Development of a Low-Cost Ozone Monitoring Module for Continuous Partial Discharge Detection in Hydrogenerators

Partial discharge (PD) measurement is a well-established predictive maintenance tool for high-voltage rotating machines, allowing the condition of the insulation to be assessed not only during machine outages, but also continuously monitored during regular operation, enabling a more efficient planning of major overhauls or possible repairs. Some types of PDs are known to produce ozone in air-cooled machines, but online ozone monitoring has not been widely available commercially for this application, perhaps with one exception which uses a complex system of tubes and valves to direct air samples to a measuring chamber, based on ultraviolet (UV) absorption. Advances in electrochemical sensors, however, have allowed for more reliable measurements at very low cost. In this article, we describe the development and prototype of an ozone monitoring module with embedded signal processing for specific application in rotating machines, using simultaneous temperature and humidity measurements to reduce the typical errors induced by the variations of these parameters. Prototypes were manufactured and installed in two 311 MVA hydrogenerators and the data collected indicates that continuous ozone monitoring can detect potential problems that may not be identified with traditional PD monitoring.