Electranix Corporation 1 Simulation and Analysis Methods for SSR/SSTI/SSCI PUCT Panel Session...

Electranix CorporationElectranix Corporation 11

Simulation and Analysis Methodsfor SSR/SSTI/SSCISimulation and Analysis Methodsfor SSR/SSTI/SSCI

PUCT Panel SessionPUCT Panel Session

Austin, Nov 19, 2014Austin, Nov 19, 2014

Garth IrwinGarth Irwin

Electranix Corporation, Winnipeg, CanadaElectranix Corporation, Winnipeg, Canada

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Presentation OverviewPresentation Overview

• SSR/SSTI/SSCI - DefinitionsSSR/SSTI/SSCI - Definitions• SSCISSCI

• 2009 event of a wind farm near a 345 kV series compensated line2009 event of a wind farm near a 345 kV series compensated line

• Simulation/Analysis Techniques:Simulation/Analysis Techniques:• Screening Methods – Impedance ScansScreening Methods – Impedance Scans

• Perturbation AnalysisPerturbation Analysis

• Advanced Multi-Port Perturbation AnalysisAdvanced Multi-Port Perturbation Analysis

• Time Domain Non-Linear AnalysisTime Domain Non-Linear Analysis

• Mitigation MethodsMitigation Methods

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SS Phenomena - DefinitionsSS Phenomena - Definitions

• ““SSR”: Sub-Synchronous ResonanceSSR”: Sub-Synchronous Resonance• Interaction between the mechanical/torsional masses in a generator (or Interaction between the mechanical/torsional masses in a generator (or

wind turbine) and the electrical resonance from a series capacitor.wind turbine) and the electrical resonance from a series capacitor.• ““TA”: Torque Amplification: Increase in peak shaft torques leading to TA”: Torque Amplification: Increase in peak shaft torques leading to

higher fatigue.higher fatigue.

• ““SSTI”: Sub-Synchronous Torsional InteractionSSTI”: Sub-Synchronous Torsional Interaction• Interactions between the mechanical/torsional masses in a generator (or Interactions between the mechanical/torsional masses in a generator (or

wind turbine) and a power electronic device (such as an HVDC link, wind turbine) and a power electronic device (such as an HVDC link, SVC, wind turbine etc…).SVC, wind turbine etc…).

• ““SSCI”: Sub-Synchronous Control InstabilitySSCI”: Sub-Synchronous Control Instability• Interactions between a power electronic device (such as an HVDC link, Interactions between a power electronic device (such as an HVDC link,

SVC, wind turbine etc…) and a series compensated system.SVC, wind turbine etc…) and a series compensated system.

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Sub Synchronous InteractionsSub Synchronous Interactions

Device Series Capacitor

Power Electronics Gas Turbine or Wind Shaft

Series Capacitor --- SSCI SSR

Power Electronics SSCI CI (control interactions can be at any frequency)

SSTI

Gas Turbinesor Wind Shaft

SSR SSTI ---

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SSCI Event in TexasSSCI Event in Texas

I

V

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Real System SSCI Event TraceReal System SSCI Event TraceSSCI Event - PSCAD Studies - Comparison of Simulation to Measured Waveforms (SLG on 345 kV line)

Sec 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 ... ... ...

-600

-400

-200

0

200

400

600

kV

Simulated:High_Side_Volts,_A Real System Measured:VA_345

-600

-400

-200

0

200

400

600

kV

Simulated:High_Side_Volts,_B Real System Measured:VB_345

-600

-400

-200

0

200

400

600

kV

Simulated:High_Side_Volts,_C Real System Measured:VC_345

Real System Traces and PSCAD Simulation6


Wind Projects with Series Compensated Transmission LinesWind Projects with Series Compensated Transmission Lines

• * Texas 2009 SSCI Event* Texas 2009 SSCI Event

• * North Dakota series capacitor/wind turbines* North Dakota series capacitor/wind turbines

• * Alberta-Montana 230 kV series compensated line* Alberta-Montana 230 kV series compensated line

• ERCOT CREZ expansion 345 kV series compensated linesERCOT CREZ expansion 345 kV series compensated lines

• Alberta southern system expansionAlberta southern system expansion

• Project in Texas with a N-0 radial 345 kV series compensated lineProject in Texas with a N-0 radial 345 kV series compensated line

• UK large scale transmission expansionUK large scale transmission expansion

• Twin circuit 275 kV series capacitor expansion AustraliaTwin circuit 275 kV series capacitor expansion Australia

• ......

