Modelling of Wind Generation for Fault Level Studies. Markus Pöller/DIgSILENT GmbH

Transcription

1 Modelling of Wind Generation for Fault Level Studies Markus Pöller/DIgSILENT GmbH

2 Fault Level Studies Relevant indices (according to IEC60909): Initial AC short circuit current Ik Initial peak short circuit current ip AC-break short circuit current Ib Peak break current ip Equivalent thermal short circuit current Ith Calculation of maximum short circuit currents for bus bar and circuit breaker rating. Calculation of voltage sags due to grid faults. Calculation of minimum fault levels for selectivity studies.

3 Methods for Short Circuit Calculation X,X R U,U

4 Methods for Short Circuit Calculation Top Envelope DC-Component i DC Bottom Envelope

5 Methods for Short Circuit Calculation Planning Conditions Simplified method (IEC, ANSI,...) Reduced data set Operational Conditions Online- short circuit calculation Complete Method Complete data set Method 1: Equivalent voltage source at fault location Method 2.1: Superposition Method Method 2.2: Solution of differential Eq. Initial symmetrical (sub-transient) short-circuit current I SC (Ikss) κ µ m, n I" k, U k i i k (t) i p I b I th

6 Wind Generator Response to Grid Faults First generation of WTGs (ASM): contribution to Ik and ip (Thevenin equivalent). Disconnection within Tb-relevant time scales. Second generation of WTGs (DFIG with crow bar): Linear contribution to Ik and ip (Thevenin equivalent). Contribution to Ib and ib hard to predict (crow bar protection). Third generation of WTGs (DFIG without crow bar, fully rated converter): Linear contribution to Ik and ip (Thevenin equivalent). Controlled response in Ib-relevant time scales, according to grid code requirements.

7 Required steady state response during grid faults (SDLWindV/Germany) Imax=1p.u. Reactive currents prioritized Additional reactive current: diq Voltage sag du

8 Required WTG response (according to SDLWindV/Germany) Voltage deviation/ add. reactive current 60ms Voltage step Add. Reactive current 30ms

9 Wind Generator Modelling for Fault Level Studies - Existing Approaches - Thevenin equivalent, likewise synchronous machines ( Equivalent synchronous generator model, definition of x and x ) Can be integrated into standard short circuit analysis tools. Accurate representation for faults close to WTG. Very low accuracy for estimating remote contribution. Short circuit analysis using time domain simulation and dynamic models. Complex model setup required. Relatively long calculation times ( e.g. calculation of fault levels at all bus bars and terminals ). Dynamic models not necessarily made for fault level studies. Accuracy for predicting subtransient time scales sometimes very poor.

10 Wind Generator Modelling for Fault Level Studies - Proposed Approach - Requirement: Simple and fast approach but sufficiently accurate for remote contribution Subtransient time scale (relevant for Ik and ip): Linear model representation (classical representation) Parameters: x (or Ik in case of solid fault) Transient time scale (relevant for Ib and ib) Nonlinear model representation modelling steady state response to grid faults (reactive current contribution). Parameters: K-factor, maximum current.

11 Wind Generator Modelling for Fault Level Studies - Proposed Approach - Iterative algorithm required for modelling controlled response Ik

12 Method, integrated in DIgSILENT PowerFactory (complete method) Calculation of Ik using linear method (with or without load flow initialisation) Calculation of Ik using current iteration (considering reactive current priority when using load flow initialisation) Calculation of ip using Ik and IEC60909 method B or C (user s choice) for decaying DC-component Calculation of Ib using Ik and Ik and assuming a transient short circuit time constant: I b = I k ' + ( ) Tb / T '' I '' I ' e k k Tb: CB reaction time T : subtransient time constant, typically two cycles (40ms)

13 Method, integrated in DIgSILENT PowerFactory (complete method) Calculation of ib (peak break current) using Ib and IEC60909 method B or C (user s choice) for decaying DC-component (at Tb) Calculation of Ith using m and n factors according to IEC The heating factor of the AC-component uses Ik instead of Ik.

14 Method, integrated in DIgSILENT PowerFactory Discussion Proposed method is easy to use and fast. Simple current iteration method can be applied for calculating transient fault currents. No additional factorisation of the Y-matrix required Converges well, typically within 5 to 10 iterations -> around 5-10 times more time required as for a conventional IEC-type short circuit calculation Additional model parameters are limited to K and Imax Additional simplification: Using du= du = u shc -u ldf instead of du= u shc - u ldf provides conservative estimate of max. fault current contribution if short circuits shall be calculated without preceding load flow.

