Resource Details

HV assets require periodic inspection and condition monitoring to prevent unplanned catastrophic failures. Defects such as cracked or contaminated insulators, developing partial discharge due to sharp voltage gradients, and overheating due to overloading or damage are all precursors to a catastrophic failure. If these defects are caught early, unplanned outages and costly repairs can be avoided.

HV assets can include any of the following:

• Overhead power lines
• High voltage cables
• Electrical Machines
• Electrical Generators
• Switchgear (isolators, air break switches, circuit breakers, etc)

Detection of Defects Before Failure

In order to detect defects early, a number of sensors are available. The following sensors can be used for various applications:

• Standard Colour Camera: When combined with a telephoto lens, can be used to photograph defects and obtain evidence needed for planning maintenance and condition monitoring.
• Radiometric Thermal Camera: To detect overheating issues and temperature differentials down to 0.05 Degrees Celsius.
• Solar Blind UV Camera (or Corona Camera): Detects partial and full discharges on high voltage assets.
• Hyperspectral Camera: Typically used for R&D applications to select an appropriate Multispectral camera for a particular task. Typically classification of materials such as identifying different types of rock, wood, and live vs dead vegetation. A Hyperspectral camera analyses a huge number of wavelengths (>100) at one time whereas a Multispectral camera only analyses a few discrete wavelengths that are necessary for classification.
• Multispectral Camera: There are a wide range of applications for multispectral cameras including classification of materials such as identifying different types of rock, wood, and live vs dead vegetation. A Hyperspectral camera analyses a huge number of wavelengths (>100) at one time whereas a Multispectral camera only analyses a few discrete wavelengths that are necessary for classification.

Figure 1. The widely used "Bath Tub" curve (see here)

Thermographic Inspections

Electrical insulation systems are extremely vulnerable to heat if the rated operating temperature is exceeded. The industry standard rule of thumb is that for every 10 degrees over the rated temperature, the life of the insulation halves. It is critical that once an electrical installation is commissioned that it be monitored regularly for any developing issues.

Figure 2.Thermographic Inspection

Thermal camera technology is changing rapidly with ever growing resolutions, greater thermal sensitivity, better optics, and lower prices have seen thermal cameras even reach the consumer market. With Thermal camera technology readily available, detecting developing issues that generate excess heat can be easily identified.

"for every 10 degrees over the rated temperature, the life of electrical insulation halves"

There are many failure mechanisms that produce heat. A few failure mechanisms that may present as excess heat are:

• Overloading of electrical devices, this presents in excessive copper losses in the form of heat. This can present in one, two or all three phases in a 3 phase system.
• Overloaded/Damaged magnetic circuits, excessive eddy current losses can present if a magnetic circuit is overloaded or damaged.
• Damaged/overloaded Bearings, excessive wear in bearings result in increased friction and heating.
• Insufficient cooling, insufficient spacing between electrical conductors or a poorly designed cooling system can produce excessive heat.

Solar Blind UV (Corona) Camera Inspections

Solar Blind UV cameras can pinpoint developing problems due ingress of contamination, insufficient clearances, and poorly designed insulation systems. Plant that is spread over a large area will benefit greatly from a highly mobile inspection system such as transmission lines where handheld inspection is impractical.

Partial/full discharges that are detected by a Corona camera are typically displayed as "blobs" with a size varying with the intensity of the detected emission. The sensitivity of the corona camera can be adjusted as needed to detect minor as well as larger problems.

Hyperspectral and Multispectral Cameras

Multispectral and Hyperspectral cameras are a relatively new technology with new applications constantly being discovered. Hyperspectral cameras are typically used in R&D applications where the specific relationships between frequency and classification are not yet known. Multispectral cameras, however, contain far fewer spectral bands and are typically used for a specific application (such as detection of live vegetation). Hyperspectral cameras can be used to classify different soils, rock formations, and classify live from dying vegetation.

Using NDVI (Normalized Difference Vegetation Index) a multispectral camera can differentiate live and healthy vegetation from dying vegetation even before the vegetation shows signs of discolouration to the naked eye. This detection technique exploits what is called the "chlorophyll knee" which is exhibited by healthy vegetation.

NDVI can be an extremely useful technique in planning tree trimming around HV assets such as overhead power lines. High risk trees can be prioritised if branches over power lines exhibit signs of dying as classified by the NDVI. NDVI is most useful when combined with 3D imagery from a UAV so that trimming intervals can be precisely calculated.

Many more applications are yet to be discovered. Hyperspectral cameras provide the tools necessary to discover these applications.

Early Detection Vehicle Mount System

Early detection is critical in preventing catastrophic failures. Using a radiometric thermal camera, solar blind UV camera and a visible camera can detect problem areas that are arising before they cause a failure.

IMC have developed a deployable vehicle based inspection system. By performing inspections from a vehicle, potential problem areas can be identified well before failures have developed.

Figure 3. IMCs deployable vehicle mount thermal inspection system

Using a non-contact FLIR long-wave infrared camera paired with a solar blind UV camera, problem equipment can be easily detected without the need for temperature measurement probes or complex site models.

IMCs system can be easily detached from the vehicle and deployed out in the field temporarily. The video feed can be viewed remotely from offices as needed.

Figure 4. Detachable remote thermal monitoring system

Designed for ease of use this system incorporates an wireless controller with inboard vehicle display. These features give this system extra flexibility and an ergonomic user interface.

Figure 5. Vehicle based thermal inspection system fully controllable from inside a vehicle

Locations of hotspots can be geo-tagged an viewed on Google maps. This allows for a containment teams to effectively plan coordinate  hazard mitigation. Having this system onsite enables early detection and prevention of line outages . It provides a means of detecting damaged experiment before they become problematic and cause downtime.

Figure 5. Images taken with the system can be geo-tagged and viewed on google maps