Fiber Bragg Grating Cable Joints Thermometry

Power cable junctions is installed between the cable and cable, so as to form a continuous circuit of the power, power cable junctions has an important role in the process of power transmission. Acorring to the actual operating experience and theoretical analysis of power cable junctions, faults of power cable junctions are not sudden accidents, the various failures of the joints produced much heat,and the heat lead to the rising of the temperature of the Power Cable Joints, at last the power cable junctions become the weakest point in the circuit of power. Overheating is a early signs for the faults of Power Cable Joints, the thermal degree of power cable junctions is the major parameter which reflects cable working situations.This paper designed a kind of Optical fiber Bragg grating temperature sensor used in the internal of power cable junctions. Sensors installed in the middle of the insulating tube cold inside the power cable junctions.The heat produced the power cable junctions passed to a capillary copper tube and Bragg grating, and then change the Reflected Wavelength of Fiber Bragg Grating.The main contents of this article are as follows:(1) Set up a Optical fiber Bragg grating temperature sensor used in the internal of power cable junctions, and deduced the sensor's sensing model.(2) Select the sensor's material and the senor's size according the power cable junctions. The sensors include:capillary copper tube length is5cm, the inner diameter is2mm, outer diameter is4mm, length of circular copper is5cm, thickness is0.5mm, a diameter is3.5cm, the PTFE bushing inner diameter is1mm,outer diameter is2mm.according the theory to calculate,the wavelength is19.84pm/℃.(3) According to related request of sensor calibration experiments, the results show that the sensor nonlinearity error is0.94%FS (0～90℃) and repeatability is2.7%FS (0～90℃), the first calibration of the sensitivity is18.4pm/℃, the second calibration sensitivity is118.6pm/℃, the third calibration sensitivity is18.1pm/℃. A power cable junctions is made for XLPE aluminum cable with rated voltage is1kV, core of conductor is3+1, core cross-sectional area of25mm2, resistance wire instead of the middle connecting tube in the yellow joint, green joint of green connector connecting pipe for the destruction of the insulation layer and not polished or aluminum conductor in the middle of the burr.(4) High and low voltage experiments of the cable joint. In the low pressure experiment about red and yellow cable core joint, applying voltage level is75V,100V and125V, and every lasting time is120min, data is recorded every20min. The experiment shows that higher voltage level leads greater temperature rise about the same joints in equal time; at the same time and equal voltage, large contact resistance has the higher temperature than the joint of normal pressure. In the high pressure experiment about red and yellow cable core joint, applying voltage level is5KV and15KV, and every lasting time is40min, data is recorded every5min. The experiment shows that higher voltage level leads greater temperature rise about the same joints in equal time. With the joints, more serious of partial discharge, the more obvious of the temperature rise.