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1436 J. A. Ardila-Rey et al.: Partial Discharge and Noise Separation by Means of Spectral-power Clustering Techniques Partial Discharge and Noise Separation by Means of Spectral-power Clustering Techniques J. A. Ardila-Rey, J. M. Martínez-Tarifa, G. Robles and M. V. Rojas-Moreno Universidad Carlos III de Madrid Departamento de Ingeniería Eléctrica Avenida de la Universidad 30, 28911, Leganés, Madrid, Spain ABSTRACT Partial Discharges (PDs) are one of the most important classes of ageing processes that occur within electrical insulation. The measurement of PDs is useful in the diagnosis of electrical equipment because PDs activity is related to different ageing mechanisms. Classical Phase-Resolved Partial Discharge (PRPD) patterns are able to identify PD sources when they are related to a clear degradation process and when the noise level is low compared to the amplitudes of the PDs. However, real insulation systems usually exhibit several PD sources and the noise level is high, especially if measurements are performed on-line. High-frequency (HF) sensors and advanced signal processing techniques have been successfully applied to identify these phenomena in real insulation systems. In this paper, spectral power analyses of PD pulses and the spectral power ratios at different frequ