MODELING OF TRANSFORMERS IN WECC BASE CASES. For WECC SRWG By Rohan Chatterjee Electrical Engineer Transmission Planning

Transcription

1 MODELING OF TRANSFORMERS IN WECC BASE CASES For WECC SRWG By Rohan Chatterjee Electrical Engineer Transmission Planning

2 Present Utility Practices Problems with present practices PowerWorld Use of Transformer Base data for calculating System Base values. PSLF Use of Transformer Base data for calculating System Base values. PSLF EPC file exported to PowerWorld & PTI RAW file format. Examples Used PGE 230/13.8kV GSU, Avista 230/115kV LTC transformer (at Boulder substation). Conclusions 2 T&D Planning

3 Present Utility Practices Modeling of transformers in various software platforms such as PowerWorld, PSLF, and PSSE is crucial to the accuracy of powerflow solutions and the efficacy of planning/operations studies. Present WECC base cases contain transformer data for most Northwest utilities in the System Base. Inconsistencies in how different utilities enter their transformer data in System Base. PGE & Avista transmission planning have discussed the benefits of having a process in place to calculate transformer modeling data from the most accurate source, i.e test reports. To accurately convert transformer data into the System Base, PowerWorld and PSLF require that the data be provided on the Transformer Base. PSSE on the other hand, offers user flexibility to provide data in either the System Base or the Transformer Base. 3 T&D Planning

4 Problems With Present Practices When provided with Transformer Base data PowerWorld, PSLF & PSSE convert it to the System Base. When provided with data on the System Base (from the.epc file), PowerWorld may not necessarily do a 1:1 transformation of this data. It calculates incorrect values for tap ratios, impedance & magnetizing admittance parameters on the System Base. Similar to PW, when provided with data in the System Base (from the.epc file), PSLF calculates incorrect System Base values for the impedance & magnetizing admittance parameters. It uses FROM & TO side input tap ratios and calculates incorrect values for transformer tap ratios on the System Base. 4 T&D Planning

5 Problems With Present Practices When.EPC files are exported to.raw file format, the impedance, nominal MVA and nominal kvs get stored as Transformer Base values by default. If the.epc file contains System Base data, much like PW & PSLF, this causes PSSE to calculate incorrect System base values for transformer tap ratios, impedance and magnetizing admittance parameters. There is a need for a standardized manual for transformer modeling. 5 T&D Planning

6 When provided with data on the System Base, PSLF calculates incorrect values for System Base transformer tap ratios, impedance & mag. admittance parameters..epc files (WECC base cases) containing System Base transformer data When provided with data on the System Base, PSSE calculates incorrect values for System Base transformer tap ratios, impedance & mag. admittance parameters. Same Issues regardless of the software platform. This isn t a software issue. The user needs to ensure that the input data is in the Transformer Base. When provided with data on the System Base, PW calculates incorrect System Base values for tap ratios, impedance & mag. admittance parameters. 6 T&D Planning

7 PowerWorld When provided with Transformer Base data PowerWorld converts it to the System Base. Transformer Base model utilized by PowerWorld System Base model utilized by PowerWorld Equations used to calculate impedance and magnetizing admittance parameters on the System Base 7 T&D Planning

8 PGE GSU Test Report Schematic diagram of the no-load loss test: a) Test Setup, b) Bushings Connection, c) Equivalent circuit Schematic diagram of the load loss test: a) Test Setup, b) Bushings Connection, c) Equivalent circuit 8 T&D Planning

9 PGE GSU Nameplate HV & LV Nominal kvs (on the Transformer/Winding base) Per Phase Impedance % Connection Information (Wye-Delta) DETC settings on the HV side 9 T&D Planning

10 Incorrect Modeling TRANSFORMER DATA ENTERED IN POWERWORLD SYSTEM BASE THE SYSTEM BASE Nominal MVA 100 Nominal MVA 100 Nominal kv (GSU High Side) Nominal kv (GSU Low Side) Nominal kv (GSU High Side) Nominal kv (GSU Low Side) R on System Base R X on System Base X Mag B on Sys. Base Mag B Mag G on Sys. Base Mag G If the impedance & magnetizing admittance parameters are entered in the System Base, their transformation will not result in identical values, because of the tap ratio on the TO side (as circled in red below). Transformer Data (from epc file) Is Entered In the System Base Equations used to calculate impedance and magnetizing admittance parameters on the System Base 10 T&D Planning

