Most electricians would agree that the essential nervous system of every facility is the electrical system. The electrical system consists of the main switch gear, branch circuit panels, transformers, motor control centers and any other critical electrical equipment.
Proper maintenance of its electrical system is essential for the survival of any facility, as well as for preventing unexpected electrical interruptions.
This article focuses on a comprehensive program that has been developed within Aschinger Electric, a St. Louis-based service provider, to help prevent electrical failures and prolong the life of electrical systems. Performed annually on all electrical equipment, it includes: infrared scanning, cleaning and torquing and, finally, an infrared re-scan.
Infrared scanning to identify problems
The infrared camera is an excellent tool for identifying potential electrical problems. All electrical equipment should be scanned as the first step of the maintenance program. The infrared camera is key to spotting connections that have been improperly torqued or are being overloaded. Fig. 1 illustrates an overtorqued electrical termination. The problematic point has a temperature of 32 C (90 F). The image at the right shows the same termination after being properly torqued; the temperature was reduced to 26 C (78 F).
The infrared camera also can identify overloaded circuits. Fig. 2 is an image of a wire drawing 22.4A. The circuit is rated for 20A. The wire was originally yellow, but due to the extreme exposure to temperature, it turned brown and brittle. The wire was able to be replaced and the circuit’s load was redistributed during a scheduled shutdown rather than during an unexpected failure of the wire.
All bus links, wire terminations and coils of transformers need to be scanned while under load.Due to the hazards of scanning energized equipment, it is a good practice to perform scans with pairs of qualified electricians that are suited up in personal protective equipment (i.e. - blast suits).
All deficiencies-overtorquing, undertorquing and overloading-should be documented At this time, an action plan should be developed for correcting the deficiencies during the un-energized torquing and cleaning step of the equipment.
Cleaning and torquing
After identifying all deficiencies using the infrared camera, the equipment needs to be cleaned, followed by torquing of all terminations to manufacturer’s specifications.
The initial step in cleaning any electrical equipment is to properly de-energize the equipment, then to lock out and tag the disconnecting means. A proper lockout/tagout program is a must in every facility.
To clean a piece of equipment, an industrial- strength hepa vacuum is needed. Vacuum all pieces of the electrical equipment. Next, using a soft paint brush with fine bristles, brush out all dust and dirt, working from top to bottom and left to right, while continually vacuuming.
After all electrical equipment has been thoroughly cleaned, all terminations should be loosened, cleaned and lubricated with a manufacturer’s specified lubricant for the materials being connected (i.e., no-ox for copper to aluminum, Fisk paste for bus links).
The final step before re-energizing is to torque all connections to manufacture’s specifications. If possible, the manufacturer should be consulted for torque settings of all equipment bolts and links. If torque values are not available, Table I is a very good reference. At this time, special care should be taken to correctly torque the deficiencies found during the initial infrared scanning.
Dry-type transformers should be cleaned in the same fashion with one addition. After the outer coils of the transformer have been removed of dirt using a paint brush, the inner windings of the coil need to be cleaned using compressed gas. Nitrogen is used because it will not bind with the atmospheric air and thus will not form water within the windings. Proper pressure of the nitrogen to blow out the windings is 25 lbs/in2 or less.
At this time, resistance testing on the transformer should be performed. Table II provides reference values if manufacturer specifications are not available. ANSI publication C57.94 is a further reference for maintenance and testing of transformers.
When all dust and debris have been removed, all metal surfaces (i.e., bus links) should be wiped down using absolute alcohol and a lint-fee rag. Alcohol cleans well and does not leave a residue when dried. It is advisable to use the alcohol on cool equipment and to let it dry before re-energizing. (IMPORTANT: Alcohol is to be used only on metal parts. Do not use alcohol on insulation or transformer coils.)
Once all terminations are torqued, all equipment should be inspected for loose tools and properly closed. The electrical system can now be re-energized. (IMPORTANT: Follow all safety precautions and make sure all workers are aware of re-energizing of equipment.)
The final step for the program is to re-scan the equipment for deficiencies. Re-scanning is a way to ensure that all terminations have been torqued properly and that initial problems have been corrected. If problems still exist, the culprits usually are overloaded circuits, incorrect torquing or faulty equipment.
An annual maintenance program of the electrical system is vital for the system’s longevity. If a preventive electrical maintenance program is diligently performed, a facility should be able to recoup the cost of the program through diminished uninterrupted shutdowns, thus saving time and/or product. The electrical maintenance program is essential in identifying and correcting problems on a planned schedule, as opposed to an unplanned shutdown due to system failure. Finally, an electrical maintenance program is a preventative means to reduce the risks of electrical fires in a facility. The life/safety issue is a cost that is usually compensated by lower insurance premiums for a company. MT