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Sensors and Technology

In a recent business as usual investment National Grid have equipped all five of our helicopters with state-of-the-art cameras and a laser measurement systems known as LiDAR (laser detection and ranging) to further its inspection capabilities in order assist National Grid in providing its world-class customer service by ensuring the lights are kept on.

This investment has produced an entirely unique capability by building on what was an already specialist platform. National Grid’s aircraft and crews are now not only able to provide the existing well proven visual inspection but also with the introduction of a third crew member operating as a mission system specialist they can now provide a non-visual inspection and capture LiDAR data all on one flight and on any voltage. The sensors are now used widely for both proactive and reactive patrols.

The LiDAR data is used primarily for vegetation management and National Grid have devised an exclusive way of utilising this data to manage the trees and vegetation around its network. Partnering with Fugro, we have replaced the previously used vegetation foot patrol with the existing helicopter inspections using both the observer and new technology to identify existing vegetation infringements and those that will become an issue in the future. This way we can target its rectification in areas that most require attention developing efficiency for both the company and its incumbent vegetation contractors. Using both spreadsheet based data and 3D modelling National Grid engineering and arborist staff can now visualise both the network and vegetation from the office with no requirement to go to site.

Camera Sensors

Trakka SWE 400 Quad-Camera System

All of the camera sensors are found within the 4-axis gyro-stabilised gimbal which is composed of aluminium and composite to ensure the lightest weight possible. The stabilisation system uses fibre optic gyroscopes and an external mechanical isolation unit that offers superior image stability and compensation for aircraft movement for the detection of the smallest faults. 

The high-definition infrared camera provides accurate non-contact temperature measurements. This camera can easily identify problems where the defect is apparent as a change in temperature. Internal defects are mainly exhibited as hot spots and thermal gradients that will not be revealed by visual or UV inspection. 
The HD Colour TV Camera provides exceptional colour images in full high-definition detail. 

The Corona detection camera is capable of detecting and producing video images of the energy generated by the corona phenomena (electrical loss or partial discharge). The UV camera consists of two imaging channels, a UV sensitive channel to image the corona discharge and a visible channel onto which the discharge is overlaid on the image. The camera is fully solar-blind and can visualize corona in full daytime without being affected by the sun´s radiation. 

In addition the high-resolution stills camera is equipped with a 36.3-megapixel detector that captures high-resolution photos used to provide National Grid network services staff with visual clarity of the defects to allow an engineering decision to be made. 

The IMU, INS AND laser range finder within the gimbal provides accurate geo/location of assets.

LiDAR Systems

The LiDAR system used is cutting edge technology provided by Riegl who are world renowned for the provision of laser measurement devices. It is lightweight and ideally suited for airborne surveying from our helicopters. The scanner provides survey-grade accuracy / precision with a scan speed of up to 200 scans / second providing a maximum effective measurement rate of up to 750,000 measurements per second. Therefore on a typical 2.0 hour sortie the system will have captured 5.4 billion measurements. The system can be flown up to a maximum operating altitude of 1,740ft (530m) above ground level and provides a field of view of up to 330° for practically unrestricted data acquisition.

 

In essence the LiDAR data is used to measure distances and in our case this is being widely used to measure the distance of vegetation from National Grid’s assets and equipment. The data captured from the LiDAR system (the point cloud) is processed, classified and turned into a 3-dimensional model of the network and associated vegetation. Using some clever algorithms the distance is measured from the closest tree branch to the conductor (the wires) in order to identify whether or not the vegetation requires cutting which is an important aspect of maintaining a safe and reliable network.

 

One of the primary differences is the depth of point cloud that we generate. As the aircraft is already low and relatively slow the LiDAR system is able to capture in the region of 125 points per metre which is significantly different from the typical LiDAR capture of between 25 and 50 points per metre. This depth in the point cloud is being used to research aspects such as tree species identification based on the reflectance of the laser and the tree crown shape. 

 

Whilst the focus is currently on vegetation management, which is a core application of LiDAR data, it has other uses which are also being utilised; these include but are not limited to line refurbishment or new builds, topographical surveys and engineering projects.