Interconnection studies

The following analyses and procedures should be performed for all new or modified interconnection facilities (generation, transmission, and end-user) to the ATC system to properly assess their reliability impact on the interconnected systems. For some analyses, a formal study report may be appropriate. For other analyses, a simple statement of assumptions and rationale may be sufficient.

Types of Analysis

The analyses are to include steady state, short-circuit, and dynamic assessments that include the requirements in TPL-001-4.

Compliance with Applicable Planning Criteria

The analyses and procedures are to comply with all applicable NERC, Regional Entity, and individual system planning criteria of the affected parties.

Coordination with Affected Entities

The results of the analyses will be jointly evaluated and coordinated by the affected entities.

Essential Documentation

All analyses should include the evaluation assumptions, system performance, alternatives considered, and any jointly coordinated recommendations.

Flow Regulating Equipment

To ensure continued operating flexibility during unexpected system conditions, consideration of adjustments to flow regulation equipment (including, but not limited to, phase angle regulators and high voltage direct current equipment) to accommodate the interconnection of new facilities (generation, transmission, and load) and the approval of Transmission Service Request is prohibited, except under unique circumstances, as defined by ATC. Mitigating system limitations via the adjustment of flow regulating equipment is allowed on a limited and carefully considered basis. Adjustments to flow regulation equipment could lead to conflicting objectives and is intentionally limited to cases that improve system robustness. Limiting adjustment of flow regulation equipment applies for equipment that is not primarily providing voltage support.

Specific Study Methodologies

Generator Interconnection Studies
  1. Shall utilize AC solution methods to screen for overloaded elements. Linear DC analysis may only be used to determine Distribution Factors (PTDF and LODF) for MISO generator interconnection studies and the impact of multiple Generator Interconnection Requests on a transmission facility for cost allocation purposes.
  2. Steady-state analysis shall utilize the following generation dispatch:
    • Shoulder Load Levels: Studied generation, local competing requests, and existing local generation dispatched at their expected output level. This corresponds to base load generating facilities being dispatched at their Pmax, combined cycle generating facilities dispatched at 50 percent of their Pmax, peaking units offline, and all wind generation at 100 percent of their Pmax.
    • Summer Peak Load Levels: Studied generation, local competing requests, and existing local generation dispatched at their expected output level. This corresponds to base load and combined cycle generating facilities being dispatched at their Pmax, peaking units at their Pmax, and all wind generation at 20 of their Pmax.
    • Additional/Alternative Seasonal Load Levels: If deemed necessary to adequately assess system reliability in the study area, other seasonal models may be required. Generating facilities should be dispatched at expected output levels, regardless of fuel type, in accordance with historical data and ATC Control Area merit order or ATC-wide merit order, depending upon what type of case is selected. In general, lighter load conditions should dispatch wind generation at 100 percent of their Pmax and winter peaking load conditions should dispatch wind generation at 20 percent of their Pmax.
  3. Dynamic stability studies shall dispatch generation in the study area to ensure expected more severe operating scenarios are assessed. Generally, this will involve dispatching all generation local to the study area regardless of fuel type, load level, or merit order. Engineering judgment and potentially sensitivity analysis should be utilized to determine a severe, yet credible dispatch.
  4. Existing generators in the study area with Interconnection Agreements allowing for higher seasonal output (e.g., combustion turbines with increased output capability at colder ambient temperatures) shall be modeled at that output level during dynamic stability studies. New Interconnection Requests with higher seasonal output levels will be analyzed at the higher output if the Interconnection Customer elects the additional capacity in the MISO Generator Interconnection Process.
  5. Power Factor Requirements for Wind Farm Installations shall be determined in alignment with the following methodology. In the System Impact Study, the required power factor range is determined by calculating the required composite power factor at the POI to maintain ATC’s standard generator voltage schedule or an area-specific transmission voltage schedule, if one exists. The two criteria to be considered are summarized as:
    • To ensure system reliability, the interconnecting generator must be capable of maintaining a POI voltage schedule that is specified by the Transmission Operator. Any generator interconnected within the ATC system is expected to maintain a voltage of 1.02 p.u. at its POI to facilitate the transmission operations reliability under normal system conditions (system intact) and P1 and P2 Contingencies, unless another voltage level is communicated to the generator by the ATC Transmission Operator (cf. NERC Reliability Standard VAR-001).
    • The interconnecting generator is not required to design for reactive power capability outside of ATC’s standard power factor range of 0.95 leading power factor (absorbing reactive power from the Network) to 0.90 lagging power factor (supplying reactive power to the Network) at the POI.

The final power factor range applicable to a wind farm is determined by replacing the wind farm representation with a generator of equivalent net real power connected to the same location as the high-side of the substation transformer, setting the voltage schedule for the generator to 1.02 per unit or any applicable variation and opening the reactive capability of the generator (i.e. Qtop = 9999 MVAR, Qbottom = -9999 MVAR). The reactive power output of this “lumped” generator is recorded for peak and non-peak models under system intact and relevant P1 and P2 Contingencies. The widest power factor range as identified by this analysis is recorded.

The final power factor range is ATC’s standard range of 0.95 leading to 0.90 lagging if a demonstration has been made for additional reactive compensation beyond the inherent capability of the wind farm as supplied by the customer during the Pre-Queue state of the MISO Attachment X process.

A portion of the required power factor capability may need to be dynamic in nature to quickly restore system voltage when minimum system voltage criteria would be violated for the pre-Contingency power factor used to hold voltage schedule.

Next: Under-Frequency Load Shedding (UFLS)