The prerequisite of transformer on-line monitoring is network with computer. Use IT technology to obtain transformer status information through standardized software or browser. Through the system analysis, calculation of measured data, combined with expert system to do comprehensive intelligent diagnosis. The technical superiority of online monitoring is mainly reflected in its own self-checking function and the ability of comprehensive fault judgment after combination.

Because the purpose of online monitoring is to prolong the life of high-voltage equipment, improve the power supply quality and economic benefit of the power department, the cost of online monitoring device should not be too high. According to the statistical analysis of the domestic power department, if the transformer accident rate is set at 0.5 ~ 1%, then the cost of online monitoring should not exceed this range.

The main feature of transformer on-line monitoring is to judge transformer operation status by continuously monitoring the variation trend of transformer parameters for a period of time. On-line monitoring can capture the precursor information of non-instantaneous failure. Its outstanding feature is that it can be monitored in real time during operation. This is the technical advantage of online monitoring. Although there are great limitations in the prediction of sudden faults in transformers based on the dynamic information captured by on-line monitoring, it is a means of modern state maintenance.

It has very important practical guiding significance for making and arranging maintenance plan and scheme in the next step. The monitoring instrument used in mutual monitoring (such as sensor, etc.) has high reliability, installed on the transformer does not need to be maintained, with high self-check function. Once the monitor itself has problems, it can automatically send out sound and light alarm. Therefore, all kinds of errors and inaccuracies caused by human beings in conventional detection methods are eliminated. The period of online monitoring is set for man and can range from a few hours to several years.