Research On Response Characteristics And Protection Technology Of EMP Protection Devices Under Different Fast Pulses

Electromagnetic pulses coupled through the front or back door,especially the fast pulses with a rise time of nanoseconds,will generate a fast rise time,large value of voltage or current pulses inside the electronic devices,resulting in the electronic devices not working properly and even burning.Since the most protection parameters of Electromagnetic Pulse(EMP)protection devices are for lightning electromagnetic pulses,this parameter may no longer be suitable for fast pulses.Moreover,due to its own characteristics,the EMP protection devices have shortcomings in practical applications,which not only affects the protection capability but also affects the normal operation of the circuit.Therefore,it is of great significance to accurately evaluate the protective performance of protection devices under fast pulses.1)Based on the internal structure and conduction mechanism of three typical Electromagnetic Pulse(EMP)protection devices,gas discharge tube(GDT),metal oxide varistor(MOV)and transient voltage suppressor(TVS),the difference between the typical nanosecond fast pulse and the lightning electromagnetic pulse(LEMP)waveform parameters and the influence of the difference on the response characteristics of the EMP protection devices were compared and analyzed.For example,under the fast rising time pulse,due to the capacitance between the internal crystal grains of the MOV and the grain boundary layer,there is a large leakage current and a spike voltage before the devices conduction.2)For the test requirements,a 3d B coaxial test fixture with a bandwidth of 1GHz was developed to study the transient response characteristics of three protection devices under different fast pulses.Firstly,the effects of ns square pulse amplitude and pulse width on the pulse spark-over voltage,peak voltage,overshoot peak voltage,clamping voltage and response time of three kinds of protective devices were analyzed.It is found that MOV and TVS have large spike voltage due to leakage current and self-inductance before conduction,and can be verified by circuit simulation by Pspice and ADS.Secondly,the influence of the amplitude of the high-altitude nuclear electromagnetic pulse(HEMP)on the overshoot peak voltage,clamping voltage and response time of the protection devices was analyzed.Finally,the relationship function between the response parameters and the injection parameters is constructed by least squares fitting.3)Firstly,based on the internal structure and conduction mechanism of the pulse protection devices,the main failure modes and failure causes of the three protection devices were analyzed.Then through the actual test,it is verified that the failure modes of MOV and TVS under the action of HEMP are mostly based on short-circuit failure.The equivalent resistance value of the protection devices after failure was extracted,and the failure circuit model and verified the correctness of the model was designed by circuit simulation.Finally,the failure threshold of the protection devices under fast pulse was analyzed,and the quantization formula of the devices failure threshold under several typical pulses was given.4)In order to improve the protection performance of the protection devices,according to the working principle,advantages and disadvantages of each protective device,the combined protection technology of GDT,MOV and TVS is proposed.Considering the coordination problem of the protection devices,according to the extracted pulse spark-over voltage and clamping voltage of the devices,a variety of coordination methods are proposed,and the conduction sequence and conduction phenomenon are theoretically analyzed,and the correctness of the theoretical analysis is verified by the test.The response characteristics and protection performance of different protection modes under two kinds of fast pulses are analyzed by using the test system,the conclusion is that series can suppress leakage current and spike voltage,and parallel can reduce spike voltage,overshoot peak voltage and prevent device failure.Finally,the selection reference for the combined protection technology of the pulse protection device is given.