the pressure correction module is added to respond to different main steam pressures.It has been verified by experiments that the correction of the low-cylinder power output and the time constant of the medium-low pressure connecting pipe has been achieved.On this basis,the concept of frequency modulation margin is put forward.The main reason for the decrease of primary frequency modulation margin is the insufficient power output of low pressure cylinder and the decrease of load response speed after the increase of extraction capacity of heat supply steam turbine.Under the rated initial load,as the main steam pressure increases,the frequency regulation margin of the unit increases.By simulating the mathematical model of the regional power grid and combining the actual regional grid structure,the frequency dynamic characteristics of the regional power grid under different tie-line power disturbances are studied,which provides a reference for the safe operation of the regional power grid and reduces the economic loss under the accident.Through the simulation analysis and the Hetian Power Grid the allowable operation mode are obtained,that is,the transmission power of the tie-line cannot exceed 65%of the total load of the local power,which can ensure the safe operation of the Hetian Power Grid.Through analysis and research on the characteristics of Hami grid,the simulation shows that under different OPC settings,the transmission power of the tie-line under 103%OPC setting can't exceed 23%of the local power consumption.The transmission power of tie-line under 105%OPC settings can not exceed 45%of the local power consumption,which can ensure the safe operation of Hami power grid.