Real-Time Voltage Sag Monitoring And Advanced Application Research

In recent years,Chinese manufacturing industry has developed rapidly.The industry relying on automatic production line,precision manufacturing technology and network information technology is increasing gradually.The voltage sensitive load in the power network also increases with it.Users pay more attention to voltage sag.Voltage sag is easy to make computers,production line controllers and other equipment work abnormal or stop working,resulting in the production of defective or waste products,data loss and other problems.When it is serious,it can cause huge economic losses.Therefore,many enterprises have to investigate the local power quality,especially the voltage quality.Voltage sag can be caused by short circuit fault,lightning strike,switching operation and so on.Monitoring and treatment of voltage sag involves the common interests of both power supply and power supply.The study of voltage sag has great practical significance.A reliable voltage sag monitoring system is the premise of voltage sag control.In this paper,a voltage sag online monitoring system is designed.At present,the voltage sag monitoring in most areas mainly depends on the power quality monitoring system.The function of power quality monitoring device is complex,sometimes it is difficult to meet the needs of multi-functional monitoring.Such as harmonic and voltage sag monitoring installation position is difficult to achieve balance.And urban distribution network gradually becomes more and more measuring points and wide distance.It is not realistic to install power quality monitoring devices in many places.In view of this situation,the voltage sag system is designed to monitor voltage sag.Using single Chip Microcomputer as the main Control Chip of Monitoring Terminal and wireless communication is used to transmit the amount of information.It has the characteristics of low cost,perfect function and reliable.The experiment shows that this method has high estimation precision and has practical value.Secondly,this paper studies two advanced voltage sag algorithms:voltage sag state estimation and voltage sag fault point location.Aiming at the problem that the voltage sag monitoring point cannot completely cover all the bus lines in the whole network,a new method for optimizing the monitoring point and estimating the voltage sag state of the whole network voltage is proposed.First,a linear programming model is established for the optimal allocation of monitors.The object of the optimization model is to minimize the number of the monitoring buses and the key constraint is to guarantee the observability of the whole system.Then based on the monitoring configuration result,the voltage of buses is simulated when a short circuit fault occurs.Based on this,a database of voltage sags mode is formed.When there is a new voltage sags event,the state recognition is completed through the matching of the fault features and the database,and the voltage sags state of the whole network is estimated.First,a linear programming model is established for the optimal allocation of monitors.The object of the optimization model is to minimize the number of the monitoring buses and the key constraint is to guarantee the observability of the whole system.Then based on the monitoring configuration result,the voltage of buses is simulated when a short circuit fault occurs.Based on this,a database of voltage sags mode is formed.When there is a new voltage sags event,the state recognition is completed through the matching of the fault features and the database,and the voltage sags state of the whole network is estimated.In the aspect of fault source location of voltage sag,the radiation distribution network and large city ring network are analyzed.A method of locating fault source of voltage sag based on the time scale method of fast measuring technique is proposed.The time difference of voltage sag traveling wave measured by monitoring point at the branch end is used to accurately locate the fault source of voltage sag.The IEEE 33-node system was selected and the sampling speed was set as 6MS/s in Simulink,which could be achieved by single chip microcomputer.The simulation results proved the feasibility of the method.For large-scale urban ring networks,a new method to solve the fault location using voltage sag state matching and positive sequence voltage variation is proposed.Firstly,a linear programming model is constructed to determine the installation position of voltage sag monitors.It can ensure that voltage sag caused by short-circuit can be monitored in a certain range of fault resistance.Then the fault position is located in two steps:the first is to determine the most probable fault line by state matching;the second is to use the positive sequence voltage variation to construct equation.The equation can solve the specific fault location of the fault line.The IEEE 39-node system data is used to test,and the simulation experiment proves that this method is fast and accurate in fault location calculation,and has practical application value.