Designing and implementation of interfacing circuit for CM of HV UG cables

Abstract

It is well known fact that the moisture content and heat generated from the cables deteriorates the insulation resistance and the cable sheath. For the comfort and reliable transaction of power of buried cables, high voltage cables are used. Oil-filled high voltage cable is most commonly used for well transmission and distribution of electrical energy. Oil-filled (132-500 kV) are laid in specially constructed concrete lined trenches. Surroundings of the cores are the combination of filler material giving the mechanical support with the capacity to conduct heat away from the cables. Theampacity of the cable to function within its characteristics and overall the structure life-time is influenced by the thermal conductivity of the adjacent materials. With the increase in moisture content, thermal conductivity also increases. For computing the data analysis of moisture content and temperature inside the cable conduit, I have designed an interfacing circuit for condition monitoring of HV buried cables which works on a relaxation oscillator phenomena and based on a Wheatstone bridge. The designed interfacing circuit utilizes two different resistive sensors (impedance moisture sensor and temperature sensor)for converting incremental resistance change due to the moisture and the temperature due to the thermal stress into frequency and duty cycle respectively. The change in resistance to the original resistance of the sensor is proportional to the moisture ingress onto the moisture sensor available in the filler material of the UG cable. This circuit is simulated on a NI Multisim software and hardware implemented on a breadboard. Both simulation results and experimental results have been captured obtained from oscilloscope is presented.