Case Metrics 2015 Summer Base Case Quality Assessment Phase I Powerflow and Dynamics Case Quality Metrics FINAL

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Karin Cook
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1 Case s 2015 Summer Base Case Quality Assessment Phase I Powerflow and Dynamics Case Quality s FINAL Introduction Powerflow and dynamics cases are the foundation of virtually all power system studies. Calculations of operating limits, planning studies, and performance analyses for various operating conditions all depend on mathematical representations of transmission topology, generation, and load. A powerflow case is a collection of steady-state models for system topology, load, generation, dispatch, and interchange that constitute a snapshot of the selected set of operating conditions. A dynamics case is a collection of dynamic models used in conjunction with a powerflow case to perform a stability analysis of system performance. There is a need to track the quality of the base cases that are routinely developed for the major Interconnections (Eastern 1, Western, and Texas). s presented in this paper are used to measure the quality of powerflow and dynamics cases developed for the summer of Trending the metrics will provide an objective trend of base case quality using metric information, providing an integrated view of reliable performance. Base case quality has two principal aspects: Case Data Quality Reasonableness of the data in the individual equipment models that comprise the case for the characteristics and operating states desired. Case Fidelity Ability of the case to accurately model measured power system behavior for: The type of system conditions the case is intended to model such as heavy summer loads, light loads, etc. The conditions measured during a distinct system event or disturbance. The metrics presented in this report focus solely on the case data quality of the individual component models comprising the base case. Validation of case fidelity or overall model performance requires comparison of the cases to actual measured system conditions and are not included in this report; Interconnection-wide measurements have not yet been scheduled. 1 The Eastern Interconnection powerflow and dynamics cases include the Québec Interconnection.

2 Criteria for Case Quality s (Phase I) Phase I of the case metric analysis uses criteria indicative of blatant errors and/or violations of modeling criteria in the steady-state and dynamics cases. The following metrics are used to assess the quality of the powerflow and dynamics cases provided for each Interconnection: Steady-state powerflow cases 1. Dispatched generator real power output should not exceed the maximum real power capability of the unit (Pgen <= Pmax). Note: Although small violations of this Pmax rule appear trivial, the result is same for all violations the case will not initialize in dynamics. 2. Dispatched generator real power output should not be less than the minimum real power capability of the unit (Pgen >= Pmin). Note: Although small violations of this Pmin rule appear trivial, the result is same for all violations the case will not initialize in dynamics. 3. Scheduled area interchanges should sum to zero MW. 4. Active voltage control devices controlling the same bus should not have conflicting voltage regulation setpoints. 5. Transformers controlling voltage should have a voltage bandwidth that is sufficiently large in relation to the tap step of the transformer. Voltage bandwidths that are too small (or tap steps that are erroneously too large) may result in the lack of existence of a powerflow solution. The ratio of tap step (p.u.) to voltage bandwidth (p.u.) should be no less than 2; ratios below 1.25 are considered flagrant violations of this criteria, as they are extremely likely to prevent a powerflow solution from being found. 6. The continuous (Rate A) and emergency (Rate B) ratings of a branch should be consistent. The continuous rating (Rate A) of the branch circuit should be less than or equal to the emergency rating (Rate B), and the ratio between the emergency rating (Rate B) and the continuous rating (Rate A) is checked against a threshold value (3.0) to identify probable errors. Selection of this ratio is based on engineering judgment. 7. Branch circuit loading should not exceed the circuit s continuous rating (Rate A); 100% of Rate A is used to identify violations, 105% of Rate A is used to identify flagrant violations. Dynamics cases 1. Generating units larger than the criteria threshold established for each Interconnection 2 should have a generator model included in their dynamics record; units without a generator model are flagged as violations of the modeling criteria. 2. Generating units larger than the criteria threshold established for each Interconnection1 and which have a model but are load netted anyway are also tallied. (This additional metric is needed to help identify all generating units without active models in the case, as item 1 above overlooks generators 2 20 MVA for the Eastern Interconnection; 10 MVA for the Western and Texas Interconnections Case s 2015 Summer Base Case Quality Assessment 2

