| The purpose of this dissertation is to develop a predictive maintenance plan to diagnose contact degradation on load tap changers, LTCs, and voltage regulators using pattern recognition techniques.The following sensor technologies have been applied to the LTC and voltage regulator. Strain gages were attached to the drive arm of the devices to detect changes in the strain associated with each tap change. Acoustic transducers and accelerometers were used to measure changes in the sound wave and vibration associated with each tap change. Both the load tap changer and the voltage regulator were run with new contacts and repeatable signals or signatures were obtained for each sensor type.Burned contacts and failed finger contacts, two common modes of failure for these machines, were obtained from Entergy. The burned contacts were installed on the voltage regulator and on each phase of the LTC and the tests were repeated. These sets of data showed that there exist distinct signatures for each equipment type experiencing this failure mode. The magnitudes of the good and bad contact signals were different enough that classification could be performed.A power spectral density was also computed for the two cases, operational contacts and burned contacts. These frequency plots show significant differences in the two modes which provide useful information for classification as well.Two classification methods were derived for the two-case study under consideration, to determine whether the unit being tested is in need of maintenance. These are template matching and a linear classifier used to partition the feature space into two non-overlapping areas. Graphical results show the validity of each method.The future of the project involves field testing the predictive maintenance program on energized substation equipment for a significant period of time. The predictive maintenance system's performance will be measured by its ability to identify equipment in need of maintenance or repair. The completion of this stage of the project will depend upon future funding and upon the cooperation of Entergy Services Inc. |
