Feature Inspection windows
Opening the window on enclosure and panel building
Incorporating electrical maintenance safety devices such as polymer windows into enclosures and panels at the point of manufacture mean inspection tasks later on can be carried out safely. Martin Robinson, CEO of IRISS, comments
aximising profit is important to any business, but so too is the avoidance of loss. A production process may be optimally designed, but if it is frequently interrupted by the failure of the electrical systems that power and control it the result can be catastrophic. Operation costs increase, personnel safety is compromised and fire risk escalates. Manufacturers are therefore increasingly taking
the smart approach through predictive maintenance and condition monitoring. Technologies such as vibration analysis, infrared imaging and airborne ultra- sound are all playing their part in detecting problems before they become costly and dangerous failures. The insurance industry is also driving their use to minimise their exposure to risk.
Whilst this pro-active strategy is paying dividends,
there is no doubt that the most valuable quantitative data is only gathered when the electrical system is energised and under load. Live testing, however, is risky and costly. Indeed, some systems are considered to be too hazardous or unviable to maintain in this way. This means critical systems are often inspected less frequently – and sometimes not at all.
Meeting the safe design initiative
Studies show that traditional open-panel inspections are both time consuming and a poor use of high-value electricians and thermo- graphers. The total time it takes for a three man electrical RCM team to inspect just one electrical panel is typically around five hours when PPE suit-up and waiting time is factored in. New developments, however, are overcoming this problem.
Underpinned by organisations such as the IEEE and its ‘Safer by Design’ initiative, electrical maintenance safety devices are being incorporated into enclosures and panels at the point of manufacture. By allowing maintenance tasks to be completed whilst the
switchgear remains closed and in a safe and guarded condition, the inspector is never exposed to the dangers of arc flash or electrocution and the process can be completed in a fraction of the time by compari- son with open panel inspection.
Personnel safety is assured and the health of all electrically systems, including those that were formerly considered to be too dangerous for live inspection, can be frequently and cost-effectively monitored. Ports for ultrasound testing and external voltage detection are classified as electrical maintenance safety devices, as are voltage tap off connections. Another, of course, is the infrared window. Thermal imaging cameras can only measure what they can see in a direct line of sight and cannot operate through glass or plastic viewing windows that are commonly fitted into switchgear. To allow inspec- tions to be complete under load, purpose-designed infrared windows are therefore used which allow the camera to see the energised, loaded connection through special lens materials.
Crystal windows Traditionally, crystal windows were used for this purpose. While these are among the best broadband transmitters and the best
Enclosure & Panel Building Solutions WINTER/SPRING 2014
Colour coding allows thermographers easy identification of inspection zones. Standard colour is electric grey found in standard switchgear
choice for high temperature applications, mechanical stresses easily fracture most crystal optics or degrade the crystalline struc- ture, increasing refraction and decreasing transmittance. Moisture, humidity and UV
light will also cause deterioration, although this process can be slowed by the application of a coating.
Furthermore, the bigger the crystal, the more fragile it becomes unless its thickness is correspondingly increased. However, as thicker materials decrease transmittance and affect temperature readings the largest crystal optic available is typically 100mm in diameter. Is this a problem? The answer is yes if you want to check an electrical system with a single pass of a thermal imaging to min- imise inspection time. To inspect a bus bar, for example, would require multiple windows.
The benefits of polymers
These practical limitations and performance uncertainties have led to the growing use of transmissive polymers instead of crystals for lens materials. Being durable, stable and immune to the effect of moisture, the elements and a broad spectrum of acids and alkalis, these are well suited to harsh industrial environments. Polymers are also extremely resilient. Because they are malleable, they will absorb impact rather than shatter and, when reinforced with grills, the optic is capable of resisting a sustained load. A polymer optic can also maintain a consistent thickness regardless of window diameter because the cells of the reinforcing material remain a constant diameter. And this means consistent transmission rates. Initially only opaque polymers were available, but now transparent versions can be specified. These allow inspection in the ultraviolet, visual and short/medium/long wave infrared spectrums. The other big benefit of a polymer window is that it doesn’t have to be round – it can be any shape or size, and this offers enclosure and panel builders a tremendous advantage as it allows products to be custom designed for the task. So instead of multiple windows, a single unit can be installed to enhance the practicality of the inspection process and also the aesthetics of the panel. The window can be square, oblong or even rainbow shaped. Different housing materials, gaskets, covers and locking devices can be specified and the unit epoxy coated in any colour and, if required, supplied complete with the manufacturers logo.
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