Protection
Importance of Relay Coordination
Why protective device coordination is critical for both safety and system reliability.
Read MorePROTECTION COORDINATION · UNITED STATES
Relay Coordination Study for US Facilities
Protection coordination decides which device clears a fault and how long it takes. Get it wrong one way and a local fault trips the whole plant. Get it wrong the other way and clearing times stretch, which raises arc flash incident energy at every location downstream. In the US both outcomes are assessed by someone: the first by your operations team, the second by an OSHA inspector reading your labels.
Free ConsultationNFPA 70EIEEE 1584OSHA CompliantNEC Standards
What a Coordination Study Has to Achieve
Selectivity and clearing time pull against each other. The study is where that trade-off gets made deliberately rather than by default.
What We Deliver
Selectivity, device by device
The device nearest the fault should operate first. We grade time-current characteristics through the system so an upstream device holds while the downstream one clears, which is what keeps a local fault local.
WHAT GOES WRONG
Where Coordination Studies Fail
Coordination problems usually only reveal themselves during a fault, which is the most expensive possible moment to discover them.
- Settings modelled from design documents rather than recorded as found.
- Selectivity optimised with no regard for the resulting arc flash energy.
- Utility upstream protection characteristics assumed rather than obtained.
- Instantaneous elements left enabled where they defeat grading.
- Study not revisited after relays were replaced or re-set.
- Arc flash labels issued from assumed clearing times rather than coordinated ones.
THE OUTCOMES
What the Report Contains
The deliverable is a settings schedule somebody can actually apply, with the time-current curves that justify it and the arc flash consequence of each choice stated alongside.
- 1Settings as found, recorded per device
- 2Time-current curves showing graded operation
- 3Recommended settings schedule for implementation
- 4Clearing times at each location
- 5Resulting incident energy where arc flash is in scope
- 6Utility protection data used, with its source
How We Run a US Coordination Study
01
Build on a validated model
Coordination needs load flow and short circuit results first, since grading depends on the fault current available at each device.
02
Record settings as found
Capture every relay and breaker setting as currently applied, including whether instantaneous elements are enabled, rather than taking the design schedule.
03
Obtain utility characteristics
Request the serving utility's upstream protection data, because grading has to hold at the service as well as inside the plant.
04
Grade and test against arc flash
Develop settings that maintain selectivity, then check the resulting clearing times against incident energy so the trade-off is made explicitly.
05
Issue an applicable schedule
A settings schedule with curves, clearing times and arc flash consequences, in a form the site can implement and verify.
Industries We Empower
Oil & Gas
Upstream, midstream, and downstream facilities
Healthcare
Hospitals, clinics, and medical campuses
Data Centers
Tier I through Tier IV facilities
Manufacturing
Production lines and industrial plants
Utilities
Generation, transmission, and distribution
Commercial Real Estate
Office buildings and retail complexes
Education
Universities, schools, and research labs
Government
Federal, state, and municipal facilities
Frequently Asked Questions
It establishes which protective device clears a fault and how long it takes, then sets the devices so the one nearest the fault operates first. That keeps a local fault local instead of tripping the whole plant, and it fixes the clearing times that arc flash incident energy depends on.
Directly. Incident energy is a function of fault current and how long that current flows. Grading an upstream device conservatively lengthens clearing time, which raises incident energy at every downstream location and can push PPE requirements to a level that makes routine work impractical. The two studies have to be solved together.
Because after years of maintenance, relay and breaker settings often differ from the original design. Coordinating against the design schedule produces a study that describes a plant you do not have. Recording what is actually set is the only way the resulting grading reflects how the system will behave in a real fault.
For facilities under NERC reliability standards, yes. The PRC-series requirements cover protection system maintenance and coordination, and they interact with the settings a coordination study produces. Running the compliance programme and the coordination study independently tends to produce two sets of records that do not agree with each other.
Grade for Selectivity Without Raising Incident Energy
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