This research was carried out during my summer internship in 1997 at the Vermont Yankee nuclear power plant. The plant is located in the small town of Vernon, in the state of Vermont. The first half of the project consisted of statistical analysis of measurement data from one of the two main electrical transformers in the plant. The data were daily measurements of different quantities associated with the electrical insulation of the transformer. We used statistical methods to assess the current state of the insulation and to predict future trends, based on the measurement data. This is crucial for proper maintenance and prevention of unexpected failures of the transformer. The second half of the project consisted of a study of the electrical methods used for testing the insulation condition of rotating machinery within the plant. We provided guidelines and recommendations regarding different methods and their applicability that were used afterwards by the field engineers responsible for this task.