NERC MOD-025 Compliance

Generator Capability Verification Compliance

Q: What is generator capability verification?

Capability verification ensures actual generator MW and MVAr output matches documented capability curves and planning data.

Q: Is testing always required?

Testing is not always required. Acceptable evidence includes manufacturer data, previous testing, or engineering analysis.

Q: What evidence is acceptable?

Acceptable evidence includes field test data, manufacturer test reports, capability curves, and documented engineering analysis.

eGridSync supports Generator Owners with real and reactive power capability verification, testing analysis, and audit-ready documentation aligned with MOD-025.

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What is NERC MOD-025?

MOD-025 ensures generator capability data used in planning accurately reflects actual machine performance.

MW & MVAr Verification

Verifies generator's real (MW) and reactive (MVAr) power capability matches documented limits and planning models

Ensures Model Accuracy

Planning models must reflect actual capability to support reliable system planning and operations

Verification Methods

Verification through field testing, manufacturer data, engineering analysis, or documented evidence

Planning Reliability

Accurate capability data prevents planning on unavailable generation, ensuring grid reliability

Who Must Comply with MOD-025?

MOD-025 applies to Generator Owners responsible for providing accurate capability data to planning entities.

Generator Owners (GO)

Entities owning BES generators requiring capability verification

BES Generators

Generators meeting applicability thresholds for size and voltage

Trigger Events

New units in service or capability changes require verification

Important: Verification is required when units are placed in service, capability changes significantly, or periodically per entity procedures. Generator capability data affects all planning analyses.

Understanding Generator Capability Verification

Generator capability defines the operating envelope for real and reactive power output.

Generator Capability Curves

Capability curves plot MW (real power) versus MVAr (reactive power) defining the generator's operating limits. Curves show continuous and short-term capability under various conditions including armature heating, field heating, end-turn heating, and stability limits.

MW vs MVAr Limits

Real power (MW) output is limited by prime mover capability and thermal constraints. Reactive power (MVAr) is limited by armature current, field current, and under-excitation stability. Both interact—maximum MW may reduce available MVAr and vice versa.

Excitation System Relationship

Reactive power capability depends heavily on excitation system performance. Field forcing capability, ceiling voltage, and AVR response determine maximum MVAr output during system voltage depression. Excitation system upgrades or degradation directly affect reactive capability.

Planning Risk from Incorrect Data

Overstated capability causes planners to rely on unavailable generation during contingencies, risking voltage collapse or inadequate reserves. Understated capability wastes available resources. Both create reliability or economic problems requiring accurate verification.

What eGridSync Delivers for MOD-025 Compliance

MOD-025 applicability determination and scope review

Capability curve review and validation

Field test data evaluation and analysis

Model vs measured data comparison

Verification reports and technical documentation

Evidence package preparation for audits

Gap assessment and remediation planning

Ongoing audit support and data request assistance

Inputs Required for MOD-025 Verification

To perform capability verification and ensure MOD-025 compliance, eGridSync requires:

Item	Examples	Why Required
Generator Nameplate Data	MVA rating, voltage, power factor, manufacturer specifications	Baseline capability limits and design parameters
Capability Curves	MW vs MVAr P-Q curves, continuous and short-term ratings	Define operating envelope for verification
Field Test Reports	Performance test data, commissioning reports, capability demonstrations	Provide measured data for verification evidence
Excitation System Data	AVR type, field forcing capability, ceiling voltage, response characteristics	Reactive capability depends on excitation performance
One-Line Diagrams	Generator connections, transformer configurations, auxiliary loads	Understand net capability to transmission system
Planning Models	PSS®E or PowerFactory models with generator data	Verify model data matches verified capability
Historical Operating Data	Real-time performance, SCADA records, operating logs	Confirm capability under actual operating conditions
Prior Audit Findings	Previous NERC findings, mitigation plans, compliance notes	Address known deficiencies and prevent recurrence

Common MOD-025 Compliance Failure Points

Understanding common pitfalls helps Generator Owners avoid violations:

Capability Overstated

Reporting higher capability than actual generator can deliver. Often results from using nameplate data without field verification, ignoring degradation, or not accounting for auxiliary loads. Creates planning risk when unavailable generation is counted during emergencies.

Capability Understated

Reporting lower capability than available due to conservative assumptions or outdated data. Wastes generation resources and creates unnecessary transmission constraints. Both over and understating capability violate MOD-025's accuracy requirements.

Missing or Outdated Test Data

Relying on manufacturer data or old test reports without periodic verification. Equipment ages, auxiliary loads change, excitation systems degrade. Capability verification requires current evidence reflecting actual as-found conditions.

Model Mismatch with Verified Capability

Planning models containing different capability values than verification documentation. Discrepancy often arises from incomplete data updates or poor communication between verification and modeling teams. Models must match verified capability exactly.

Poor Documentation Traceability

Inability to trace capability values from verification evidence to planning models. Auditors require clear lineage from test data or analysis to reported capability to model inputs. Missing links create compliance findings.

