Analysis and verification of signal propagation as method for temperature monitoring of underground power cables

Wave-Velocity Based Real-Time Thermal Monitoring of Medium-Voltage Underground Power Cables

“…The variation in a received signal Ur after travelling over distance Lc along a power cable at temperature T with respect to a reference at Tref in the frequency domain f can be expressed in terms of the change in the propagation coefficient γ as shown in [14], [15]:…”

“…The imaginary part of γ involves the wave velocity, which is mainly determined by the per-unit-length capacitance C and inductance L of the cable via v=1/√LC. In [14] it is shown, that for frequency components relevant for pulse propagation in power cables (100 kHz -10 MHz), the temperature influence on the cable inductance is small. The temperature dependency of the transit time is therefore attributed to the temperature dependency of the relative dielectric permittivity εr of the insulation material.…”

“…It causes a shift in the transit time. Equation (1) can be analyzed based on a detailed model of the cable propagation coefficient as in [14]. However, since the peak shape of the received waveform is found to hardly vary with temperature, the variation in transit time can also precisely be obtained from directly measuring the signal arrival time.…”