Conference Agenda

This study presents a comprehensive evaluation of aluminum radiators as a replacement for conventional steel radiators in power transformers, with a primary focus on their thermal and mechanical performance. Experimental investigations, including initial laboratory and field tests, demonstrate that aluminum radiators offer superior cooling efficiency compared to their steel counterparts, attributed to the material’s higher thermal conductivity and optimized design.

While the primary focus is on technical performance, the adoption of aluminum radiators may also support industry efforts to improve resource efficiency and reduce environmental impact. The research addresses the need for new performance formulas and design guidelines to accurately describe the cooling behavior of aluminum radiators, ensuring their effective application across a range of transformer types and operating environments. Initial trials and field deployments have confirmed the readiness of aluminum radiators for industrialization, with results demonstrating consistent performance improvements and reliability under real-world conditions. The study also considers the implications for long-term maintenance, noting that the enhanced corrosion resistance and reduced need for protective coatings can simplify lifecycle management and mitigate risks.

Given these advantages, aluminum radiators are well positioned for adoption in emerging and demanding markets such as offshore renewable energy installations, data centers, and other applications where small footprints and high reliability are critical. In conclusion, aluminum radiators represent a significant innovation in transformer cooling technology, offering enhanced efficiency, durability, and adaptability while supporting the development of more robust electrical infrastructure. Their adoption has the potential to set new benchmarks for performance and operational excellence in the design and operation of power transformers.

In this work, a linear dynamic model of the single-phase transformer based on magnetic fluxes as state variables is analyzed, with the purpose of analyzing its state transition matrix, a fundamental tool for transient analysis and the formulation of explicit solutions of electromagnetic systems. From the differential equations of the coupled circuit, the state-space representation and its corresponding transfer function are constructed. Subsequently, fundamental matrix is obtained through two mathematical approaches: the Cayley–Hamilton theorem and modal decomposition. It is evidenced that both methods generate equivalent expressions for the fundamental matrix, which allows for the cross-validation of the analytical solution of the single-phase transformer. Finally, the time responses obtained via numerical integration with Runge-Kutta and via state transition matrix found analytically in this work are compared, observing errors of the order of 10-18, which confirms the consistency of the model and the accuracy of the analytical solution. This work establishes the foundations for future applications in transient analysis, control, parametric identification, and advanced diagnosis of single-phase transformers.

Significant efforts are being made to find suitable replacements of SF6 gas in high-voltage gas-insulated switchgear (GIS). Current solutions include SF6 alternative gases with a lower global warming potential (GWP) than that of SF6 and vacuum interrupters with the insulation system of vacuum-dry air or vacuum-solid dielectric. Recent research has shown promising dielectric properties for supercritical fluid CO2 (scCO2) and the mixtures, which may serve as a replacement to SF6. Rather than relying on fluorinated gases with high electronegativity, the high-pressure scCO2 achieves the superior dielectric properties through its high density and thus short mean free path. This paper presents an experimental setup that has been built to study the arc quenching capabilities of scCO2, with a fast-moving contact system similar to that of nowadays high-voltage gas-insulated circuit breakers. The experimental results show that scCO2 is able to quench the peak current of 8.9 kA, which has been demonstrated for the first time. This result is very inspiring for designing the scCO2 insulated circuit breakers, genuinely SF6- free.

This study presents a fundamental laboratory investigation into the dielectric performance of SF₆ -free gas mixtures, utilizing a MATLAB-based numerical framework validated against an extensive experimental dataset (n=600). The dataset was systematically obtained across a multi-parameter space encompassing varied electrode geometries, diverse cathode materials (Al, Cu, Stainless Steel, and Graphite), absolute pressures up to 0.4 MPa-0.6MPa, and variable inter-electrode gap distances. A fundamental correlation (R^2=0.708) was established between the electrode work function (ϕ) and the resultant dielectric enhancement, demonstrating that breakdown initiation is a surface-dependent phenomenon governed by the cathode-gas interface rather than bulk gas-dynamic properties. Experimental results indicated that Graphite-Steel hybrid configurations significantly enhanced insulation stability by mitigating field-dependent electron emission. While these findings provided a preliminary characterization of design trends under AC (≤200kV) and DC (≤500kV) regimes, it establishes a deterministic foundation for the optimization of compact, sustainable gas-insulated systems.

Supercritical carbon dioxide (scCO2) is a fluid with outstanding dielectric strength, suitable for a large range of high voltage power apparatus such as circuit breakers, disconnect switches, electrostatic machines, as well as instrumentation and power transformers. Besides its high dielectric strength, it also offers low permittivity, low viscosity, excellent heat transfer, and low cost. One of the challenges is that it needs to operate in narrow band of temperature compared to alternatives such as SF6, oil, or vacuum. To maintain optimal conditions, typically between 30°C and 45°C, a system was developed that pumps heat between the medium and ambient. Temperatures below the critical temperature of CO2 need to be avoided since they would lead to a separation into an incompressible liquid phase and a gaseous phase, which could damage the rotor in an electrostatic machine or the nozzle and the actuator mechanism in a circuit breaker. Very high temperatures are also problematic since they could lead to exceeding the rated pressure for the vessel besides secondary effects such as speeding up the contact opening velocity in a circuit breaker beyond the maximum allowable velocity. Besides environmental factors such as ambient temperature and solar irradiation, the temperature of the scCO2 medium is also affected by Joule heating in the conductors as well as arcing during opening operations in a circuit breaker.

The concept for the thermal management system is shown for the 72 kV-class TESLA (“Tough and Ecological Supercritical Line Breaker for AC”) circuit breaker prototype. It is designed to both heat and cool the fluid to maintain a narrow band of temperature while achieving a high coefficient of performance to minimize auxiliary losses while maximizing the power density. The concept will be demonstrated in reduced-scale experiments and compared to a simple, yet effective numerical simulation based on a thermal network model.

This research investigates the influence of cathode surface roughness on DC breakdown voltages and pre-discharge currents in pressurized synthetic air. A physics-based computational model is presented for predicting breakdown voltages in insulating gases under high-voltage stress. The model combines electron ionization and attachment processes along the discharge path to calculate the evolution of the primary electron avalanche. The model considers gas pressure, gap distance, electrode geometry and electric field distortions due to electron avalanches, and had been validated with a huge number of experimental breakdown measurement series with smooth electrode geometries in synthetic air.

In the present work this model is extended to include the influence of electrode surface roughness on breakdown behavior. To accomplish this, cathodes with varying roughness levels were characterized using laser scanning microscopy and corresponding local field enhancements at the surfaces are calculated by numeric simulation. Those, locally non-uniform electric field distributions were used as input for the computational model to predict breakdown voltages. Finally, breakdown and pre-discharge measurements of sphere spark gaps with different electrode surfaces are presented and compared to the model predictions.

Validations against these experiments at pressures up to 1.5 MPa show strong agreement between measured and calculated breakdown voltages.

The results demonstrate that cathode surface features in the micrometer scale can significantly reduce the insulation strength of pressurized synthetic air and that the proposed model is able to predict this effect.