One Minute Summary - NERC PRC-027-1 

Coordination of Protection Systems for Performance During Faults 

Purpose:

• Maintain the coordination of protection systems

• Detect and isolate faults

• Relay operates in the intended sequence during faults

Benefits

• Isolate Faulted Equipment

• Reduce BES Instability and Cascading Risks

• Keep Remainder of BES Operational

• Protect Equipment from Damage

• Minimize Removal of BES Elements

• Prepare for Next Contingency

Functional Eentity

• Transmission Owner

• Provide the Fault current data upon request by the Distribution Provider or Generator Owner

• Generator Owner

  • Ensure that generation Facilities are not unnecessarily disconnected

  • Determine whether a change in Fault current from the baseline

• Distribution Provider

  • Provide an electrical interconnection and path to the BES

  • Coordinated with other Protection Systems

  • Determine whether a change in Fault current from the baseline

R1 Establish a process to develop new and revised protection system

• Ensure  accurate settings

• Internal and external checks to minimize the possibility of errors

• There is no a one-size-fits-all  criterion for “Protection System coordination”, different entities might have varying technical criteria

• Line differential is not required

• Backup protection systems

  • Use current or apparent impedance with time delay

  • Must be coordinated with other protection systems

  • Does not trip unnecessarily for faults outside of the differential zone.

1.1 Review and update of short-circuit model data

• Impedances and Fault currents for

  • Line

  • Transformer

  • Generator

• System network as the actual system

• Information from

  • Interconnected Transmission Owner

  • Generator Owner

  • Distribution Provider

1.2 Review of the developed protection system settings

• Peer reviews

• Automated checking programs

• Review procedures

1.3. Coordination with electrically join facilities (only apply to electrically join facilities)

• 1.3.1. Share the proposed protection system settings

  • Other entities can review the settings and determine issues

• 1.3.2. Respond to any owner(s) that provided its proposed Protection System settings:

  • Identifying coordination issues

  • OR confirming no issues were identified

• 1.3.3. Verify coordination issues are addressed

  • Exclusion for Individual Dispersed Generation Resources in Requirement R3, R3.1

• 1.3.4. Communicate about revised Protection System settings:

  • Unforeseen circumstances during implementation or commissioning,

  • Misoperation investigations

  • Maintenance activities

  • Emergency replacements required due to Protection System component failure.

R2 Timeline to perform a Protection System Coordination Study

Option 1 (Time-based): 

Perform a Protection System Coordination Study every six years

Option 2 (Fault current-based): 

Compare present Fault current values to an established baseline and perform a study if there is a 15 percent or greater deviation (for either three-phase or phase-to-ground faults), within a six-calendar-year interval.

Option 3: Use a combination of Option 1 and Option 2

Protection System Coordination includes:

21 – Distance if:

• Infeed is used in determining reach for phase 21 and ground distance 21

• zero-sequence mutual coupling is used in determining reach (ground distance).

50 – Instantaneous overcurrent

51 – AC inverse time overcurrent

67 – AC directional overcurrent if used in a non-communication-aided protection scheme

Establish and maintain an Fault current baseline

• Initial Establishment of Baseline 

  • • • Established by the effective date of the Reliability Standard.

• Provisions for Missing Initial Baseline:

  • Establish the baseline by performing a Protection System Coordination Study.

• Update the Baseline:

Updated each time a Protection System Coordination Study is performed.

• Baseline for BES Generating Resources

Fault current baseline can be established at:

• At the generator

• At the generator step-up (GSU) transformers

• At the common point of connection at 100 kV or above.

• Dispersed Power Producing Resources:

  • Fault current baseline can be established at

    • at the BES aggregation point, provided the total capacity is greater than 75 MVA.

R3 Utilize established process in requirement R1

• Consistent approach

• Decreases the possibility of errors

• Increases the likelihood of maintaining a coordinated Protection System