3 that have models but are load netted anyway, and item 3 below overlooks generators that lack models and are dispatched out-of-service in the case.) 3. Generating units larger than the criteria threshold established for each Interconnection should not be netted as negative load; any such units that are netted are flagged. 4. Generating units larger than the criteria threshold established for each Interconnection 3 should not be modeled with a classical generator model. 5. Generating units should have consistent generator reactance values. For example, the following measures are used to assess consistency of round rotor generators: D-axis synchronous reactance (Xd) should not be less than d-axis transient reactance (Xd ). D-axis transient reactance (Xd ) should not be less than d-axis subtransient reactance (Xd ). Subtransient reactance (Xd ) should not be less than stator leakage reactance (Xl). Q-axis synchronous reactance (Xq) should not be less than q-axis transient reactance (Xq ). Q-axis transient reactance (Xq ) should not be less than q-axis subtransient reactance (Xq ). Software Differences Two power simulation software packages are primarily used for assembling Interconnection-wide cases: PSS/E from Siemens PTI (for the Eastern and Texas Interconnections) and PSLF from GE (for the Western Interconnection). Because of differences in the handling of data by these two programs, the methodology for calculating the number of instances of criteria violations may vary between Interconnections for some of the metrics: PSS/E stores the voltage setpoint for generators and static VAR systems with the device data record, whereas PSLF stores the voltage setpoint for these types of devices with the bus data record. Therefore, in PSLF, it is not possible to have voltage schedule conflicts for multiple generators and static VAR systems which are regulating a common location. (However, transformer data records in PSLF have their own voltage regulation data.) 3 50 MVA for the Eastern and Texas Interconnections; 0 MVA for the Western Interconnection Case s 2015 Summer Base Case Quality Assessment 3

4 Numerical Scores for Case s Generally, the raw count of each of the instances of data issues specified in the criteria above is not, by itself, a suitable metric. Most of these raw counts need to be scaled to reflect the size of the Interconnection being evaluated. This scaling is done here by expressing each of the raw counts as a percentage of the total number of elements to which the corresponding criteria is applicable in the case: Steady-state Powerflow Cases 1. Pmax Violations: number of generators with such violations, expressed as a percentage of total number of in-service generators 2. Pmin Violations: number of generators with such violations, expressed as a percentage of total number of in-service generators 3. Schedule interchange sum: sum of desired interchange values for all areas in MW (scaling not recommended) 4. Voltage schedule conflicts: (PSS E) number of transformers with under load tap changing enabled, generators, and switched shunts with auto switching enabled with voltage objective conflicts; (PSLF) number of transformers with such violations, expressed as a percentage of total number of transformers 5. Tap step violations: number of transformers with such violations, expressed as a percentage of total number of transformers 6. Inconsistent emergency ratings: number of branch sections (line sections and transformers) with such violations, expressed as a percentage of total number of branch sections 7. Thermal overloads: number of branch elements (lines and transformer windings) with such violations, expressed as a percentage of total number of branch elements Dynamics Cases 1. Generators without models: number of generators meeting Interconnection size criteria for modeling with no dynamics model, expressed as a percentage of total number of generators (in-service and outof-service) meeting Interconnection size criteria for modeling 2. Netted generators with models: number of generators meeting Interconnection size criteria for modeling with a dynamics model but load netted anyway, expressed as a percentage of total number of in-service generators meeting Interconnection size criteria for modeling 3. Netted generators: number of generators meeting Interconnection size criteria for modeling that are load netted, expressed as a percentage of total number of in-service generators meeting Interconnection size criteria 4. Generators with classical models: number of generators meeting Interconnection size criteria for nonclassical modeling with a classical model, expressed as a percentage of total number of generators (inservice and out-of-service) meeting Interconnection size criteria for non-classical modeling Case s 2015 Summer Base Case Quality Assessment 4

5 5. Generators with faulty reactances: number of generators with inconsistent reactance data (e.g., Xd < Xl), expressed as a percentage of total number of generators (in-service and out-of-service) with models for which the reactance criteria is applicable (e.g., genrou, gentpj) In addition, for each of these five metrics, the maximum real and reactive power limits for each unit found to violate the criteria are totaled. Other Considerations In reading the data for a generator to determine its size, it is found that the generator MVA base value in the powerflow data record (MBASE) is not a reliable value to use for generator size, since many small generators have the program default value of 100 MVA entered for this parameter. Therefore, a more comprehensive approach is used; generator MVA size is determined as the maximum value of the following: Dispatched MVA of the unit PP2 gggggg + QQ2 gggggg, where Pgen and Qgen are the dispatched real and reactive output of the unit in the case MVA of the unit at maximum real and reactive limits PP2 mmmmmm + QQ2 mmmmmm, where Pmax and Qmax are the maximum real and reactive output limits of the unit in the powerflow data MBASE value unless value is MVA (default value), in which case this parameter is ignored Case s 2015 Summer Base Case Quality Assessment 5

