On the scaling of digital cameras to quantify the intensity of corona discharges

• Corona and surface discharges emit ultraviolet and visible light. • Digital cameras can be used to detect and locate such discharges. • Calibrated sensors are essential for informed engineering and maintenance decisions. • This paper proposes a method to calibrate digital cameras for PD measurements. • Calibration relates the optical response to the electrical charge of the discharge. Corona and surface discharges emit ultraviolet and visible light. Therefore, imaging sensors can be used to detect and locate such discharges. These sensors offer many advantages, including high sensitivity, high resolution, high immunity to electromagnetic noise, low cost, and direct localization of discharge points. However, information about their scaling is lacking, i.e., how to relate the optical response of the sensor to the electrical charge involved in the discharge process. Using adequately scaled sensors is essential for making informed engineering and maintenance decisions. This paper focuses on this issue by proposing a method to scale digital camera responses by establishing a relationship between digital image intensity and the charge involved in electrical discharge phenomena. Though not a standard method, it allows for simple, direct localization of the discharge region and objective quantification of discharge severity. The proposed scaling method is applied to three electrode geometries—needle-plane, rod-plane, and sphere-plane—that generate discharge pulses between 20 pC and 1200 pC. Despite the wide variation in electrode geometries, the scaling results presented in this work prove to be consistently reliable and accurate. The fitted scaling curves achieve coefficients of determination greater than 0.998