Research On Active Monitoring And Isolation Measures For The Dc System Fault Of The Power Plants And Corresponding Device Development

With the widespread use of automation equipments in power plants,DC system that provides emergency power supplies is increasingly important.Failures to handle DC system problems timely often widen the scope of accidents,resulting in equipment damage and large-scale power outages.At present,the research on DC system fault discrimination and the manufacture of related instruments and equipment have made some achievements at home and abroad,which guarantees the safe operation of DC system to a certain extent,but there are still many problems.It is necessary to conduct in-depth research on DC system fault monitoring,fault branch selection,fault isolation and device development.This paper analyzes the existing problems in fault handling of power plant DC system in details,summarizes the technical achievements of DC system fault discrimination monitoring at home and abroad and distills the shortcomings of DC system monitoring measures in fault monitoring.It proposes the necessity of active fault monitoring and isolation technology research and device development,then carries out researches from DC system fault modeling,fault monitoring and isolation methods,related device development and testing.Firstly,DC system data of power plant is summarized,the composition of DC system of power plant is extracted and the model of DC system of power plant is established.The behavior of electric parameter change in short circuit fault of DC system is analyzed,and the cause of grounding,insulation reduction and AC intrusion of DC system is summarized.Models of short circuit,grounding,insulation reduction,and AC intrusion failure are established.Simulations for DC system are conducted,concluding that the fault current signal-to-noise ratio is low.Secondly,it summarizes the advantages and disadvantages of traditional measures for short circuit,grounding,insulation reduction,AC intrusion fault monitoring and isolation,and proposes an active monitoring method for short circuit faults and active monitoring measures based on MUB unbalanced bridge principle for grounding,insulation reduction and AC intrusion.The working principle is analyzed and the signal processing method of fault collection is proposed.The effectiveness of monitoring measures is verified via both the simulation platform and the actual experiments.The fully controlled active isolation method for DC fault based on power electronics technology is proposed and analyzed.The effectiveness of the isolation method is verified by simulation platform.Thirdly,the system architecture of fault monitoring and isolation device is designed and its working mode is described.The signal acquisition and fault detection technology routes are optimized.On this basis,the overall design scheme of monitoring isolation device is formed.According to the scheme,the software and hardware are designed separately.The prototype was developed and two test schemes were designed to test the interface signals.The ground fault simulation test was also carried out,and the characteristics and functional parameters of the device were analyzed based on test results.It is then concluded that the device performance meets the designed requirements.Finally,the on-site test plan for the active monitoring and isolation device of the DC system is determined.The various faults were simulated on the site and the engineering application in a selected power plant lasted for 6 months as well.As a result,the effectiveness of the integrated active monitoring and isolation measures for the DC system fault of the power plant is verified.