Non-Segregated Bus Life Extension Measures

In most plants, while there is a hierarchy of provisions established for avoiding failures and maintaining major plant equipment, such as the transformers, generators, etc., there is usually not much attention on preventative measures to extend the life of non-segregated bus systems. Without any moving parts, metal enclosed bus systems are stand-alone, custom made for each plant, and non-redundant. When a failure occurs, the entire energy producing system shuts down. This can become problematic and often results in a prolonged unplanned outage, catastrophic failure of critical equipment, and places onsite personnel at serious risk. Therefore, having routine bus system inspection and preventative maintenance plan, per industry best practices, is critical in protecting the overall generation system and those around it.

For nearly 50 years, EBI’s uniquely qualified and specialty trained bus duct experts have identified and documented numerous case studies on the most common causes of non-segregated bus duct failure due to lack of proper inspection and maintenance. One of the most common issues EBI has addressed in non-segregated bus systems is degraded and/or worn-down insulation. History has shown that insulation made with polyphenylene oxide (PPO) can become brittle, cracked, and is prone to failures. Even the NRC has documented this type of insulation as problematic which is why it is no longer used. If you have an older system with PPO insulation, the bus bars should be addressed during your next scheduled outage.

Another common issue associated with non-segregated systems is contamination. Because non-seg bus systems typically have a bolted design construction, compared with the isolated phase bus, which is a continuously welded design construction, they are more vulnerable to contamination issues. Especially those located within environments that have humidity, drastic temperature fluctuations, salty sea air, sand/dust, coal/forest fire smoke, etc. These factors amplify deterioration and contamination, and therefore inspection and maintenance intervals need to be increased. General foreign material intrusion and moisture introduction can also be caused by degraded seals, poor gasketing, inadequate hardware at the bolted covers, and deterioration of the outdoor enclosures. What’s worse; the presence of moisture and dirt/debris buildup, coupled with cracked and deteriorated insulation and the presence of ground currents, causes the release of ozone and promotes a Nitric acid reaction. This chemical reaction will eventually eat away all surfaces, particularly metal, which can create electrical tracking paths potentially causing phase-to-phase or phase-to-ground events, often resulting in catastrophic failure of the non-segregated bus system.

In addition, because of the number of joints associated with non-segregated bus, improper bolt torque, wrong, missing or improper hardware, compromised vibration boot assemblies, lack of or compromised silver plating, are also common issues that can cause failure due to lack of or improper inspection and maintenance practices.

Routine maintenance and inspection, by EBI’s qualified and trained personnel, is the most effective way to maintain the health of these system critical electrical components and mitigate opportunities for a forced outage. If your non-segregated bus system has not been inspected by EBI in the last 18-24 months, there’s a good chance these conditions exist. Cleaning, refurbishment, and/or repairs are necessary to prevent a catastrophic failure. EBI leads the industry with our thorough electrical asset life extension and repair services; including replacement, refurbishment, or emergency fabrication of obsolete or hard to procure replacement components. If the unexpected occurs, rest assured you can rely on EBI’s nearly 50 years of experience to get you back online as quickly and safely as possible. If you have an upcoming maintenance outage planned, have critical projects that require bus duct expertise, have fabrication needs, or would like to learn more about extending the life of your electrical assets, contact us at 877-297-0616 or [email protected].