Origo Corporation Corona Camera Product Inquiry 1 Introduction This Whitepaper describes Origo s patented corona camera R&D project. Currently, lab and daylight proof-of-concept tests have been conducted with good results. The project is now ready to move to the product stage. Origo always solicits potential user inputs prior to final design to ensure the final production product meets the needs of the utility industry. As this camera can be implemented in different forms, Origo is seeking inputs as to which type of implementation would be most useful to users. Corona Electrical corona is a partial discharge in the air surrounding an electrical conductor. It occurs when the electric field around the conductor exceeds a minimum critical value strong enough to ionize the air surrounding the conductor but not sufficient to ionize a flash-over. Corona is a problem because it can cause power loss, audible noise, radio interference, and corrosive effects on conductors and insulators through the formation of nitric acid. Corona Cameras Electrical corona emits spectral energy in the ultraviolet (UV) region above the normal range of human vision. However, it can be detected and viewed using corona cameras optimized for viewing UV. All modern corona cameras are designed for use during daylight by using a so called solar blind filter which removes normal sunlight but still passes some of the corona spectrum. A beam splitter inside the corona camera sends the faint solar blind filtered light to an image intensifier sensor and the sunlight illuminated scene light to a normal camera image sensor. Camera electronics then overlays the two images for viewing by the operator. In this way, the exact location of the corona discharge can be seen. Origo Proposed Corona Camera Daylight corona cameras have been continuously improved over the last decade and current cameras work very well. Their main downside is that they are very expensive ($40K+) and usually only affordable by the larger utilities. Users and distributors of these products have opined that a much larger number of corona cameras could be sold if their cost were around $15K or less. Accordingly, Origo has undertaken this corona camera R&D project in an attempt to achieve this goal. A lab proof-of-concept test, daylight substation tests, anticipated product specifications, and possible product implementations are illustrated below.
Origo Corporation Corona Camera Product Inquiry 2 Lab Proof of Concept Test 7500 volts, 1 gap, 22 foot range Minor corona (single spot found) while wet after rain. Corona disappeared when conductor dried. Camera position far across from substation.
Origo Corporation Corona Camera Product Inquiry 3 A standard commercial daylight corona camera verified corona on the 500KV insulator below. The camera indicated random corona over much of the insulator, but most was concentrated in the area of the wide gap when low gain was used. The photon count indicated this corona would be something the utility would normally fix. However, it has existed for a year and has not caused any issues. The frames below were collected using the Origo proof-of-concept camera at noon on a cloudy day. Unlike the previous lab and substation tests, this corona was not concentrated in a streamer. Therefore, corona extraction processing was used to image the corona. Sensitivity is adjusted via gain, threshold, and area selection. The brightness of the red squares indicates relative intensity above threshold. Large squares integrate corona over a larger area which increases sensitivity. The same frame below was processed using two different size squares. Note the sensitivity increase using the larger squares.
Origo Corporation Corona Camera Product Inquiry 4 A couple other frames are illustrated below. The left frame suggests this corona burst occurred via arcs along the insulator's left side and center. The right frame suggests this arc propagated from left to right across the insulator. Any size square can be processed. It is assumed the operator would select a large square to detect the presence of corona, and then drill down using smaller squares to indicate its actual location. If a strong streamer is present (as in the previous lab picture), it can be viewed directly using full resolution. This corona appears random over much of the insulator (not concentrated at a particular location). The ability to image individual corona bursts may provide valuable information about its cause and severity (sharp point, cleanliness, insulator failure, etc.).
Origo Corporation Corona Camera Product Inquiry 5 Theory of Operation All current daylight corona cameras are based on spectral discrimination between discharge corona and solar corona. That is, the solar blind filter simply removes all solar corona while passing a small amount of discharge corona to an image intensifier. A beam splitter prior to the filter sends the sunlight illuminated scene light to a normal camera image sensor where it is combined with the corona image. In contrast, the Origo corona camera is based on temporal discrimination instead of spectral discrimination. That is, discharge corona is only present during the high voltage period of the 60 Hz (or 50 Hz) power sine wave. Near the zero crossings, the voltage is too low to support corona so only the ambient sunlight image is present and not the corona image. By subtracting the ambient image during zero crossings from the corona plus ambient image during voltage peaks, the corona image can be viewed. A single optical path is used for both the corona and visible images which eliminates the cost and complexity of combining images for display. Additional details are available at http://www.origocorp.com/patents/us9291494.pdf. Corona Characteristics Since independent discharge corona bursts occur each power cycle, no two are exactly the same. Below are individual corona bursts across a well defined 1/2" needle point gap energized through 20 megohms with 7500 VAC 60 Hz. First 4 in still room (range 40 feet). Second 4 in breezy room (range 1 foot).
