Research And Application On High-Voltage Overhead Line Breakage Fault Protection

As a main medium for electric power transmission,high-voltage overhead lines are prone to various types of faults.The protection for short-circuit faults has tended to be complete.Line breakage faults which are caused by natural factors and human operation are easy to be ignored because of its light fault characteristics,little impact on the stability of the power system,and low occurrence probability,which makes that the line breakage faults are difficult to be quickly and accurately identified by the existing line protection.With the increase of the urban population density and the crossing between public facilities and high-voltage overhead lines,if the line breakage faults could not be removed in time,the contact of the live line with the ground will not noly cause a short-circuit fault,but also endanger the personal and social pubic safety.If the line did not contact the ground after line-breakage fault,the existing line protection device can not identify and remove the faulty line in time.The asymmetric component and the ferromagnetic resonance overvoltage will endanger the relay protection device and the electrical equipment.At present,there is little research on the protection principle of high-voltage overhead line breakage faults,thus it is of great sianificance to carry on the reaserch of the line breakage fault protection principle and the development of the corresponding protection devices,so as to avoid the personal safety accidents and public property damage by accurately identifying and removing line breakage faults before the line is grounded.In view of the above problems,this dissertation takes typical high-voltage overhead line as the research object,and conducts research of high-voltage overhead line break fault protection from two aspects: theoretical research and prototype development.The analysis of high-voltage overhead line breakage fault characteristics and the study of the principle of line breakage protection are included in theoretical research.In the analysis of line breakage fault characteristics,the symmetrical component method is used analyze the characteristics of the sound line current and the busbar voltage on both sides of the faulty line when the sigle-phase and two-phase line breakage faults occur in different operation mode.Based on the fault characteristics analysis,the principle of line breakage fault protection based on the voltage drop difference is proposed.The proposed protection principle uses the currents and line impedance to calculate the ideal line voltage drop,and uses the busbar voltage on both sides of the line to obtain the actual line voltage drop.The line breakage faults are identified by comparing the amplitude of those two voltage drops.The simulation results show that the proposed protection principle can accurately identify vaious types of line breakage faults.Based on the ANSYS software,the overhead line model is established to simulate the line breakage and landing process.By estimating the time from the line breakage to the faulty line contacting the ground,it can be verified whether the proposed protection principle action speed meets the requirements or not.The simulation results shows that,according to the minimum height limit for high-voltage lines away from ground stipulated in the national standard,it takes at least 1 second when the faulty line contacts the ground.If the line breakage protection can accurately operate in one second,the goal for identifying the line breakage fault before the fault line contacting the ground is achieved.The development of the prototype involves practical criteria,setting methods,protection schemes,real time digital simulator(RTDS)testing and pilot operation.The transient process and steady-state error of current transformer(CT)and capacitor voltage transformer(CVT)are analyzed,and the suitable error range is given;a practical protection criteria is proposed and the caculation method of the setting value is given with fully consideration of the measurement errors and the line parameter error.It is proposed that the protection device adopts a comprehensive start method of adding a line breakage protection start module on the basis of a low threshold start component,which can avoid the maloperation caused by the CT disconnection and the frequent start of the protection device due to the load fluctuation,and at the same time improve the sensitivity of the proposed protection under light load condition.On this basis,a high-voltage overhead line breakage fault protection scheme is formed and a prototype of 110 k V high-voltage overhead line breakage fault protection device is developed.Based on the RTDS testing system,the prototype of the line breakage fault protection device is fully tested under different types of line breakage faults.The RTDS experimental results show that,except for the extremely light load conditions,it takes no more than 76 ms to operate under different types of internal line breakage faults,and the prototype has the high reliability under external faults and abnormal conditions.The pilot operation of the protection device prototype is introducedAt the end of the disseratation,the research work and reaults are concluded and the further research direction is given.