Detection of HV Winding Radial Deformation and PD in Power Transformer Using Stepped-Frequency Hyperboloid Method

Detection of winding deformation and partial discharge (PD) is essential for monitoring and failure risk assessment of power transformers. Recently, an online method based on electromagnetic waves has been proposed for detecting radial deformation (RD) in high-voltage (HV) transformer winding using ultra wide band pulses, called the hyperboloid method. In this method, a short pulse is transmitted toward HV winding and its reflection captured using a set of antennas. By comparing and analyzing signals in sound and deformed conditions, the RD can be detected. On the other hand, signals radiated from PD defect in transformers are generally appeared in the range of UHF band (0.3–3-GHz frequencies). In this paper, the hyperboloid method is proposed for implementation in UHF band, and the PD effect on the result of the hyperboloid method is investigated. Thus, a set of UHF sensors can be used for the detection of PD and detection and localization of RD defect. Results show that PD signals can affect the signal of the hyperboloid method and lead to wrong localization of RD. In order to solve this problem, the UHF stepped-frequency method is proposed, utilized, and tested on the HV winding of a 1.6-mega volt ampere (MVA) distribution transformer. Experimental results show the capability of the proposed method for detecting both defects using only one set of UHF antennas.