pssewindandsolarmodels_casestudies

©© 2011 Siemens Energy, Inc. All rights reserved.2011 Siemens Energy, Inc. All rights reserved.

PSS®E Wind and Solar Models.

CaseCase StudiesStudiesofof Wind Park ModelingWind Park ModelingUWIG/EnerNex/DOE Workshop UWIG/EnerNex/DOE Workshop MISO, St. Paul, MNMISO, St. Paul, MNAugust 16August 16--17, 201117, 2011

Yuriy KazachkovYuriy KazachkovSiemens PTISiemens PTI


PSS®E Wind Models

Page 3© 2011 Siemens Energy, Inc. All rights reserved.

Siemens Power Technologies International

Current View of PTI Web Site

http://www.pti-us.com/pti/software/psse/userarea/wind_farm_model_request_download_submit.cfm

Your request to download PSS®E Wind Farm models has been submitted. You will receive an email from PSS®E Support with further instructions.

Self-extracting files for most widely used vendor specific models are available for all PSS®E releases from 29 to 32. Models of Acciona, Enercon, GE wind turbines, and the WT3 and WT4 user written generic model can be directly downloaded, others will be provided upon manufacturer’s authorization.All communications related to downloading the PSS®E wind models have to go via the PSS®E support.



Siemens – PTI PSS®E ModelsLately, we also developed PSS®E dynamic simulation models for: AMSC WindTec 1.5 MW 50Hz & 1.65 MW 60Hz Wind to Energy W93 and T93 Northern Power NPS2.2-93 Several Chinese manufacturers: Sinovel, Mingyang, Sany, United Power,

Sewind.



Other Non-PTI PSS®E Models

Siemens PTI is aware of several other PSS®E wind modeling packages NOTdeveloped and therefore NOT supported by Siemens PTI, such as: Vestas V52 850kW, V66 1.75MW, V80 2MW, V90 3MW, V90 1.8MW DeWind D6 1.25MW and D8 2MW Gamesa G5X 850kW and G8X 2MW Clipper SuzlonSome manufacturers recognize the importance of their

models being supported by PTI and approached us with the request to review, modify, release and support their models.Acciona is a good example.



© 2011 Siemens Energy, Inc. All rights reserved.

Wind Models Simulation Infrastructure in PSS®E



Handling wind turbine modelsin PSS®E Load Flow

The user is responsible for aggregating the actual wind turbines into equivalent machines. For N lumped machines, the output of the equivalent machine cannot exceed N times the rated output of theindividual units.

The power factor correction shunt capacitors must be added (if available) and connected to the terminals of the equivalent machine by the user. For example, for the original Vestas V80 machine, the total

compensation available is 12 capacitors of 72 kVAr each. After compensation, the reactive power flow from the terminal bus to the system should be in the range of +40/-40 kVAr per machine.



Handling wind turbine modelsin PSS®E Dynamics

The user prepares a dynamic input data file by following the example files included in the modeling package documentation.All vendor specific models are provided in the format of

user’s written (defined) models.The dynamic simulation models implemented by Siemens

PTI are self-initializing, as with all other PSS®E simulation models.



Application Features of PSS®E Software Packages

In rev 31+, the new category of machine, namely wind machine, is introduced, along with new wind related common variables. This makes simulation more convenient and efficient. In the near future, a new name, like “Renewables”, might be needed to have

solar and other inverter based generation fit in this category. All four generic models using a wind machine category, namely WT1, WT2,

WT3, and WT4, are standard starting from rev 31.1. These generic models will not be available for rev. 29 and 30 – please upgrade

to 32! The old user written WT3 generic model using the conventional machine in LF

is available for rev 29+. Please note: this model is different from the standard generic WT3 model. Probably, at some point in foreseeable future we will “close” the option of

treating the wind machine as a conventional machine.



The latest wind turbine model infrastructure in PSS®E – a reminder

Wind machines are specified on the existing generator record of the Power Flow Raw Data File.

The following additional data items, appended to the end of the record, are specified for wind machines: 0 if this is not a wind machine (this is the default value). 1 if this is a wind machine which participates in voltage control,

with the values of QT and QB on the data record specifying the machine’s reactive power limits.

2 if this is a wind machine which participates in voltage control, with the specified power factor (see below) andthe machine’s active power setting (PG on the data record) used to set the machine’s reactive power limits.

