492 / 2022-03-18 20:07:44

Control Strategy Optimization of Controllable Arrester Based on Voltage Short-time Fourier Transform

Controllable arrester,short-time Fourier transform,switching over-voltage,spectrum characteristics,harmonic distortion rate

The controllable arrester is a kind of high-performance over-voltage protection device which can effectively reduce the switching over-voltage level of UHV AC transmission system. In order to achieve the purpose of reliable operation to limit the switching over-voltage and reduce the absorbed power frequency over-voltage energy, it is necessary to identify the switching over-voltage and power frequency over-voltage, analyze the conditions of triggering pulse locking and recovery of the controllable switch, optimize the control strategy of the controllable arrester, and improve the reliability of the controllable arrester. The transient process of UHV AC transmission system is studied, and the amplitude frequency and phase frequency characteristics of voltage in any time window are obtained by using short-time Fourier transform. The relationship between the frequency characteristics of voltage and the operation state of the system is studied. Based on the spectrum analysis of  closing no-load line voltage and instantaneous single-phase grounding voltage,  the harmonic distortion rate (THD) is obtained, which is used as the criterion to identify the switching over-voltage and the power frequency over-voltage. The spectrum characteristics of voltage in transient process are obtained by using short-time Fourier transform. Based on the obtained spectrum characteristics, the control strategy of the controllable arrester is proposed. When the voltage amplitude exceeds the action threshold of the controllable arrester, the controllable switch is triggered to conduct, the voltage waveform collection is started, and a group of data analysis THD is conducted every 20ms. The harmonic distortion rate (THD) of switching over-voltage is not less than 10% and THD of power frequency over-voltage is less than 10%. This is used as a criterion to identify switching over-voltage and power frequency over-voltage. When the voltage amplitude is greater than the action threshold and the THD is less than 10%, the trigger pulse of the controllable switch is locked until 0.5s, and the locking is released to restore the normal condition of the controllable arrester function.