NERC MOD-025-2: Verification and Data Reporting of Generator Real and Reactive Power Capability

Planning models must reflect what generators can actually produce, not nameplate assumptions

What Is MOD-025-2?

Transmission planning studies assume that generators can produce specific amounts of real and reactive power. Those assumptions directly influence how the grid is planned, operated, and maintained. If the assumptions are wrong (because a generator is derated, its cooling system has degraded, or it was never accurately tested to begin with), the planning model is wrong too, and the grid may be operated with less margin than planners believe exists.

MOD-025-2 requires generator owners to verify what their generators can actually produce and report that verified data to the transmission planner. The standard applies to both real power and reactive power capability, and requires testing under operating conditions defined by the standard, including leading power factor operation, which is often the most constrained and least-tested capability.

The standard also establishes re-verification requirements, so that the data stays current as machines age and operating conditions change.

Who Must Comply?

MOD-025-2 applies to Generator Owners (GO) of applicable generating units connected to the BES. The standard covers both synchronous generators and certain IBRs with reactive power capability. Applicability is based on generator type and nameplate rating per the standard's applicability table. Generally applicable to:

Synchronous generators above defined nameplate thresholds
IBRs with defined reactive power capability connected at BES voltage levels
Facilities that have undergone modifications affecting real or reactive capability since their last verification

Re-verification is required at defined intervals or following significant equipment changes. Owners who haven't tested since commissioning (which is common) are out of cycle and need to prioritize the testing.

Key Requirements

Real and Reactive Power Testing

Conduct field tests per the procedures defined in the standard to verify the generator's actual real power capability and reactive power capability in both lagging (overexcited) and leading (underexcited) operation. Tests must be performed at the operating conditions specified in the standard.

Data Submission to Transmission Planner

Submit verified capability data to the applicable transmission planner in the format required. The data is used to update the planning model for the facility and must be resubmitted whenever a re-verification is performed or a significant change occurs.

Periodic Re-Verification

The standard requires re-verification at defined intervals and following changes that could affect capability: major overhauls, stator or rotor work, cooling system modifications, or AVR replacements. Owners must track their re-verification schedule proactively.

Test Records and Documentation

Test results, the operating conditions during the test, instrumentation used, and the data submitted to the transmission planner must all be documented and retained as evidence of compliance.

Common Compliance Challenges

Leading Power Factor Testing Is Operationally Difficult

Testing at leading power factor (underexcited operation) requires the generator to absorb reactive power from the system, which pushes it toward the stability limit. This mode of operation is unfamiliar to many operators and requires coordination with the system operator, careful monitoring, and engineering oversight during the test. Many facilities have avoided it for years, creating a compliance gap.

Capability Has Degraded Since Commissioning

Generators age. Rotor insulation degrades, stator cooling passages foul, and cooling system capacity decreases. The actual capability of an older machine may be meaningfully less than its nameplate rating or its original commissioning test results, and the planning model may be assuming a capability the machine can no longer provide.

Test Scheduling and System Operator Coordination

Testing requires the unit to operate at specific points away from normal dispatch setpoints for a defined hold period. Coordinating an operational test window with the system operator, particularly for dispatch-constrained units or units in tight markets, takes time and advance planning.

IBR Reactive Capability Constrained by Firmware

For IBRs, reactive capability is often limited by inverter firmware settings and grid code configurations rather than physical constraints. Documenting this correctly (distinguishing between inherent hardware capability and configured operating limits) requires familiarity with how the specific inverter platform manages reactive control.

How TWC Can Help

TWC supports generator owners with MOD-025-2 testing, verification, and data reporting, with experience in both synchronous generator and IBR capability assessments.

Test Planning and Coordination

We develop the test plan, coordinate with the system operator for an acceptable test window, and confirm that the test procedure meets the standard's requirements before the test date.

On-Site Testing Support

We provide engineering support during the test, including monitoring the operating point, confirming hold periods, and capturing the data required to document the results. Leading power factor testing is performed with appropriate stability monitoring in place.

Capability Curve Development

We develop the verified capability curve from the test data in the format required by the transmission planner and prepare the data submission package.

Compliance Documentation

We prepare test records and compliance documentation that covers each requirement in the standard, including the test conditions, instrumentation, and submission records.

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