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Protecting Yourself from Hydrogen Sulfide
Tip submitted by: Mike Sharlon, President Thermasearch, Inc.

Infrared inspections of live transformers require line of sight access to the connections and windings. Removing covers on energized dry-type transformers can present shock and arc flash hazards. In this Tip, we discuss an alternative to removing covers for an infrared inspection.

Many small dry-type transformers feature removable steel covers that enclose electrical connections and windings. In general, there are two popular styles of front covers. The first style has a slit at the top right and top left edges of the cover. These slits require tilting the panel sideways to remove them. Attempting to remove such covers can lead to electrocution or arc flash since some transformers have energized connections just a few inches below the top lip of the cover.

To inspect transformers with this type of cover, leave the top right and top left bolts installed on the cover and remove the remaining bolts. Gently pull back the base of the cover a few inches and view the internals of the transformer with your imager from the bottom right and/or left corners. For most thermal imagers, this will be sufficient to detect thermal anomalies.

The second style of transformer cover does not have the slits that keep the cover from tipping out at the top. With this type of cover, leave the bottom bolts installed and gently tip the top of the cover out enough to inspect the windings and connections. Regardless of cover type, infrared imaging should only be performed once the cover has been opened and secured to permit a safe inspection.

Lastly, never remove the top cover to a live transformer! Depending on transformer design, this can cause internal components to shift and drop resulting in an arc flash. For transformers that require removal of the top cover in order to remove side covers, it is best to de-energize them for cover removal and replacement.