Network Inspection: Heating up network inspections

An energy supplier’s most valuable asset is its network, so it is essential that this is properly maintained. The following case study shows E.ON Bayern successfully employing thermal imaging cameras to inspect and maintain its transmission network in Bavaria, Germany.

The network is clearly an electricity supplier’s most valuable asset, and therefore it is vital that this asset is properly maintained. This is not only to prevent blackouts to its private and corporate customers, but also to ensure an energy supplier maintains its long term success in the power market. No where is this more true than in the European Union market, as it continues to undergo deregulation and liberalization of its power supply.

E.ON AG is recognized as one of the world’s largest private-sector energy services companies, and holds strong positions in central and northern Europe, and the Midwest region of the United States E.ON Bayern, which is headquartered in Regensburg, Germany, is part of E.ON Energie AG, a major power supplier in central Europe, and is said to invest some €200 million ($273 million) per year in its network.

An E.ON Bayern thermographer in action
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Thermography is not a new issue at E.ON Bayern. Some 15 years ago when infrared cameras became smaller and affordable, the local Isar-Amperwerke supplier started to use the thermal cameras for inspection purposes. However, in that time the feasibility of thermography has been fully investigated by E.ON Bayern, particuarly in the wake of deregulation and the subsequent restructuring at the companies, which eventually merged into E.ON Energie. The conclusion reached was a positive one and thermography is now recognized as a vital non-contact inspection method for power networks. E.ON Bayern’s thermographers are now integrated into the the company’s Messtechnik – measurement engineering – department.

Network inspection

The task of an thermographer task at E.ON Bayern sounds easy – inspection of infrastructure that generates, transmits and distributes electrical power on a middle and low voltage level. The facts and figures, however, paint a very different picture. E.ON Bayern’s power network covers a 50 000 km2 area, which represents three-quarters of Bavaria, Germany’s largest federal state. It involves a 175 000-km long low and middle voltage network, stretching from the outskirts of Frankfurt to the Austrian Alps, and a total of 43 000 objects – transformers, substations, switchgear, terminal blocks, distributors, have to be inspected at a rate of a couple of thousand per year. the question that springs to mind is: How do they cope with such figures?

The answer is a team of eight thermographers, manned with ThermaCAM P65 cameras, inspect all installations everywhere, including switchgear in remote Alpine areas. These thermographers are specialists in using the infrared camera outdoors. They are acquainted with typical pitfalls such as the distorting effects of reflection, wind speed, and the effect of weather conditions on the measurements. Employing the thermal imaging camera anywhere requires skill, i.e. it is not a tool that can just be picked up and used straight away without training. If we look at what the camera sees – infrared radiation emitted by an object – it is important to understand how this radiation leaves the surface of the material, what happens to it as it travels through the atmosphere and what other factors are present that can interfere with it.

Initially, the surface of the object under inspection needs to be taken into consideration – is shiny, dull or somewhere in between? The value this is given is called emissivity and has a value of 0 for a perfect reflective surface or a value of 1 for what is a perfect emitter. These values need to be entered into the camera to ensure the correct temperature measurement. Regarding emissivity levels, E.ON Bayern’s thermographers use the standard settings as provided in the camera’s menu, while adapting them for some specific measurements.

The immediate area around the target is extremely important when taking a measurement. Reflected radiation from surrounding objects can bounce off the target object and be picked up by the camera, and therefore interfere with the final reading. The surrounding atmospheric conditions such as humidity and wind speed can also play havoc with readings. In the latter conditions, the wind acts to cool the cameras’ target object. Thus if you are cataloguing faults by severity then not taking the wind into account can seriously affect the results.

Inspection cycles

The inspection cycles at E.ON Bayern are adapted to the role, type and location of the switchgear. There are inspection cycles carried out every five, nine, and 12 years. However, installations near busy traffic intersections or dusty industrial environments, which can be affected by pollution such as salt, dust, smoke or soot, are inspected at least once a year, generally in the springtime.

In addition, the thermography team keeps a 24/7 stand-by service, which essentially provides documentation prior to or after reparation works at transformers. “We can be called up at anytime for an urgent inspection by an inspector or a technician, who does not like the sound of the transformer in his substation,” says Helmut Holzapfel, a thermographer at E.ON Bayern.

Result management

The inspection reports are filed into Flir System’s Reporter software. The data are fed into a predictive maintenance module of the German software giant SAP, while the images are kept separately in a database based on the Reporter software.

Examples of thermal images (A = repair required within next few months; B & C – requires urgent repair and D – no urgent repair required)
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To organize its maintenance priorities, E.ON Bayern has defined three levels of urgency to maintain its low and middle voltage installations:

  1. L1 stipulates a repair at the next inspection;
  2. L2 requires a reparation within 6 months;
  3. L3 level urges repair within one working week.

The thermal cameras used by E.ON Bayern’s thermographers contribute to managing the workload: “We use all major features of the ThermaCAM P65 intensively”, says Holzapfel. “Its visual camera and detachable LCD screen are a big asset and absolutely indispensable. And, there is another important rule to carrying out our inspections: care comes before speed – as we have large inspection cycles, we inspect our objects very carefully”, he adds.

From a collaborative, assisting position within the power supply network maintenance, thermal cameras at E.ON Bayern have grown into a strategically important inspection and reporting tool. Drawing on a consistent long term measurement policy and the expertise of the camera operators, thermography has established itself as a technique able to support the change process from a monopolizing power supplier to an energy provider caring about its main assets.

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