Analyses On Radiation Characteristics Of Lightning Transient Electromagnetic Field And Suppression Methods

In order to explore the radiation characteristics of lightning electromagnetic field and its suppression method,we establish a lightning transient electromagnetic radiation model,which is equivalent to a lightning channel,to study the parameters and radiation characteristics.To find the law of coupled lightning electromagnetic pulse and explore the energy amplitude characteristics of the induced lightning overvoltage,we use the lightning impact platform to simulate the lightning current,and take the overhead lines to receive the lightning electromagnetic pulse.By simulating the lightning test on the transistor,the method of suppressing the lightning overvoltage on the electronic device and the lightning protection measures taken in the lightning protection project are obtained,which lay a foundation for the research on the radiation,coupling and suppression of the lightning electromagnetic pulse,and the conclusions obtained are as follows:(1)The radiation intensity in a transient electromagnetic emission system is related to the coil parameters(including the number of turns,the area)and the current frequency.It is better to select a larger transmitting coil,and the radiation distance can be increased by appropriately reducing the number of turns of the coil under other conditions.When we choose to transmit the current pulse frequency,the low frequency effect is better,the device can be well matched,and the radiation distance is relatively farther.During verification,a rod antenna can be successfully coupled to the electromagnetic emission system pulse to generate a sinusoidal voltage waveform.(2)We use the electromagnetic pulse caused by the impact platform couples the overhead line and the value of the overvoltage is related to the magnitude of the lightning current and the length of the overhead line.The longer the overhead cable,the greater the voltage and energy of the lightning electromagnetic waves it can couple.(3)The main cause of damage to the transistor caused by lightning overvoltage is thermal unstable secondary breakdown.The transient suppression diode connected in parallel with the transistor can effectively protect the transistor,significantly increasing the impact level of the transistor's withstand lightning voltage.(4)In the actual amplifying circuit,the applied voltage reduces the tolerance level of the transistor,but in a transistor with transient suppression diode protection,its tolerance level is still higher than that in the unprotected state.Transient suppression diodes can be applied to actual circuits to protect transistors in parallel.