Research On-Line Monitoring Technology For Low-Voltage Circuit Breaker Based On Wavelet Analysis

On-line monitoring for mechanical characteristics of low-voltage circuit breaker is the precondition of predicting maintenance,is the key element of reliable run,and is the important supplement and updated development to the traditional off line preventive maintenance.Advances in measuring and testing technology continue to provide more reliable and efficient methods for on-line monitoring of mechanical characteristics of low-voltage circuit breaker.The greatest emphasis on monitoring for mechanical characteristics of low-voltage circuit breaker should be placed on the operating mechanism.In this paper,the principle and the special ways of on-line monitoring for mechanical characteristics of low-voltage circuit breaker are introduced,and test results are also analyzed.Firstly,the Hall current sensor that sensitive to instantaneous signal is used to monitor the current signal of close(open) coil in the operating mechanism,Linear variable differential transformer(LVDT) displacement transducer of DC(direct current) with a higher accuracy,is adopted to measure mechanical displacement signal of movable contact,and converts it into the synchronous voltage signal.In this paper a new single chip microprocessor PIC 16F877 made by Microchip Company,is regarded as the core in whole system,and the peripheral hardware interface circuits are designed,which includes input of sensor,handling of analog signal,A/D conversion,input and output of switching value,expansion of I/O port and data storage device,design of keys and nixie display,the serial communication between the single-chip microprocessor and personal computer,design of power supply etc,and the software program is compiled by assemble language.The communication standard between the master computer and the subordinate computer adopts RS485 serial communication interlace agreement,which can transmit accurately the acquired data to personal computer that will display the waveshape and process the data.Thus the mechanical characteristic parameters of low-voltage circuit breaker can be calculated,for example,close(open) time, average speed,length of travel,overtravel,etc.Furthermore,some measures of anti-interference are taken,the techniques in hardware design consist of isolation,earth connection,shielding,wave filtering,etc.The techniques in software design consist of order redundancy,watchdog timer,wave filtering of slipping average value,etc.At last,Visual Basic language is used to accomplish design of man-machine interface and display of test waveshape.Wavelet analysis is a kind of method to process non-stationary signal in these years. Having good time-frequency localization character,and correctly identifying singularity point in fault signal,which is the main analysis method in this paper.This paper is rightly based on this good character,applying it to fault analysis of power system.After studing the basic theory of wavelet transfer and its applying in fault analysis,this paper mainly illustrated samples of apllying wavelet transfer to power system.In this paper,a de-noise example was list to explain how to remove noise from signal,and Lipschitz exponent method was applied to identify the singularity in power system fault signal analysis and a simulation example was given in the last chapter.At last,we studied the application combining the wavelet and BP neural networks to fault detection and simulated system fault diagnose by computer and proved the advantages of using wavelet method in fault detection.With the rapid development of sensor technology,signal processing technology,the microelectronic technology and computer communication technology,on-line monitoring technology for mechanical characteristics of low-voltage circuit breaker will get more consummation and improvement,which will promote development process of intelligent circuit breaker.The development of on-line monitoring technology for mechanical characteristics of circuit breaker will be the key to successful development of intelligent circuit breaker.