The article presents the results of diagnostic measurements of partial discharge signal propagation from the winding insulation in electrical machinery, which were performed using an on-line method. This paper describes the results of experiments and the acquired experience in the monitoring of winding insulation in high power and high voltage electrical machines which are important in industrial production processes. The authors show the measurement techniques employed in their research. Representative measurement results are presented along with their analysis. The authors use an SKF monitoring systems to measure: vibrations, temperature, and humidity, as major factors affecting partial discharge activity in the from winding insulation of electrical machines.