High-voltage applications raise a concern about corona discharges. Using straightforward approaches, it is crucial to detect and pinpoint the discharges as soon as possible. A recent study published in Sensors compares the sensitivity of a portable wideband sonic camera and digital single-lens reflex (DSLR) camera with a matrix of micro-electromechanical microphones for identifying and pinpointing the source of discharges.
Both cameras are capable of producing an image of the area under investigation. The investigation uses electrode geometries, positive and negative direct current (dc) sources, and 50 Hz alternating current (ac). It also examines the impact of the separation between the sensor and the discharge locations.
Importance of Partial Discharges Detection
Electrical discharges are common in insulation systems used in high-voltage applications owing to the ongoing impacts of the high electric stress. Partial discharges are localized electrical discharges that only partially cross the insulation between two electrodes.
Partial discharges are observed in high-voltage applications but can also occur in medium-voltage and low-voltage applications, including fast-switching semiconductors and inverter-fed loads. Affected components in these applications include motors and cable systems.
Partial discharges are present in inhomogeneous sites of gaseous, liquid, or solid insulation systems and the contact between the floating metallic element and a conductor.
Partial discharges cause thermal, mechanical, chemical, and structural changes and environmental aging.
Partial discharges prematurely age organic insulating systems. Identifying the partial discharge sources and monitoring partial discharge activity to take corrective action before serious insulating damage occurs.
Methods of Partial Discharge Detection
Partial discharges emit UV and visible light, as well as chemicals, a local temperature rise, and current pulses. As a result, partial discharges are frequently detected using electromagnetic techniques, such as X-ray detectors, UHF and VHF antennas, acoustic and ultrasonic sensors, optical and infrared detectors, and radio interference voltage and partial discharge detectors. Only particular detection techniques enable the precise determination of partial discharge sites.
Overview of Corona Discharge
Corona discharges are partial discharges that occur in a gaseous medium. They are produced in highly inhomogeneous electric fields and are formed at lower voltages needed for a complete breakdown.
Corona discharges ionize the gaseous insulation surrounding an energized electrode when the electric field intensity surpasses a critical inception value.
Similar to partial discharges, corona discharge also produces other chemical elements such as ozone or NOx compounds, as well as ultraviolet and visible light, electromagnetic radiation, audible noise (AN), and other types of radiation.
Corona discharge is challenging to detect in daylight because of the low level of visible radiation. High-voltage laboratories often use high-performance digital cameras to find corona discharges at night.
Limitations of Sensors and Cameras Used to Detect Corona Discharges
Acoustic sensors, radio interference voltage, partial discharge detectors, and other sorts of sensors are used to detect corona discharges. However, they are too costly, intricate, and challenging to utilize in field applications. They are also hampered by electromagnetic noise and cannot direct the corona discharges' location.
Commercial Sonic Cameras for the Detection of Corona Discharges
Recent research works have examined the behavior of a commercial sonic camera made up of a matrix of microphones for detecting corona discharges. The sonic camera identifies partial discharges in power-line components and it can do so while being operated by technicians with little training.
The sonic camera is less accurate than the partial discharge detector, but it is easier to use and best suited for on-site and online testing.
Comparison of Cameras Used for Corona Detection
Riba et al. compared the sensitivity of a digital single-lens reflex camera (DSLR) and a sonic camera for on-site identification of corona discharge spots. Both cameras have a sensor made up of a matrix of sensing components, which produces an image that makes it possible to identify the corona discharge sites.
The minimum voltage at which corona discharge is observed for both cameras is determined. This work contributes to the field of corona discharge location. The areas examined by the researchers have a lot of promise for use in predictive maintenance of high, medium, and low-voltage electric system.
Which Camera is Better for Detecting High-Voltage Corona Discharges?
The effectiveness of two cameras, an optical DSLR camera and a novel sonic camera that enables identifying and detecting the origins of corona discharges has been assessed and compared in this study.
The DSLR camera is as sensitive as a commercial partial discharge detector based on apparent charge (a common technique for partial discharge detection). Therefore, due to its excellent sensitivity, the DSLR camera is used as the standard.
Traditional partial discharge detection technologies lack a straightforward and uncomplicated localization of the actual discharge spots in contrast to the cameras examined in this work.
The sonic camera is less sensitive than the DSLR camera for complicated electrodes with complex geometry. But the results of this study demonstrate that both cameras have a similar sensitivity regardless of the distance between the discharge sites and the sensor in the range of 1–10 m.
The sonic camera is around 15 times more expensive than the same DSLR camera model.
The most significant benefit of the sonic camera is that it can be used in daylight and is relatively simple to use in contrast to the DSLR camera, which requires total or partial darkness.
The DSLR camera requires long-exposure shots to maximize its sensitivity to capture more photons produced by the corona discharge, whereas the response of the sonic camera is virtually instantaneous.
The findings of this study demonstrate that even in the very early stages of corona discharges, the sonic camera enables quick, easy, and sensitive source detection and localization. These features are crucial for choosing the best camera for a specific application.
Riba, J.-R., & Bas-Calopa, P. (2022) Use of DSLR and Sonic Cameras to Detect and Locate High-Voltage Corona Discharges. Sensors, 22(19), 7250. https://www.mdpi.com/1424-8220/22/19/7250/htm
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