Model building methodology

ATC will strive to develop and maintain consistency in the power flow models used for planning efforts and in assessing whether and under what conditions transmission service is available. The starting point for ATC power flow models will be MMWG models. ATC will use load forecasts provided by the company’s end-use load-serving customers as input into future model building efforts, both internally and in conjunction with NERC, Regional Entity (RE), and Regional Transmission Organization (RTO) initiatives. These forecasts may be adjusted by ATC if adjustments are needed for transmission planning purposes either with concurrence from the company’s customers or independently of the company’s customers. All ATC power flow models will be developed using PTI PSS/E software.

Further details can be found in Methodology and Assumptions

(Applicable NERC Standards: MOD-032)

Voltage Schedule

  1. The power flow models will implement ATC’s generator voltage schedule. The generator voltage schedule is defined as a:
    1. Target voltage of 102 percent of the nominal transmission voltage as measured at the point of interconnection between the generator and the transmission network unless another voltage schedule has been identified and,
    2. Normal voltage range of 95 to 105 percent of nominal transmission voltage.

    Due to limitations imposed by the NERC model building process, the generator voltage schedule target modeled in the NERC power flow models may only approximate ATC’s voltage schedule at the point of interconnection. (Applicable NERC Standard: VAR-001)

  2. Generators that do not have automatic voltage regulation (AVR) or are not controllable (unmanned stations and no remote control) have been considered. When modeling these generators, special attention must be given to the limitations of these units.
  3. Generator Interconnection studies follow the dispatch guidelines in the Specific Study Methodologies write up of the Interconnection Studies section.

Generation Dispatch

General Dispatch Methodology
  1. Generation reported by ATC’s members will be dispatched in accordance with contractual and local or regional economic dispatch considerations as applicable.
  2. Voltage and Local Reliability (VLR) units identified in a MISO standing Operating Guide will be dispatched in accordance with the standing Operating Guide.
  3. Generator Interconnection studies follow the dispatch guidelines defined in the Interconnection studies page.
Distribution Connected Generation

Distribution connected generation (DCG) will be modeled according to the “ATC Generator Modeling Decision Methodology” which is accessible at

Wind Generation Dispatch Methodology
  1. Power-Voltage (P-V) analysis shall model wind generation at its full output level.
  2. Generator Interconnection studies will model wind generation following the guidelines in the MISO Business Practice Manual for Generator Interconnections.
  3. Generally, for each system load condition case, wind generation is modeled at 20 percent of its reported capability level for general planning studies, although sensitivity analyses may dispatch wind generators at various output levels.
Hydro Generation Dispatch Methodology
  1. The summer peak Pmax dispatch levels have been reflected in the powerflow models unit Pmax capability. In some instances Pmax may not be equal to rated power.
  2. If documented typical summer peak dispatch information is available it may be used, provided it does not exceed the latest available Generator Owner’s MOD-025 test data.
  3. If documented typical summer peak dispatch information is not available then a default dispatch of 30 percent of unit rated power will be applied.  If the 30 percent of unit rated power value exceeds the MOD-025 test data then the unit will be dispatched to the Pmax derived from the Generator Owner’s MOD-025 test data. If the 30 percent of unit rated power value is less than the MOD-032 Pmin data for the unit, the unit will be dispatched to its Pmin value.
  4. Studies for fall, winter and spring may use different assumptions.

Net Scheduled Interchange

  1. Net scheduled interchange for the ATC system will be coordinated with the necessary regional and interregional parties.
  2. Net scheduled interchange for the ATC system may be altered to evaluate realistic system conditions of significance for system planning purposes.

Dynamic Load Modeling

  1. The PTI PSSE power flow simulation software has Complex Load Modeling options, as a set of CLOD load models. The set of CLOD models have parameters for dynamic load simulation. Their parameters include: percent large motor, percent small motor, percent transformer excitation current, percent discharge lighting, percent constant power, and remaining load.
  2. Based on literature review and heuristics, WPS/PTI developed a table for converting typical peak load splits of major customer classes to the CLOD load model parameters. ATC uses this table to create CLOD load models at transmission interconnection points from the load forecast and customer class information that is provided by the distribution companies. The table is given below.
Customer ClassLarge MotorSmall MotorDischarge LightingTransformer Excitation CurrentConstant PowerRemaining LoadKp of Remaining Load

Next: Facility Condition Methodology