11 Correct Modeling Transformer Base System Base Nominal MVA 130 Nominal MVA 100 Nominal kv (GSU High Side) Nominal kv (GSU High Side) 230 Nominal kv (GSU Low Side) 13.2 Nominal kv (GSU Low Side) 13.8 R on XF Base R If the impedance & magnetizing admittance parameters are entered in the Transformer Base, they will be correctly transformed to the corresponding System Base values. X on XF Base X Mag B on XF Base Mag B Mag G on XF Base Mag G GSU Test Report Transformer Data Is In the Transformer Base GSU Nameplate It is therefore critical that the impedance and magnetizing admittance parameters be entered into PowerWorld in the Transformer Base. 11 T&D Planning

12 Equations used to calculate the transformer tap ratio on the System Base TTTTTTTTTTTTTT = 11 FFFFFFFFFFFFFFFFFFFF TTTT NNNNNNNNNNNNNN SSSSSS NNNNNNNNNNNNNN TTTT NNNNNNNNNNNNNNNNNN TTTT NNNNNNNNNNNNNNNNNN SSSSSS TTTTTTTTTTTTTT = = TTTTTT SSSSSSSSSSSS = CCCCCCCCCCCCCC TTTTTT RRRRRRRRRR TTTT + FFFFFFFFFFFFFFFFFFFFFFFF TTTT 11 TTTTTTTTTTTTTT = = If the FROM & TO side tap ratios are entered in the System Base, it ends up calculating incorrect System Base values for transformer tap ratio. 12 T&D Planning

13 If the FROM & TO side tap ratios are entered in the Transformer Base, PowerWorld correctly calculates the System Base transformer tap ratio. TTTTTTTTTTTTTT = 11 FFFFFFFFFFFFFFFFFFFF TTTT NNNNNNNNNNNNNN SSSSSS NNNNNNNNNNNNNN TTTT NNNNNNNNNNNNNNNNNN TTTT NNNNNNNNNNNNNNNNNN SSSSSS TTTTTTTTTTTTTT = = TTTTTT SSSSSSSSSSSS = CCCCCCCCCCCCCC TTTTTT RRRRRRRRRR TTTT + FFFFFFFFFFFFFFFFFFFFFFFF TTTT 11 TTTTTTTTTTTTTT = = All calculations have been documented in the manual on the modeling of PGE transformers. These are values calculated by PowerWorld in the System Base (i.e 100 MVA, 230kV & 13.8kV). It is therefore critical that FROM & TO side tap ratios be entered in PowerWorld in the Transformer Base. 13 T&D Planning

14 GE PSLF When provided with Transformer Base input data PSLF converts it to the System Base. Transformer Base model utilized by PSLF When provided with System Base input data, the tap ratios, impedance & magnetizing admittance parameters are calculated incorrectly in the System Base. Please note that PSLF requires that the Nominal MVA (i.e tbase) and the data items tapp, tapfp, tapfs, vnomp and vnoms be entered on the Transformer Base. The conversion of the data from the individual transformer bases to a common system base for network solutions is handled internally by PSLF. 14 T&D Planning

