Power Grid Protection… Don’t Wing It!

5 July, 2018 | Blog

RÉMI HALLÉ, P.Eng.

Electrical Engineer

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Power grid protection devices are unprofitable and unnecessary for regular grid operations… until there’s an electrical failure!

These devices can remain inactive for up to 5, 10 or 20 years… or more. However, when the time comes, they must be able to detect and eliminate a failure within milliseconds. If these protection devices don’t work in time, the consequences on equipment, operations and even personnel safety can be catastrophic.

Protection devices come in all shapes and sizes: fuses, circuit breakers, protection relays, etc. Understanding how they work and what their limitations are when there’s a failure is critical when performing protection and coordination studies, and incident energy analyses.

Improper coordination or selection of protection levels could impact operations. No business wants to lose all power because of a simple motor problem. If a person wrongly assesses the coordination, or worse, wings it, the flaw wouldn’t be detected until after the fact.

When there’s an electrical failure, the short-circuit current is several tens of times greater than the usual current. The protection reaction time depends on this current value. But how are these failure current levels calculated? What settings affect this current? What current value will the protection devices come up against? How much time will it take to eliminate the failure?

There are many software programs on the market that can respond to these questions, but the programs are only tools and in no way replace the expertise of a professional. Like any calculation software, results depend on input data. The correct values must be entered and their importance understood. The software’s default value settings aren’t necessarily the most appropriate. Also, users must be critical of the results. Just because the software doesn’t produce errors during the simulation doesn’t mean the results are realistic.

Several criteria must be considered when adjusting and selecting protection devices:

  • Downstream or upstream protection devices
  • Maximum or minimum short-circuit values detected by the protection devices
  • Nominal conductor and equipment capacity
  • Connected motor loads
  • Grounding plan

In recent years, the arc’s current value in case an arc flash occurs was added to the preceding criteria. How can incident energy be reduced using existing protection devices? Properly adjusted protection devices help reduce the level of incident energy by dropping elimination time; improperly adjusted protection devices cause the opposite. These adjustments could mean the difference between a firecracker or a bomb. Personnel safety depends on these adjustments.

All in all, winging it in the protection industry is never a good idea.

This content is for general information purposes only. All rights reserved ©BBA

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