Plant Name: Cholla Generating Station
Project Location: Joseph City, AZ
Owner: Arizona Public Service (APS)
EBI Client: Arizona Public Service (APS)
0 OSHA recordable incidents
Project completed ahead of schedule

Why EBI:

Circulating currents and overheating issues are symptoms of a larger problem. Left unaddressed, they can lead to costly failures.

Arizona Public Service (APS) called us in when they identified those red flags at their Cholla Generating Station. To determine the root cause and assist with future outage planning, we performed isolated phase bus EMI diagnostics while the plant was still online.


We inspected for the following:

  • Loose & broken support insulators
  • Contaminated insulators (dirt, cement dust, water)
  • Loose & corroded bus hardware
  • Stray circulating currents outside bus enclosures
  • Defective isolated phase bus enclosure insulation
  • Foreign metal objects inside bus enclosure
  • Defective bus potential transformer connections
  • Open PT high voltage fuses
  • Loose AUX transformer connections
  • Loose GSU transformer connections
  • Defective surge capacitor connections
  • Loose disconnect switch components
  • Loose breaker connections
  • Verify correct maintenance was/was not performed


  • Our online isolated phase bus EMI diagnostics revealed that an immediate offline inspection of Cholla Generating Station and a cleaning of its IPBD system were required.