One of the methods currently being investigated as a possible non-intrusive diagnostic tool for condition monitoring of power transformer and cable is the recovery voltage measurement, which will be improving the ability of detecting the content of water concentration and the ageing process in the insulation system and may thus be an indicator of insulation quality and its ageing status.

As a non-destructive diagnostic technique,return voltage measurements based on dielectric response theory have been introduced for condition assessment of transformer insulation,especially for the evaluation of water content in transformer pressboard.

n this paper, we take the 40Wp user photocell source system controller for example, mainly discuss the cause for oscillation and its solving method in the control circuit designed to protect storage battery from overcharge and overdischarge, this is called hysteresis voltage method, describe the design main idea and operating principle, give a simple and utility diagram.