Infrared windows - an installer's guide
29 November 2011
Chapter six of ‘The Power of Knowing’ covers all the dos and don’ts of installing infrared windows. It starts with a pre-installation check list and takes you through target identification, emissivity standardisation, things to consider during the installation process, identification labelling and the importance of benchmark inspection to set the base line.
Proper installation of the infrared window is critical for the long-term use of the window and for the long-term performance of the panel and equipment enclosure. Although an infrared window is not as strong as the steel it replaces, installing an IR window is no different than many other modifications that are commonly performed on switchgear and other electrical applications. Therefore, if a company has a policy for modifications such as: replacing or adding an ammeter or similar device, installing a visual inspection pane or modifying a cabinet to add a new conduit run, then it is logical to include infrared windows under the same policies. For example, one would want to refer to any existing policies relating to: pre-planning, design/installation approval, installation best practices and post-installation inspection by an in-house or external authority.
Do Not Pass “Go”
Confirm the following prior to planning any modifications to an electrical equipment enclosure:
• Ingress Protection: Ensure that the NEMA or IP rating of the IR window or other component is rated for at least the same level of protection that the current enclosure is rated for. Never install an infrared window or any other component with a lower rating than the equipment onto which it is being installed.
• Tests and Certifications: Ensure that the IR windows have been tested and approved by the relevant certification bodies. Official test certificates and documentation should be easily obtained from the manufacturer.
• Explosion Ratings (if applicable): Enclosures located in intrinsically safe areas should never be modified in the field unless designs have been cleared with, and post installation inspection and re-certification will be performed by an Authority Having Jurisdiction prior to start-up.
Identify All Targets
Start the process by identifying specific targets on each piece of equipment. In addition to fuses and breakers, most infrared surveys focus on bolted connections within the gear, as these areas are considered the weakest points. These areas include:
• Cable connections
• Bus bar connections
• Isolator or circuit breaker connections
Make a quick inspection of the interior of the switchgear to identify these targets. Once identified, make every effort to standardize their emissivity while equipment is de-energized. Common methods include use of electrical tape, high-temperature paint or IRISS IR-ID labels. After emissivity standardization is complete, it is important to photograph each target since these photos will be used for report templates and future reference.
On many switchgear models, it is advisable to install viewing windows in the front and back for better access to the main breaker and bus connections. Ask the manufacturer for drawings and suggestions regarding the critical inspection locations for your equipment. This information, along with the experience and knowledge of the site maintenance engineer, will prove useful when calculating window placements and quantities.
Before picking up that drill, it is imperative to consider the following to ensure a successful, safe and useful installation:
• Internal obstacles:
Seek the permission from the local safety manager before removing internal Lexan TM (Perspex) covers. In some cases, you may not be able to remove the covers entirely. If this is the case, modify the covers by drilling or punching holes (without losing the IP2X requirement for some switchgear), or investigate custom guards that would allow for infrared transmission (such as the IRISS CAP Series.)
• Internal Cable Routing:
Work from drawings on brand-new switchgear to confirm the internal cable routes. Make sure that contractors do not route these cables in front of the infrared windows.
• Dielectric Clearances (distance from energized components):
Where the IR window contains grills, or inspection orifices, it must comply with IP2X (13mm 0.5”). Safe dielectric clearances must be maintained for each window. IEEE C37.20.2, Table 1 specifies a minimum clearance distance for live components (versus maximum rated voltage).
Complete a detailed Risk Assessment (identifying all hazards that may be present during the installation) and a detailed Method Statement (detailing how the installation will be performed). Make sure that the installation crew has the correct levels of PPE to complete the task safely, especially if the installation involves energized work, in which case an energized Work Permit will also be required per NFPA 70E/CSA Z462. All work procedures, assessments and permits must be outlined in the Risk and Method statement.
Ensure that you comply with the Installation Instructions like those in Figure 1, provided by the window manufacturer. These will provide you with all the necessary information to ensure that the windows are installed correctly.
Before starting any installation, double-check to be sure that all required tools are readily available. Traditionally, IR window installations take place during plant shutdowns therefore you will need to ensure that you have all the cutters, drills, drill bits, metal treatments, etc. already kitted and at-hand (including spares). Remember, that you will probably not be able to run to a hardware store to purchase new punches at 2 in the morning! A complete list of required tools can be obtained from the IR window manufacturer.
Affixing information labels is an important final step in the installation process. One label should identify what the window is and how to use it. A second sticker should contain the following information that will be critical in performing a thorough and accurate infrared inspection:
• Each inspection window should be given a unique number. This will be invaluable, especially, if there are multiple windows on one electrical panel.
• Document the type of window (MW or LW) and the effective wavelength of the window (as detailed in Chapter 2).
• Record the transmission rate of the window, and the proper transmission compensation value for the MW and LW.
• Record all target data on the on the ID label. The most common method of documenting target location is the clock face method: i.e. bus bar connections at 4 o’clock. It should be noted that there may be multiple targets being surveyed through the IR window.
• Some cameras do not have the ability to adjust the external optics transmission; therefore, thermographers may use the emissivity settings on the camera to cover transmission and emissivity losses. Multiply the target emissivity by the transmission rate of the window (as detailed in Chapter 4).
After the window installation is completed, the thermographer should conduct a benchmark inspection to set the base line. Data for each inspection point should be recorded in a spreadsheet or database for trend analysis over several surveys. There are software programs available to assist with database management and trending of infrared data.
What Can I See Through an Infrared Viewing Pane?
An infrared window allows you to check the condition of electrical conductors and circuit parts. As with traditional thermographic inspections, the camera is very good at detecting and displaying even slight temperature differences very clearly. Therefore, when there is an electrical fault producing a temperature rise, the camera will display the image of the faulty components very clearly. However, if everything is at temperature equilibrium, it is difficult for the camera to display an image showing much of anything.
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