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IEEE 1584 · Engineering

Relay Coordination Study In Mexico

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Settings your maintenance procedure can rely on

NOM-029-STPS-2011 requires electrical maintenance to run on analysed risk and documented procedure. A protection scheme nobody has verified leaves every one of those procedures resting on an assumption.

What We Deliver

As-found settings recorded first

Values are read out of every relay and adjustable trip unit before anything is proposed. On plants extended more than once the device and the settings schedule routinely disagree, and documenting that gap is often the most useful output.

WHY IT MATTERS

One fault should not stop the plant

When a downstream fault trips the incomer instead of the local device, the cause is rarely defective equipment. It is grading set at commissioning and never revisited as the installation grew.

  • Grading verified against calculated fault levels at each device position rather than against the generic curves supplied with the relay.
  • CT ratio, class and burden checked, because a saturating CT delivers distorted current and the relay then operates correctly on wrong information.
  • Instantaneous elements examined specifically, since an instantaneous set too low is the most frequent cause of a downstream fault taking the incomer.
  • Coordination assessed on utility supply and on any standby generation, as decaying generator contribution can leave a downstream fault uncleared.
  • Every recommended change reported with its effect on incident energy, so selectivity is never bought at an unexamined safety cost.
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DELIVERABLES

What you receive

Issued against NOM-001-SEDE and signed by the engineer who performed the grading.

  1. 1As-found settings register covering every relay and adjustable trip unit on site
  2. 2Time-current curves per grading path with the achieved margin annotated
  3. 3Discrimination register naming each failing pair and the fault range where it fails
  4. 4Recommended settings in the entry format your devices use, ready to apply
  5. 5A stated arc flash consequence for each recommended change
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How the study runs

01

Audit the protection

Settings are read from every device on site and CT ratios, polarity and burden are verified against the schematics rather than assumed to match them.

02

Establish fault levels

Grading depends on fault current at each device position, so a verified short circuit basis is established first, from an existing study or within this scope.

03

Build the curves

Manufacturer characteristics are modelled for every installed device, including intentional delays configured into electronic trip units.

04

Calculate the margins

Margins are calculated at each level with explicit allowances for relay operate time, breaker interrupting time and measurement error.

05

Resolve the trade-off

Where selectivity and clearing time conflict, options are put to your engineering and safety teams with the incident energy consequence of each.

06

Issue and verify

Settings are issued for application with a verification checklist, so applied values can be proven afterwards against the approved schedule.

Frequently asked questions

A network can run for years without a fault in the position that would expose bad grading. No mis-operation means you have not yet had the wrong fault in the wrong place; it is not evidence the scheme is correct. The study determines which of those two situations you are actually in.
NOM-029-STPS-2011 requires electrical risk to be analysed and maintenance carried out under documented procedure. Protection behaviour determines both how a fault is cleared and how much energy is released while it burns, so a verified grading study is part of the technical basis those procedures depend on.
Yes, and it is the central trade-off. Selectivity is often achieved by delaying the upstream device, which lengthens arcing duration and raises incident energy at that location. Every recommended change is reported with its energy consequence so the choice is made deliberately rather than discovered later.
Either arrangement works. Where your team applies them we issue settings in the format your devices are configured in, with a verification checklist. Where we apply them, as-found values are recorded first so any change is fully traceable if an investigation later needs to reconstruct what was altered.

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