Research On The On-line Monitoring System Of The Power Cable Based On Fiber Bragg

In recent years, with the rapid development of our nation's economy, the city's expanding, the demand for power electricity is increasing, and the requirements of the reliability of power supply are also increasing. Coupled with the level of city planning in China continues to improve, major cities have been working to improve the rate of the city's underground power cables, this will not only reduce the vertical and horizontal crossed and spider-like overhead lines which are largely existed in city, and can make the city more appearance, while mentioning the power supply reliability. Such as the main streets of Wuhan overhead lines have been insteaded by the voltage level of 11OkV XLPE insulated power cables laid in the cable tunnle. With the further development of our economy, the demands for power electricity will be further increasing, which requires higher voltage level of power cables to increase the capacity of power transmission. Generally power cables laid in a special cable tunnel or in the soil. Since the power cable has a high initial investment, which makes the the monitoring,the operation and the management of the power cable are becoming more and more important.In fact, as early as 1893 A.E.Kennelly has already begun to study on the capacity of the underground power cable. Followed by Neher and McGrath made a further study, and their research is the basis of IEC-60287. This paper which will study on the on line monitoring system of the power cable based on fiber bragg will study mainly from the following several aspects:The first is the manner in which to obtain the temperature parameters. Since the laying of the power cables are generally in a long distance, usually a few kilometers, so the long distance transmission of measurement signals is a problem which can not be ignored; In addition, some power cables are laying in the cable tunnel, but there are a large number of power cables directly buried in the soil, so the measuring devices require a relatively high characteristics of the corrosion resistance and moisture. Therefore, the traditional measuring temperature which relied on the thermocouples and other cable can not meet temperature requirements on the power cables. This paper will introduce the ber Bragg grating temperature sensor through many aspects of it,which include discussing the theory of the optical fiber grating temperature sensor, analysising the signal transmission of optical fiber grating temperature sensor, describing the physical and chemical properties and the working environment of the optical fiber grating temperature sensor. It also will be disgussed that how the fiber Bragg grating temperature measurement system to achieve the required temperature parameters for power cable monitoring.The second is how to convert the monitored temperature into the ampacity and others power-related parameters. In this regard, related research has been done by previous, IEC also has relevant criteria. This article will first introduce the structure of the basic components of power cable, analysising power cable of the heat principle layer by layer, the spread of the heat and basic diffusion path. That the heat source of power cable as the power source, the propagation path of heat as the conductive circuit, the structures which have the function of obstacling the spread of the heat or storing the heat as the basic circuit components such as resistors, capacitors and so on. Thereby establishing the correspondence between the thermal circuit and the electrical circuit, using the lumped parameter method to establish a more complete thermal circuit model of power cable. According to established thermal circuit model of power cable we can derive the mathematical relationship between steady-state ampacity and the environment temperature and the skin temperature of the power cable; Then the thermal circuit model will be simplified to obtained a relatively simple thermal circuit of power cable model with two network according to IEC standard. And through its mathematical derivation, we can obtaine the transient temperature rise which is the temperature of power cable's conductor relative to the temperature of the skin temperature; At last we can have the temperature of conductor when the power cable is dynamic. This paper will also establish a mathematical model of the medium in which the power cables lay, to analyze the spread of the heat in the medium. Such as the power cables laid in the soil, the spread rate of the heat is related to the soil quality, soil moisture and other factors. This article will describe it by the exponential integral function.The insulation characteristic of power cables has not been a real-time monitoring, the paper introduces and analyzes the the physical meaning and applications of the insulation's dielectric constantεand dielectric loss angle tangent tgδin the power cable, to establish the mathematical relationship between insulating properties and the temperature drop of the insulating layer, and to monitor the real-time changes of the insulation properties.Finally, according to the thermal circuit model and the IEC related standards, this paper writes the software of power cable carrying capacity with the VB. And introduces the physical structure of the on-line monitoring system of the power cable based on fiber bragg. For the sake of the security of operation data in power sector, the system will use C/S structure to realize the processing and displaying of the monitoring data.