Substation surveillance using RFI and complementary EMI detection techniques

The successful implementation of a substation asset management strategy depends heavily on predictive maintenance assessments with surveillance based techniques used to identify potential sites of degradation followed by more investigative and invasive quantitative techniques. The deployment of radio frequency interference (RFI) measurement can provide an efficient non-invasive surveillance technique to detect and locate partial discharges (PD) to individual high-voltage (HV) apparatus. This paper demonstrates the benefits of combining the assessment of RFI emissions with targeted deployment of other complementary non-invasive electromagnetic interference (EMI) detection techniques. This provides an increased level of confidence in the location, identification and assessment of severity of degradation and is of particular importance with complex HV apparatus such as transformers where the propagation paths for RFI are less well defined. Frequency sweep data and time-resolved traces acquired from substation surveillance scenarios are presented and compared with follow up assessments using complementary EMI couplers such as high frequency CTs (HFCT) and transient earth voltage (TEV) couplers. Key parameters that characterise RFI emissions in the frequency domain and in the time domain (e.g. RFI intensity and bandwidth, repetition rate) that provide a measure of severity of degradation and a means to classify or fingerprint suspect fault mechanisms, are correlated with those derived from measurements using other complementary PD detection techniques. The RFI surveillance technique followed by the deployment of complementary PD detection techniques is proven to be effective with a wide range of HV equipment to confidently characterise and trace electrical deterioration with a high degree of confidence.