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The associated daily maintenance effort and cost has been increasing with the growing use of high-voltage (HV) cable circuits. This study proposes a time-delay concept-based approach to maintenance scheduling of individual HV cable components, to allow periodicity of inspection to be optimised with consideration of time-delay interval between the instant of defect inception and final failure. Here, the progress from a defect to its resultant final failure can be represented as a two-stage process, one being a stochastic process of defect arrival and the other being a delay-time interval from defect to failure. Then an optimisation model is established to schedule maintenance activities based on the two statistical processes, where the objective function is set as the minimal maintenance cost. Cable circuits are divided into five components in accordance with the objects of inspection and testing. The components within different service ages are considered individually in the statistical models, and their accumulate failure numbers during each service year are used to automatically formulate and update periodicity of inspection. To illustrate the feasibility of the approach proposed, theoretical analysis on thousands of cable circuits are carried out. Results show that the economic expenditure could be reduced by 22.2% after optimisation.

Among all failures in cable circuits, the failure rate of cable joints is much higher than that in cable bodies. In an effort to reduce cable failure rates and improve the reliability of power cable systems, this article studies the possibility of increasing the length of a cable section and thus reducing the number of cable joints via alternative sheath bonding methods. As the maximum length of an electrical cable section is governed by the permissible sheath standing voltage, this article first proposes a precise sheath voltage calculation model without approximations and simplifications. The sheath voltage per unit length has then been calculated for each bonding method using the proposed model. The maximum length of a cable section has then been calculated, based on the permissible sheath standing voltage, for the various sheath bonding methods. Results show that the traditional 500-m minor section length could be increased to 2.21 km by using the single-point bonding method. The maximum distance can be further lengthened by increasing the physical spacing among the three-phase cables. The economic comparison for each bonding method has also been made. Finally, the proposed method has been applied to a HV cable circuit already in operation, and the operational data confirms the feasibility.

On-line partial discharge (PD) monitoring is being increasingly adopted to improve the asset management and maintenance of medium-voltage (MV) motors. This study presents a novel method for autonomous analysis and classification of motor PD patterns in situations where a phase-reference voltage waveform is not available. The main contributions include a polar PD (PPD) pattern and a fractal theory-based autonomous PD recognition method. PPD pattern that is applied to convert the traditional phase-resolved PD pattern into a circular form addresses the lack of phase information in on-line PD monitoring system. The fractal theory is then presented in detail to address the task of discrimination of 6 kinds of single source and 15 kinds of multi-source PD patterns related to motors, as outlined in IEC 60034. The classification of known and unknown defects is calculated by a method known as centre score. Validation of the proposed method is demonstrated using data from laboratory experiments on three typical PD geometries. This study also discusses the application of the proposed techniques with 24 sets of on-site PD measurement data from 4 motors in 2 nuclear power stations. The results show that the proposed method performs effectively in recognising not only the single-source PD but also multi-source PDs.

Power cables are integral to modern urban power transmission and distribution systems. For power cable asset managers worldwide, a major challenge is how to manage effectively the expensive and vast network of cables, many of which are approaching, or have past, their design life. This study provides an in-depth review of recent research and development in cable failure analysis, condition monitoring and diagnosis, life assessment methods, fault location, and optimisation of maintenance and replacement strategies. These topics are essential to cable life cycle management (LCM), which aims to maximise the operational value of cable assets and is now being implemented in many power utility companies. The review expands on material presented at the 2015 JiCable conference and incorporates other recent publications. The review concludes that the full potential of cable condition monitoring, condition and life assessment has not fully realised. It is proposed that a combination of physics-based life modelling and statistical approaches, giving consideration to practical condition monitoring results and insulation response to in-service stress factors and short term stresses, such as water ingress, mechanical damage and imperfections left from manufacturing and installation processes, will be key to success in improved LCM of the vast amount of cable assets around the world.