ARC FLASH PROTECTION From PG

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ARC FLASH PROTECTIONFrom PGE Wood River
Refinery Substation Incident - A Testament to
Electrical PPE

• As you probably know by now, on Tuesday, Wood
  River experienced a significant electrical arc
  flash incident in one of our substations.
  Fortunately, there were no injuries and it looks
  as though we will have the substation back in
  service in the next 3 or 4 days. A more detailed
  communication of the learnings may be sent out
  later but we wanted to provide you with a
  preliminary general explanation of the event and
  most importantly some information with
  before/after PPE photos to illustrate the value
  of PPE.
• Incident Overview
• One of the two feeders to our substations had
  been replaced during our turnaround. Both main
  feeders had been energized but not yet tied
  together or double-ended. Prior to connecting
  the new energized feeder to the substation, phase
  testing was being performed in order to validate
  that all three phases on both feeders were
  aligned in the appropriate position. This is
  mandated by procedure because closing the tie
  when the feeders are out of phase would result in
  a major fault. The phase testing was being
  conducted inside one of the 4160V main breaker
  cubicles in the substation. The phase testing
  procedure being conducted at the time of the
  incident involved inserting 2 probes from a
  voltage meter into holes (see first picture) to
  make contact with energized stabs located up
  inside the holes (see second picture). This is
  old switch gear configured with grounded steel
  shutters that are opened and closed over the
  holes and you can see the edge of the open
  shutters in the second picture. During a phase
  test these shutters are in the open position to
  expose the live stabs but the edge of the
  grounded steel shutter remains very close to the
  opening where the probe is inserted (also
  demonstrated in the second picture). We
  speculate that the initiating event occurred when
  the metal edge on one of the voltage meter probes
  touched the edge of the grounded steel shutter.
  As the tip of the probe was moved closer to the
  live 4160V stab, an initiating arc jumped from
  the live stab to the probe. When the COP
  employee saw and heard the large arc, he
  immediately began to egress. As the probe was
  withdrawn from the hole, the arc followed the tip
  of the probe causing the arc to grow in length
  and form conductive gases. We speculate that the
  gases eventually migrated to one of the other
  phases causing a pathway for a phase to phase
  fault and ultimately an explosion. It is
  estimated that within a matter of 2 to 3 seconds
  from the initial arc the gases formed a path for
  the other phases to join through the ionized air.
• Testament to PPE
• Again, thanks to the PPE, there were no injuries.
  For reference and comparison, the third picture
  ( 3776) shows a new 65 calorie flash hood
  similar to the one being used by one COP employee
  and two contractors during our incident earlier
  this week. You can see in the fourth picture (
  3767) how the hood looked after being exposed to
  the arc flash but what you cant see is that the
  inside of the hood looks like new. A few years
  ago we upgraded our electrical safe work
  practices and our electrical PPE to state of the
  art gear.

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