In order to avoid power supply outages, vegetation in the vicinity of overhead lines must be pruned at regular intervals. In many cases, the lines concerned cannot be isolated electrically. In the past, this work was performed by skilled personnel; owing to economic constraints, however, it is increasingly being subcontracted to companies employing lay people in the electrical field. The accident patterns indicate an alarming increase in the number of electrical accidents, particularly involving the use of elevating platforms. Many of these serious accidents resulted from violation of the safety clearance (of three metres in the case of voltages between 1 and 110 kV) to the live parts of the installation. However, estimation of the safety clearance itself is difficult for the individual involved. The objective of this project was the creation of an outdoor measurement system involving laser scanners, by which the clearances between overhead lines and vegetation or elevating platforms can be measured precisely in three dimensions.
A two-dimensional laser scanner was mounted on a turntable which can be rotated by a stepper motor. The laser scanner faced skywards and measured the hemisphere above the scanner in all three dimensions in sphere co-ordinates. The minimum distance from objects such as branches and leaves or overhead lines was measured for each angular segment in each spatial dimension in a radius of up to 20 metres. By transformation of the co-ordinates, the distance between the vegetation and the overhead line could be determined in each plane. The situation was presented in a three-dimensional image on an on-site PC such that the distances between vegetation and overhead lines could be determined.
The studies show that laser scanners can be used up to a distance of 25 m for the surveying of high-voltage lines in the vicinity of vegetation. Precise surveying on the PC is possible, provided the vegetation is not too dense. Where vegetation is dense, the shadow area must be estimated by means of the rotational symmetry of trees. With a little practice, this is possible on the PC by observation from different perspectives, without further technical aids. Besides surveying itself, the method also offers interesting perspectives for the control of elevating platforms in or near buildings. The reflectivity of the objects, which is generally high, enables them as a rule to be surveyed reliably in all spatial planes. Further work is however required in close co-operation with manufacturers of elevating platforms, in order for this information to be used to control the drive of an elevating platform.
electrical engineeringType of hazard:
Elektrische Gefährdungen, Gestaltung von Arbeit und TechnikCatchwords:
Arbeitsunfall, Gestaltung von Anlagen und Verfahren, MessverfahrenDescription, key words:
tree pruning beneath overhead lines, laser scanner, three-dimensional presentation, hazard assessment, transformation of co-ordinates