3 if this is a wind machine which operates at a fixed power, with the machine’s reactive power output and reactive power upper and lower limits all equal, and set based on the specifiedpower factor (see below) and the machine’s active power setting (PG on the data record).

Power factor: ignored if the wind control mode is 0 is used in setting the machine’s reactive power limits when the wind control mode is 2 or 3 negative value may be specified when the wind control mode is 3, and is interpreted as a leading power factor

(i.e., the wind machine produces active power and absorbs reactive power).

Bus #

Bus Name Id Code Status

Pgen (MW)

Pmax (MW)

Pmin (MW)

Qgen (Mvar)

Qmax (Mvar)

Qmin (Mvar)

Mbase (MVA)

XSource (pu)

Wind machine Control Mode

Wind machine PF

1 INFINITE 1 3 1 -49.618 9999 -9999 -0.993 9999 -9999 100 0.2 Not a wind machine 1 5 WT 1 2 1 50.25 105 0 -4.317 34.3 -51.1 111.69 0.8 Standard QT, QB limits 1



The latest wind turbine model infrastructure in PSS®E – a reminder

Any wind model may include one or several of the following wind modules:

New variables of two categories have been added to support the wind models in PSS®E: Variables accessible for users, e.g., model outputs Variables not accessible for users: primarily for model developers.

IC index Wind module type 101 Generator 102 Electrical control 103 Mechanical control 104 Pitch control 105 Aerodynamics 106 Wind Gust/Ramp 107 Auxiliary control



The Latest Wind Turbine Model Infrastructure in PSS®E – (continued)

To add the wind dynamic module as a user written model, the statement in the dynamic data file should be added as follows:

IBUS ‘USRMDL’ ID ‘ModelName’ IC IT NI NC NS NV parameters/

IT = 1 for IC = 101IT = 0 for IC = 102 to 107




Simulating Manufacturer Specific PSS®E Wind Models using Python Module – pssewindpy

The idea is to allow for a quick and automatic model setup process for manufacturer specific wind generation models in order to help users in their familiarization with these models



Module pssewindpy

Provides Python functions to simulate PSS®E manufacturer specific wind models: Acciona AW15/AW30, Fuhrlaender FL2500, GE 1.5/2.5/3.6 MW, Mitsubishi MWT 92/95/100, Mitsubishi MPS1000A, Vestas V47/V80/V82/NM72, Generic WT3.

Provides demo Python functions to simulate these models.

Provides example Python scripts which can be edited/modified to select/specify desired wind model: To add a WTG to any PSS®E load flow case To create WTG model dyre records (.dyr file created).



5 bus demo test work

Demo run python scripts: Add selected WTG, its GSU and other components if required (like fixed shunt,

switched shunt etc.) Update the base case and base snapshot Simulate WTG response to bus fault or complex wind input (if applicable)

WTG G

99971BUSWTG

99972COLLECTORBUS 99973

LVBUS99974

HVBUS99975

SWINGBUS

34.5 kV 34.5 kV 138 kV 138 kV

added by pssewindpy functions

Demo Simulation



GE 1.5 MW WTG Demo SimulationPython Script to set up GE 1.5 MW demo:import pssewindpypsseversion = 32 # PSS(R)E Versionwtg_mdl = 'ge15' wtg_units = 67 # Number of WTG Unitspct_dispatch = 100.0 # % dispatch, e.g. 100.0 for 100%wtg_mass = 1 # Shaft Model, =1 for Single, =2

for Double massfreq = 60 # Network base freq in Hzpssewindpy.wtg_init(psse version)cnvsavfile, snpfile = pssewindpy.wtg_demo_ge(wtg_mdl, wtg_units,pct_dispatch, wtg_mass, freq)

Python Script to run Simulation:outfile1 = pssewindpy.wtg_demo_run_collect_bus_flt(cnvsavfile, snpfile)outfile2 = pssewindpy.wtg_demo_simulate_complex_wind(cnvsavfile,snpfile)



