Study On The Electromagnetic Compatibility Of Shaft End Speed Sensors In CRH3 Electric Multiple Unit

To improve the electromagnetic compatibility of CRH3 EMU (Electric Multiple Unit) shaft end speed sensor, EMI (Electromagnetic Interference) problems of CRH380BL EMU and CRH380CL EMU were studied. Using electric dipole theory it analyzed the electromagnetic characteristics of arc discharge during the bow down. From the point of radiation coupling it analyzed the reasons of the formation of car body’s disturbance voltage. From the perspective of port coupling it analyzed the interfering coupling mechanism of car body’s disturbance voltage to TCU speed sensor and gave a solution. Combined with working conditions of CRH380CL EMU and actual measurement results it confirmed the electromagnetic interference source of BCU speed sensor and its magnitude-frequency characteristic, it established car body impedance network model under this working conditions, from the point of magnetic coupling it analyzing the disturbance process of interference source to BCU speed sensor and gave solving method. It pointed out the mutual restriction of methods which solved the electromagnetic interference issues of two types speed sensors, and come up with comprehensive solutions.The results show:1) Arc discharge generated when CRH380BL EMU drops bow is equivalent to a electric dipole antenna, and it will arouse strong electromagnetic field in the surrounding space, through measurement we got the maximum magnetic field amplitude in the surrounding space is almost 60dBμA/m, and the maximum electric field amplitude is 7.3V/m, whose frequency is mainly distributed around 5MHz. Such strong magnetic field will generate induced current on the car body surface, using Ansoft/Maxwell electromagnetic simulation software we calculated that 1A and 5MHz current excitation will generate 2.3mA induced current on car body. Affected by CRH380BL EMU single port protective grounding, when induced current flows along car body, it will form disturbance voltage, through measurement we got No. TC02 car body’s maximum potential voltage that relative to ground (rail) is 78.4V. Because the transmission cable shielding layer of TCU speed sensor is single-ended centralized grounded, when car body exists disturbance voltage, electric field around the grounding port of shielding layer will become very uneven, thereby forming interference voltage at the speed sensor signal port;2) When the windshield of CRH380CL EMU No.BC09 car and No.TCIO car is in the insulation section, for the magnetizing impedance of impedance transformer is much larger than rail impedance and affected by CRH380CL EMU multipoint grounding, traction return current will flow into car body through protective grounding of EMU. By measuring we got that when the sum current from No.TC10 car and No.TC15 car’s traction transformer was more than 20A, the current through impedance transformer was only 4.5A, so most of the current would flow through No.TC10 car. As the transmission cable shielding layer of CRH380CL EMU BCU speed sensor is double-ended grounded, part of the current will flow into cable shielding layer, thus it can disturb the speed signal in the core line through magnetic coupling between shielding layer and core line. Experiment shows that when 7A fundamental current flows into shielding layer, it will produce maximum of induced voltage at 0.72V in the core line.By increasing the protective grounding to reduce the car body’s potential, we can effectively solve the EMI problem of TCU speed sensor in CRH380BL EMU. By increasing 0.5Ω grounding resistance in protective grounding line to limit traction return current flows into vehicle, we can settle the EMI issue of BCU speed sensor in CRH380CL EMU. Through the use of SiC resistance, we can overcome the mutual constraints of methods about two types speed sensor EMI problems, which is a kind of integrated method.