* Indicates real-system SSCI events.* Indicates real-system SSCI events.

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SSCI - DescriptionSSCI - Description

• Voltages and currents are distorted due to the series capacitor Voltages and currents are distorted due to the series capacitor and electrical resonanceand electrical resonance

• Difficult to filter:Difficult to filter:• Can be close to 60 HzCan be close to 60 Hz

• Resonant frequency changesResonant frequency changes

• Distorted inputs signals are processed by turbine controls, Distorted inputs signals are processed by turbine controls, and ultimately fire IGBTs/power electronics (creating a and ultimately fire IGBTs/power electronics (creating a feedback loop).feedback loop).

• Overall controller response can introduce negative damping, Overall controller response can introduce negative damping, resulting in instabilities (growing or sustained oscillations)resulting in instabilities (growing or sustained oscillations)

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Doubly Fed Induction Generator Wind Turbine

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A

B

C

D

Q

0

IRA

IRB

IRC

Rotor Side Currents

QOrder

POrder

D +

F

-I

P

QMeasured

D +

F

-

PMeasured

IRDMeasured

IRQMeasured

D +

F

-

IRDMeasured

IRDOrderedI

P

URDOrdered

I

P

D +

F

-

IRQMeasured

IRQOrderedI

P

URQOrdered

D

Q

A

B

C0

URAOrdered

URBOrdered

URCOrdered

IGBT_Pulse_A

IGBT_Pulse_B

IGBT_Pulse_C

PWM Comparator

Firing Pulse Generator

Cascaded PI Controller – Outer and Inner PI Loops

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SS – Analysis Methods OverviewSS – Analysis Methods Overview

1.1. Screening StudiesScreening Studies

• SSR/SSCI: Harmonic Impedance ScansSSR/SSCI: Harmonic Impedance Scans

• SSTI: Unit Interaction FactorsSSTI: Unit Interaction Factors

2.2. Perturbation AnalysisPerturbation Analysis

• SSR/SSTI: Used to determine generator electrical damping vs freqSSR/SSTI: Used to determine generator electrical damping vs freq

• SSCI: Used to determine Effective Dynamic Impedance of a power SSCI: Used to determine Effective Dynamic Impedance of a power electronic deviceelectronic device

3.3. Advanced Screening StudiedAdvanced Screening Studied

• SSCI: Uses a combination of Harmonic Impedance Scans (linear portion SSCI: Uses a combination of Harmonic Impedance Scans (linear portion of a system) and Perturbation Analysis (Effective Dynamic Impedance)of a system) and Perturbation Analysis (Effective Dynamic Impedance)

4.4. Full Time Domain AnalysisFull Time Domain Analysis

• SSR/SSTI/SSCI: Uses fully detailed models of all devicesSSR/SSTI/SSCI: Uses fully detailed models of all devices

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SSR/SSCI – 1) Screening StudiesSSR/SSCI – 1) Screening Studies

• Harmonic Impedance ScansHarmonic Impedance Scans• Determine net system impedance (as seen from behind the generator equivalent Determine net system impedance (as seen from behind the generator equivalent

impedance) as a function of frequencyimpedance) as a function of frequency• Determines approximate frequency of electrical resonanceDetermines approximate frequency of electrical resonance• Impedance “dip” an approximate indicator of the likelihood of SS interactionsImpedance “dip” an approximate indicator of the likelihood of SS interactions

(large dips indicate “closer to radial” connections – transition from positive to negative (large dips indicate “closer to radial” connections – transition from positive to negative reactances)reactances)

• Limitations:Limitations:• How should nearby SVC/Statcom/HVDC/non-linear-devices be represented?How should nearby SVC/Statcom/HVDC/non-linear-devices be represented?• What is the equivalent impedance of a wind turbine?What is the equivalent impedance of a wind turbine?• Does SSCI depend on the magnitude of a disturbance/oscillation?Does SSCI depend on the magnitude of a disturbance/oscillation?• If there are 2 or more wind farms nearby, how does a turbine non-linear controller affect If there are 2 or more wind farms nearby, how does a turbine non-linear controller affect

the impedance as seen from the other farm?the impedance as seen from the other farm?

