| With the rapid construction and operation of ultra-high voltage direct current(UHVDC)transmission lines in China,the problem of audible noise caused by corona discharge of high voltage direct current(HVDC)transmission lines has become one of the important factors restricting conductor selection and structural design.It is of great significance to study the characteristics of corona noise of HVDC transmission lines.In this paper,the time-domain characteristics of corona noise under different voltage levels are studied based on the real transmission line of the UHVDC test base in Changping District,Beijing.Different from the small corona cage in the laboratory,the real transmission line can reflect the actual operation state of the transmission line to a great extent,and analyzing the time-domain characteristics of its corona noise has important reference value for solving the corona noise problem of transmission lines.In this paper,firstly,the equipment situation of the test base and the measurement and recording process of corona noise are introduced.According to the time domain pulse signals of corona noise measured at different voltage levels,the peak value of sound pressure fluctuation in the time domain is statistically analyzed,and the cumulative distribution ratio of the peak value is calculated.Because the corona noise measured in practical engineering can’t isolate the background noise,in order to reduce the influence of the background noise,spectrum analysis and sound pressure level analysis are adopted.Firstly,whether the signal contains the characteristic component of corona noise is judged by spectrum analysis,and then the sound pressure level fluctuation in the signal per second is compared to eliminate the invasive noise.After the above two steps,the time period with less background noise and relatively stable corona discharge can be selected from the original measured signal,and then the time-domain sound pressure fluctuation characteristics of corona noise can be studied for this time period.Secondly,in order to extract the time-domain pulse waveform of real line corona noise,aiming at the time period when the sound pressure is relatively stable in the experiment,this paper puts forward a method that takes the peak value of sound pressure in the time domain as the target and the sampling interval between the target points as the pulse judgment standard,that is,the waveforms of different frequencies are extracted by changing the number of sampling points in a pulse cycle.In this paper,taking the positive polarity 1000kV and negative polarity-1100kV voltage levels with strong corona discharge as examples,the pulse waveforms with the same frequency under the two voltage levels are extracted respectively,and the number of pulses is compared,and the average sound pressure at sampling points is taken as the basic pulse waveform,and the waveform characteristics such as rise time and pulse peak value are statistically analyzed,and the reasons for the different frequencies of corona noise pulse waveforms are explored.Finally,for the basic waveform of the extracted corona noise pulse,the sampling point is not continuous in the time domain because of the limitation of the sampling frequency of the equipment.In order to restore its complete waveform in the time domain,this paper proposes to use Gaussian function to fit it,and compares the fitting effect with double exponential function,and analyzes the application scope of the two functions,which provides a new analysis idea for corona noise waveform fitting in practical engineering.The research results of this paper are helpful to understand the mechanism of DC corona noise,and are of great significance to study the prediction method and suppression measures of DC transmission line corona noise. |
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