Adding WTG model to PSS®E CasePython function to add any manufacturer specific WTG model to any PSS®E Casechngpyfile, dyrfile = wtg_create_chng_dyr_files(wtg_mdl, bus_collect, bus_wtg, wtg_units, pct_dispatch=100,aw_extqctrl=True, aw_cnvrmvar=True, # AW1530

gewt_mass=1, # GE 1.5/3.6/2.5 MWge15_old=False, # GE 1.5mwt_crowbar=0, mwt_ndh=0, # mwt92/mwt95v8047_shaft=1, # v80/v47 (enable/disable shaft model)v82nm72_qctrl='pf', v82nm72_svctype='local', # V82/NM72v82nm72_bus_wtg2=None, v82nm72_gridsvc_kvar=None, v82nm72_svc_bus=None # V82/NM72 grid SVCv82nm72_svc_wtgside_bus=None, v82nm72_svc_gridside_bus=None,v82nm72_pf=0.95, # V82/NM72 when qctrl=pfv82nm72_kvar=0.0, # V82/NM72 when qctrl=varwt3_data={}, wt3_mass=1) # generic WT3



Adding WTG model to PSS®E Case (continued)

Python function to create converted case and snapshot-From base snapshot:cnvsavfile, snpfile = pssewindpy.wtg_create_cnvsav_snp_files(chngpyfile, dyrfile, basesnpfile=bassnpfile, convertpyfile=None )

-From base DYR file:

cnvsavfile, snpfile = pssewindpy.wtg_create_cnvsav_snp_files(chngpyfile, dyrfile, basedyrfile=basdyrfile, convertpyfile=None )



Adding WTG model to PSS®E Case (continued)Python function to add Voltage or Frequency protection modelpssewindpy.add_protection_relay(dyrfile, relaymdl, bus_mon, bus_gen, gen_id, threshold, t_pickup, t_breaker=0.08)

For Voltage protection, model names are: 'vtgdca', 'vtgtpa'For Frequency protection, model names are: 'frqdca', 'frqtpa‘ 'vtgdca' -> Under Voltage / Over Voltage Bus Disconnection Relay 'vtgtpa' -> Under Voltage / Over Voltage Generator Disconnection Relay 'frqdca' -> Under Frequency / Over Frequency Bus Disconnection Relay 'frqtpa' -> Under Frequency / Over Frequency Generator Disconnection Relay

bus_mon = Bus number where voltage or frequency is monitoredbus_gen = Bus number of generator bus where relay is locatedgen_id = Generator IDthreshold= Voltage (pu) or Frequency (Hz) threshold (upper or lower threshold)t_pickup = Relay pickup time (sec)t_breaker= Breaker contact parting time (sec), default = 0.08 sec.




Generic Wind Generation Models in PSS®E



Generic Wind Model WT1

The model structure:

WT1G model is a modification WT1G model is a modification of the standard induction of the standard induction machine modelmachine model



Type 2 Wind Turbine




The first generic model developed was of Type 3.

The model includes 4 modules responsible for: WT3G1, WT3G2 , doubly-fed induction generator which is mostly an algebraic model to calculate the current

injection to the grid based on commands from controls, with or without the PLL control. WT3E1, electrical control including the torque control and a voltage control. WT3T1, the turbine model including a two-mass shaft mechanical system and a simplified method of

aerodynamic conversion, namely ΔP=Kaero*θ*Δθ where P is mechanical power, θ is a pitch angle; this method was validated against results obtained when using the Cp matrix;

WT3P1, the pitch control.




The machine is decoupled from the grid by a power converter: no angular stability problem, the power conversion is controlled by converters on the machine and grid sides; the latter is also capable to control

voltage, MVAr flow, or power factor.



Siemens Wind Turbine Generic Model

The WT4 generic model includes the special entry for Siemens 2.3 MW wind turine. It was carefully parameterized jointly by Siemens PTI and Siemens Wind Power. We are planning to separate the Siemens wind turbine model as a separate standard model.Per SWP’s request we have converted the WT4 generic model to earlier PSSE releases as a user written model.This is the example of “parameterization” of the WT4 generic model to match the response of the vendor specific model of the Siemens 2.3 MW wind turbine.

Oscillations in Pel from the vendor

specific model cannot be

replicated by the WT4 model

because it does not take the

machine dynamics into account



Generic wind models as a basis for manufacturer specific models

Some manufacturers approached us with the request to Try to parameterize the generic model in order to match their

benchmark - Availability of the benchmark is a must! If testing with the adjusted parameters shows a significant mismatch

add new features to the generic model and make a new vendor specific model

Example: for the Fuhrlaender 2.5 MW wind turbine model the active power up-ramping was added to the WT3




“Hot” issues



Ficticious Frequency Spikes

Prevent abrupt change in bus voltage angle during and after the fault to prevent fictitious frequency spikes.

