This two-part paper proposes a revised method for calculating HV (High Voltage) cable sheath currents, and for fault location of cross-bonded HV cable systems. The equivalent circuit and the cable impedance per unit length under short-circuit fault conditions are revised from those under non-fault conditions. Part 1 of this paper proposes a revised phasor domain mathematical model for the sheath current calculation under fault conditions, following demonstration that short-circuit faults can cause changes in the equivalent circuit of the cable metal sheath, and causing changes in the cable impedance per unit length. The calculation results, as given in a case study, show that there exists a unique relation between the fault position and the sheath fault currents, making it possible to locate a fault by analyzing the characteristics of the sheath currents during a fault. Part 2 of the paper focuses on the fault location method via sheath current monitoring.

Due to electromagnetic interference in power substations, the partial discharge (PD) signals detected by ultrahigh frequency (UHF) antenna sensors often contain various background noises, which may hamper high voltage apparatus fault diagnosis and localization. This paper proposes a novel de-noising method based on the generalized S-transform and module time-frequency matrix to suppress noise in UHF PD signals. The sub-matrix maximum module value method is employed to calculate the frequencies and amplitudes of periodic narrowband noise, and suppress noise through the reverse phase cancellation technique. In addition, a singular value decomposition de-noising method is employed to suppress Gaussian white noise in UHF PD signals. Effective singular values are selected by employing the fuzzy c-means clustering method to recover the PD signals. De-noising results of simulated and field detected UHF PD signals prove the feasibility of the proposed method. Compared with four conventional de-noising methods, the results show that the proposed method can suppress background noise in the UHF PD signal effectively, with higher signal-to-noise ratio and less waveform distortion.

Impulse performance of grounding grid is needed for lightning protection design of power system. This paper describes an impulse test facility established for the full-scale grounding grid (50 m long and 52.5 m wide) in a 110 kV substation. Test method is presented, including configuration of current injection and return point, measurement of potential rise and longitudinal current. Impulse test is carried out with 2.6/50 and 8/20 μs current waveform, and the maximum current amplitude is 4 kA. A Current Distribution, Electromagnetic fields, Grounding and Soil structure simulation for the tested grounding grid is also adopted. Impulse performance of full-scale grounding grid is affected by soil ionization and conductor inductance. There is steeper peak on the potential rise waveform near the injection point with shorter wave front current, which leads to more uneven potential rise distribution. Partial soil ionization could increase the current dispersing into the soil at partial area of the grounding grid, and the longitudinal current flowing to the next area decreases. These two factors pose a high potential difference hazard to the secondary equipment via the secondary cable.

The epoxy spacers in SF₆ Gas Insulated Switchgear (GIS) are vulnerable to discharge. Once the surface of the epoxy spacers is deteriorated under discharge, insulation break down may occur subsequently. From a number of experiments carried out on 110 kV GIS, a new gas CS₂ was detected when creeping discharges occur on the epoxy spacer surface. In order to verify the correlation between CS₂ and the degradation of epoxy spacers, the quantum chemistry analysis was used to investigate the mechanism of CS₂ development. Based on the results, the relation between CS₂ and spacer insulation degradation was determined.

Partial discharge (PD) localisation in air‐insulated substations (AIS) can be used to assess insulation condition efficiently. The localisation results of previously published methods were in the form of coordinates or bearings, and showed large errors on coordinates. Further research is required if the fault is to be pinpointed. In this study, a novel localisation method based on directional antenna and multi‐point measurement is proposed to improve the accuracy of localisation result and inform the possible error distribution, which reflect the fact that where the PD ultrahigh frequency signal radiates from is not a point but the non‐metallic area of the source equipment. Through the single point measurement, the bearing of the PD source is obtained. With the multi‐point measurement, an accurate result and its error distribution are made available. An onsite test in a 220 kV testing AIS was performed, and compared with an existing method. The results show that the proposed method is more accurate than the existing method, and it is efficient to locate the faulty equipment with additional information of the error distribution.