Research And Software Design On Fault Detection Of DC Feeder In Smart Substation

DC system is an important part of smart substation.Whether it can be operated stable and reliable or not have a great relationship with the level of a country’s power.As the DC system of station runs in a complex environment and long time,there will appear some failure inevitably.The ground fault occurs most frequently.For ground fault in DC system,Timely and accurate detection is so necessary as to avoid huge losses on people’s lives and the country’s economy.At present,many detection methods have been applied in practical engineering.But there always exist some limitations.Now the DC system of station has not yet fully realized the smart transformation.However,there is a trend of the times can be expected that with the improvement of the intelligent degree of power grid,the DC system will be implemented with IEC 61850 and diagnosis with intelligent methods.So,this article launched a series of studies about fault detection of DC feeder in smart substation and the design of corresponding software.The main work of this paper includes:(1)Introduce the detail method and principle of DC ground fault which is commonly used.Analyzes the advantages and disadvantages of these methods.The equivalent circuit model of the substation DC system in the normal operation state and the ground fault condition is studied,and the equivalent model under the AC injection method and the DC detection method is analyzed respectively.Then,based on the existing methods,a modified bridge method and leakage current sensor method are combined to detect the DC system ground fault.The modified bridge method is to add a measuring resistor on the basis of the original bridge resistance and form a star resistive network with the original bridge resistance,so as to calculate the positive and negative resistance of the DC system to the ground resistance by collecting the ground voltage difference of the measured resistance,As the DC system ground fault detection,when the parallel resistance is reduced when the use of star bridge circuit and leakage current sensor to calculate the grounding branch and grounding resistance.(2)Aiming at the characteristics of the parameters collected by the improved detection method.The paper studies the method of predicting the fault of the branch road by using the improved gray prediction method and the method of predicting the bus fault by using case reasoning.(3)Combine the related parameters required by DC ground fault diagnosis.And built DC ground fault diagnosis function logic node that conform to IEC61850.(4)On the basis of functional requirements analysis,Using the QT compiler environment design and implementation of the DC system fault detection software.This paper elaborates the design of the detection software function module and focuses on the data processing module and graphical interface display module design process.Finally,through the modeling and simulation analysis of the improved method,the correctness and validity of the improved detection method and the forecasting method are verified.At the same time,this paper uses the combination of physical and simulator to create fault environment,test and verify the design of the detection software function.