Abstract: With the continuous development of the power system, the use of medium-voltage equipment, especially ring main units, cable branch boxes, and gas-insulated switchgear, has become increasingly common. The reliability of these devices is crucial to the stable operation of the power grid. Cable failures, especially heating issues caused by insulation and poor contact, have become a major challenge for power supply departments. Traditional fault detection methods are difficult to accurately locate the fault point due to the insulating material's thermal insulation properties. This article introduces a new type of insulation plug temperature sensor that adopts electric field energy harvesting technology. With wireless data transmission, high-precision perception, and strong anti-interference capabilities, it can effectively monitor the temperature changes of electrical nodes in medium-voltage equipment, providing a new technical means for early warning of power grid faults.