Dynamic derating of three-phase underground power cable under current harmonic distortion

Underground power cables have significant importance of transmitting and distributing power in the electrical power systems. The thermal analysis of such cables has a major interest due to the continuous stresses of their constructive materials as a result of current application. It is well recognized that the current carrying capacity (ampacity) of the cable is a robust function of the thermal distribution inside the different constructive parts of the cable due to conductor current injection. Current harmonics will give rise to increase the temperature of the conductors inside the cable which may exceed its maximum permissible value. Consequently a derating process should be initiated in order to meet the maximum allowable conductor temperature and hence conserve the insulation lifetime. This paper proposes a dynamic derating process of the cable as a result of current harmonic distortion through a transient thermal network modeling of three-phase underground cable. Prony analysis-Hilbert transform approach is used to extract the magnitudes, frequencies and phase angles of the distorted current signal. Therefore, this coupling between transient modeling and harmonic extraction approach can be used as online condition monitoring and derating of cable ampacity due to any harmonic distortion of the current signal.