• Screening Method – used to determine system condition (for later study Screening Method – used to determine system condition (for later study with more accurate methods).with more accurate methods).

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SSR/SSCI – 1) Screening StudiesSSR/SSCI – 1) Screening Studies

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SSR/SSTI2) Perturbation AnalysisSSR/SSTI2) Perturbation Analysis

• Consider open loop transfer function from generator rotor Consider open loop transfer function from generator rotor speed to electrical torque…speed to electrical torque…

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• Enable PSCAD Multi-mass feature on a generatorEnable PSCAD Multi-mass feature on a generator

• Force the speed to be 1 pu plus a small oscillation at 5 Hz (this will rock the Force the speed to be 1 pu plus a small oscillation at 5 Hz (this will rock the full system at 5 Hz)full system at 5 Hz)

• Run until steady state in the time domainRun until steady state in the time domain

• Measure the relative magnitude and angle between the electrical torque and Measure the relative magnitude and angle between the electrical torque and delta Wdelta W

• May require a variable/tuned filter on both Te and W to remove noise and DC, or (better) May require a variable/tuned filter on both Te and W to remove noise and DC, or (better) use FFT methods.use FFT methods.

• The electrical damping is the real part of dTe/dWThe electrical damping is the real part of dTe/dW

• Compute and store the damping factor for this frequencyCompute and store the damping factor for this frequency

• Increment the frequency to 6 Hz and repeatIncrement the frequency to 6 Hz and repeat

• Use multiple run features to sweep from 5 Hz to 55 HzUse multiple run features to sweep from 5 Hz to 55 Hz

• Plot damping vs frequencyPlot damping vs frequency

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D +

F

+

G1 + sT

Phase

FreqMag

Sin

TIME

0.0

DW*1.0

RAMP

FR

WIN

To multi-mass interface on the machine...

MultipleRun

V1.

.

.

DW

TE

Ref

Sig

cmpx14_new .f

N

D

N/D1.0

FR

Z_FR

new

new

1TIME

FR

Phase

mrun_source.f

Damping Factor

Ref

Sig Phase

Real(DF)

LogDecRef

LogDecSig

New_PhasePhase

Damping Factorfactor

LogDecTELogDecTE

LogDecWLogDecW

60.0 *

2 Pi

FR

1

EnableOutput File Writer

Multiple Run

5

TSSRStart2.0

Phase

3

Factor Factor

2

LogDecW

4

LogDecTE

5

LogDecW

LogDecTE

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• HVDC links can directly affect torsional dampingHVDC links can directly affect torsional damping• Not a problem however, as SSDC stabilizers are easy to design and very effectiveNot a problem however, as SSDC stabilizers are easy to design and very effective

• Should be studied using detailed models (PLL and main PI controls are critical)Should be studied using detailed models (PLL and main PI controls are critical)

• SVCs are usually not an SSR concern, however indirect effects SVCs are usually not an SSR concern, however indirect effects through nearby loads can cause interactionsthrough nearby loads can cause interactions

• Interpolation in SVC and HVDC firing controls is essential!Interpolation in SVC and HVDC firing controls is essential!

• Exciter and governor models are often not validated at torsional Exciter and governor models are often not validated at torsional frequencies – simplified PSS/E models often are not valid.frequencies – simplified PSS/E models often are not valid.

• Impact with and without mitigation methods can be testedImpact with and without mitigation methods can be tested

• We We alwaysalways recommend TSRs (torsional stress relays) for all generators recommend TSRs (torsional stress relays) for all generators near series caps, HVDC links or SVCs.near series caps, HVDC links or SVCs.

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3) SSCI Advanced ScreeningDynamic Effective Impedance3) SSCI Advanced ScreeningDynamic Effective Impedance

• Perturbation Analysis can be used to determine the Dynamic Effective Perturbation Analysis can be used to determine the Dynamic Effective Impedance of a non-linear device (wind farm):Impedance of a non-linear device (wind farm):

• Perturb voltage with sub-synchronous componentsPerturb voltage with sub-synchronous components• Measure sub-synchronous magnitude and phase of measured terminal currentMeasure sub-synchronous magnitude and phase of measured terminal current• Impedance (Z) = V/I (performed with complex vectors at each frequency)Impedance (Z) = V/I (performed with complex vectors at each frequency)• Table of Z (R + jX) as a function of frequencyTable of Z (R + jX) as a function of frequency

• Calculation for wind turbines (Dynamic Effective Impedances) can be Calculation for wind turbines (Dynamic Effective Impedances) can be added to linear system impedance (including the series capacitor).added to linear system impedance (including the series capacitor).

