Corona Detection Goes 21st Century High TechMarch 27, 2017
Ofil has released their latest, top-of-the-line, handheld, high-definition (HD) corona detection equipment, the DayCor® LuminarHD. This high quality Solar-Blind UV camera uses proprietary UV sensors and optics which contribute to the camera’s high sensitivity to corona signal. LuminarHD allows for detailed inspection of electrical settings from remarkable distances, providing crystal clear, sharp, high resolution imaging of the inspected scene.
Corona partial discharge created in high voltage transmission, distribution and industrial settings can lead to power losses and reduced reliability. Problems associated with corona are: components degradation, RFI interference, noise and other compromising effects to equipment and surroundings. Corona cameras serve to see the signals and through them to fix the problems.
Ofil’s DayCor LuminarHD presents a combined UV-visible image, accurately displaying the exact location of the targeted corona. This provides a real-time reference as well as a recordable visual log throughout the corona inspection session.
The LuminarHD features ergonomic design including an easy grip, large lighted control buttons, a pictorial menu, large bright and adjustable display and a powerful zoom. These features work alongside a heavy duty rechargeable battery to allow for extended use in the field. A full suite of sensors and detectors including GPS, voice annotations, temperature and humidity create a wealth of valuable data stored on-board to be later downloaded via dedicated database software, coronaWise.
When searching for corona, the OFIL LuminarHD provides a comfortable handheld detection system that can identify, collect and store corona image and location data. It accurately pinpoints sources of corona partial discharge, micro-arcing and arcing that lead to audio noise, radio/TV interference and electrical mechanical failures. The HD optics, sensitive UV and visible light camera sensors and HD video recording enables fine differentiation of inspected details for capture and later analysis. A LuminarHD product data sheet is accessible here.
What is corona and why is it bad?
Technically speaking, corona is a luminous partial discharge from conductors and insulators due to ionization of the surrounding air. High local electric, which exceeds a critical value, ionizes the air and cause chemical reactions of air molecules during which excited nitrogen molecules in the air emit UV radiation. As long as the electric field strength exceeds tolerable levels, ionization and corona discharge will occur. The short video to below shows corona on a high voltage transmission line. The electromagnetic discharge is actually invisible to the eye; the video demonstrates the outcome of a corona camera where the UV image overlaps the visible.
Partial discharge can damage the integrity of polymer insulators. It produces ozone, nitric oxides (which yields nitric acid under conditions of high humidity) and emits ultraviolet radiation, causing the decomposition and erosion of the insulators. Damage to mechanical and electrical properties will shorten insulator lifespan and risk safety. Radio interference from corona (RI/ RFI) disrupts AM transmissions and smart grid communications, and audio noise can disturb residents living in the area that these corona discharges are occurring.
There are practical methods to mitigate corona such as using proven high voltage design practices, maximizing distances between conductors, using large radius conductors and avoiding the use of components with sharp corners and edges. In the accompanying image, corona rings are being used to distribute electromagnetic field gradient along insulators to protect corona-prone material and connections.
How to detect corona?
When corona occurs, our senses perceive some of the created by-products. Our ears can hear the hissing and cracking, at our eyes detect a faint purple glow of corona, our noses detect the distinct smell of ozone. However, these senses are not fine-tuned enough to locate the discharge source, especially when keeping a distance from the high power electric equipment. Partial discharge emits noise, ultraviolet and high frequency radio waves. These energies can be detected and pinpointed using instruments designed for the particular energy emission. UV systems perceive corona UV and convert it into visible light to allow pinpointed visual identification. Ultrasound systems receive ultrasound waves and provide directional indication. Ultrasound location is less accurate and when detecting from a distance, special microphones are needed. IR is another visual location technique that lacks the ability to detect corona UV due to the fact that corona produces very little—if any—heat.
Conventional UV sensors and filters are “blinded” by normal daylight. Using solar blind filters, detection of weak UV signals is enabled in full daylight. Pinpoint location makes UV visualization the most effective way to inspect for corona discharge.
Shrinking remote aerial corona inspections
An irony of electric power is that electricity is often produced great distances from where it is used. Transmission lines span long distances and are often in remote locations. An important task of electrical utilities is to maintain transmission line reliability and reduce energy and revenue losses. Hard to reach transmission line inspection can present problems. Aerial inspection is an efficient way to monitor the grid when considering labor cost, time consumption, distances, topographic barriers and safety. Originally, handheld units were carried to inspection locations by helicopter. Later, a gyro-stabilized gimbaled system with a UV camera, IR camera and an HD TV camera were mounted under the helicopter.
While helicopter inspection works for long spans of remote lines, costs of using a helicopter to inspect nearby, out-of-reach equipment is comparatively high. Advancement of unmanned aerial vehicle (UAV) technology and the miniaturization of cameras and controls allow line and equipment inspection in hard and perhaps dangerous to access places not a great distance away. Ofil has introduced compact and lightweight corona imagers for UAV aerial inspection systems. This miniaturized inspection system transmits the inspected data to a base unit. Additionally, Ofil also offers a complete UAV platform, called aviROM, that flies autonomously along predetermined routes and uses a special "Follow Mode" feature to keep the installed cameras on target. The system is quickly assembled and collapsed and fits in the trunk of a car. Specifications such as 30 minute flight time, 1.5 km flight radius and a 150 m altitude ensure that it will be embraced by inspection teams.
Ofil, your source for corona detection equipment
UV inspection is used for locating faulty equipment and for predictive maintenance of high voltage apparatuses. The value proposition of UV inspection is its ability to pinpoint corona. Ofil developed Solar Blind visible bi-spectral imaging to overcome daylight confounding issues. They offer a complete range of devices for finding corona. In addition to LuminarHD and UAV systems, they also provide additional UV inspection solutions. Superb OD/XD is a very robust, sensitive, handheld, bi-spectral, visible-UVc detection camera with high pinpointing resolution. UVollé-X corona cameras are light in weight, have a slim silhouette and extended LCD display, and are designed to be comfortably held in the hand. Scalar is a high value, low cost, affordable corona detection camera for indoor inspection of motors and switches. Ranger is a tilt-and-pan vehicle-mounted corona inspection system for driven applications and Rail provides fully automatic stand-alone corona inspection system dedicated to high speed railway use.
Ofil’s systems are renowned for having the highest sensitivity to UV discharge and are used in the power transmission industry globally. DayCor® corona cameras are used by electrical utilities for inspection of high and medium overhead transmission lines, distribution, substations, lab and industrial locations. Ofil research and development investments enable product line expansion, new accessories and software upgrades. CITI, the Corona Inspection Training Institute, sponsored by Ofil, offers training worldwide in UV inspection techniques.
Ofil has a very informative website including thorough technical articles located here.