© 2012 siemens industry, inc. all rights reserved. answers for infrastructure. ercot rarf workshop...

© 2012 Siemens Industry, Inc. All rights reserved.© 2012 Siemens Industry, Inc. All rights reserved.

Answers for infrastructure.

ERCOT RARF WorkshopSiemens PTI ProceduresAlicia DortchAlicia DortchNelson J BacalaoNelson J BacalaoSiemens PTI Houston OfficeSiemens PTI Houston Office

August 2013August 2013

© 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”

Apr 19, 2023


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.

Apr 19, 2023


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.

Apr 19, 2023


Data Identification and TrackingTracking Spreadsheet.

Apr 19, 2023


Data Identification and TrackingTracking Spreadsheet.


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.

Apr 19, 2023


Collection of Values for Missing Data

The process to resolve the missing data:1. Initial Resource Entity RE call:

1. ERCOT introduces the RE to the tracking sheet and Siemens PTI.

2. Tracking sheet reviewed and missing data points explained,

3. Provide suggestions for acquiring data in house & set plan for resolving any remaining missing data items.

Follow-up with RE

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.

Apr 19, 2023


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.

Apr 19, 2023


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.

Apr 19, 2023


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 (Z0H-Y), primary to secondary (X0H-X) and secondary to tertiary (X0X-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.

Apr 19, 2023


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 (XH-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.

Apr 19, 2023


PTI Estimation – 3 winding transformersEstimation 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 XH-X and the tertiary MVA rating the impedance medium to tertiary XX-Y can be estimated from Ratio 1.

■ Once this value is known then the impedance high to tertiary XH-Y can be estimated from Ratio 3:

Apr 19, 2023


PTI Estimation – Ratio 1

y = 0.374ln(x) - 0.3529R² = 0.6406

0%

50%

100%

150%

200%

250%

300%

0 20 40 60 80 100 120 140 160 180

Rati

o 1:

Med

ium

to Te

rtiar

y as

% o

f Hig

h to

Med

ium

Tertiary MVA Rating

Series1 Log. (Series1)

Apr 19, 2023


PTI Estimation – Ratio 3

y = 7.9425x-0.624

R² = 0.6306

0%

50%

100%

150%

200%

250%

300%

0 20 40 60 80 100 120 140 160 180

Ratio

3: X

Hig

h to

Ter

tiary

as

% o

f Med

ium

to

Terti

ary

Tertiary MVA Rating

Series1 Power (Series1)

Apr 19, 2023


PTI Estimation – Ratio 2 (Not Used)

y = 0.1976ln(x) + 0.4771R² = 0.2538

0%

50%

100%

150%

200%

250%

300%

0 20 40 60 80 100 120 140 160

Rati

o 2:

X H

igh

to Te

rtiar

y as

% o

f Hig

h to

Med

ium

Tertiary MVA Rating

Series1 Log. (Series1)

Apr 19, 2023


PTI Estimation – 3 winding transformersEstimation 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:

Apr 19, 2023


PTI Estimation – 3 winding transformersEstimation 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.

Apr 19, 2023


Ratio Zero to Positive sequence vs population of transformers

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%1 11 21 31 41 51 61 71 81 91 101

111

121

131

141

151

161

171

181

191

201

211

221

231

241

251

261

271

281

291

301

311

321

331

341

351

361

371

381

391

401

411

421

431

441

451

461

471

481

491

X0 1-2 / X 1-2

X0 1-3/ X 1-3

X0 2-3/ X 2-3

Apr 19, 2023


PTI Estimation – 3 winding transformersExamples

■ 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 2 Case 3

Apr 19, 2023

H Base 48 MVA T Base 41.3 MVA Ratio 1 109.5% Ratio 3 77.9%

Estimated Actual

X H-X 14.4% 14.4%

X X-Y 14.9% 11.0%

X H-Y 11.6% 11.9%

H Base 56 MVA T Base 33.6 MVA Ratio 1 96.2% Ratio 3 88.6%

Estimated Actual

X H-X 11.8% 11.8%

X X-Y 11.4% 9.2%

X H-Y 10.1% 17.8%

H Base 100 MVA T Base 100 MVA Ratio 1 137.0% Ratio 3 44.8%

Estimated Actual

X H-X 16.9% 16.9%

X X-Y 23.1% 14.0%

X H-Y 10.4% 18.0%


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*Rrotor] )

This same value X’ can be used as an approximation for the negative sequence impedance.

