Voltage Sag State Estimation Research Based On The Optimal Allocation Of Monitoring

With the modernization of power grids and the improvement of science and technology level, more and more digital automatic control technology, such as frequency conversion speed regulating device and programmable logic controller, is being used on a large scale in the industry producing. These electrical equipments are putting forward higher requirements on power quality. Among the many problems concerned with the power quality, voltage sag is very common and may cause serious power quality problems with a larger scope of influence. As a result, the position of the voltage sag should be found out quickly and figure out the affected area, which is very important.To know clearly about the voltage sag information in the power grid, it is necessary to make an entire network monitoring system to learn about the network’s operation state. Once the voltage sag happens, the monitoring information can be quickly collected. To locate the voltage sag source and take measures to eliminate failures. But the power system is very large with a lot of nodes, considering the cost and efficiency problem, not all nodes can be monitored with power quality devices. So it is necessary to analyze the entire network. Select the key node to install monitoring device and it can reflect any node’s voltage sag in the network failure.The paper puts forward a method to optimize the placement of the monitoring device. The paper first analyses the relationship between voltage sag types and short circuit faults, presenting the method to estimate the short circuit fault type; considering the transformer’s influence on the voltage sag transmission, classify the nodes according to the voltage level and then discusses the monitoring points’arrangement. Based on the voltage sag analysis, make an analysis about the network to determine the monitoring device’s installation location. Select a finite number of monitoring stations to implement other nodes’voltage sag monitoring. So on the basis of the above method, we can reduce the cost of installing monitoring devices and redundancy of data information.After determining the monitoring point arrangement location, according to the wave record information like voltage waveform, analyze the network’s topology to get the impedance matrix. Then symmetrical components method will be used to analyze the voltage sag characteristics under different fault types; combine with the sag information to determine the sag position.Then the network’s voltage sag condition can be estimated. Based on the voltage sag source location, Further to analyze the network structure, network topology, form the node impedance matrix. Combine with the short circuit calculation to judge no monitoring points’ information such as the voltage and the running state of the network and the influence of voltage sag.The method proposed in the paper is tested with a3-machine-9-node system and a220kV power supply network in Yangquan, Shanxi Province. The feasibility and accuracy of the method is validated, and on this basis, the voltage sag state estimation is made.