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1SINTEF Energy Research

2:nd Workshop, Trondheim, 29. January 2004

Power System Stability Assessments –Part 3: Controlled Series and Shunt

CompensationKjetil Uhlen

SINTEF Energy Research

Stefan Elenius

Helsinki University of Technology

2SINTEF Energy Research

OutlineObjectives and approach

Main objectivesModelling approachMethods applied

Controlled series compensation AnalysisControl designMain results and performance assessment

Controlled shunt compensation AnalysisControl designMain results and performance assessment

Preliminary conclusions

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Main objectivesStudy the use of Thyristor Controlled Series Capacitors (TCSCs) placed on strategic locations in the Finnish transmission grid to provide improved damping of inter-area modes. This includes

identify the best locations for installing TCSC(s) to achieve optimal performance.

modelling of the TCSC(s)

design and verification of appropriate controls.

Study the use of Controlled Shunt Compensators, SVC(s) or STATCOM(s), to improve voltage control and damping of inter-area modes.

identify the best locations for controlled shunt compensation

modelling of the SVC(s)/STATCOM(s)

design and verification of appropriate controls.

Follow up on the modelling of the Fennoskan HVDC link, and assess its impact on the Swedish system.

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Modelling approachSame power system model as in previous studies:

”Complete” PSS/E model of the Nordel transmission system with adaptations to enable linear analysis

Load flow data is used directly (PTI .raw format)Some dynamic models on PTI format have been replaced with other (simpler) models or have been omitted.

Simple models of the FACTS devices:Linear devices with limitations in speed and range of controllability:

TCSC: Variable (controllable) series capacitanceSVC: Variable (controllable) shunt susceptanceSTATCOM: Variable (controllable) reactive current injection

Base case: Low (summer) load condition with high export from Finland to Sweden. Number of online generators 784. Load in Finland 7266 MW.

Main results from the linear analysis are compared and verified against non-linear simulations.

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Methods appliedEigenvalues to identify frequency and damping of low damped inter-area modes (0.34 Hz, 0.57 Hz)

“Mode shapes” to assess the observability of the criticaleigenvalues in power flows and bus voltage angles.

Transfer function ”residues” and frequency responses for controllability assessment (identify most effective locations for controlled series and shunt compensation).

Transfer functions to aid control design (frequency responses)

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Transfer functionsTransfer function residues :Xij Pij :

for transfer functions from power line series reactance to active power flow (in the same line).

Bshunt,i θι : for transfer functions from bus shunt susceptance to voltage angle (mainly 400 kV buses).

Frequency responces :Xij PHasle-Borgvik and Xij PKeminmaa-Svartbyn

on transfer functions from controlled series reactance in selected transmission lines to measured active power flow in ”Hasle-Borgvik” and ”Keminaa-Svartbyn”.

Bshunt,i PHasle-Borgvik and Bshunt,i PKeminmaa-Svartbyn

on transfer functions from controlled shunt susceptance in various main 400 kV nodes to measured active power flow in ”Hasle-Borgvik” and ”Keminmaa-Svartbyn”.

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Controlled series compensation

Main results from linear analysisMode shapesTransfer function residuesFrequency responses

Interpretation of results

TCSC control design

Simulation results and performance assessment

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Modal and frequency analysis

Mode shapes of 0.34 Hz and 0.57 Hz power oscillations in the 400 kV AC lines

Transfer function residues Xij Pij

Frequency responsesXij PFIN-SWE , Xij PNOR-SWE

Power variation in a Finland-Sweden and a Norway-Sweden 400 kV AC line in response to modulations in the line reactances in the power lines with the highest mode shape components

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Pij mode shape 0.34 Hz

0

0.4

0.8

1.2

1.6

2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

modesh

1 Circuit # 4041/30117 4 KI4L 111 SVARTB.42 Circuit # 4040/ 4041 4 KI4 4 KI4L 3 Circuit # 4030/ 4042 3 PR4 4 KI4I4 Circuit # 4040/ 4042 4 KI4 4 KI4I5 Circuit # 4020/30112 2 PT4 111 ISOVA.O4 6 Circuit #30109/30111 111 LETSI..4 111 ISOVA.V47 Circuit #30117/30240 111 SVARTB.4 112 STORNO.48 Circuit # 4072/ 4073 3 NI41P 3 NI41E9 Circuit # 4073/ 4110 3 NI41E 11 AJ410 Circuit # 4074/ 4110 3 NI42P 11 AJ4

Observability analysis

Mode: 0.34 HzMode shape magnitudeObserved in: Active power flow in main transmission lines

0.250.260.50

0.72

0.39

0.280.18

0.30.19

0.19

0.37

0.3

0.280.27

0.16

0.28

0.24

0.3

0.71

0.18

Observability analysis

Mode: 0.34 HzMode shape magnitudeObserved in: Active power flow in main transmission lines