Apr 19, 2023



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.

Apr 19, 2023


WTG Typical Data

Type 1 Type 1 Type 1 Type 1 Type 2 Type 2 Type 2 Type 2 Type 3 Type 4General Data Case 1 Case 2 Vestas V82 M1000 Case 1 Zuzlon Vestas V80 Vestas V4760 GE SiemensPositive Sequence (pu) 3.93 2.106 3.9452 3.927 3.776 2.486 5.035 3.734 0.8 0.65Negative Sequence (pu) 0.177 0.158 0.154 0.177 0.303 0.109 0.302 0.236 4 4Zero Sequence (pu)* 0.1 0.0873 0.08985 0.1 0.126 0.0536 0.12602 0.1115 50 50MW 1.67 1.82 1.65 1.00 1.67 2.28 1.80 1.80 1.50 2.30Voltage, kV 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6* Generators are ussually not grounded

Estimated short circuit current (does not include the GSU Transformer.) For Type 2 worst case decay, no external resitance. For Type 3 assumes crow bar operationInitial Short Circuit Reactance 0.1773 0.1581 0.1543 0.1773 0.3030 0.1088 0.3022 0.2356 0.2Maximum Initial current (pu) 5.64 6.32 6.48 5.64 3.30 9.19 3.31 4.24 5.00Current @ 1 Cycle 3.78 4.23 4.68 4.25 2.83 7.60 2.84 3.47 4.00Current @ 2 Cycles 2.53 2.83 3.38 3.20 2.43 6.28 2.44 2.84 4.00Current @ 3 Cycles 1.69 1.90 2.44 2.41 2.08 5.20 2.09 2.32 3.00Current @ 4 cycles 1.13 1.27 1.76 1.81 1.79 4.30 1.80 1.90 3.00

I max instantaneous (with control action) 3.00 3.00I @ 2 to 3 cycles 1.25 1.54I @ 4+ cycles 1.11 1.11

Modeling DataX, synchronous reactance, pu on machine base 3.930 2.106 3.945 3.927 3.776 2.486 5.035 3.734X', transient reactance, pu on machine base 0.177 0.158 0.154 0.177 0.303 0.109 0.302 0.236X", subtransient reactance, pu N/A N/A N/A N/A N/A N/A N/A N/AXl, leakage reactance, pu 0.100 0.087 0.090 0.100 0.126 0.054 0.126 0.112Inertia, H 5.300 4.870 4.804 5.296 3.460 4.106 4.356 4.95 N/AXA, stator reactance, pu 0.087 0.126 0.054 0.126 0.112XM, magnetizing reactance, pu 3.926 6.840 2.600 6.840 4.230X1, rotor reactance, pu 0.072 0.180 0.056 0.181 0.128Rotor resitance (no external) 0.008 0.010 0.008 0.008 0.007 0.003 0.007 0.008RPROT_MAX, a sum of R_ROT_MACH and total external resistance, pu 0.010 0.110 0.100 0.110 0.105

Apr 19, 2023



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.

Apr 19, 2023


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.

Apr 19, 2023


PTI Estimation – Generator Grounding ResistanceDrawings 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 Rg1 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) :

Apr 19, 2023


PTI Estimation – Generator Grounding ResistanceDrawings 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.

