DeltaV CIOC Power

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DCS Newbie

• 25 Apr 2018 6:50 PM
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• Andre Dicaire

  

  • 25 Apr 2018 8:01 PM

  A short circuit on a single fused circuit should not cause loss of power to the balance of the equipment. The DeltaV Power supplies and most modern power supplies provide additional power for the sudden extra load caused by a short circuit and the time the fuse takes to open. If the fuses are not adequately sized for current and time to open i.e. fast blow vs slow blow, the overall voltage profile may be affected.
  
  Every situation requires careful attention to the Power distribution. It is common practice to use a redundancy module to connect both Primary and Secondary power to a common 24 VDC feed for the Baseplate Injected power. Each baseplate is limited to 10 Amps at 24 VDC, which is distributed by design to a maximum of 1 amp per CHARM.
  
  If a short on the instrument circuit did not blow the fuse, causing extended high current draw and eventual over current of the Power supply that should be investigated. I recommend that each supply feed the CIOC directly from one of its outputs, and that the feed to the redundancy module/common bus be fused independently.
  
  One scenario could be a partial ground to fault that draws elevated current but not enough to blow a fuse, but enough to create a sustained excess load might result in an eventual shutdown of the supplies from their internal protection. This would indicate a flaw in the power distribution fuse ratings. On the baseplates, each channel has a 2 amp fuse. drawing an extra couple of amps across two adequately rated power supplies should not lead to total power failure. However, if the two supplies are combined using ORing Diodes, one supply can be running close to its maximum, if it shuts down, the second supply will take the demand and soon follow. The redundancy modules help balance the draw from both supplies.
  
  Adding additional power supplies is one solution, but we have to balance cost, footprint and other factors. I would rather understand the failure mode of the system and root cause of this event. Rating of power supplies, normal demand, fuse ratings, use of redundancy modules vs Diodes, etc.
  
  I'm curious if anyone else has had similar issues, or have tested the redundancy module designs and power supply fuse blowing capacities.

  Andre Dicaire

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