Power cable in distribution grids usually operates in nonuniform environments, leading to segmental aging of cable insulation. Location of segmental aging is highly desirable for early maintenance of power distribution grids, which can avoid severe insulation faults and improve system reliability. In this paper, a novel segmental aging location method based on voltage and leakage current measurements under multi-frequency common-mode (CM) monitoring signal injection is proposed. Segmental aging models for various types of cables are first developed, and a model-based location algorithm of segmental aging is then designed. Comprehensive simulations and case studies in PSCAD/EMTDC are conducted to prove the effectiveness of the proposed method. Compared with existing approaches, the proposed method achieves more accurate location of aging accounting for various measurement noises, parameter uncertainties, and distribution grid structures.

The majority of converter failures are caused by overheating and temperature fluctuation. Therefore, online thermal monitoring methods for converters are necessary to enhance reliable operation capacity. Conventional thermal monitoring methods mainly focus on a single semiconductor device. Monitoring cost is high, and measuring circuits are difficult to integrate. Moreover, converter structure must be adjusted in industrial applications for these methods. To solve these problems, a novel online thermal monitoring method for IGBT-based converter systems is proposed. The aim is to obtain an overall temperature evaluation of the converter. First, leakage current in DC bus (I_leakDC) is selected as an indicator for converter thermal monitoring. Theoretical analysis and offline experiments prove I_leakDC is quasi-exponential to temperature. Then, temperature-related parameters (T_CONU and T_CONL) are defined corresponding to I_leakDC, respectively, to characterize thermal state of converters. Next, an extraction method for I_leakDC is proposed based on state-delay converter control method. Using online extracted I_leakDC, a novel thermal monitoring strategy is developed. Online experiments validate effectiveness of the proposed strategy in different operating conditions. The proposed method gains advantages in low cost, easy integration, feasible and convenient implementation for system-level thermal management.