This paper presents an application of a single-phase five-level converter as a low-voltage source fed to a high-voltage (HV) transformer for HV and partial discharge (PD) tests on potential transformers with a voltage rating of 33 kV. The converter was constructed with two H-bridge sets of insulated gate bipolar transistor (IGBT) switches, and the sinusoidal pulse width modulation (SPWM) technique was utilized to control the converter. Also, an additional filter was implemented in the testing system to mitigate the background noise level in the HV testing system, and the suitable modulation index and carrier frequency were analyzed. To evaluate the performance of the developed testing system, the difference in the voltage, the total harmonic distortion, and the background noise in the PD tests were examined by simulations and experiments without and with a test object. From the simulation and experimental results, it was found that (i) the difference in the voltage is below 1%, (ii) the total harmonic distortion is below 1%, and (iii) the background noise is below 2 pC. The performances of the proposed converter in terms of output voltage distortion and switching interference are superior to those of the conventional three-level converter. This makes the developed system very attractive for use in practical HV and PD tests.