6 2015 Data Quality Scores Use of the Scores The goal of the data quality metrics is to promote good modeling practices and to strive to reduce data errors. Therefore, since the performance score is the percentage of elements that have data errors, the goal translates into attempting to drive all performance scores to zero. Eastern Interconnection Case Analysis The 2015 summer peak case (2015SUM) is analyzed in this section. This case represents a seasonal powerflow and dynamics case used for short-term reliability assessments such as those conducted in transmission operations. Steady-State s Score (%) Pmax Violations 5 out of 5, Pmin Violations 2 out of 5, Scheduled Interchange Sum 0.2 Voltage schedule conflicts 27 Tap Step Violations 8 out of 18, Tap Step Violations (Flagrant) 3 out of 18, Low Emergency Rating 9 out of 83, High Emergency Rating 88 out of 83, Thermal Overloads 147 out of 83, Thermal Overloads (Flagrant) 111 out of 83, Dynamics s Pmax Qmax Score (%) (MW) (MVAR) Generators without Models 58 out of 6, ,046 1,470 Netted Generators with Models 41 out of 4, ,476 Netted Generators 70 out of 4, ,794 3,300 Generators with Classical Models 16 out of 4, ,591 3,400 Generators with Inconsistent Reactances 27 out of 5, ,927 1,346 Case s 2015 Summer Base Case Quality Assessment 6

7 Texas Interconnection Case Analysis The calendar year 2015 summer peak case (CY2015) is analyzed in this section. This case represents a seasonal powerflow and dynamics case used for transmission planning reliability assessments. Steady-State s Score (%) Pmax Violations 146 out of Pmin Violations 19 out of Scheduled Interchange Sum 0.0 Voltage schedule conflicts 1 Tap Step Violations 20 out of 1, Tap Step Violations (Flagrant) 1 out of 1, Low Emergency Rating 1 out of 7, High Emergency Rating 1 out of 7, Thermal Overloads 19 out of 7, Thermal Overloads (Flagrant) 17 out of 7, Dynamics s Pmax Qmax Score (%) (MW) (MVAR) Generators without Models 39 out of ,190 1,105 Netted Generators with Models 6 out of Netted Generators 16 out of , Generators with Classical Models 4 out of ,855 10,767 Generators with Inconsistent Reactances 17 out of , Case s 2015 Summer Base Case Quality Assessment 7

8 Western Interconnection Case Analysis The WECC 2015 Heavy Summer case (15HS4A) is analyzed in this section. This case represents a seasonal powerflow and dynamics case used for short-term reliability assessments such as those conducted in transmission operations. Steady-State s Score (%) Pmax Violations 7 out of 2, Pmin Violations 5 out of 2, Scheduled Interchange Sum 0.0 Voltage schedule conflicts 189 out of 8, Tap Step Violations 157 out of 8, Tap Step Violations (Flagrant) 14 out of 8, Low Emergency Rating 46 out of 24, High Emergency Rating 5 out of 24, Thermal Overloads 9 out of 25, Thermal Overloads (Flagrant) 4 out of 25, Dynamics s Pmax Qmax Score (%) (MW) (MVAR) Generators without Models 188 out of 3, ,837 6,489 Netted Generators with Models 1 out of 2, Netted Generators 9 out of 2, , Generators with Classical Models 3 out of 3, Generators with Inconsistent Reactances 120 out of 3, ,485 1,768 Case s 2015 Summer Base Case Quality Assessment 8

9 Case Quality Observations & Conclusions The following are initial observations from the field trials of the case metrics under I. To deal with the presence of machines with values of 100 MVA (default value) for the machine base, a more comprehensive approach was used that includes generated quantities and maximum capability quantities as well as the machine base value. The total generation lacking dynamics models in the Eastern Interconnection is approximately 0.5% of the total generation capacity in the Interconnection. Although comprising a relatively small number of units, an even larger fraction of the generation capacity in the Eastern Interconnection case has dynamics models which have been netted. The metrics concerning load netting of generators require further expansion. The metrics show that a very large fraction of the generation in the WECC case (both number of units and capacity) are missing models; this situation raises significant concerns. NERC staff should work with WECC staff to address this problem. The large number of units in the ERCOT case which are dispatched above their stated maximum real power limits may be reflective of the operations oriented case that was provided by ERCOT. Additional discussions with ERCOT are warranted. Case s 2015 Summer Base Case Quality Assessment 9

MOD Data for Power System Modeling and Analysis

MOD Data for Power System Modeling and Analysis MOD-032-1 Data for Power System Modeling and Analysis A. Introduction 1. Title: Data for Power System Modeling and Analysis 2. Number: MOD-032-1 3. Purpose: To establish consistent modeling data requirements