Calibration of UV-sensitive camera for corona detection
Date
2007-03
Authors
Du Toit, Nicolaas Serdyn
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Electrical energy is continuously transported across the world by high voltage transmission lines. These
transmission lines are however subject to losses beside the inherent resistive and dielectric losses. This
additional loss phenomenon is described as corona. The CSIR has developed an optical system to detect
the radiation caused by the corona so that preventive measures can be taken to reduce these losses.
The corona mechanism and how it results in measurable radiation is explored and the structure of the optical
system is analyzed. The optical emissions detected by the present optical system offer no indication of the
severity of the corona discharge. This issue is addressed in this thesis as correlations are sought between
the illuminated pixels displayed on the camera’s display and physical quantities. A blackbody is employed
to find a correlation between these illuminated pixels and radiation. Deviations from the correlation drawn
is explored regarding the saturation mechanisms of the optical system and the distance from the blackbody.
A corona cage is next employed to find a correlation between the illuminated pixels and electrical corona
loss, a quantity indicative of the severity of corona losses on a transmission line. Further tests are also
performed at a reduced gain as it was discovered that the optical system’s response is more linear at reduced
gain than at full gain. It is also indicated that this usage of reduced gain does not have a detrimental effect on
the sensitivity of the optical system. The corona cage measurement employs a small spheric source which
is taken as a base measurement against which all other measurements can be compared. The deviation
of this base analogy is explored against deviations in the corona discharge geometry used, the prevalent
weather condition, and the saturation of the optical system itself.
Both the corona cage and blackbodies used are quite bulky pieces of laboratory equipment. The use of a
smaller, more portable calibration source is therefore also explored. A literature study is made of lasers,
lamp sources, and laser diodes that can be employed as a more portable calibration source. The final choice
of calibration source is shown to be a lamp source. Tungsten calibration lamps are explored in depth and a
circuit is designed to keep the radiation from a lamp source constant in order to improve on its ability as a
calibration source.
Description
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007.
Keywords
Corona (Electricity), Overhead electric lines, Dissertations -- Electrical engineering, Theses -- Electrical engineering