Defected connections make up the majority of electrical related issues identified with thermography.
In a distribution panel each connection and fuse has a very small resistance. When current passes through a circuit it’s components heat up. As a connection deteriorates the resistance increases with a corresponding increase in temperature. When the temperature rises above a pre-determined value, the component is deemed as defective.
It is important to recognize the thermal gradients associated with defected connections on electrical components.
An increase in electrical resistance on a connection will cause localized heating. Heat is conducted away from the local resistance, thus creating a thermal gradient.
Example below – A contactor and overload relay unit. Defected connections identified on contactor on phase2 & 3. Excessive overheating is identified between the contactor and the overload relay unit. This indicates that the contacts at this point are defected. In this arrangement the links are part of the overload assembly. If damaged the overload unit should be replaced.
Contactor defected phase 2 & 3 connections. Overload relay defected link to contactor (ROI’s removed)
When a connection is identified as defected it does not always mean that it is loose.
It can be oxidized, corroded, or have dirty contact surfaces. There may be a problem with the cross threading or the wrong bolt or screw could be in place. The connection can be wrongly sized or the conductor strands could be broken away from the fitting.
Often, applying a specific torque (or re-tightening) will not solve the problem.
Where defected connections are identified they should be dismantled and investigated. Contact surfaces should be cleaned and remade, applying the correct pressure to restore full electrical contact.
Excessive overheating (as in our example) at either terminal connection or contacts causes cable insulation damage and pitting of the contacts, therefore accelerating their temperature rise. Wires and components should be replaced if subjected to excessive overheating (as in the example image above).
Sometimes with electricity we get inducted heat (induction).
Induction can take place on metalwork exposed to changing magnetic fields, for example generators or cable entry plates. It is a result of the location of the metal and its proximity to electricity.
It is not unusual to find unwanted inducted heat on metalwork located near electricity or electrical components, particularly on cable entry plates in panels where the individual conductors are brought through single entry holes.
For the purposes of this article, we wish to discuss induction in cable entry plates.
The phenomenon only occurs on ferrous (ferromagnetic) metals such as mild steel. As wire passes through a magnetic field a current is produced. If the cycle is reversed and we leave the wire stationary, but move the magnetic field the same thing will happen. In the case of AC electricity the magnetic field expands and collapses at a rate of 50/60Hz, so there is potential for induction to take place.
Where heat caused by conduction is detected it is important to asses if it needs to be repaired or not.
Does it present a burn risk or act as an ignition source, it may not be dangerous.
Is the temperature sufficient to damage the metallurgical properties. Often the temperatures can be low enough not to cause damage to the metal.
Is there potential for secondary damage to other materials such as electrical cables.
Once the above is considered, a decision must then be made whether to monitor the problem, or attempt to eliminate it.
If attempting to eliminate, a couple of things to consider:
Firstly (and often not so practical) is to break the flow path, if possible. Good practice on cable entry panels is to bring all associated conductors through the same hole. The magnetic fields will then cancel each other out.
Secondly, the most common method for eliminating induction is to replace the affected metalwork with a non ferrous material. For example plastics, aluminium or stainless steel. The equipment manufacturer should be consulted to ensure material compatibility and to confirm material certification is not affected.
In electricity, the phenomenon of induction is exploited, particularly with transformers. We use mutual induction to transform electricity from one voltage to another. It is not uncommon to find unwanted heat on metalwork exposed to changing magnetic fields. It is important to identify these areas, highlight and assess them correctly considering all of the above.
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A thermal camera (microbolometer) detects infrared energy and converts it into an electronic signal, which is then processed to produce a thermal image, allowing us to perform temperature calculations.
Thermal cameras do not detect colour because the wavelength that they operate is beyond that of visible light. Instead, they create ‘false colour’ representations, in the form of images that can be interpreted. These Images are presented visually using colour palettes, to represent variations in temperature.
When conducting a thermal inspection or generating a report, there are many colour palettes that can be used to present your images.
The palette you choose is largely a matter of personal preference. Clearly, some palettes are better suited to particular applications. More often than not, a thermographer will have one or two good palettes of choice that they tend to stick to.
Linear Ironbow colour palette
High contrast colour palette
During an inspection my preference is to use a high contrast palette, to quickly observe small temperature variations. I then analyse my images in software and for reporting output i choose a palette that best presents my findings in a way i believe my client will understand.
A report can lose impact when the end user has to try and decipher which colour or shade corresponds to which temperature.
A very effective palette for presenting anomalies is the isotherm (or “Alarm”) palette, found on most modern cameras and software. The Isotherm can be used to highlight temperatures above, below or at an interval for any specific temperature value you input.
This is great for immediately drawing attention to a specific region in an image, and when presenting to the untrained eye, sometimes simplicity is key.
Isotherm “Above” and “interval” example
Isotherm “above” example image
There is no right and wrong to which palette we use, providing we highlight our faults in the most effective way possible.
