Research On The Technology Of Fast Cutting For Low Voltage Auxiliary Power Of Large Thermal Power Plant

With the development of China’s power industry,the installed capacity of thermal power plant is higher and higher,at the same time,the reliability and continuity request of the power supply is increasingly arising.Although according to the provisions of China’s power regulations,low-voltage standby power supply needs to switch with manual switching mode,but with China’s power enterprises "going out",In order to meet the international requirements that many countries require fast function of low-voltage power plant,the research on the low-voltage fast cutting of auxiliary power is of significance.It is necessary to study the changes of residual voltage of the working bus,to analyze the switching condition of low-voltage power supply and to complete the switching operation at the most favorable time,which can improve the safety,reliability and continuity of the power supply system.In another word,it is also of great significance to the security of the whole power system.The main contents of this paper are as follows:By reading a large number of literature,collecting corresponding data to analyze the research situation of fast cutting at home and abroad,The paper describes the significance of the study of fast cutting in low voltage power supply.Because induction motor is the main load of the power plant,the transient and steady-state operation process of the induction motor is analyzed theoretically,and the load classification,calculation principle and method of thermal power plant are analyzed.The self-starting classification and verification method of the induction motor are analyzed.In addition,The minimum self-starting voltage of the induction motor and the minimum voltage of the working bus which allows the induction motor group to start are analyzed theoretically.Last but not the least,the principle and switching mode of the fast switching are researched and analyzed.The paper uses the ETAP simulation software to build a large-scale power supply model of thermal power plant based on the actual power plant’s network structure and the actual power plant data.The simulation shows the residual voltage changes of working buses after the power of working bus is lost.According to the switching principles of fast cutting and the actual operation situation of the thermal power plant,the changes of residual voltage of the five bus bars with large number of induction motor in the actual low-voltage power plant are analyzed,the problems that may be encountered in low voltage fast cutting process are also analyzed.In addition,the paper simulates and analyzes the residual voltage of the working bus after cutting off the small capacity induction motors,the transient process of several switching modes is analyzed.At last,To compare the differences of residual voltage before and after removal of part of small capacity of induction motor.In order to ensure the safety of low-voltage power plant,the paper takes the inverter power supply to help low-voltage auxiliary power to achieve rapid switching,When power of low-voltage bus is lost,some small-capacity asynchronous motor was removed quickly,and then uses the inverter to provide power to the small capacity motor which are separated already,The characteristics of the inverter power supply and its control mode are analyzed,to control the inverter circuit so that the output voltage of the inverter device is consistent with the standby power source,When the fast cutting operation is successful,namely the standby power supply successfully switch to the bus which lost power before.then putting the small-capacity motor into the work bus again,at the same time,removing inverter power away.By using the inverter equipment successfully can help to achieve switching of low-voltage auxiliary power,to improve the continuity and reliability of plant power.