The use of infrared ther mography has become a well-established and proven method for inspect ing live electrical equipment on mine sites and in plants.
To carry out tests, a ther mographer usually works with live energised equipment and requires a clear line of sight to the target.
However, there are still a number of dangers still preva lent when inspecting these wires with IR equipment, despite the relative safety of the monitoring equipment, shorting faults in particular.
A particularly hazardous type of shorting fault – an arc fault – occurs when the insu lation or air separation between high voltage conductors is compromised while being inspected.
When an arc-fault is trig gered, a plasma arc – the arc flash – forms between the shorted components.
Once established, a plasma arc has a virtually unlimited current-carrying and damage capacity.
The result is often a release of explosive energy which can create a number of hazards such as a thermoacoustic (dyna mic) pressure wave, a high intensity flash and in worst case scenarios – a superheated ball of gas.
An arc flash can result in considerable damage to equip ment and serious injuries to nearby personnel, especially in a mine site.
Thermographers must be especially aware of the hazards with arc flashes, the current legislation and safety issues, and the techniques and equip ment best suited to minimis ing risks when working in these dangerous environments.
The goal of any electrical thermographer is to prevent unplanned shutdowns in a manner that is reliable, repeat able and above all, safe.
Since thermographers work with the target equipment online and on load, which is coupled with the fact that IR cameras cannot “see” through panel covers, thermographers face severe safety hazards when attempting to scan elec trical distribution equipment.
Taking any measurements with a cover removed is not a safe option.
Leaving the cover closed increases safety and reduces the background reflection quotient and reduces the inter ference, making readings more repeatable.
The ideal and safest solu tion is the provision of a perma nent “access point” in the equipment housing.
For infrared thermogra phy, there are three types of access points for preventative maintenance, an infrared port, an infrared pane or the construction of an infrared window.
An IR port is simply a hole or series of holes, whereas an IR pane is a thin polymer optic.
However the problem arises that both limit physi cal access to live equipment.
Added to this is that in the event of an arc fault, neither option provides an effective protective barrier between the thermographer nor the exposed conductor and any arc flash source.
The safest option is an infrared window which pro vides a solid barrier between the thermographer and the live conductors.
Typically, infrared windows are manufactured from a crystal optic material that allows infrared and visual inspection via the same product.
This material choice, if designed and implemented correctly, can withstand an electric arc and provide a measure of protection to the thermographer.
It is important that inspec tion equipment is constructed from suitable arc-resistant materials because optic mate rial that may melt during an arc flash and cause contact burns.
Products such as Fluke IR windows can limit the expo sure of a thermographer to energised equipment, reduce the hazards of both electro cution and arc flash and sig nificantly reduce the need for bulky personal protective equipment.