Abstract: Current transformer（CT）inductive energy extraction is the most effective power supply method for

online monitoring equipment of power transmission cables. However，the low current of the transmission cable will

cause the CT to fail to obtain energy，which will lead to the occurrence of equipment energy supply dead zone，and endanger the safety of the power system. Therefore，a CT magnetic core structure based on series combination of Mn-Zn ferrite and silicon steel sheet was proposed to solve the problem of CT low current energy extraction. In order to verify the effectiveness of the low-current energy extraction of the core structure，the relationship between the ratio λ of the different materials of the combined core structure and the initial permeability was obtained by using the superimposed magnetic flux method，and then the value of λ that meets the actual project requirements was obtained.A CT energy extraction experimental platform was set up to verify the correctness of theoretical analysis. The experimental results show that when the low current of the transmission cable is 12 A，the combined magnetic core structure can increase the induced voltage by about 30%，reduce the weight by about 15%，and increase the overall power by about 24% compared with the conventional silicon steel sheet energy extraction CT，and the problem of energy supply dead zone is solved to the maximum extent，which has a certain engineering practical value.

      Key words: low current；transformer energy extraction；permeability；transmission cables