Abstract：Due to their excellent electric-field control and low-loss characteristics, semiconductor electric shielding materials have attracted increasing attention in the design of medium-voltage, medium- and high- frequency transformers, particularly in applications requiring high power density and compact structures. Such shields are typically used to mitigate electric-field stress and enhance insulation reliability. Theoretically, a grounded semiconductor shield, owing to its finite conductivity, can maintain an equipotential surface, effectively divert displacement currents, and suppress regions of high field strength. However, recent engineering practice and experimental results indicate that under high dv/dt conditions—especially when the excitation voltage is supplied by a pulse-width modulation (PWM) converter—the equipotential characteristic of a grounded semiconductor shield may be compromised. In such cases, significant potential differences can arise across different locations within the shield, leading to high potentials relative to adjacent grounded components, such as the transformer core. In narrow air-gap regions, this potential difference may trigger dielectric breakdown, leading to severe insulation failure. This paper investigates the shielding performance of semiconductor materials under high dv/dt PWM voltage stress. A generalized resistor-capacitor (RC) equivalent model is developed for a typical medium-voltage transformer structure. The model incorporates key components affecting voltage distribution, including the high-voltage winding, insulating medium, semiconductor shield, air-gap region, and core. Then, approximate analytical expressions for the shield voltage under both sinusoidal and PWM excitations are derived. Numerical simulations are performed in COMSOL Multiphysics to validate the analytical model and assess parameter sensitivity. The study examines the influence of winding excitation voltage, shield surface resistivity, insulation permittivity, and air-gap size on shielding performance. Simulation results show that under sinusoidal excitation, increasing the voltage amplitude or frequency moderately increases the shield voltage. Still, it remains significantly lower than the winding voltage, indicating effective electric-field suppression. In contrast, under PWM excitation, the peak shield voltage is largely insensitive to the switching frequency itself but strongly and positively correlated with the dv/dt of the PWM waveform edges. A higher dv/dt produces a greater transient shield voltage peak, substantially exceeding that observed under sinusoidal conditions. It underscores the importance of assessing shielding performance in medium- and high-frequency PWM converter applications, where dv/dt can be several orders of magnitude higher than in power-frequency systems. Experimental validation is performed using a half-bridge converter test platform and simplified transformer models incorporating semiconductor shields with different surface resistivities. Comparative measurements confirm the theoretical and simulation results. Based on the theoretical, simulation, and experimental studies, practical guidelines are proposed for shield material selection, surface resistivity optimization, and insulation coordination design, ensuring that electric field strength requirements are met in critical narrow-gap regions. This paper provides references for the performance limiting evaluation of semiconductor shields and the proper application of wide-bandgap devices in medium-voltage systems.
夏伟, 张风娟, 丰昊, 冉立. 高dv/dt下中压中/高频变压器半导体电屏蔽层的电场抑制性能[J]. 电工技术学报, 2026, 41(10): 3411-3422.
Xia Wei, Zhang Fengjuan, Feng Hao, Ran Li. Electric Field Suppression Performance of Semiconductor Shielding in Medium Frequency Medium Voltage Transformers Subjected to High dv/dt Voltage. Transactions of China Electrotechnical Society, 2026, 41(10): 3411-3422.
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