Sustained and reliable power supply is required by an online measuring device installed on high voltage transmission lines. A new power supply technology based on electricfield induction is proposed

the main idea of which is a constant displacement current is induced from a metal sheet installed between power line and earth to discharge a small energyacquiring capacitor. Then

the stored energy will be transferred to another large energystoring capacitor by means of a discharge circuit. Once the stored energy gets enough

it will supply a subsequent measuring device. Since the voltage of power line is stable

this power supply mode is less affected by the load and environment. The principle and optimal design of this electricfield induction energyacquiring technology based on the discharge method is described in detail. The technology is applied in a temperature measuring and wireless transporting system for disconnecting switches. The effectiveness of the power supply technology is verified by the system’s successful online operation in a 110 kV substation. This work is supported by National Natural Science Foundation of China (No. 51477134).