Research On EMC Immunity Test Devices And EMC Of Microprocessor Protection System

In order to ensure safety and stability of power system,microprocessor protection devices in power system must meet the relevant demand of the intemational and Chinese EMC(Electromagnetic Compatibility)standards,and pass the correlative EMC immunity tests.The two severest EMI(Electromagnetic Interference)of all are the EFT/B(Electrical Fast Transient Burst)and surge.The paper mainly investigates EFT/B and surge immunity tests of microprocessor protection devices.EFT/B always interferes with microprocessor protection devices in power system, because it has such features as short rise time,short duration,high amplitude and high repetition rate.Study of anti-jamming of EFT/B is at the beginning in China and concentrated mainly on the countermeasures in practice.Investigations on the aspect are still in great demand.Therefore,one of the main tasks of the paper is to investigate anti-jamming of EFT/B.At present,disturbance signal generators for EMC immunity test are mainly imported and are very expensive.Thus,An EFT/B generator and A CWG(combination wave generator) are designed and made according to the standards of IEC and GB/T in this paper.Firstly,An EFT/B generator is designed and made according to the standards of IEC61000-4-4 and GB/T17626.4 in this paper.A switching mode power supply is developed as the high-voltage DC power supply.A hydrogen thyratron is used as the main circuit switch.And the developed EFT/B generator is very cheap.Secondly,a CWG is also designed and made according to the standards of IEC61000-4-5 and GB/T17626.5.Spark global gap switch with triple electrodes is developed as the main circuit switch.AT89S52 chip is adopted in the control system of the two devices as the core of the circuit,which realizes the intelligence and vision of control. Experimental results show that the output signals of the developed EFT/B generator and WCG can be used in EFT/B and surge immunity test.Based on the three factors of EMC:interfering sources,coupling path,sensitive objects, anti-jamming EFT/B of microprocessor protection devices is deeply investigated.Improving for self-anti-jamming of EFT/B for microprocessor protection devices is investigated as an emphasis.First of all,the reasons for logic confusion,program mistake,display error and malfunction are analyzed when EFT/B interferes with the microprocessor protection device. Then,for the sake of investigation on the general countermeasures and concrete measures for anti-jamming EFT/B of microprocessor protection devices,EFT/B and surge immunity tests are performed on microprocessor protection devices with the EFT/B developed in this paper. The microprocessor protection device is under EFT/B immunity test.Improved distribution power supply,ferrite core,EMI filter and transient voltage suppressor can be used in the microprocessor protection device to control EFT/B through experiments.In the end,EFT/B and surge immunity tests are performed on a vacuum on-line condition monitoring system made in laboratory with the EFT/B and surge generators developed in this paper.The system's immunity capability is improved with the countermeasures and the serviceability of concrete measures brought forward in this paper is validated.