Continuous operation of a power system during a ground fault can be achieved by employing either a High Resistance Grounded (HRG) power source or a floating power source. However, if a second ground fault occurs in the system it can cause significant problems and therefore the presence of the First Ground Fault (FGF) must be detected, located, and repaired quickly. In this study, an active impedance based fault location method is proposed to locate the FGF in a HRG power system. The study presented shows that the magnitude of the fault resistance has only a small influence on the proposed technique. However, for unbalanced faults, the impedance of the healthy phases can distort the impedance measured and impair the accuracy of the fault location method. Therefore, a new compensated method is proposed to compensate for this distortion. The results show that a high accuracy can be achieved with the compensation, with a location error lower than 5%.

Electrolytic capacitors continue to be used for the DC-link in motor drive systems due to their high specific capacitance. The degradation of electrolytic capacitors can lead to increased equivalent series resistances (ESR) and reduction in capacitance. This can impair the drive behaviour (e.g., reducing the ability of the motor-drive to maintain a steady voltage and thereby maintain steady speed set-points), but will also lead to additional heating and a further cycle of degradation until failure occurs. On-line condition monitoring is useful to understand and predict failure, and can potentially be embedded into a more holistic condition monitoring regime through, for example, the Internet of Things (IoT). It is possible to measure and track currents and voltages through the DC-link and estimate in real-time the corresponding capacitor impedances. The method proposed in this paper will estimate the impedance in a frequency related domain to ensure that the proposed approach is robust to changes in operating conditionsload variation, ambient temperature, drive temperatureand also allow the impedance to be estimated over a wide frequency range. Therefore, different transform methods have been investigated: the Fast Fourier Transform (FFT); the Short-Term Fourier Transform (STFT); and the Continous Wavelet Transform (CWT), making use of two different mother wavelets (complex and bump). It was found that the CWT provided optimal results with fine granularity in time, although selection of a mother wavelet may lead to loss of salient information.