• Relatively easy for 1 wind farm connected through 1 port to a series Relatively easy for 1 wind farm connected through 1 port to a series compensated system.compensated system.

• Can be applied for a 2 port (2 wind farm) scenario:Can be applied for a 2 port (2 wind farm) scenario:• Requires 3 system harmonic impedance scans for each system conditionsRequires 3 system harmonic impedance scans for each system conditions• Solve 3 equations in 3 unknowns to device a 2x2 two port linear network equivalentSolve 3 equations in 3 unknowns to device a 2x2 two port linear network equivalent• Add wind Dynamic Effective Impedances, solve 2x2 network as seen from each deviceAdd wind Dynamic Effective Impedances, solve 2x2 network as seen from each device

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3) SSCI Advanced ScreeningDynamic Effective Impedance3) SSCI Advanced ScreeningDynamic Effective Impedance

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Perturbation AnalysisLimitations for SSCIPerturbation AnalysisLimitations for SSCI

• Some devices have a damping characteristic which is Some devices have a damping characteristic which is “magnitude sensitive”“magnitude sensitive”

• Non-linearities in the system and device models are not Non-linearities in the system and device models are not consideredconsidered

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SSR/SSTI/SSCI Analysis4) Complete System Time Domain Analysis

SSR/SSTI/SSCI Analysis4) Complete System Time Domain Analysis

• Ultimate Simulation… Model the entire system including Ultimate Simulation… Model the entire system including multi-mass shaft models, HVDC/SVC/Statcoms, wind farms multi-mass shaft models, HVDC/SVC/Statcoms, wind farms etc…etc…

• Apply a small signal disturbance and measure log-decrement Apply a small signal disturbance and measure log-decrement (quantify damping)(quantify damping)

• Apply faults and observe large signal disturbances (and watch Apply faults and observe large signal disturbances (and watch for tripping/ride through)for tripping/ride through)

• Time consuming (varying loadflow conditions, contingencies, Time consuming (varying loadflow conditions, contingencies, wind turbine combinations, two segment series capacitors…)wind turbine combinations, two segment series capacitors…)

• Used in conjunction with Screening Studies (to focus on most-Used in conjunction with Screening Studies (to focus on most-concerning cases)concerning cases)

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Mitigation MethodsMitigation Methods

SSR SSCI SSTI Description

Select other transmission or generator options (higher voltage AC lines etc…)

Select Series Compensation Level to Avoid Problems

Use transfer trips to avoid trouble conditions

Design damping controllers (SEDC, SSDC…)

SSCI resistant wind farm controllers

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Mitigation MethodsMitigation Methods

SSR SSCI SSTI Description

Add generator step up transformer filters

Add shunt compensation with stabilizers (SVC/Statcom)?

Series Capacitor Bypass Filters

FACTS Devices (TCSC, SSSC, UPFC…)

Combinations of all of the above

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New Simulation ProductsNew Simulation Products

• E-TRAN Plus for PSCADE-TRAN Plus for PSCAD

Parallel Processing of PSCAD SimulationsParallel Processing of PSCAD Simulations

- break the PSCAD simulation into several cases and - break the PSCAD simulation into several cases and run them in parallel talking with each other run them in parallel talking with each other

• E-TRAN Plus for PSS/EE-TRAN Plus for PSS/E

Hybrid SimulationHybrid Simulation

- PSCAD and Transient Stability simulations are run - PSCAD and Transient Stability simulations are run in parallel talking with each otherin parallel talking with each other

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Thanks!Thanks!

Garth IrwinGarth IrwinElectranix Corporation – Engineering ConsultantsElectranix Corporation – Engineering Consultants

Winnipeg, Manitoba, CanadaWinnipeg, Manitoba, Canada

1-204-953-18311-204-953-1831

[email protected]@electranix.com

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Electranix Corporation 1 Simulation and Analysis Methods for SSR/SSTI/SSCI PUCT Panel Session...

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