Problem is very acute in weak systems.

Causes false frequency relay trips.

Temporary Solution:Disabling Frequency Relay.

Mid-Term Solution:External Intelligent Frequency Relaywith smoothen frequency measurement.



Network Non Convergence

Prevent network non-convergence during 3-phase faults

• Terminal bus voltage angle is uncertain because the reference frame is lost: no machine flux dynamics for WT3 or PLL for WT4

• Many planners use PSSE setups that include the so called “Shut down” model: it calculates a number of “Network not converged” (NNC) events and stops the simulation if it exceeds the given threshold, e.g. 6 NNCs.



Network Non Convergence

The existing model for GE WTs of 1.5 MW , 1.6, 3.6 MW (Type 3) and 2.5 MW (Type 4): two NNCs were observed when testing the 1.5 MW and 2.5 MW WTs, with 3-phase bolted fault applied to the POI bus 2 – one at the fault inception, another at the instant of fault clearingThe upcoming model for GE WTs of 1.5 MW, 1.6 MW (Type 3) and 2.5 MW, 2.75 MW, 4.0 MW (Type 4) – no NNCs with SCR as low as 3.

s1

Slide 30

s1 stykayu1, 6/30/2011




Frequency Events



Modeling frequency events

Can generic models be used and trusted for simulating frequency events: loss of generation or loads?This question first should be addressed to vendor specific models that provide a benchmark for generic modelsCollecting information from field tests or tests using the detailed equipment level models (PSCAD/EMTDC, MatLab/Simulink) is of urgent importanceBelow are some examples illustrating some concerns. The main question is: does the wind turbine respond to frequency events, as provided by vendor specific or generic models, seem realistic?



Test System

• Bus 15 – wind turbine 100 MW unit

• Bus 19 – Hydro 1000 MW unit

• Bus 19 – GT 100 MW unit

• 100 MW Load

• 1000 MW load



No governors: drop the WT unit

• Under-frequency event: only conventional units • Accelerating power (PMECH-PELEC) is negative• Loads are intact. To compensate for the lost generation, outputs of on-line

machines increase at the expense of the rotor kinetic energy: inertial response!• New reduced frequency is such that there is a balance between generation, loads,

and losses• For on-line units, rotor speed and system frequency are the same



Under sudden low frequency conditions, when load demand exceeds the generation, increase of the machine active power output by means of converting the rotor kinetic energy into the electrical energy is a sound response.For a conventional generation unit, the under-speed protection may shut it down.



Hydro Governor Impact: drop the WT unit

• Accelerating power (PMECH-PELEC) restores to ~0• New steady state frequency depends on the governor droop



The GEWT (DFIG) vendor specific model: drop the GT unit, no Hydro governor

After the GT was dropped off, all the

lost power was picked up by a Hydro.

WT’s power does not change.

Great difference between the WT rotor

speed and the system frequency.

Note: the initial WT rotor speed is

about 1.2 pu (72 Hz). For conventional

machines, rotor speed follows the

frequency. For DFIG it stays constant.



The GEWT (DFIG) vendor specific model: drop the GT unit, no Hydro governor; WindInertia enabled

WindInertia increased WTG

Pelec by 4% at the expense of

the rotor deceleration –

very different physics.



MPS-1000 versus WT1; drop GT unit; hydro governor

• Similar response

• Trustworthy: the full order machine model for both models

• WT rotor speed and the system frequency have a similar pattern



V80 60 Hz (VRCC) versus WT2; drop GT unit; hydro governor

• Similar response

• Trustworthy: the full order machine model for both models

• WT rotor speed and the system frequency have different patterns



Replace vendor specific GEWT (DFIG) model by generic WT3 model; drop GT unit; no hydro governor

Full Load

Partial load

WT3 and GEWT provide

identical response



For under-frequency events, the system response shown by generic models is very close to one shown by vendor specific models.For under-frequency events, the system response shown by both models seems realisticResults from the field and from full order models are badly needed to verify the stability model performance