15 Example Linear Method Substation/BB2 102,517 Substation/BB1 102,517 Ikss=2,588 ip=6,788 Iks=2,006 Ib=2,054 ib=5,327 0,932 0,390 Tr DIgSILENT Externes Netz 0,326 ka 0,326 ka 0,326 ka 0,326 ka 1,794 ka 1,794 ka 1,794 ka Synchronm.. G ~ 20kV Station/BB Ikss=2,59 ip=6,79 Iks=2,01 Ib=2,05 ib=5,33 Ikss 0,802 ka Iks 0,213 ka Ib 0,261 ka 0,802 ka 0,213 ka 0,261 ka Cable 2,460 0,123-5,890 0,205 ka 0,053 ka Cable(3) 2,917 0,146-5,827 0,201 ka 0,053 ka Cable(2) 3,281 0,164-5,756 0,198 ka 0,053 ka Cable(1) 3,402 0,170-5,731 0,197 ka 0,053 ka Ikss 5,95 ka Iks 1,55 ka LV(3.. 0,202 0,293 Trf(3) 5,954 ka 1,551 ka LV(2.. 0,213 0,309 Trf(2) 5,840 ka 1,544 ka LV(1.. 0,222 0,322 Trf(1) 5,749 ka 1,538 ka LV 0,225 0,326 Trf 5,719 ka 1,536 ka Ikss 5,72 ka Iks 1,54 ka -128,689 5,954 ka 1,551 ka -130,248 5,840 ka 1,544 ka -131,363 5,749 ka 1,538 ka -131,712 5,719 ka 1,536 ka G4 G3 G2 G1 DIgSILENT PowerFactory Wind Generation Modelling for Fault Level Analysis Example Linear Method Projekt: Demo Grafik: Netz Datum: Anhang 1

16 Example Iterative Method Substation/BB2 102,517 Substation/BB1 102,517 Ikss=2,588 ip=6,788 Iks=2,025 Ib=2,071 ib=5,351 0,932 0,390 Tr DIgSILENT Externes Netz 0,326 ka 0,326 ka 0,326 ka 0,326 ka 1,794 ka 1,794 ka 1,794 ka Synchronm.. G ~ 20kV Station/BB Ikss=2,59 ip=6,79 Iks=2,02 Ib=2,07 ib=5,35 Ikss 0,802 ka Iks 0,231 ka Ib 0,278 ka 0,802 ka 0,231 ka 0,278 ka Cable 2,460 0,123-5,890 0,205 ka 0,058 ka Cable(3) 2,917 0,146-5,827 0,201 ka 0,058 ka Cable(2) 3,281 0,164-5,756 0,198 ka 0,058 ka Cable(1) 3,402 0,170-5,731 0,197 ka 0,058 ka Ikss 5,95 ka Iks 1,67 ka LV(3.. 0,202 0,293 Trf(3) 5,954 ka 1,673 ka LV(2.. 0,213 0,309 Trf(2) 5,840 ka 1,673 ka LV(1.. 0,222 0,322 Trf(1) 5,749 ka 1,673 ka LV 0,225 0,326 Trf 5,719 ka 1,673 ka Ikss 5,72 ka Iks 1,67 ka -128,689 5,954 ka 1,673 ka -130,248 5,840 ka 1,673 ka -131,363 5,749 ka 1,673 ka -131,712 5,719 ka 1,673 ka G4 G3 G2 G1 DIgSILENT PowerFactory Wind Generation Modelling for Fault Level Analysis Example Iterative Method Projekt: Demo Grafik: Netz Datum: Anhang 1

17 Modelling of Wind Generation for Fault Level Studies - Summary International short circuit standards, like IEC60909 or ANSI C37 don t provide any guidelines for the modelling of wind generation. Unlike conventional synchronous or asynchronous machines, converter driven generators have a controlled response within the time scales that are relevant for fault level studies. The proposed method combines elements of IEC60909 and G74 with an iterative approach. WTG model definition only requires two additional parameters, K and imax for modelling the reactive current response of WTGs. The proposed iterative method is based on a fast current iteration, which typically requires 5 to 10 iterations (and no re-factorisation of matrices during iteration) The proposed method is available in the new version of DIgSILENT PowerFactory (V14.1).

18 Thank You Markus Pöller DIgSILENT GmbH Heinrich-Hertz-Str Gomaringen