The electromagnetic interference (EMI) shielding effectiveness of the epoxy polymer composite reinforced with carbon fiber mat (CFM), short carbon fiber (SCF), and multi‐walled carbon nanotube (MWCNT) is studied in the X‐band (8–12 GHz). Single‐layer unidirectional CFM of 30 wt% epoxy composite with 0° and 90° orientations resulted in EMI shielding of 5 dB and 29.6 dB, respectively. To avoid the influence of CFM orientation on the EMI shielding, SCF of distinct weight percentages (1 and 5 wt%) with fixed weight percentage (1 wt%) of MWCNT are reinforced into epoxy matrix. The EMI shielding provided by 2 mm thick epoxy composite reinforced with 5 wt% SCF along with 1 wt% MWCNT (CNT‐SCF5) is 35.4 dB. The microstructural study revealed uniform dispersion and better adhesion of MWCNT and SCF in the epoxy matrix. The dielectric properties of the fabricated samples indicated an increase in permittivity, electrical tanδ, and conductivity with the grading of SCF and MWCNT. The mechanical properties such as tensile strength and strain of the CNT‐SCF5 showed an increment in ultimate tensile strength and Young's modulus. The homogeneous CNT‐SCF5 epoxy composite with enhanced EMI shielding ability and mechanical properties could be utilized as an efficient EMI shielding material.

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A detailed study of the influence of internal defect parameters on partial discharge (PD) induced ultrahigh frequency (UHF) signals propagated through an L section of metal encapsulated gas insulated switchgear (GIS) is presented. The study is carried out using PD defect model with varying rise time, defect size, location, and orientation, an ultrawideband UHF internal sensor, and 3 m long L-GIS with dielectric spacers, shorting plates, hand holes and bus bar with disconnector. Presence of higher order modes, multipath propagation, losses, and dispersion inside L-GIS were observed to influence the time and frequency domain characteristics of PD signals induced in the internal UHF sensor with 0.5 to 6.8 GHz operating bandwidth and directional radiation pattern. The rise time of PD signals significantly influenced UHF signal characteristics in time and frequency domains while PD defect size, location and angular orientation primarily affected the signal amplitude. UHF sensor measurements confirmed the complex behavior of PD induced electromagnetic wave propagation inside L-GIS for varying defect parameters in agreement with the simulations. Despite the complex behavior, it is concluded that PD sensing in GIS is possible using ultrawideband internal UHF sensor.INDEX TERMS Gas insulated switchgear, partial discharge, protrusion defect, ultrahigh frequency.

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