Case Study by: Paul Wright, The Snell Group


A power outage caused by a ground fault in a 13800/4160 volt plant main substation.  The outage was caused by a main substation tripping on ground fault but the issue was what caused this.


Initially both an infrared and ultrasound inspection was performed around the perimeter of the substation with no indication.  A closer inspection was required.  An external infrared scan of the components did not show any problem so ultrasound was used to scan.  The ultrasound equipment located an indication of severe tracking at a specific location.


Based upon the ultrasound findings a plant shutdown was scheduled, visual inspection was conducted and the repair was made.  The repair discovered tracking along with dirt and other visible contaminants within a cabinet.  Insulation materials were damaged due to the tracking and arcing.  The main power input connections had severe pitting damage.

The potential cost/savings had a failure occurred:  $40,000 – $50,000 in repairs plus an estimated 3-5 days of unscheduled facility downtime, plus an estimated $1.6 million per day in lost production.

Ultrasound proved the value of a PdM program, created a change in inspection policy in this facility, initiated the installation of infrared inspection ports and changed the method of the routine inspections from outside the perimeter of the substation to inside.