Partial Discharges and Ozone

The main method to monitor the condition of the stator insulation in hydrogenerators is the measurement of partial discharge pulses through capacitive couplers. However, partial discharges exposed to air also produce ozone, whose concentration can be measured through different types of sensors. This parameter can be valuable when assessing the condition of a machine, especially if the measurements are continuous. Since ozone concentration is affected by many variables, such as temperature, humidity, discharge voltage, airflow, etc, its value alone is not very meaningful, but it can be a good complement to typical partial discharge measurements, since it may reveal localized faults that would otherwise go unnoticed. It is also important to understand that very high ozone concentrations can chemically damage a generator, since it combines with atmospheric nitrogen and humidity creating nitric acid, which can corrode metals and degrade insulating materials.