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.

In this paper,the progress was made that high and low thres holds of voltage hysteresis comparators were adjusted alone.

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.

The paper analyzes the reason for the system error in the calibration to powerful DC transformer by means of Voltage-difference-method, The mathematic formula of system error of current-voltage transformer and current-current transformer are derived.

This paper points out the influence on the start-up circuit of the differential-voltage protection when the capacitor s primary connec- tion is changed.