15 Round Butte VR3 * From bus ROUNDB N R from-tert pu * Variable V tap pu * To bus ROUND B X from-tert pu * Step size pu(deg) * Circuit Id 1 R to-tert pu Max var. tap pu(deg) Project Id 0 X to-tert pu Min var. tap pu(deg) * Trans Status 1 *From wind nom volt Kv Max Cont V(P) pu (MW) The table shows the information pertaining to nominal MVA, nominal kv, impedance and admittance parameters in an epc file. (all in System Base). Normal Status 0 *To wind nom volt Kv Min Cont V(P) pu (MW) * Tap control type 1 *Tert wind nom volt Kv G-Core loss pu * From-To Base MVA * From fixed tap pu B-Magnetizing pu R from-to pu * To fixed tap pu * X from-to pu * Tert fixed tap pu If the FROM & TO side tap ratios are entered in the System Base, it results in incorrect System Base values for transformer tap ratio. TTTTTT RRRRRRRRRR SSSSSSSSSSSS BBBBBBBB = tttttttt + tttttttttt 11 tttttttttt TTTT kkvv nnnnnnssssss TTTT kkvv nnnnnntttt FFFFFFFF kkvv nnnnnntttt FFFFFFFF kkvv nnnnnnssssss ; TTTTTT RRRRRRRRRR SSyyyyyyyyyy BBaaaaaa = = (IIIIIIIIIIIIIIIIII) OOOOOO NNNNNNNNNNNNNN TTTTTT RRRRRRRRRR SSSSSSSSSSSS BBBBBBBB = kkkk LLLL, VVVVVVVVVVVVVVVV/FFFFFFFFFF TTTTTT PPPPPPPPPPPPPP kkkkllll, SSSSSSSSSSSS NNNNNNNNNNNNNN kkkk LLLL, FFFFFFFFFF TTTTTT PPPPPPPPPPPPPPPP kkkkllll, SSSSSSSSSSSS NNNNNNNNNNNNNN = = (Correct) 15 T&D Planning

16 * From bus ROUNDB N R from-tert pu * Variable V tap pu * To bus ROUND B X from-tert pu * Step size pu(deg) * Circuit Id 1 R to-tert pu Max var. tap pu(deg) Project Id 0 X to-tert pu Min var. tap pu(deg) * Trans Status 1 *From wind nom volt Kv Max Cont V(P) pu (MW) 0.00 The table shows the information pertaining to nominal MVA, nominal kv, impedance and admittance parameters in an epc file for Round Butte VR3. (all in Transformer Base). Normal Status 0 *To wind nom volt Kv Min Cont V(P) pu (MW) * Tap control type 1 *Tert wind nom volt Kv G-Core loss pu * From-To Base MVA * From fixed tap pu B-Magnetizing pu R from-to pu * To fixed tap pu * X from-to pu * Tert fixed tap pu If the FROM & TO side tap ratios are entered in the Transformer Base, it results in correct System Base values for transformer tap ratio. TTTTTT RRRRRRRRRR ssssssssssss bbbbbbbb = = When this epc file is opened in PowerWorld, we see the input information as it should be on the Transformer Base. Using the input Transformer Base data, these are values calculated by PowerWorld in the System Base. 16 T&D Planning

17 The Nominal KV, impedance parameters and Nominal MVA are stored in the Transformer Base. I/O code 2 in PSSE parlance. The magnetizing admittance parameters are stored in the System Base. I/O code 1 in PSSE parlance. When the epc file containing the data in the System Base is exported to the Siemens PSSE raw file format, it is stored in the raw file in the Transformer Base. This creates the following issues; The FROM & TO winding nominal kvs and the winding nominal MVA are set equal to their respective nominal System Base values. The System Base transformer tap ratio is calculated incorrectly. The System Base values for impedance and magnetizing admittance parameters are calculated incorrectly. tt SSSSSSSSSSSS BBBBBBBB = tt ii tt jj VV bbbbbbbb ii nnnnnnnnnnnnnnnnnn VV bbbbbbbb ii dddddddddddddd VV bbbbbbbb jj dddddddddddddd VV bbbbbbbb jj nnnnnnnnnnnnnnnnnn = = (iiiiiiiiiiiiiiiiii) PSSE Two-Winding Transformer Circuit RR ssssssssssss BBBBBBBB = tt jj 22 RRTTTTTTTTTTTTTTTTTTTTTT BBBBBBBB VV bbbbbbbb jj nnnnnnnnnnnnnnnn VV bbbbbbbb ii dddddddddddddd 22 MMMMMM dddddddddddddd MMMMMM nnnnnnnnnnnnnnnnnn = = pp. uu (iiiiiiiiiiiiiiiiii) 17 T&D Planning

