The ambitious transition towards a renewable future is being made possible by power electronic systems that facilitate effective control and efficient conversion of energy. One such system is the solid-state transformer (SST) which aims to replace conventional transformers by offering larger energy densities and flexible power flow. However, these benefits come at the cost of severe mixed-frequency stresses experienced by the medium frequency transformer (MFT) of the SST. These stresses are characterised by fast-rising pulsed waveforms of several tens of kilovolts repeating at frequencies of up to a hundred kilohertz. In contrast to pure sinusoids, the behaviour of dielectrics undermixed-frequency stresses is to a large extent unknown. This research gap forms the core motivation behind this thesis project. To analyse these exciting yet extreme phenomenon, the first objective was to build a pulse modulator for testing cellulosic dielectrics under voltages up to 10 kV with rise-times ≈ 2 μs at frequencies between 10 to 50kHz. The topology consists of a rectified DC supply feeding a SiC H-bridge pulse generator connected to a 4:200 pulse transformer and other variable test elements. The work began with selecting the switch and gate driver, simulations in LTspice and TINA-TI, and the fabrication of the PCB pulse generator prototype using Altium Designer. Next, a novel third-order PQR equation was derived for a PT with capacitive load involving the parasitic leakage flux Ls and distributed capacitance Cd. The influence of bobbin geometry on parasitics was studied with 20 different 3D printed iterations designed in Fusion 360. A failure mode analysis was conducted to identify weak points in a transformer, and the solutions detailed in this report. The final objective was to apply the produced waveforms of T_r ≈ 1.8 µs across single-layer OIP samples at 10 kHz and 50 kHz. The sample strength was determined through ramp tests with 1 kV/s slope. The lifetime curves were obtained by performing ageing tests at 10 field strengths each for 21-41 samples, and fitting the median failure time into an inverse power-law model. The results show a clear reduction in lifetime at higher frequencies hinting at the unsuitability of OIP in its current form as an insulation for MFTs. A transition point was observed indicating a shift in the ageing mechanism at lower fields. The report ends with a discussion on future scopes of research.