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Rotating Machines and Partial Discharge Detection: A Comparison Between a Solar Blind UV Camera and the Blackout Test

Rotating Machines in the Industry

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).


The Increasing Concern of Partial Discharge

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.

Motor insulation burnt by PD

Technologies and Methods for Corona PD detection and localization: Blackout Test vs. SBUV Camera

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. 


Comparative Analysis: Blackout vs. SBUV

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.

Test Setup


Results as seen by human eyes (illustration)

The image represents a visual illustration of how the human eye perceives the scene under the conditions of a blackout test. There's a subtle glow or signal present, which can be challenging to discern with the naked eye.

Results as seen on camera

The image provides a clear view of the discharge and accurately pinpoints its exact location with precision.

During the blackout test: 

  • An initial faint glow, indicating a corona discharge, was observed at 3.53 kV by one participant.
  • A unanimous observation of the glow was made at 3.61 kV.
  • The glow ceased to be visible at 3.3 kV.


Using the SBUV camera:

  • The camera detected the initial discharge glow even earlier, at 3.2 kV.
  • A distinct point source of the discharge was clearly visible at 3.5 kV.
  • The corona discharge became undetectable at 3.1 kV.


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.


Comparative Insights: Blackout Test vs. SBUV Camera

Blackout Test:

  • While being economically feasible, the blackout test is primarily recognized for its minimal costs associated with its implementation.
  • Operational hurdles become evident when one considers the interruption of activities and the lengthy preparatory time (at least 20 minutes) inherent to the method.
  • The test’s subjective nature introduces potential inconsistencies in results, where two observers might have varied interpretations.
  • Post-test adjustments mandate a reiteration of the entire procedure, adding to its cumbersome nature.
  • Its major limitation, however, is the challenge in identifying PD sources accurately due to the complete darkness, restricting its application.


SBUV Camera:

  • Efficiency and ease of use stand out for the SBUV camera. It swiftly sidesteps the need for prolonged setups, ensuring immediate deployment.
  • The camera’s ability to function efficiently in daylight underscores its versatility.
  • Safety concerns, often a point of contention with the blackout method, are significantly allayed with the camera’s usage, avoiding the pitfalls of navigating in blackout conditions.
  • In terms of detection, the SBUV camera offers remarkable precision, adeptly identifying and pinpointing PD occurrences.
  • Offers comprehensive recording features for post-test examination.


Concluding Remarks:

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.

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