In order to realize the effective protection of high-altitude electromagnetic pulse（HEMP）

a typical ethernet for control automation technology（Ether CAT） slave communication module is selected for HEMP conduction injection test. The sensitivity of this kind of device to HEMP and influence of multiple pulse accumulation effects are researched. Suitable protection devices for the network port are selected

and their response characteristics of HEMP are investigated. Then

a port protection scheme is proposed. Experimental results indicate that test port is sensitive to HEMP conduction injection. The damage threshold voltage of test port for HEMP is about 450.1 V with a signal pulse

and is about 273.5 V with 10 pulses. Obviously

pulse number has an accumulation effect. The damage threshold voltage of protection devices is about 9.67 k V with a signal pulse

and is about 8.97 k V with 10 pulses. When the protection device is connected in parallel to the test port

the Ether CAT system is still not damaged under the injection of 3 k V HEMP. The results show that the damage threshold of the Ether CAT slave communication module can be raised up to 3 k V.