Origo Corporation Corona Camera Product Inquiry 6 On outside insulators in the breeze or wind, corona bursts can vary widely. If the corona is due to a sharp point or debris, at least one end of the corona discharge should originate at or near the same point. It is expected that an ability to image individual corona discharges will aid in determining the cause of the corona. If the corona bursts are completely random across an insulator, it may indicate a dirty or failing insulator. Implementation This proposed corona camera can be implemented in many different forms as discussed in the next section. However, for the lowest cost and greatest application diversity, Origo's initial Corona Inspector TM camera will be composed of a modified CMOS camera, selectable filters, optics, laptop PC, custom software, and display. This allows the user to optimized the system for their particular application. The picture on the right illustrates a typical machine vision USB camera that has been modified for UV sensitivity. The USB cable plugs into the laptop USB port. A wide variety of UV lenses and filters can be attached to the camera. In general, UV lenses are very expensive compared to visible camera lenses. A custom Windows program allows the user to select camera operating modes, select display settings, process the images, save images to files, etc. Either the laptop display or virtual image goggles can be used to point and view the corona. The picture on the right illustrates a low cost alternative to using UV lenses. The camera can be attached to a Newtonian telescope which can be either mounted on a tripod or on a Dobson mount (as shown). The complete assembly can be simply set on the hood or bed of a vehicle and pointed. A Dobson mount is widely used in astrometry and is very stable and easy to point.
Origo Corporation Corona Camera Product Inquiry 7 Alternate Implementations The core technology of this new corona camera can be implemented into almost any configuration required. Origo invites user comments as to what form would best serve their needs. For drone applications, the camera with UV lenses and an adequate communication link would allow the processing and display to be implemented at the drone control site. This would provide a small lightweight drone package. For normal linemen use, the camera could be packaged as a handheld unit. Listed below are some thoughts on potential implementations. Proposed Camera Specifications (non-uav versions) Approximately 3 to 6 inches in diameter by 6 to 12 inches long. Viewing on either smartphone, laptop, or goggles. All images can be recorded. Sensitivity constant with range but resolution decreases as image shrinks. Larger optics allows range to increase to miles. HD resolution. Zoom to pixel level. View insulator or conductor with or without corona. Mount on stabilized platform for mobile use (vehicle or helicopter). Absolute linearity of corona energy measurement (don't need photon counter). Daytime use. On the order of 1/3 the price of current units. Possible Implementations Portable UV camera for use by linemen to inspect for corona. A short range automated UV camera for substations to continuously inspect for corona. A long range automated UV camera to continuously inspect for corona. A small UAV mounted UV camera.
Origo Corporation Corona Camera Product Inquiry 8 Current Corona Camera User Comments Based on a small number of discussions with people knowledgeable with current corona cameras and their usage, Origo has been told the following: For transmission voltages greater then 69 KV, most corona observed is benign and that which is not usually causes a slow degradation process, taking years before failure. Corona is typically not a problem for voltages below 230 KV. Even then, it takes years to do any significant damage to insulators. One large utility claims they fly HV transmission lines once every 6 months to check for visual damage and do corona inspection once every 4 years. Based on the user comments above and other information, Origo is lead to conclude the following: At least one corona camera is required by utilities to quickly pinpoint an obvious problem such as RF interference complaints or audible corona (for both distribution and transmission voltages). They are also required for testing new construction to ensure it is corona free. There doesn t appear any need to perform routine surveys on distribution voltages. Automated cameras (short or long range) would be useful to search for intermittent corona that is causing RF interference complaints or audible corona. Handheld linemen and vehicle mounted cameras are the most useful implementations. Small lightweight UAV mounted cameras appear to be the most important implementation going forward, since inspections by drones are the latest trend for utilities, as drones become more affordable and capable. Marketing Survey Origo s conclusions above are based on a very small user input sample. There may be other useful applications we are not aware of. We would appreciate any suggestions or comments from potential users. Contact Please call or email any questions, interests, or comments you may have. Thanks. Greg Piesinger President Origo Corporation www.origocorp.com 480-473-1995 gpiesinger@origocorp.com