With the implementation of the grid transformation, especially the transformation and construction of city network continuously. Using a substantial amount of power cable is increased. The rate of underground cables in the central area of the city continues to improve, which leads to the operation management, power cable monitoring and maintenance work becomes more and more important. And the amount of T was significantly increased. Operating temperature is an important parameter of cable. When the cable is running at rated load, the core temperature reaches the allowable value. Once the cable is over loaded, the core temperature will rise rapidly, accelerate the insulation aging, and even the thermal breakdown. For example, it is found that when the operating temperature of the crosslinked polyethylene (XLPE) cable exceeds 8% of the allowable value, the service life will be halved; if more than 15%, the service life of the cable will be only about 1 / 4t”. Therefore, it is necessary to control the operating temperature of the cable, which requires the power to run the Department of the actual load of cable scheduling. In the power cable selection and installation stage, since it is not possible for a comprehensive consideration of the actual operating environment, are usually carried out according to the standard of environmental temperature, which will cause the cable at the higher ambient temperature operation in overheating, reduce operating life. In order to avoid this situation in practice, it can be solved by the method of proper load capacity, but it makes the use of cable uneconomical. Therefore, if can according to the actual running condition and environment load in real time scheduling and cable adjustment, not only to ensure the safe operation of the cable. The load carrying capacity into full play, but also can solve the problem of electricity supply in power dispatching in emergency situations in some cases.



          therefore, from the point of view of the safe operation of power cable, or from the point of view of power system dispatching, it is necessary to monitor the load capacity of power cable in real time. This is accomplished by on-line monitoring of cable temperature.



1 related hardware configuration



1.1 temperature sensor thermocouple or



          temperature monitoring system is the traditional temperature sensor (such as fiber Prague grating) fault prone or thermocouple is placed in the line in the place. Such as cable terminations and joints, local hot spots or cable, to monitor the temperature of these parts. This method has small investment, simple operation, but poor precision. And can only get the local temperature of the old line.



1.2 infrared instrument


          in recent years, some scholars have put I leaves J using infrared thermal imager shooting thermal image of the cable surface. Thus a method for measuring the surface temperature of cable, carried out the inversion calculation of core temperature of the cable, J paint temperature non-contact, real-time visible Online diagnosis. Although this method breaks through the limitation of the traditional contact detection technology, it is not suitable for the long cable lines, especially the complicated underground laying.



1.3 temperature sensing fiber /

          if the temperature along the fiber laying cable line (Fig. 1), or the binding of the cable outer sheath, the temperature can be monitored in the line. So as to obtain the temperature information of the whole cable line. This method is easy to realize the long distance large fan with multi-point temperature measurement, and high temperature measurement accuracy, installation and use is also more convenient. However, due to the optical fiber measurement of the surface temperature of the cable, it is necessary to establish the corresponding relationship between the cable surface temperature and the core temperature to obtain the core temperature. Under the influence of environmental factors, the real-time performance is poor, and there are some errors in the calculated core temperature M.