Practical Research On Line Selection Device For Non-direct-ground System

Due to the high reliability,the low-voltage powrer grid commonly uses the non-direct-ground system in China.However,beacause the fault feature is not obvious, fault line selection for the non-direct-ground system has been a challenge.This paper concentrates on the difficult problems of faulty line-selection in neutral indirectly grounded system,including Fault line-selection algorithm,Influence of the unblanced current and the realization of software and hardware.In terms of algorithm, Prony algorithm and mathematical morphology will be combined to form the new line-selection algorithm, and the specific process of the algorithm will be given,Unblanced current affects the results of line selection.The specific reasons for its formation is discussed and the corresponding solution is given.This paper gives the anti-jamming measures taken by the device, and the program flow specifically in the algorithm and hardware control.Because of its advantages of simple and low requirement to the hardware,steady-state algorithm is used widely in line selection device.However,in some cases the steady-state levels reduce,in particular by the impact of arc suppression coil,making use of steady-state algorithm becomes difficulty. The excellent line-selection data can be got by using the better denoising capabilities of morphological filters, and then it analyses the line-selection data corresponding to the frequency of amplitude and phase using Prony algorithm,it can form a new line-selection algorithm.According to the analysis based on Prony algorithm,The influnce of the unblanced current to free shaking component is small.But because of its excessive attenuation,the requirement of the hardware must be high.Using the corresponding subtraction for zero sequence current of failure before and after can greatly reduce the effect of unblanced current.If the use of pitch component can not give reliable fault line,it can take advantage of free shaking component to improve reliability.For the proposed transient algorithm and methods for unbalanced current treatment,a higher line selection requirements.In strong electromagnetic fields, interference performance of the selecting device is the premise and key for correct line selection.This paper dealts with parts of device for selection line, achieving a good anti-interference effect.In terms of software design, DSP section includes the program of line-selection calculation and management of scheduling,andwhile the SCM focuses on the underlying hardware device drivers. Both complement each other to form a complete line selector.