Rotating machines are fundamental in various industrial operations. From oil and gas exploration, where motors are essential in pumps and compressors, to manufacturing processes such as steelmaking, paper production, and backup power systems. Moreover, in sectors like mining and utilities, they power heavy-duty equipment and generate electricity.
Rotating machines are typically classified based on their voltage ratings: Low Voltage (Up to 1kV), Medium Voltage (1kV-6kV), and High Voltage (Above 6.6kV).
Recent industry trends show that while machine sizes, weights, and costs have been reduced, their life expectancy has decreased. A decade ago, it took over ten years for motors to show signs of Partial Discharge (PD). Now, the emergence of PD can be seen in less than half that time. This decline can be attributed to factors such as an increase in working voltage stresses, alterations in design with minimal change in materials, and production costs reduction.
PD is defined by IEEE1799-2022 as “an electric discharge that only partially bridges the insulation between conductors”. These discharges can manifest internally within the insulation due to voids or externally, often influenced by contamination and humidity. Particularly concerning is the corona PD, which appears when the local electric field crosses a critical threshold. The impact of corona PD is profound – the creation of ozone during a discharge can attack insulation, leading to cracks and damage, even in low concentrations.
The harmful effects of corona on insulation materials underscore the importance of adequate design considerations and preventative measures in power systems. By understanding and addressing the causes and effects of corona, we can enhance the lifespan and performance of electrical equipment, leading to more reliable and efficient power systems.
Blackout Test – per IEEE1799-2022
A test performed after eliminating all ambient light, specifically on energized electrical equipment, to detect external or surface discharges visible with the human eye (“naked eye”) after at least 20 min of acclimatization.
Solar Blind Ultra-Violet (SBUV) Camera
Solar-blind Ultraviolet (SBUV) cameras are specialized electronic devices that are sensitive exclusively to ultraviolet (UV) light, specifically below approximately 280 nm.
SBUV cameras can detect corona discharges and surface discharges. Such detections can take place even under daylight conditions.
Typically, SBUV cameras are designed as bi-spectral imaging devices, operating at two spectral bands: the solar-blind UV-C band and the visible light band. They produce output images by merging UV and visible light imagery, thereby presenting a comprehensive view of the observed scene.
In our pursuit to better understand and compare the efficacy of the Blackout test and the SBUV camera for PD detection, we adhered to the rigorous methodology described in the IEEE1799 standard.
Needle-Plane Setup: Central to our tests was the needle-plane setup as prescribed by the IEEE1799 standard. This arrangement allowed us to simulate corona discharges, the key phenomenon we aimed to detect.
Human Eye Sensitivity Benchmark: Before introducing any tools, we determined the discharge inception voltage (DIV) using the naked eye in pitch-black conditions. After a 20-minute dark acclimatization period, the participants observed the needle for visible glows, signaling the start of a corona discharge.
Instrument Test: The same test was then conducted using the SBUV camera, but without the need for darkness. The camera’s detection capabilities were compared with human eye sensitivity to evaluate its performance.
During the blackout test:
Using the SBUV camera:
When relying solely on the human eye during the blackout test, the visual information is minimal. This makes it extremely challenging for observers to obtain a clear orientation or accurately pinpoint the precise location of the partial discharge (PD). The signal produced by the PD is incredibly weak.
Blackout Test:
SBUV Camera:
When compared, it’s evident that the SBUV camera presents a more contemporary, efficient, and safer approach to PD detection. The traditional blackout test, though tried and true, showcases several operational challenges. The SBUV camera, with its adaptability and pinpoint accuracy, solidifies its position as an indispensable tool for modern industries.
Ofil develops and manufactures UV Bi-spectral optical and digital inspection systems with embedded proprietary patented Solar Blind technology. Ofil aims at providing precise solutions for science, industry and environmental wellness. Ofil owns the brand name DayCor® that stands for Daytime Corona detection.
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