Wave‐Velocity‐Based Temperature Monitoring Applied to Underground Power Cables in Medium‐Voltage Networks—Discrimination of Individual Cable Temperatures in a Distribution Grid

ABSTRACT

The thermal state of underground power cables can be monitored based on the temperature dependency of the dielectric permittivity of the insulation material. The resulting temperature‐dependent wave velocity is used as a thermometric property. To this end, the signal propagation time along a cable of an injected signal is determined. Its variation provides real‐time temperature information with a resolution down to 1°C. To allow for a cost‐effective implementation in medium‐voltage networks, cable systems with multiple sections need to be monitored, differing in thermal behaviour and load current. This paper addresses challenges due to signal distortion related to the presence of other network components and overlapping reflections. The proposed method omits the need for detailed knowledge of the network component designs that, in a practical setting, is not likely to be available. Basically, knowledge of cable type and length is sufficient, provided that the temperature dependencies of the dielectric permittivity for the involved cable types have been determined. Two‐sided pulse injection and detection combined with time‐domain reflectometry can resolve possible ambiguity in interpretation of waveforms that suffer from overlapping reflection and allow retrieving temperature information at the level of individual cable segments.