Detection And Experiment Research On Vacuum Pressure In Vacuum Tube By Ultrasonic And Impulse Current Method

With the upsurge of "non-oil" in the distribution system, vacuum interrupter has been applied widely in the field of medium voltage distribution because of its particular superiority. The key part of vacuum interrupters is vacuum tube, whose pressure is an important parameter. Insulation strength in vacuum is related to the vacuum pressure, and therefore it is significant to detect the pressure. Generally speaking, the measurement of vacuum pressure in vacuum tube can be concluded to the off-Kne and on-line detection, and so far the former method, used at home and abroad, is mature. However, when compared to the mature method, the later method is less perfect whose corresponding testing instrument is inconsistent with each other. Hence, studies on the measurement and the online detection technique of vacuum pressure within vacuum tube have important academic and practical meanings.When the vacuum pressure varies, its corresponding electrical and non-electrical signals change. Based on this fact, the on-line detection of vacuum pressure in this paper is proceeded by ultrasonic method and impulse current method respectively.According to the basic principles of acoustic emission detection, namely, acoustic emission of discharge will occur in vacuum tube when vacuum pressure increase, the paper adopts an acoustic emission sensor and designs a corresponding amplified-filtering circuit. Sensitivity, reliability and safty of the designed sensor are analyzed according to the practical requirement of test-field and engineering application.When vacuum pressure deteriorates, pre-discharge current between electrodes and shield will increase gradually with the operation of inner electrods and contains high frequency impulse signals. Due to these, the on-line detection of vacuum pressure by using a wide band magnetic core current sensor are proposed in this paper. Moreover, equivalent current model of sensors are established. After the deduction of transfer function of sensors, frequency characteristic are analyzed under different parameters by Saber.A vacuum pressure detection system for ultrasonic and impulse current detecting equipment is designed respectively. Testing data are obtained by the designed system which indicate that the maximal amplitude of discharge signal increase with the strength of discharge which can represent the discharge of vacuum tube when vacuum pressurevarys. Acoustic emission signal is more feeble than impulse current signal and difficult to be used for gas pressure detection in vacuum tube. Ultrasonic detection method is mainly used in judging the existence of discharge qualitatively, and the current sensor can quantificationalry analysis the relation between impulse current and gas pressure in vacuum tube.