The high voltage power transformer is the critical element of the power system, which requires continuous monitoring to prevent sudden catastrophic failures and to ensure an uninterrupted power supply. The most common failures in the transformer are due to partial discharge (PD) in electrical insulations which are the results of the insulation degradation over time. Different approaches have been proposed to monitor, detect, and locate the partial discharge in power transformers. This paper reviews and evaluates the current state-of-the-art methods for PD detection and localization techniques, and methodologies in power transformers. Detailed comparisons of PD detection techniques have been identified and discussed in this paper. The drawbacks and challenges of different partial discharge measurement techniques have been elaborated. Finally, brief reviews of PD denoising signals, feature extraction of PD signals, and classification of partial discharge sources have been addressed.

Recently, nanofluids are introduced in the power utilities for the dielectric performance enhancement of power transformer oil. The compactness and fault improvement of the power transformers has resulted in the necessity of next-generation insulating fluid with inflated dielectric properties. This paper investigates the dielectric performance of the novel ester oil-based magnetic nanofluids with different nanoparticles under different electric stress conditions. Two biodegradable fluids used as the base liquid for the experiment are synthetic ester oil and natural ester oil while three magnetic nanoparticles used to synthesize nanofluids are iron (II, III) oxide, cobalt (II, III) oxide, and iron phosphide. The concentrations of the nanoparticles are varied to optimize the characteristics of the prepared nanofluids. The dielectric breakdown and relative permittivity of the nanofluids have been experimentally investigated. Further, the breakdown predictions have been performed using Weibull statistical distribution-based regression analysis. The experimental results show the improvement in the characteristics of prepared nanofluids with the change in nanoparticle concentration as compared with the host fluids.

Purpose: This study aims to experimentally evaluate and compare a conventional voltage transformer and two non-conventional voltage transformer sensors to assess accuracy, robustness and suitability for modern power system measurement and digital substation applications. Design/methodology/approach: Comprehensive laboratory tests were performed under identical conditions to examine voltage sensor performance in terms of ratio accuracy, linearity, frequency response, burden capability, overvoltage withstand and temperature stability across a wide operating range of voltages, frequencies, loads and ambient temperatures. Findings: The conventional voltage transformer demonstrated superior accuracy, burden handling, and thermal stability under nominal conditions but showed limitations under frequency deviation and overvoltage due to core saturation. The non-conventional voltage transformer sensors maintained linear operation over wider voltage and frequency ranges but exhibited higher temperature sensitivity and required calibration to achieve high accuracy. Quantitatively, the conventional VT achieved ratio errors below 0.2% within its rated range, while the NCVT sensors exhibited approximately 0.5%–2% error prior to calibration but maintained linear operation up to 1.9 per-unit voltage without saturation. Originality/value: This work presents a direct, side-by-side experimental comparison of conventional and non-conventional voltage transformer sensors using unified test procedures, providing practical insight into sensor-level trade-offs relevant to future digital substation deployment.