Generic Solar Photovoltaic Model in PSS®E



PSS/E Implementation

Voltage

Irradence Model

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10

Time

Irrad

ence

WT4Converter/el. control

PSS/EIrrad (I) Pdc (I)

IR,IQ

Irradiance Model PV Panel Model Converter ModelRest of System

PVGU1, PVEU1IrradU1 PANELU1



Irradiance Model

Irradence Model

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10

Time

Irrad

ence

Standard Model that allows user to vary the amount of solar irradiance.User enters up to ~10 data points (time(s), irradiance(W/m2)) as consInitializes based on steady state P/PmaxFor each time step, outputs linearizedirradiance level



PV Panel Model

Standard Model for a PV panel’s I-V curvesPV panel’s output varies with Irradiance, temperature, terminal voltage (set by MPPT)User enters maximum Pdc (per unitized) for different irradiance levels as consFor each time step, reads irradiance level, outputs linearized power order



Converter Model – use slightly modified WT4 full converter model

Largely ignores dynamics from DC side. Different reactive control modes: Voltage control, PF control, Qcontrol For each time step, outputs linearized irradiance level


Case StudiesCase Studiesof Wind Park Modelingof Wind Park ModelingJames W. Feltes and Bernardo Fernandes James W. Feltes and Bernardo Fernandes Siemens Power Technologies International Siemens Power Technologies International (Siemens PTI)(Siemens PTI)[email protected]@[email protected]@siemens.com

PingPing--Kwan KeungKwan KeungNow with Alberta Electric System Operator (AESO)Now with Alberta Electric System Operator (AESO)[email protected]@aeso.ca



Overview

Introduction

Importance of proper modeling of wind energy projects in system studies

Wind Turbines Equipment Models

Case Study - System Modeling

Analysis Performed

- Power Flow- Short Circuit - Transient Stability

Conclusions



Introduction

The US is geographically large

Areas with rich wind resources

US Department of Energy in 2008 estimated the wind generation that can be technically developed:

300 GW needed for a 20% wind scenario

Estimates of the number of buses required to represent each wind turbine in detail in a load flow model would be 200,000 buses (average size of 3 MW)

Computers of 2030 will likely have no problem doing the calculations

Unlikely that the engineers will be overjoyed at the efforts required to validate, maintain, and perform studies with this vast amount of extra data.



Wind Farm Modeling

There has been research on techniques for the aggregation of the wind turbines in a wind farm to reduce the size and complexity of the model.

Among others, the methodology proposed by the Western Electricity Coordinating Council (WECC) represents a straightforward approach that is quite easy to apply.

It is reported that simulation results using the simplified models derived with this methodology match simulation results using more detailed models.

However, it is not always clear when these approximation techniques can be used or when the extra time and effort to develop a full representation of the wind farm is justified.

This paper compares both models using an actual wind farm configuration employing calculation results



Wind Turbines Equipment Models

The response and model of a wind farm is very dependent on the type of equipment used.

Directly connected induction generators (Type 1)

Wound rotor induction generators (Type 2)

Doubly-fed induction generators - DFIG (Type 3)

Power converter connected to synchronous or induction generators (Type 4)

Case study performed with the most common types of wind turbines being installed in utility scale wind farms

Only Type 3 and 4 machines are used.



Case Study - System Modeling

The wind farm is loosely based on an actual wind farm. Consistent with an actual wind farm layout and turbine spacing.

There are almost 500 turbines in the wind farm.

Five 34.5 kV feeders. Lengths range from a few hundred feet to several miles and have between 50 and 150 turbines each.

The wind farm is distant from load centers and is connected via a long 345 kV transmission line.



Wind Farm Generation

Summary of the units modeled in the wind farm

Doubly-fed induction machines (GE - Type 3)

Full converter units (Siemens - Type 4)

Group # Units Model Type

Turbine Type

Size (MW)

Total (MW)

1 76 DFIG 3 1.5 114 2 142 DFIG 3 1.5 213 3 80 FC 4 2.3 184 4 149 DFIG 3 1.5 224 5 50 FC 4 2.3 115 Total 497 - - - 850



Wind Farm Models

Detailed Model representing each of the individual units and the connections between these units and the system.

- 1119 buses- 1095 branches.

Very detailed data on the feeder cable system connecting the wind turbine/generators was used to create this representation.