18 The Nominal KV, impedance parameters and Nominal MVA are stored in the Transformer Base. I/O code 2 in PSSE parlance. The magnetizing admittance parameters are stored in the System Base. I/O code 1 in PSSE parlance. When the epc file containing the data in the Transformer Base is exported to the Siemens PSSE raw file format, it is stored correctly in the raw file in the Transformer Base. This results in; The FROM & TO winding nominal kvs and the winding nominal MVA are set equal to their respective nominal Transformer Base values. The System Base transformer tap ratio is calculated correctly. The System Base values for impedance and magnetizing admittance parameters are calculated correctly. tt SSSSSSSSSSSS BBBBBBBB = tt ii tt jj VV bbbbbbbb ii nnnnnnnnnnnnnnnnnn VV bbbbbbbb ii dddddddddddddd VV bbbbbbbb jj dddddddddddddd VV bbbbbbbb jj nnnnnnnnnnnnnnnnnn = = (cccccccccccccc) PSSE Two-Winding Transformer Circuit RR ssssssssssss BBBBBBBB = tt jj 22 RRTTTTTTTTTTTTTTTTTTTTTT BBBBBBBB VV bbbbbbbb jj nnnnnnnnnnnnnnnn VV bbbbbbbb ii dddddddddddddd 22 MMMMMM dddddddddddddd MMMMMM nnnnnnnnnnnnnnnnnn = = pp. uu (cccccccccccccc) 18 T&D Planning

19 Avista Boulder Substation 19 T&D Planning

20 Avista Boulder Substation 20 T&D Planning

21 Avista Boulder LTC Transformer Test Report Schematic diagram of load losses test: a) Test Setup, b) Bushings Connection, c) Equivalent circuit Schematic diagram of no-load losses test: a) Test Setup, b) Bushings Connection, c) Equivalent circuit 21 T&D Planning

22 Avista Boulder LTC Transformer Nameplate Information HV & LV Nominal kvs (on the Transformer/Winding base) LTC/NLTC settings on the HV/LV sides Per Phase Impedance % Wye-Wye primary-secondary connection with delta connected tertiary winding 22 T&D Planning

23 Boulder (Incorrect Modeling) TRANSFORMER DATA ENTERED IN POWERWORLD SYSTEM BASE THE SYSTEM BASE Nominal MVA 100 Nominal MVA 100 Nominal kv (GSU High Side) Nominal kv (GSU Low Side) Nominal kv (GSU High Side) Nominal kv (GSU Low Side) If the impedance & magnetizing admittance parameters are entered in the System Base, their transformation will not result in identical values, because of the tap ratio on the TO side (as circled in red below). R on System Base R X on System Base X Mag B on Sys. Base 0 Mag B 0 Mag G on Sys. Base 0 Mag G 0 Transformer Data (from aux file) Is Entered In the System Base Equations used to calculate impedance and magnetizing admittance parameters on the System Base 23 T&D Planning

24 Boulder (Correct Modeling) Transformer Base System Base Nominal MVA 250 Nominal MVA 100 Nominal kv (GSU High Side) Nominal kv (GSU High Side) 230 Nominal kv (GSU Low Side) Nominal kv (GSU Low Side) 115 R on XF Base R If the impedance & magnetizing admittance parameters are entered in the Transformer Base, they will be correctly transformed to the corresponding System Base values. X on XF Base X Mag B on XF Base 0 Mag B 0 Mag G on XF Base 0 Mag G 0 Boulder LTC Test Report Boulder LTC Nameplate Information Transformer Data Is In the Transformer Base It is therefore critical that the impedance and magnetizing admittance parameters be entered into PowerWorld in the Transformer Base. 24 T&D Planning

25 Conclusions New PGE practice - All transformer data required for the ColumbiaGrid/WECC base case development process will be provided by PGE in the Transformer Base. EPC files containing Transformer Base data can be faithfully exported to the PowerWorld and PSSE platforms without any data skews or distortions. Providing Transformer Base input parameters to the software platforms enables their accurate internal conversion to the corresponding System Base parameters. PGE & Avista agree & strongly recommend that utilities submit transformer data in the Transformer Base for the WECC base case development process. This will result in WECC-wide uniformity in transformer modeling for system planning studies. Update the Data Preparation Manual to have utilities provide their transformer data only in the Transformer Base. 25 T&D Planning