1. © 2012 Siemens Industry, Inc. All rights reserved. Answers for infrastructure. ERCOT RARF Workshop Siemens PTI Procedures Alicia Dortch Nelson J Bacalao Siemens PTI Houston Office August 2013

2. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Agenda ■Introduction ■Identification and tracking of missing data ■Collection of values for missing data ■Derivation of data “still missing” August 15Page 2

3. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Introduction ■Siemens PTI was contracted by ERCOT to assist with the collection, analysis, and production of data in completion of the Resource Asset Registration Forms. ■In this presentation we will go over the procedures proposed by Siemens PTI to aid ERCOT in the completion of RARF missing data. ■This is ongoing work and some of these procedures, in particular those for estimation of parameters may be fine-tuned as we finish the project. August 15Page 3

4. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Data Identification and Tracking ■Siemens PTI developed a data tracking sheet to record, categorize and organize the missing data needed for short circuit, dynamics, and steady state simulation models. ■This sheet was populated from a query of RARF data in the ERCOT HUB. It assists with communicating all missing or suspect data to the Resource Entities using a single document outside of the multiple document RARF forms. ■The next slide provides a view of this spreadsheet. August 15Page 4

5. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Data Identification and Tracking Tracking Spreadsheet. August 15Page 5

6. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Data Identification and Tracking Tracking Spreadsheet.

7. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Data Identification and Tracking Explanation Tracking Sheet: ■Columns A – E: Uniquely identify the unit of discussion ■Columns F – I: Specifies which portion of the dynamics data is of concern (i.e. exciter, generator, governor, stabilizer) since this is currently not included as actual fields of the RARF 5.1 version ■Columns J – M: Refer to the original RARF missing data file. This links the tracking information back to the original RARF data file of discussion. ■Columns N – P: Denotes communication between ERCOT and Siemens PTI to help with Siemens review and discussion with Resource Entities (REs.) ■Column Q: Simply denotes the original value of the data point. It will be null or blank if referring to missing data and will have a number if referring to Suspect data (identified in ERCOT audit checks as outside of an expected value). ■Column R – T: Directly relate to column Q. Provides more detail comments on any identified suspect data along with the commenter and comment date. August 15Page 7

8. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Collection of Values for Missing Data The process to resolve the missing data: 1.Initial Resource Entity RE call: ERCOT introduces the RE to the tracking sheet and Siemens PTI. Tracking sheet reviewed and missing data points explained, Provide suggestions for acquiring data in house & set plan for resolving any remaining missing data items. 2.Follow-up with RE 3.Contact TSP The TSP is used as a data source calling on their experience from case builds, interconnection studies or test reports/data sheets. The TSP is contacted in situations when the RE is unable to produce the required RARF data. August 15Page 8

9. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Collection of Values for Missing Data 4.PTI Estimation Siemens PTI provides a procedure for selecting typical parameters when the RE or the associated TSP cannot or have not yet provided the information required for the RARF. Siemens PTI methodology proposed is expected to produce reasonable parameters, but the actual equipment on site may be unique and its parameters deviate, possibly significantly, from this typical data. Therefore typical data should be highlighted as such and replaced by actual data when it becomes available. In the balance of this presentation we will discuss Siemens PTI methodology. August 15Page 9

10. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation Procedures will be presented to cover the following areas that were identified as the most frequently lacking: ■Information to represent three winding transformers with buried tertiary. ■Typical parameters for Wind Turbine Generators (WTG.) ■Methodology to estimate grounding impedance of generators. ■Methodology to estimate saturated impedances when unsaturated data is available as well as the machine’s saturation curve. ■Methodology to find “peers” for units that can be used to estimate the data for plants whose information is lacking. August 15Page 10

11. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Overview ■WTG plants sometimes use a three winding transformer with Y grounded on the high (H) and medium (X) sides and have a delta connected tertiary (Y). ■The tertiary role is just to control harmonics and there are no external connections to it. Its rating is generally known. ■The positive impedance primary to secondary are also usually known (X +H-X ). ■From tests it is possible to determine the zero sequence impedance primary to tertiary (Z 0H-Y ), primary to secondary (X 0H-X ) and secondary to tertiary (X 0X-Y ). ■The corresponding positive impedances to the tertiary cannot be determined from tests, as there is no access to the tertiary. ■Tests need to be carried out for a number of units and this will take time. August 15Page 11

12. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Overview (con’d) ■Based on a large population of over 100 three winding transformers with 34.5 kV class secondary, 115 or 138 kV primary (345 kV limited) and a tertiary, we developed a procedure by which the corresponding impedances primary to tertiary and secondary to tertiary can be estimated given the positive impedance primary to secondary (X H-X ). ■With this method, The two winding equivalents can be determined, when the tests above are available. The data for three winding models in PSS®E can be produced. It can also be used to estimate missing parameters, while the tests are yet to be carried out. August 15Page 12

13. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Estimation of Impedances ■Various methods for estimation were investigated and the least volatile was found to be making the estimation based on the following ratios, where the equations correspond to the trend line approximation (see next): ■Thus given the impedance high to medium X H-X and the tertiary MVA rating the impedance medium to tertiary X X-Y can be estimated from Ratio 1. ■Once this value is known then the impedance high to tertiary X H-Y can be estimated from Ratio 3: August 15Page 13

14. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Ratio 1 August 15Page 14

15. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Ratio 3 August 15Page 15

16. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Ratio 2 (Not Used) August 15Page 16

17. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Estimation of Impedances ■With this procedure all the positive sequence impedance between windings can be obtained and based on them the equivalent impedances of the “three winding transformer” model can be determined using the following equations: August 15Page 17

18. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Estimation of zero sequence impedances ■In the cases that the tests have not yet been carried out and the zero sequence impedances are unknown, we have two cases; 1.If the zero sequence primary to secondary is known, calculate the ratio of this impedance to the corresponding positive impedance and use the ratio to estimate the corresponding zero sequence impedances primary to tertiary and secondary to tertiary. –Note that this is an approximation as the ratios are not necessarily the same. 2.If no zero sequence is known, then while the tests are to be conducted a conservative ratio of 80% of the positive impedance could be used. –Note that as shown in the next figure, it is expected that this ratio in the actual transformer will be greater, thus the zero sequence is likely to be larger and the short circuits lower. August 15Page 18

19. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Ratio Zero to Positive sequence vs population of transformers August 15Page 19

20. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – 3 winding transformers Examples ■We show some examples below that illustrate the level of error to be expected with this method ■As can be observed the values are not accurate (it was never expected), but are in the order of magnitude and allow the representation of the path to ground in the zero sequence. Case 1 Case 2Case 3 August 15Page 20

21. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Wind Turbine Generators Overview ■For wind turbine generators the typical parameters depend primarily on the generator type (I to IV) and manufacturer. ■Typical parameters are provided:  For Type 1 and 2 the impedance correspond to the impedance of the machine seen from the stator at an estimated rated slip.  For Type 3 and 4 the values provided correspond to an approximate equivalent impedance that reproduces the contribution to a remote short circuit.  For short circuit we provide for Type 1 and Type 2 an impedance value (X’) that can be used to estimate initial contribution to the short circuit.  We also provide the decay using the rotor time constant ( X’/[377*R rotor ] )  This same value X’ can be used as an approximation for the negative sequence impedance. August 15Page 21

22. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Wind Turbine Generators Overview ■Typical parameters are provided (cont.):  For Type 3, if there is crow-bar operation, the control are by-passed and the machine behaves like asynchronous generator. We provide similar parameters to those for the Type 1 and Type 2.  For Type 4 machines and Type 3, if the controls operate, we provide typical values for just after the short circuit and various cycles afterward.  Finally the zero sequence impedance of a Type 1, Type 2 and Type 3 with crow-bar operation is approximately equal to the stator leakage.  Type 4 and Type 3 with controls in place oppose the zero sequence and present fairly high impedance, we approximate it with a value of 50.  WTG are normally not grounded. ■The following table provides the typical information for WTG that can be used to estimate missing data. August 15Page 22

23. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International WTG Typical Data August 15Page 23

24. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Wind Turbine Generators Recommended procedure to estimate WTG missing data using Table above: 1.First determine the turbine type for which data is missing, its manufactures and size. 2.Check if there is a similar turbine in the system with a valid RARF that can be used as a guide (Reference RARF.) 3.With the type, size and manufactures, enter in Table and find the closest machine. If a similar turbine was found in the step above, then the parameters should be close and can be incorporated in the RARF to be sent to the RE for validation. 4.If there is disagreement between these sources, an assessment of the applicability of Table to the particular turbines should be made and if valid then Reference RARF should be reviewed to identify special conditions. 5.If no similar machine exist in the system, then use the closes machine’s parameters in Table as a temporary value(s) 6.Finally the estimated parameter should be replaced from actual data as soon as it becomes available. August 15Page 24

25. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Generator Grounding Resistance Overview ■Synchronous machines are not designed to withstand single line to ground currents hence they are connected to the system with Delta-Y GSU transformer with delta on the generator size and their neutral is grounded through a very high resistance. ■The value of the resistance should be represented on pu of a 100 MVA basis (system basis), however in some occasions the information is in generator drawings with values in ohms connected to the generator neutral via a transformer and it is not clear how to produce the required value in pu. ■We discuss two cases; a) drawings are available with the values in ohms and b) no grounding information is available. August 15Page 25

26. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Generator Grounding Resistance Drawings are available ■The following information is available  Rg0 = Resistance in ohms connected to the LV side of the neutral transformer.  VH = Nominal high voltage of the neutral transformer.  VL = Nominal low voltage of the neutral transformer; where the resistance is connected.  VM = Nominal generator voltage. ■The resistance referred to the generator’s neutral R g1 is given by: ■…and to be used in the zero sequence model is multiplied by 3, so: ■Using this last resistance we estimate the single line to ground short circuit current as follows (ignore reactance's) : August 15Page 26

27. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Generator Grounding Resistance Drawings are available: Example of Application ■The table below shows the results of the application of the procedure above to three generators: ■Here we note that the neutral current is in the order of a few amperes. August 15Page 27

28. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Generator Grounding Resistance Drawings not available ■If the drawings are not yet available, we can make the assumption that the current has to be limited to a value in the order of a few amperes, ■Based on the example above, we propose using maximum neutral current of 10 Amps ■The following formula can be used to estimate the grounding resistance in pu, where the MVA base defines whether it is on the generator or system base. August 15Page 28

29. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Saturated Impedance Overview ■The RARF requires both saturated and unsaturated values. In general the unsaturated values are available as these values are the ones employed in stability evaluations as the saturation is modeled explicitly, but saturated values may be missing. The saturation is non linear and its effect on the impedances is heavily a function of the machine’s design and its operating point. ■Particularly during transients this effect becomes more complicated due current displacements (i.e. unidirectional currents) in the machine. ■When available the machine’s manufacturer provides the saturated values obtained from detailed models of the machines and assumptions with respect of its operating conditions. ■To take advantage of as much information as possible and approximate the procedure used by the machine’s manufacturer, we propose using the classical equations of the synchronous machine to obtain an estimation of the saturated values. August 15Page 29

30. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Saturated Impedance Procedure ■The following equations and equivalent circuits provide a relation between the machine’s impedance X d, X d ’ and X d ” and the magnetizing impedance X ad, Eq 1 Eq 2 Eq 3 August 15Page 30

31. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Saturated Impedance Procedure ■First X ad, X fl and X Dl are determined using the following equations: ■Next the saturated values X ad must be obtained, which are derived from the formula: ■Where S is the saturation factor and normally S(1) and S(1.2) are known August 15Page 31

32. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Saturated Impedance Procedure (cont) ■For other values of S(V) we use the equation: ■The coefficients A and B are determined using S(1) and S(1.2) and that the machine at 0.9 pu should have little or no saturation. ■For steady state S(1) is proposed. ■For the transient period S(1) gives incorrect results, as the saturation conditions are very different and tests with the model identified that a value of S(2) gives reasonable approximations. ■Finally with X ad-s and Eq 1 Xdv is found, Eq 2 gives Xd’v and Eq 3 gives Xd”v. ■The next slide shows results for 4 generators. August 15Page 32

33. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – Saturated Impedance Tests August 15Page 33

34. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – “Peer” Identification Overview ■For all remaining missing data, PTI is compiling a list of typical data from similar non-wind unit types (i.e. CCP, coal fired, etc.) in the ERCOT territory with known data and of similar type and output. If there is nothing similar in the ERCOT system, we will then use a listing of generators in the Eastern Interconnect as a data source for typical values. ■Machine parameters are largely based on manufacturer. In lieu of knowing the manufacturer for all units in ERCOT, we are using the machine type as a filter with the assumption that for each type of unit / unit output combination there will be a small subset of manufacturers therefore allowing for a “peer” identification based on similar parameters. August 15Page 34

35. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International PTI Estimation – “Peer” Identification Procedure 1.Determine generator type of unit with missing data 2.Compile list of units of similar type with completed data. 3.In the case of CCPs, there is an additional level of categorizing based on plant configuration (i.e. 2x1, 3x1). The further increases the likelihood of accurate ‘peer’ detection. 4.Identify candidates with similar output 5.The detailed parameters of the candidates should then be compared to the available parameters of the machine of question. The most similar candidate is now identified as a ‘peer’. 6.Complete the missing RARF with values from the indentified ‘peer’ machine. August 15Page 35

36. © 2012 Siemens Industry, Inc. All rights reserved. Siemens Power Technologies International Questions Contact Information: Nelson Bacalao Nelson.Bacalao@siemens.com Alicia Dortch Alicia.Dortch@siemens.com