Thermal Imaging cameras provide us with an image of temperature distribution on a surface or object. This is hugely useful when installing or maintaining heating systems, from a commercial to a domestic level.
You can pinpoint any irregularities in temperature distribution very quickly. Underfloor pipes or pipes behind walls can be located and leakages identified. Heating system performance can be assessed and radiator inefficiencies can be identified, among other things.
Amazingly, quite a lot of information can be gathered from the thermal condition of a heating system.
Below are some examples (Images from Intec Analysis Ltd. FLIR T450sc)
Radiator with trapped air.
Because air bubbles in the gas central heating system rise, you’ll find air collects at the top of radiators and steadily gathers, making your home colder as the problem worsens. So if a radiator isn’t heating up, or is cool at the top and hot at the bottom, you’ll need to learn how to bleed it.
Radiator with sludge build up.
Sludge is essentially dirty water. Particles of dirt from the water in the system combine with rust (iron oxide) from the inside of radiators, pipes and soldered joints. The older the system is, the more likely it is to have some heating sludge build up. Dirt and rust combine to make a gooey liquid. As this passes through the central heating components it deposits some of the particles. It can block pipes and radiators to a point where the heat is patchy on radiators, radiators don’t work properly or get to temperature, or they don’t heat up at all. It can physically block important components such as the boilers heat exchanger which is incredibly expensive to fix.
Thermal Imaging inspections are an important diagnostic tool to prevent leaks from heating systems becoming serious enough to cause significant damage to a property.
Below: A leak identified from a residential home (Images from Intec Analysis Ltd. FLIR T450sc).
This was identified in a residential living room ceiling. The yellow square from the thermal image represents the temperature profile from a water heater located in the cupboard upstairs. The dark area on the thermal image was wet. This was caused by condensation dripping from adjacent pipework on the water heater. Over time it had soaked part of the upstairs cupboard floor and had made its way through the living room ceiling.
Identified with a thermal camera and confirmed with a moisture meter. Note that no visible damage can be seen from the digital image. This was caught just in time and costly repair work to the roof was avoided.
For more information on home thermography inspection including related blog posts please click here.
Thermal imaging cameras translate thermal energy (heat) into visible light to allow us to analyse an object or scene.
They provide us with an image of temperature distribution on a surface or object. They can be used for immediate diagnosis or processed through specialised software for further evaluation, accuracy and report output.
Cameras and Software are loaded with many colour palettes that can be utilised, and the palette you use is generally a matter of personal choice.
Beyond impressing your customer with great images the main objective is to deliver useful data, accurately and clearly.
Below we have a main power switch in a compressor panel. There is a defective connection on ph2 between the busbar and the terminal.
Image 1, a typical thermogram that highlights the anomaly very clearly. In many circumstances, this would be the image i would use for my report.
004 Intec Analysis – Main power switch busbar connection.
Image 2, the same image with the Active ROI scaling mode applied to the anomaly area. This allows you to assess the values within the selected ROI only. Temperature data below 52 C is blacked out of the image. The thermal gradient is presented very clearly.
005 Image 2 – Active ROI (region of interest)
Both images are very relevant for different reasons. As explained the priority is to deliver the data clearly and precisely, however sometimes it’s good to experiment and in some applications we may need to isolate all other temperatures in order to monitor heat distribution.
Overheating can damage electrical circuit components and can cause fire, explosion and injury. The potential catastrophic consequences of electrical system failure and hazards must be avoided at all costs.
Predictive maintenance (PdM) inspections on electrical systems allow companies to detect and correct problems early. This helps to avoid equipment shut down, loss of production and safety incidents.
It is important that the person conducting the inspection is not only adequately certified, but that they also use the correct thermal camera for the task in order to achieve reliable results.
Two key features of a thermal camera that should be understood for optimal results from an electrical predictive maintenance inspection.
Thermal resolution is important in thermography. Every single pixel is a measuring point, therefore the higher the resolution, the more measurement points you have and the more accurately you will measure. When you measure more accurately, you detect anomalies earlier, avoiding unnecessary damage for your customer.
When you look at a normal photograph on a digital screen, you’re really observing thousands of individual little points of colour. In the same way, radiometric thermal imaging cameras capture temperature data for each of the thousands of points in what we call a thermogram or thermal image.
The other feature that is equally important is thermal sensitivity (NETD, or Noise Equivalent Temperature Difference).
This is expressed the ability of an infrared camera to display a very good image even if the thermal contrast in a scene is low. A camera with good thermal sensitivity can distinguish between objects that have very little temperature difference between them.
006 Defected connections.
Both features described above are critical for a successful inspection yet are often overlooked. For lots of applications, lower budget thermal cameras are sufficient, electrical predictive monitoring is not one of them.
The goal after all, is to avoid equipment break down, loss of production and most importantly safety incidents.