Preparation and acoustic properties of high-temperature acoustic emission sensor based on La_(3)Ga_(5)SiO_(14) crystal

With the rapid development of modern industries,the high-temperature piezoelectric sensors that can work in extreme environments are in great demand.In this work,langasite(La_(3)Ga_(5)SiO_(14),LGS),as a high-temperature piezoelectric crystal with stable electro-elastic performance,is used as core element,and air and porous Al_(2)O_(3) are selected as backing layers respectively to prepare two kinds of high-temperature acoustic emission(AE)sensors.The detection sensitivities at 25–500℃ are analyzed by the ball falling test and Hsu–Nielsen experiment.Under the condition of 25–500℃,the received amplitude signals by both sensors are maintained above 90 dB stimulated by the ZrO_(2) ceramic ball dropping.In the Hsu–Nielsen experiment,as the temperature rising from 25℃ to 500℃,the signal amplitude of sensor with air backing layer decays from 447 mV to 365 mV,while the signal amplitude varies from 270 mV to 203 mV for the sensor with porous Al_(2)O_(3) backing layer.Signiffcantly,compared with the bandwidth of the air-backing sensor(37–183 kHz),the sensor with porous Al_(2)O_(3) backing layer broadens bandwidth to 28–273 kHz.These results show that both these AE sensors have strong and stable response ability to AE signals at high-temperature of 500℃.Therefore,piezoelectric AE sensor based on LGS has great potential application in the ffeld of high-temperature structural health monitoring.

New technique:Detection and location of partial discharge in cast-resin dry-type transformers using a waveguide and a new acoustic emission sensor pair design

The acoustic emission (AE) method could be used to detect and locate partial discharges (PD) in cast-resin dry-type transformers.However,due to the high sound attenuation in the filled epoxy,the signal is prone to interference from external noises and thus,in practice,there is little possibility of detecting PD.In this study,two techniques were developed to alleviate the shortcomings of the AE method.First,a waveguide is installed on the high-voltage (HV) windings,so that the acoustic signals of PD will propagate to the AE sensors that are installed on both terminals of the waveguide.The location of the winding that has PD can then be detected from the difference in arrival time of the acoustic signals.Test results indicate that the waveguide technique is able to enhance the safety of a measurement system and offers the advantages of easy installation and higher flexibility.Second,a specially designed AE sensor pair is used to distinguish whether acoustic signals are generated by PD inside the HV winding or by the corona outside the transformers.Using these two techniques of waveguide and AE sensor pair not only greatly improves sensitivity but also increases the reliability of the measurement system.Practical test results show that the new techniques can be used to locate precisely the PD in HV windings.