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Midstates Energy

Bus Systems

The primary causes of bus system failures are due to age and lack of ongoing maintenance. Over time, seals and gaskets break down causing moisture and debris intrusion, loss of insulating properties causes tracking and grounding issues, and bad connections lead to overheating. Bus systems need periodic maintenance and insurance providers require them.

Online and Offline inspection and testing allow plant operators to better prepare for maintenance of bus systems by evaluating the condition of the bus while the system is online, prior to an outage, or during a planned outage.

Online Inspection


  • EMSA Testing: EMSA (Electromagnetic Signature Analysis) testing can be performed to locate electrical partial discharge and arcing, loose connections, and broken insulators while online.
  • IR Inspection: Thermography can be performed to locate any potential heating issues and circulating ground currents.
  • Visual Inspection: Visual inspection of the bus system exterior is performed to determine general condition and locate areas of concern for further inspection.

Offline Inspection


  • General Condition Assessment: (LEVEL 1) A condition assessment inspection is a minimally invasive inspection used to follow up online testing if no major areas of concerns are found.
  • Offline Inspection and Maintenance: (LEVEL 2) During a full offline inspection, all accessible interior and exterior areas of the bus are inspected and primary components cleaned by hand, including insulators, flexible braids, and bushings.
  • Cryogenic Cleaning: (LEVEL 3) If significant buildup of debris and contamination is expected, or carbon from arcing is present, cryogenic cleaning can be performed to thoroughly clean the interior of the bus.

The Need For Routine Maintenance

The need for inspections and regular maintenance of bus duct systems cannot be overstated. Far too often, these critical and essential passive systems that deliver generator power are neglected and ignored. A lack of regular maintenance can ultimately result in costly repairs and unplanned outages.

Routine bus duct system inspections are recommended to ensure moisture intrusion, high temperatures, dust and dirt, and equipment failures are identified and repaired quickly. Regular inspections are the key to maintaining peak operating conditions that help to avoid expensive repair work and downtime.

Retrofit and Repair Solutions


  • New transformer bushing boxes and modifications for transformer replacement
  • Bus design and platforms for replacement or retrofit of Generator Circuit Breakers
  • Design and Installation of tap boxes for addition of auxiliary equipment
  • Additions of heaters, access ports, or online monitoring equipment
  • Iso-Phase bus retrofits for access to transformer and seal off bushings
  • Design for maintenance; allow for bushing removal for replace/regasket, and iso-phase removal for generator repairs.

Common Bus Failures

  • Moisture Intrusion
  • Moisture Causing Cracks
  • Seal Off Bushings Failure
  • Expansion Bellow Cracking
  • Torn Bellows
  • Debris Accumulation
  • Damaged Gaskets
  • Damaged Insulators & Flex Links
  • Bolted Connection Failures