It is of great significance for the reliability and safety of power system operation to monitor power equipment to ensure its stable operation. With the continuous development and maturity of on-line monitoring technology, and the successful application of on-line monitoring technology in China's power system in recent years, the replacement of periodic maintenance by condition based maintenance has been accepted and recognized by the power system, which has become the inevitable trend of equipment maintenance.

For a long time, China's power system has implemented the regular maintenance system for power equipment, that is, according to the planned time cycle for equipment detection and maintenance, so there are defects of excessive and insufficient maintenance. With the new changes of defect forms of power equipment, the online monitoring of partial discharge, chromatography and SF6 gas quality began to increase. State Grid Corporation of China (SGCC) clearly put forward that it is necessary to comprehensively promote the implementation of equipment condition maintenance from 2010, comprehensively improve the level of equipment intelligence, promote the application of intelligent equipment and technology, and realize online warning of power grid security and intelligent monitoring of equipment.

The on-line monitoring technology of power equipment refers to the measurement and diagnosis system and technology which can record the characteristic quantity of the running state of the equipment directly installed on the power equipment. Online monitoring system is generally composed of advanced sensor technology, computer and information processing technology, communication system, expert analysis system and more complete system data base.

Taking the main on-line monitoring system of primary equipment in substation as an example, there are: on-line monitoring of capacitance and dielectric loss of capacitive equipment; on-line monitoring of full current and resistive current of metal oxide arrester; on-line monitoring of insulation oil chromatography of transformer body, on-line monitoring of optical fiber temperature measurement, on-line monitoring of ultra-high frequency partial discharge of transformer body, on-line monitoring of bushing partial discharge, on-line monitoring of dielectric loss and dynamic characteristics of on load switch On line monitoring; GIS UHF PD on-line monitoring, micro water on-line monitoring; switch mechanical characteristics monitoring and switch cabinet fiber temperature on-line monitoring, SF6 gas density on-line monitoring, etc.

The value of investment in the field of online monitoring of power equipment is outstanding, and the high growth of downstream demand for online monitoring products can be maintained. First, the strategy of condition based maintenance and construction of smart grid has been determined, and the requirements for grid reliability are more stringent, and online monitoring products have become an indispensable part of it; second, in addition to the demand for new substations, there is more room for stock transformation; third, online monitoring products have a trend of development from single product monitoring to integrated monitoring system of substations. In addition, with the increasing number of power equipment and the shortage of line workers, the power grid needs to rely on online monitoring products to improve management level.

According to the bidding situation of State Grid Corporation of China, the market of online monitoring products is mainly concentrated in the power transformation of smart grid. State Grid Corporation of China has also taken the construction of substation condition monitoring system as an important part of intelligent substation in its planning report. Intelligent substation realizes on-line monitoring of main equipment and important parameters, such as transformer oil color spectrum, partial discharge of combined electrical appliances, full current of arrester, etc. through condition monitoring unit, providing basic data support for power grid equipment management. After the real-time state information is analyzed and processed by the expert system, a preliminary decision can be made to realize the self diagnosis function of the intelligent equipment in the station.

Listed companies involved in online monitoring of power equipment include: Siyuan electric, science and engineering monitoring, and Tianwei Xinyu (30% of Tianwei baobian).