Equivalent Model. Detailed model is reduced to represent five major groups of turbines through

- Lumped Sum WTG - Equivalent Padmount Transformer- Equivalent Collector System

The methodology proposed by the Western Electricity Coordinating Council was used to create the equivalent



Analysis Performed

Power FlowDetermine flows on transmission lines and transformers and voltage profile

- Voltage Control- Losses in the Collector System

Short Circuit AnalysisWind Turbine Generators contribution on the system side

Transient StabilityCheck synchronism after disturbances, damping of oscillations, and voltage recovery following fault clearing are adequate

- Stability transfer Limit

- Power System Oscillations

- Low Voltage Ride Through (LVRT)



Power Flow

Steady State System Studies

The similarity of both aggregate and detailed models in terms of wind farm responses to contingencies in the system is dependent on the accuracy of the equivalent model.

From the system studies standpoint, an equivalent model is sufficient

Optimal voltage control strategy

A detailed model is desirable. It reflects the voltage profile variation along the feeders.Reactive power generated or absorbed.For the same terminal voltage setpoint, a WTG at the far end of a given feeder will not respond the same way as the ones closer to the collector bus.



Voltage Control Strategy

Figures show the voltage profile for a given feeder of the Group 1 units in steady state conditions: 1.000 puterminal voltages setpoint.

Colors indicate voltage levels. Tending to yellow = higher voltages. Tending to blue = lower voltages.

WTGs controlling their own terminal voltages

For an event resulting in a voltage drop in the 345 kV system, the WTGs do not respond the same way



Voltage Control Strategy

Analysis Results

- Detailed Model: Units at the far end do not provide as much reactive support as the ones closer to the collector bus

The voltage drop is not as severe at the far end of the feeder.

- Equivalent Model: aggregated generator detects the voltage drop and injects all available reactive power.

Therefore, the effective reactive injection is unequal along the feeder in the detailed model, but the net effect into the system is similar



Losses in the Collector System

The losses evaluated in steady state are essentially due to the collector system, transmission lines and transformers

The generator related equipment losses are not taken into consideration

No significant differences between the two wind farm representations in terms of system losses

EQVModel

FullModel

EQVModel

FullModel

EQVModel

FullModel

EQVModel

FullModel

850 510 0 823.0 822.8 757.4 756.3 1.050 1.049 0.999 0.991

800 340 0 777.0 777.2 721.5 721.7 1.038 1.038 1.020 1.021

750 340 0 730.8 730.8 684.9 685.1 1.048 1.048 1.044 1.045

700 340 0 683.8 683.8 645.5 646.9 1.055 1.056 1.060 1.061

650 170 0 636.2 636.0 603.2 603.2 1.039 1.039 1.067 1.068

600 170 -110 587.4 587.4 559.0 559.0 1.040 1.040 1.048 1.048

500 170 -110 491.4 491.7 472.6 472.7 1.049 1.050 1.067 1.068

400 0 -110 394.6 394.6 382.5 382.5 1.035 1.035 1.077 1.078

Voltage at POI Voltage at WF 138 kVWF

Output (MW)

Power to138 kV Bus Power to POIReactive

Supportat POI(Mvar)

Reactors (Mvar)



Wind Farm Contribution (A) Total Fault Currrent

(A) Group 1 Group2 Group 3 Group 4 Group 5

3 Ph Fault

Location

EQV Full EQV Full EQV Full EQV Full EQV Full EQV Full Main

138 kV 6157 6178 767 755 1390 1394 1137 1167 1235 1275 831 832

Main 345 kV 2418 2420 707 694 1271 1273 1043 1071 1132 1162 765 764

POI 345 kV 12548 12537 419 410 708 704 601 623 650 641 450 446

Short Circuit Analysis

Type 3 and Type 4 machines have significantly different dynamic behavior than either conventional synchronous or induction machines as seen from the system

X” represents an effective equivalent reactance and is not the actual subtransientreactance of the machines

The manufacturer’s recommended values are applicable to remote system faults, not for faults on the WTG terminals

No significant differences between the two wind farm models in terms of short circuit contributions



Transient Stability

Stability simulations were performed for two contingencies involving 345 kV transmission lines in the area surrounding the POI:

- Substation 1 to Substation 2, ckt 1- POI to Substation 3, ckt 1

All contingencies simulated are three-phase faults cleared by line tripping with a total clearing time of 6 cycles



Stability Transfer Limits

Contingency AnalysisInitially the system was tested for stability at full wind farm output, for both equivalent and detailed models

The wind farm did not remain stable following contingencies. The loading of the wind farm was reduced to the level at which both the wind farm and the system remained stable for the tested contingencies.

