Design Of Broadband Miniaturized Antenna And Detection System For Emu Discharge Detection

The high-voltage electrical equipment on the EMU is an important part of the train traction system,and its condition affects the operation of the EMU.Abnormal discharge such as partial discharge is caused by the degradation of insulation performance,which may cause driving accidents in severe cases.Therefore,it is urgent to carry out online monitoring.Condition monitoring based on electromagnetic radiation signals is a new type of advanced monitoring method.It intelligently analyzes the degree and type of discharge,and achieves accurate positioning in a non-contact form.Research on wide-band,miniaturized,high-gain antenna sensors and high-sensitivity,wide-dynamic-range detection systems is an important prerequisite for the realization of monitoring status.The basic parameters of the antenna,the broadband antenna technology,the miniaturized antenna technology and the related theory of the detection system were first described.The butterfly antenna and the Vivaldi antenna were designed by the broadband miniaturized antenna technology.The hardware part of the detection system was systematically analyzed,and the important units was simulated completed.Finally,the positioning method based on time difference was used in discharge positioning of EMU.The specific work is as follows:Firstly,based on the basic structure of the traditional butterfly antenna,the butterfly antenna sensor were designed for the design goals of broadband and miniaturization.The current path was increased by bending the edge of the radiation arm.The reflected current was reduced by bending the end of the radiation arm to improve the surface current distribution.The unidirectional radiation was increased by loading a reflective cavity,and the low-frequency reflection coefficient was reduced.The input impedance was reduced by0.3-0.4 GHz by loading resistors on the slit near the end of the antenna radiating arm.The plane size of the butterfly antenna is 200 mm × 100 mm.The simulation and experimental results show that the standing wave ratio is less than 2 in the frequency band of300-1800 MHz,and the highest gain is 3.7 d Bi.Through the antenna discharge detection experiment,the antenna can effectively receive the electromagnetic radiation signals of the pantograph discharge and insulator discharge of the EMU.Secondly,based on the basic structure of the traditional Vivaldi antenna,the Vivaldi antenna sensor were designed for the design goals of broadband,miniaturization and the lower operating frequency.By loading a resistor on the rectangular resonator,shorting the feeder and the radiating patch and optimizing the structure of the gradient feeder,the Vivaldi antenna had a small reflection coefficient at very low frequencies.Further reduction of low frequency reflection coefficients was achieved by loading resistors and metal patches above the radiating patches.The plane size of the Vivaldi antenna sensor is 180 mm × 122.4 mm.The simulation and actual measurement results show that the standing wave ratio is less than2.5 in the 10 MHz-3 GHz frequency band,and can detect various abnormal discharges including partial discharges.Thirdly,in view of the problems of low sensitivity and narrow dynamic range of the current detection system,the detection system was designed.The requirements was determined for the software and hardware of the overall detection system.Then the hardware part was systematically designed,and the detection system was divided into two channels according to the power for signal conditioning.After the system link design was completed,the band-pass filter,RF switch,low-noise amplifier and envelope detector unit were designed respectively.The simulation results show that the designed detection system composed of each device unit has a high sensitivity of-60 d Bm and a wide dynamic range of70 d B.Finally,in view of the situation that electromagnetic detection technology has not been systematically used for monitoring the status of high-voltage electrical equipment on EMU,the positioning method based on time difference was studied.For simulating the discharge environment,an actual vehicle body model and a dipole discharge source were established.The planar rectangular positioning array was constructed from the designed Vivaldi antenna.The position of the discharge source was calculated by the time domain waveform of the signal received by the antenna.The analysis results show that the positioning error is within10 cm,which can be used for the discharge positioning of the high-voltage electrical equipment on the roof of the EMU.