This paper presents a laboratory test procedure to determine the parameters of the inverse hysteresis model (IHM) applicable to single-phase toroidal transformer low-frequency modeling. The model parameters are obtained through a fitting procedure of the history-independent IHM of a series of open-circuit experiments and waveform recordings. These experiments can be easily executed during the transformer acceptance testing at the factory laboratory. The performance of the model is verified under various operational conditions, such as sinusoidal excitation, varied frequencies and voltages, and non-sinusoidal excitations. The results show that the model performs very well under all tested conditions giving great confidence that the proposed method can be used for parameter determination.

Protection relays monitor system voltage through Capacitive Voltage Transformers (CVTs), which scale voltages to safe levels. However, during voltage collapse, CVTs lag in transmitting the event due to their internal capacitors, impairing protection performance. Because of this, manufacturers and relay operators need an accessible, simple and reliable model to design and predict CVT behavior under collapse conditions. This paper presents an analytical model of CVT transient response during voltage collapse. The proposed model is validated against an established Electromagnetic Transient (EMT) simulation tool. Our model predicts the output voltage under sustained short circuits at the input without simulations, eliminating the need for specialized software or extensive training. Derived from an accepted equivalent circuit, it depends only on CVT parameters and construction. The model applies across wide burden ranges, accuracy classes, and several ferroresonance suppression circuit types (resistive, electronic, or non-linear). Compared with EMT simulations, the model achieves over 90% accuracy and dependability across all tested cases. The model can be readily integrated into CVT design workflows using standard software, enabling faster and more economical modeling of CVT behavior during voltage collapse tests as required by industry standards.

This letter presents a novel hybrid dielectric system for current transformers (CTs) designed to reduce dielectric fluid volume while maintaining thermal and dielectric performance. The proposed approach incorporates a metallic joint bellow with a hybrid insulation scheme that employs synthetic ester in the upper section and silicone gel in the bushing section of the CT. Numerical Finite Elements (FEM) simulations are conducted to evaluate the dielectric field distribution and thermal behavior under rated operation conditions. Results indicate that the bellow modification alone reduces the dielectric fluid volume by 16.4%, while the hybrid configuration achieves a total reduction of 36.5% when compared to the original design. Electric field simulations reveal a decrease of about 10% in maximum field intensity in critical regions, attributed to the dielectric properties of the alternative materials. Thermal simulations confirm that the proposed configuration maintains equivalent heat dissipation to the original design (same hot spot value). The solution is technically viable, allows material volume savings, and improves operational reliability without any loss of performance.

Access to reliable low-voltage power is challenging where distribution networks are unavailable or uneconomic, including switching substations, construction sites, and remote communities. Station Service Voltage Transformers (SSVTs), also known as Power Voltage Transformers (PVTs), address this problem by supplying useful low-voltage power from transmission or subtransmission networks. This paper reviews SSVT terminology, operating principles, construction architectures, electromagnetic and thermal modeling, testing, reliability, monitoring, and applications. The most extensively documented applications concern substation auxiliary services, while rural minisubstations are supported by SSVT-specific development studies and selected field reports. Electric mobility has progressed beyond a prospective concept: an SSVT-based, transmission-connected micro-substation pilot has demonstrated direct 220 kV-to-low-voltage supply for electric-vehicle (EV) charging. However, SSVT-specific characterization for this application, long-term operating data, and application-oriented design guidance remain limited. Key research gaps concern coupled multiphysics validation, nonlinear-load performance, reliability statistics, techno-economic assessment, and life-cycle analysis. Particular attention is given to distinguishing applications already demonstrated with SSVT technology from emerging uses for which validation, standardization, or long-term operating experience remains limited. The review concludes by proposing a roadmap to develop reproducible, experimentally validated, and digitally supported SSVT platforms for remote energy access and selected electric-mobility applications.