Equivalencing the Collector System of a Large Wind Power Plant

Transcription

1 Equivalencing the Collector System of a Large Wind Power Plant Presenter: Ed Muljadi National Wind Technology Center National Renewable Energy Laboratory Golden, Colorado USA IEEE Power Engineering Society Montreal, Quebec, Canada June 18, 006

2 Disclaimer and Government License This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-99GO10337 with the U.S. Department of Energy (the DOE ). The United States Government (the Government ) retains and the publisher, by accepting the work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes. Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe any privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the Government or any agency thereof. The views and opinions of the authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the DOE, the Government, or any agency thereof.

3 Co-authors E. Muljadi C.P. Butterfield A. Ellis J. Mechenbier J. Hochheimer R. Young National Renewable Energy Laboratory 1617 Cole Blvd Golden, CO Public Service Company of New Mexico Alvarado Square, MS 0604 Albuquerque NM FPL Energy LLC 700 Universe Blvd. Juno Beach, FL N. Miller R. Delmerico General Electric International, Inc. 1 River Road, Bldg Schenectady, New York 1345 R. Zavadil J.C. Smith Utility Wind Integration Group 004 Lakebreeze Way Reston, VA 0191

4 Acknowledgement We acknowledge the support of the following: U.S. Department of Energy Public Service Company of New Mexico FPL Energy General Electric Utility Wind Interest Group (UWIG) William Price, from General Electric International Inc., for help and discussions during the development of this project

5 Issues A large wind power plant covers a very large area (>100 square miles) and consists of many wind turbines (>100). The power system network within a power plant is intricate, with long line feeders. The wind plant representation must be accurate enough to maintain the validity of the wind plant behavior. The wind plant representation must be simple enough to be simulated and analyzed.

6 Objectives Derive an equivalent circuit of a wind power plant. The equivalence must be valid for large or small wind plant. The equivalence must be sufficient to represent the behavior of a wind plant under steady-state and dynamic conditions.

7 136 turbines representation Equivalence Wind Farm (R + jx) j B 34.5 kv 345 kv kv 34.5 kv (R XFMR + jx XFMR ) values to be determined. Values to be determined ( j0.088) (0.00+j0.00) Taiban Mesa Infinite Bus Equivalence to be derived

8 Approach Analytical approach Assumptions made: All turbines generate rated currents. All currents are identical in magnitude and phase angle. Equivalence is based on real and reactive losses. Define circuit configurations found in the wind plant. Derive the equation representing each circuit configuration. Identify the sub-circuits found in the wind plant represented by each circuit configuration. Combine the sub-circuits found in the entire wind plant, and find the equivalence of the wind plant up to the main substation. Deduction approach

9 Analytical Approach Circuit configurations found in the wind plant IS Z 1S Z S Z 3S I 1 I I 3 I T Z 1 Z Z 3 Z 4 I 1 I I 3 Z 1P Z P Z 3P Z1 Z Z3 I 1 I I 3 I 4 I S (a) n 1 n n 3 n 1 n n IS ZS Figure 3 a) single series daisy-chain b) equivalent representation of circuit (a) (b) IP ZP Figure 4. Parallel connection of three groups of turbines through series impedances Z 1, Z, and Z 3 I T Z T Figure 5. Parallel series connection of three groups of turbines Corresponding equivalent impedance n m= m Z 1 m S Z = n n n 1 m Z m= m P n Z = m= 1 n m Z = np ns ns nz i ip+ nj ZiS i= 1 i= 1 j= 1 T np i= 1 n i

10 Analytical Approach The voltage drop across each impedance, can be easily derived as follows. The voltage drop across Z 1 = V Z1 = I 1 Z 1 = I Z 1. The voltage drop across Z 4 = V Z4 = (I 1 + I + I 3 + I 4 ) Z 4 = 4 I Z 4 The power loss at each impedance, can be computed as: S Loss_Z1 = V Z1 I 1 * = I 1 I 1* Z 1 = I I* Z 1 = I Z 1 S Loss_Z4 = V Z4 (I 1 + I + I 3 + I 4 ) * = 4 I Z 4 S = I (Z + Z + 3 Z + 4 Z ) Tot_loss Tot_loss n m= 1 m S = I m Z I 1 Z 1 Z Z 3 Z 4 I IS I 3 ZS I 4 I S Figure 3 a) single series daisy-chain b) equivalent representation of circuit (a) S = I Z Tot_loss S S (a) (b) n m= m Z 1 m S Z = n

11 Analytical Approach Wind turbine transformer Shunt representation Turbine # kv 34.5 kv (0.357+j3.3370) R + j X B/ B/ Turbine # kv 34.5 kv (0.357+j3.3370) B tot n = B i= 1 i kv 34.5 kv Z PMXFMR_WF = Z PMXFMR_WTG /n turbine Wind Farm (136 turbines) (0.357+j3.3370)/136 = (0.006+j0.0454)

12 Analytical Approach Equivalence of complete circuit (EOCC) Equivalence of major lines (EOML) Taiban Mesa Infinite Bus kv Taiban Mesa Infinite Bus kv kv kv D N kv kv D3 N3 D11 m8 m3 N8 D1 D N1 N4 D13 D1 D17 N6 N D6 D7 m1 N1 N3 N m D3 D14 D18 D8 N4 m4 m6 N6 D4 D5 N5 D15 D16 D19 D0 N7 D9 D10 N5 m5 m7 N7 D1

13 Deduction Approach Deduction approach Assumption made: The voltages, currents, and real and reactive losses used are computed by power flow. The voltages and currents have unique phase angles and magnitudes. The current outputs of each turbine may not be identical with respect to its neighbor. Identify the groups of turbine and the corresponding line feeder to be equivalenced. Tabulate the real and reactive losses within the group. Tabulate the current for each group identified. Compute the equivalent model to represent each group identified.

14 Deduction Approach Impedance computed from losses R pu = P Loss base 3I Z Z base = V LL _ base S base X pu = Q V B S tot _ Loss pu pu base 3I Zbase

15 Comparisons deduction analytical Collector System Losses Losses Complete (136WTG) EOCC EOML Ploss 4.13 MW.0%.69% 1.81% Qloss 5.33 MVAR.61% 4.99% 4.15% Line Impedance Z (p.u.), B, X/R and B/R

16 Conclusions The equivalence of a collector system using EOCC produces the highest impedance due to conservative assumptions that all turbines produce rated current at the same magnitude and phase angle. Using EOML, the result is closer to the Complete representation. The ratio X/R is very consistent for the EOCC, EOML, and Complete representations. The ratio B/R for the complete equivalent circuit is over-predicted. Very large and diverse wind power plants can be represented by dividing the large wind power plant into smaller groups of wind turbines with similar attributes. This approach for calculating X, R, and B using EOCC was tested and validated by the authors and has been adopted by the wind developer for estimating equivalent impedance of proposed wind power plants for interconnection study purposes. Recommendations were provided to PNM to adjust the equivalentcircuit representation for this project. Rather than estimating the impedance by visual inspection as initially done, a much more accurate result can be obtained by taking into account the number of wind turbine generators that are injecting currents into each branch.