Study Of On-line Temperature Monitoring Technology For High-voltage Switches

Nowadays it has been paid wide .attention to realize on-line real-time monitoring for the temperature of electrical facilities and a new research project on the safe operation of power system arises. Because of the troubles of high-voltage insulation and intense electromagnetic interference, normal measurement technology has not been applied into this kind of facilities. However, the appearance of optical fiber sensor has provided a brand-new resolution to the research of temperature monitoring for high-voltage electrical facilities. The present project adopted the combination approach of electrical temperature probe and optical fiber transmission. Based on the mature technology of electrical detection, high-voltage insulation and anti- electromagnetic interference of optical fiber couple, the multi-channel itinerate detection system controlled by single-chip microcomputer has been designed to implement the on-line temperature monitoring for the most familiar electrical facilities ?contact points of high-voltage switches in power systems. In the present project, integrated temperature sensor AD590 is selected as the direct sensitive device to temperature. AD590 is an integrated two-end temperature-current sensor which is applicable to the temperature range of -55 ~C -~ +1500C. When the exciting voltage is 4~?0V, it shows the excellent performance of 1 ~?A/K high-impedance constant current modulation, and its linear error is 0.5 ~C. Based on the analysis of AD590 characteristics, temperature-frequency transform circuit is designed. The detected temperature signals are transformed into pulse frequency signals to drive LED. Then the pulse signals. modulated by temperature are transmitted by optical fiber to the control port of the second instrumentation. After photoelectric conversion, amplification and plastic process, and frequency count by single-chip microcomputer through a multi-channel selective switch, the functions of temperature display, multi-channel iterative/mono-channel measurement and over temperature warning have been realized. The present paper presented in detail circuit design and operation principle of each component in the temperature monitoring system. In the light of the analysis of probe power losses, the probe driven by silicon photoelectric cell worked in high-voltage area. In addition, this paper paid much attention to measurement precision and working stability of the whole system under ?11 ? high-voltage and intense electromagnetic field situation. In view of the effective insulation and anti-interference measures, satisfactory operation performance has been acquired in industrial pilot site. The temperature-monitoring instrument for optical fiber transmission high- voltage switch contact point developed by this project has been conducted pilot testing in Sichuan Electrical Facilities Corporation and Gansu Tianshui Electrical Facilities Plant. Rectified by a standard .thermocouple temperature-measuring instrument, the testing results in situ showed that the temperature-monitoring instrument has fast response speed, accurate location for temperature arising over set limit, small measurement error within ?1 慍. And it has high reliability, security and economization. Therefore the research of this project will offer important engineering practical value for operation safety of electrical facilities in power system.