Excitation System Changes Not Reflected

AVR upgrades, field modifications, or excitation system degradation without updated capability verification. Reactive capability is highly dependent on excitation system performance. Any excitation change triggers reverification requirement.

Unclear Verification Basis

Capability reported without clear documentation of verification method used (testing, manufacturer data, analysis). MOD-025 allows multiple verification methods but requires clear identification of which was applied and supporting evidence.

Ambient Condition Assumptions Unclear

Capability values without documented ambient temperature, cooling water temperature, or altitude assumptions. Capability varies with ambient conditions. Verification must clearly state assumed conditions matching planning case assumptions.

Frequently Asked Questions

What is MOD-025?

MOD-025 is a NERC Reliability Standard requiring Generator Owners to verify generator real and reactive power capability through testing, manufacturer data, or engineering analysis. Verification ensures planning models accurately reflect actual generator performance. Accurate capability data prevents planning on unavailable generation during emergencies.

Who must comply with MOD-025?

MOD-025 applies to Generator Owners of BES generators meeting applicability thresholds based on generator size and voltage level. Compliance is required when units are placed in service, when capability changes significantly, or periodically per entity procedures. Verification applies to both new and existing generators.

What is generator capability verification?

Capability verification confirms generator's actual MW and MVAr output matches documented capability curves and planning data. Verification compares measured performance against expected limits considering armature heating, field heating, stability, and prime mover constraints. Process ensures planners can rely on stated capability during system stress.

Is testing always required?

No. MOD-025 accepts multiple verification methods including field testing, manufacturer test reports, commissioning data, or documented engineering analysis. Testing is most definitive but not always practical. Method selection depends on unit age, modifications, available documentation, and compliance risk tolerance.

What evidence is acceptable?

Acceptable evidence includes field test data, manufacturer performance test reports, commissioning records, capability curves with engineering justification, historical operating data demonstrating capability, or combination thereof. Evidence must demonstrate capability under specified ambient conditions and configuration. Traceability to capability values is essential.

How often is verification required?

MOD-025 requires verification when units are placed in service or when capability changes. Entities may establish periodic verification schedules (every 5-10 years) as good practice. Trigger events include excitation system changes, prime mover modifications, transformer replacements, or significant equipment degradation affecting capability.

How do capability curves affect planning?

Planning studies use capability curves to determine available MW and MVAr during contingencies, voltage support requirements, and system adequacy. Incorrect curves cause planners to overestimate available resources (reliability risk) or underestimate capability (economic inefficiency). Accurate curves enable optimal resource utilization.

What happens if capability changes?

Capability changes trigger MOD-025 reverification and planning model updates. Changes result from equipment modifications (excitation upgrades, turbine replacements), degradation, auxiliary load changes, or cooling system alterations. Generator Owners must promptly notify planning entities and provide updated capability data.

What are common audit findings?

Common findings include capability not supported by current verification evidence, model data not matching verified capability, missing documentation of verification method, unclear ambient condition assumptions, excitation system changes without reverification, and poor traceability from evidence to planning models.

How long does MOD-025 compliance take?

Initial verification typically takes 1-3 months depending on data availability and verification method. Field testing requires planning, execution, and analysis (2-4 weeks). Engineering analysis from existing data takes less time (2-4 weeks). Evidence compilation and audit preparation adds 2-4 weeks.

Do manufacturer ratings meet MOD-025?

Manufacturer ratings are acceptable if verified through factory testing and documented. However, field conditions (altitude, cooling water temperature, auxiliary loads) may differ from factory test conditions. Manufacturer data should be adjusted for actual site conditions or supplemented with field verification.

How does MOD-025 relate to MOD-026 and MOD-027?

MOD-025 verifies steady-state capability (MW/MVAr limits). MOD-026 verifies excitation system dynamic models. MOD-027 verifies turbine/governor models. Together, they ensure complete generator model accuracy for planning. All three standards work together ensuring reliable planning data.

What if verification shows lower capability?

Lower verified capability requires updating planning models, notifying planning entities, and potentially revising interconnection agreements or power purchase agreements. May trigger review of planning studies, transmission limits, and resource adequacy. Financially significant changes may require dispute resolution.

Can simulation replace field testing?

Detailed engineering analysis and simulation can support verification if based on validated models and manufacturer data. However, field testing provides highest confidence. Simulation is acceptable when supported by historical operating data, prior tests, or when testing is impractical. Documentation must justify simulation methodology.

How does eGridSync support MOD-025 audits?

eGridSync provides organized evidence packages including verification reports, capability curves, test data analysis, model validation, traceability documentation, and technical justifications. We prepare audit-ready materials and support Generator Owners during NERC data requests and technical discussions with auditors.

Official References

For complete standard requirements and technical guidelines, refer to official NERC resources:

NERC MOD-025-2 Official PDF

Current version of the MOD-025 Reliability Standard

NERC Reliability Standards Library

Complete library of all NERC Reliability Standards

Important: This page summarizes MOD-025 compliance concepts in original language for educational purposes. Always refer to the official NERC standard for authoritative requirements. eGridSync does not copy or reproduce NERC standard text.

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