Simulation ResultsIndicated that the wind farm presents unstable dynamic behavior or WTG trips for loading greater than approximately 700 MW, which indicates the stability limit for the case study

When the lack of reactive support and/or need for system reinforcements is prominent, both equivalent and detailed wind farm models present the same dynamic performance.



Power System Oscillations

Stable Case – Wind Generation set to 85% of the installed CapacityOutage of one 345 kV lines between substations 1 and 2. Figure shows the active power delivered at the POI for both equivalent and

detailed modelsThe results show a very similar dynamic behavior for both wind farm models.

238 - POWR 70461 TO 7046 CKT 1 : 720MW_CTG 1-2_EQV Model4555 - POWR 70461 TO 7046 CKT 1 : 720MW_CTG 1-2_Detailed Model

Time (seconds)109876543210

Act

ive

Pow

er (M

W)

900

800

700

600

500

400

300

200

100

0

-100

-200



Power System Oscillations – Sensitivity Case

Sensitivity Case: Created to evaluate performance under contingencies of both models for a low generation scenario. The wind farm output was adjusted to 25 %. Same Contingency as previous

62 - VOLT 7046 [L_KENDAL345.00] : 212.5MW_CTG SB1 to SB2_EQV Model62 - VOLT 7046 [L_KENDAL345.00] : 212.5MW_CTG SB1 to SB2_Detailed Model


Volta

ge a

t the

PO

I (pu

)

1.3

1.2

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3



Low Voltage Ride Through (LVRT)

Low Voltage Ride Through (LVRT) capability of the wind turbines defines that the wind farm should not trip off line for faults for specific under voltage conditions.

A three phase fault at the POI was simulated, cleared by the outage of the 345 kV line between the POI and Substation 3. The wind farm loading is 85% or 720 MW.

Simulation Results:

The detailed model shows WTG trips due to the wind turbine’s low voltage protection of Group 1 and Group 2 units, while the equivalent model results show no wind turbine trips occurring.



Low Voltage Ride Through (LVRT)

The trips occur due to the lack of ability of the wind turbines to provide the necessary reactive support to restore the post contingency voltages inside the plant.

Results indicates that, in marginally stable cases, it is essential to use the detailed model

A detailed model better takes into account the WTG responses along the feeders

A higher voltage profile along the feeders may help prevent the turbine trips

238 - POWR 70461 TO 7046 CKT 1 : 720MW_CTG POI to SB3_EQV Model4555 - POWR 70461 TO 7046 CKT 1 : 720MW_CTG POI to SB3_Detailed Model


Act

ive

Pow

er (M

W)

900

800

700

600

500

400

300

200

100

0

-100

1733 - VOLT 61248 [G103 0.5750] : 720MW_CTG POI to SB3_Detailed Model3369 - VOLT 62268 [K-61 0.5750] : 720MW_CTG POI to SB3_Detailed Model

Time (seconds)2.2521.751.51.2510.750.50.250

WTG

Ter

min

al V

olta

ges

(pu)

1.5

1.4

1.3

1.2

1.1

1

0.9

0.8

0.7

0.6

0.5



Conclusions

The case studies presented are useful in making decisions on the level of modeling needed to evaluate the wind farm performance. There is trade-off in accuracy versus complexity of wind park modeling

Intent of aggregated model is to reflect the response of the wind farm as seen from the system

For the majority of the steady state studies to evaluate the impact in the system of a given wind farm, an equivalent representation is sufficient

For detailed steady state studies like the design of voltage control or reactive power strategies in the wind farm, a detailed model is desirable

A detailed modeling effort is justified in stability studies, since the models must represent accurately the plant dynamics and its response, particularly for large wind farms in weak systems

A detailed representation can lead to more realistic results, especially when the dynamic transfer capability is limited

Obviously, in planning practice detailed layout and data are not available.

Documents

pssewindandsolarmodels_casestudies