The image below shows some very typical electrical distribution equipment with a very common fault.
Components like this are found in EVERY factory or facility that produces electricity.
This type of problem has the potential to burn your factory or premises to the ground.
In this instance the issue is a connection defect. There is increased in resistance and localized heating at the connection with a corresponding thermal gradient.
There could be a number of reasons for the cause of failure (loose, oxidized, corroded or dirty contact surfaces are just a few examples).
There is tremendous value identifying electrical faults at an early stage, none more important that potentially saving your life.
Don’t cut corners!!
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Thermal Imaging inspection can reduce insurance premiums.
Many insurance companies now provide reduced insurance premiums to businesses who undertake thermal imaging inspections of their electrical equipment.
Businesses benefit, in many cases the survey effectively ‘pay for itself’ through the insurance reduction.
They also obtain a status report detailing all the pending electrical problems in their facility, allowing them to plan and schedule maintenance activities in advance. This helps keep their operations running smoothly, minimizes downtime and most importantly, keeps safety at a premium.
Thermography inspection is a critical part of any condition monitoring / predictive maintenance program. It provides a safe, clean and visual way of assessing the condition of live electrical equipment. It is the most effective method to identify high resistance joints, defected connections, overloaded circuits and other faults BEFORE they reach critical failure and become a fire and safety hazard.
Such problems are virtually impossible to identify by any other means.
A growing number of insurers are now making thermographic surveys compulsory with regard to fire prevention.
Below: Defected connection on a contactor.
To qualify for a reduction in your insurance premiums inspections must be completed by a Certified Level 2 infrared thermographer, as a minimum acceptable criteria.
Level 2 Inspectors are experienced within the application of electrical thermograpahy and troubleshooting. They are trained in infrared physics, heat science and infrared measurement equipment and its application. They are proficient in the areas of equipment selection, techniques, limitations, data analysis, corrective action and reporting.
Thermal Imaging is supplemental to and does not replace electrical inspection and testing. It should be considered as an essential tool to reduce the risk of catastrophic fire events, reduce downtime and increase safety.
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The following images are examples of defected (or poor) connections on electrical components, in various color palettes for illustration purposes. 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 1 – Contactor and Overload relay assembly with a couple of connection issues. High contrast color palette, pretty standard.
Contactor and overload relay unit defected connections.
Example 2 – Isolator switch, L1 busbar connection to control circuit live connection is defected. Linear Fusion palette, smooth color distribution.
Main isolator with a defected connection on L1 to control circuit live.
Example 3 – Main Isolator connection defect on phase 2. An active ROI is applied to visualize only the heat distribution from the connection that is defected. When it comes to analyzing the images in software it is possible to pull some fantastic data from thermal images.
005 Image 2 – Active ROI (region of interest)
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).
Thanks for reading.
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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.
Thanks for reading.
For more information about our electrical inspection service please click here.
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.