A Control Method for Suppressing Steam Turbine Overspeed under High-frequency Power Grid Accident

Abstract

The invention relates to a method for controlling fiction steam turbine excessive rotational speeds in power grid high-frequency accidents. The method has the advantages that steam turbine comprehensive valve location instructions are corrected from multiple directions, accordingly, unit load can be quickly reduced, difference between power supply load and power utilization load in isolated grid systems can be eliminated, and the isolated grid operation frequency stability level can be improved; the amounts of unbalance of power of power grids can be computed according to the soaring speeds and the soaring amplitude of the rotational speeds of steam turbines when the rotational speeds of the steam turbines reach 3040, corresponding comprehensive valve location values can be obtained by means of conversion, regulating valves of the steam turbines can be preliminarily switched off, accordingly, the unit load can be reduced, and the difference between the power supply load and the power utilization load in the isolated grid systems can be eliminated; comprehensive valve location instructions are corrected after OPC (over-speed protection control) resetting, and can be recovered to beK2 times of the comprehensive valve location instructions prior to OPC actions, accordingly, the unit load further can be reduced, the difference between the power supply load and the power utilization load in the isolated grid systems can be eliminated, and electric quantity supply and demand of the isolated grid systems can be balanced; soaring of the rotational speeds of the steam turbines canbe effectively inhibited, and accordingly the operational stability of the isolated grid systems can be greatly improved.

Description

technical field [0001] The invention relates to a method for controlling the speed of a steam turbine of a thermal power unit, in particular to a control method for suppressing the overspeed of a steam turbine under a power grid high-frequency accident. Background technique [0002] The isolated grid system is a special operation mode under extreme conditions of the power system. If a certain grid has a single fault and the load shed exceeds 8% of the grid load (the load shedding rate is 8%) and there is a possibility of forming an isolated grid, it will be lost instantly. More electricity loads cause unbalanced power supply load and electricity load of the power grid. Moreover, all generating units in most isolated grid systems account for a large proportion of thermal power units in the regional power grid, and their self-balancing ability is poor. The same load Unbalance will cause relatively large frequency fluctuations, resulting in overspeeding of the steam turbine. If...

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Problems solved by technology

[0002] The isolated grid system is a special operation mode under extreme conditions of the power system. If a certain grid has a single fault and the load shed exceeds 8% of the grid load (the load shedding rate is 8%) and there is a possibility of forming an isolated grid, it will be lost instantly. More electricity loads cause unbalanced power supply load and electricity load of the power grid. Moreover, all generating units in most isolated grid systems account for a large proportion of thermal power units in the regional power grid, and their self-balancing ability is poor. The same load Unbalance will cause relatively large frequency fluctuations, resulting in overspeeding of the steam turbine. If the overspeeding of the steam turbine cannot be quickly suppressed, it may cause the unit to shut down and cause the power grid to collapse

[0003] At present, primary frequency modulation and OPC (Over-speed Protection Control) are commonly used methods for thermal power units to suppress overspeeding of steam turbines. It is a Chinese patent of 201310309143.6; the conventional OPC action can quickly reduce the load. When the OPC is reset and the steam turbine control valve opens to the opening before the OPC action, it is easy to cause repeated OPC actions, which is not conducive to the rapid stability of the isolated grid system

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