Apr 19, 2023

Generator xxx_UNITy xxxx_UNITw xxxx_UNITz Generator MVA Basis 147 147 645 Generator Voltage KV 12 13.8 22.0 MVA Basis 100 100 100 V high (kV) 12.00 14.40 22.90 V low (kV) 0.240 0.240 0.240

Rgo ohms (low side) 0.635 0.66 0.2689

Rg1 ohms (high side) 1588 2376 2448

Rg1 pu (system) 1102 1248 506

Rg1 pu (machine) 1621 1834 3263

Rzero = 3 * Rg pu (system) 3307 3743 1517

Rzero = 3 * Rg pu (machine) 4862 5502 9788 I zero SLG pu (system) 0.00030236 0.00026717 0.00065900 I zero SLG pu (machine) 0.00020569 0.00018175 0.00010217 I zero SLG (Amps) 1.45 1.07 1.7294

I neutral SLG (Amps) 4.36 3.21 5.19


PTI Estimation – Generator Grounding ResistanceDrawings 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.

Apr 19, 2023


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.

Apr 19, 2023


PTI Estimation – Saturated ImpedanceProcedure

■ The following equations and equivalent circuits provide a relation between the machine’s impedance Xd, Xd’ and Xd” and the magnetizing impedance Xad,

Eq 1

Eq 2

Eq 3

Apr 19, 2023



Procedure■ First Xad, Xfl and XDl are determined using the following equations:

■ Next the saturated values Xad 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

Apr 19, 2023



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 Xad-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.

Apr 19, 2023


PTI Estimation – Saturated ImpedanceTests

Apr 19, 2023

Data (unsaturated values) Parameter BBSES Unit 1 BBSES Unit 2 CTA STD-Axis Synchronous Reactance Xd 2.052 2.064 2.173 2.177D-Axis Transient Reactance X'd 0.381 0.381 0.248 0.260D-Axis/Q-Axis Sub-Transient Reactance X"d = X"q 0.302 0.304 0.159 0.154Leakage Reactance Xl 0.236 0.236 0.125 0.138Open Circuit Saturation factor S(1.0) 0.136 0.136 0.152 0.133Open Circuit Saturation factor S(1.2) 0.529 0.529 0.571 0.684Base MVA 696 700 143.4 169

Saturation Parameters B multiplier for exponent in B*Exp(A*V) 0.0582059 0.0578336 0.0478286 0.0373813A multiplier for exponent in IM = B*Exp(A*V) 2.3775758 2.3775758 2.4643658 2.7243146K(v) for Xd 0.88028169 0.88028169 0.8680556 0.8826125K(v) for transient state (Xd' and Xd") 0.162858729 0.162858763 0.1477161 0.1128883

Model ParametersMagnetizing D axis (unsat) Xad 1.816 1.82769 2.0483 2.039Magnetizing D axis (sat-steady state) Xad_s_1 1.60 1.61 1.78 1.80Magnetizing D axis (sat-transient) Xad_s_2 0.296 0.298 0.303 0.230Field Leakage Reactance Xfl 0.157582286 0.157494874 0.130858 0.1297642Damper winding leakage Xdl 0.121139241 0.12854931 0.0469888 0.0184151

ResultsD-Axis Synchronous Reactance (Sat) - Estimated Xd (estimated) 1.835 1.845 1.903 1.938D-Axis Synchronous Reactance (Sat) - Actual Xd (actual) 1.804 1.815 1.956 1.956D-Axis Transient Reactance (sat) - Estimated Xd' (estimated) 0.339 0.339 0.216 0.221D-Axis Transient Reactance (sat) - Actual Xd' (actual) 0.335 0.337 0.222 0.222D-Axis Sub-Transient Reactance (sat) - Estimated Xd"(estimated) 0.292 0.293 0.156 0.153D-Axis Sub-Transient Reactance (sat) - Actual Xd" (actual) 0.261 0.262 0.146 0.154


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.

Apr 19, 2023


PTI Estimation – “Peer” Identification

Procedure1. 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.

Apr 19, 2023


Questions

Contact Information:

Nelson [email protected]

Alicia [email protected]

© 2012 siemens industry, inc. all rights reserved. answers for infrastructure. ercot rarf workshop...

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