0.23

0.160.16

0.16

0.17

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Pij residues and frequency response 0.34 Hz

0

0.4

0.8

1.2

1.6

2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

residue

0

0.4

0.8

1.2

1.6

2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41

freq. resp Xij --> P(NOR-SWE)

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Pij mode shape 0.57 Hz

00.20.40.60.8

11.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Mode Shape

1 Circuit #51021/51027 51 HASLE4 51 HASLE4B 2 Circuit #30316/51027 113 BORGVI.4 51 HASLE4B 3 Circuit #30359/51011 113 SKOGSS.4 51 HALDEN4 4 Circuit #51011/51027 51 HALDEN4 51 HASLE4B 5 Circuit #51021/51041 51 HASLE4 51 TEGNEBY4 6 Circuit #30359/30381 113 SKOGSS.4 113 KILAND.4 7 Circuit #51021/51211 51 HASLE4 55 TVEITEN4 8 Circuit #51211/51231 55 TVEITEN4 55 ROD4 9 Circuit #51041/51151 51 TEGNEBY4 51 SYLLING4 10 Circuit #30381/30391 113 KILAND.4 113 STENKU.4

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Pij mode shape 0.57 Hz (2)

11 Circuit #30380/30381 113 HORRED.4 113 KILAND.4 12 Circuit #51231/51232 55 ROD4 55 ROD3 13 Circuit #53151/53152 53 AURL1-4 53 AURL1-3 14 Circuit # 4030/ 4042 3 PR4 4 KI4I 15 Circuit # 4041/30117 4 KI4L 111 SVARTB.4 16 Circuit # 4040/ 4041 4 KI4 4 KI4L 17 Circuit #53152/56012 53 AURL1-3 63 FARDAL3 18 Circuit # 4040/ 4042 4 KI4 4 KI4I 19 Circuit #30236/30362 112 RÄTAN..4 113 TANDÖ.N4 20 Circuit #55021/55051 60 SAURDAL4 60 KVILDAL4 21 Circuit #30362/30365 113 TANDÖ.N4 113 TANDÖ.S4 22 Circuit #51231/55061 55 ROD4 54 HOLEN4 23 Circuit #30316/30365 113 BORGVI.4 113 TANDÖ.S4 24 Circuit #55021/55022 60 SAURDAL4 60 SAURDAL3 25 Circuit #30316/30381 113 BORGVI.4 113 KILAND.4 26 Circuit # 4020/30112 2 PT4 111 ISOVA.O4 27 Circuit #30235/30239 112 RAMSEL.4 112 STORFI.4 28 Circuit #51061/51081 51 FOLLO4 51 FROGNER4 29 Circuit #51041/51061 51 TEGNEBY4 51 FOLLO4 30 Circuit #30111/30112 111 ISOVA.V4 111 ISOVA.O4

Observability analysis

Mode: 0.57 HzMode shape magnitudeObserved in: Active power flow in main transmission lines

0.14

0.20

0.09

0.09

0.11

0.09

0.09

0.09

0.1

0.18

0.1

Observability analysis

Mode: 0.57 HzMode shape magnitudeObserved in: Active power flow in main transmission lines

0.49

0.460.45

0.37

0.44

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Pij residues and frequency response 0.57 Hz

00.20.40.60.8

11.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Residues 0.57 Hz

00.20.40.60.8

11.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

freq. resp Xij --> P(FIN-SWE): 0.57 Hz

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Frequency responses

00.20.40.60.8

11.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

freq. resp Xij --> P(NOR-SWE): 0.57 Hz

0

0.5

1

1.5

2

2.5

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

freq. resp Xij --> P(NOR-SWE): 0.34 Hz

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Interpretation 1

0.34 Hz mode:The linear analysis indicates that the Svartby-Keminmaa-Pikkarala 400 kV lines are the most suitable for controlled series compensation for damping the 0.34 Hz mode.

Reliability requirements may necessitate controlled series compensation in parallel lines to the Svartby-Keminmaa-Pikkarala lines.

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Interpretation 2

0.57 Hz mode:The linear analysis indicates that the Hasle-Borgvik 400 kV line is the most suitable for controlled series compensation for damping the 0.57 Hz mode.

Reliability requirements may necessitate the use of series compensation in parallel line paths.

The 0.57 Hz mode is also controllable by series compensation in the FIN-SWE 400 kV lines.

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Interpretation 3

A controlled series compensation in the FIN-SWE 400 kV lines should mainly control the 0.34 Hz mode.

A controlled series compensation for the south NOR-SWE region must be able to control both the 0.34 Hz and the 0.57 Hz modes.

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Design of TCSC controllers for damping purposes

Not a straight forward task. Trade-offs have to be made to avoid adverse impacts on either low or high frequency dynamics

Only classical linear continuous control design has been considered so farA ”lagging” type of controller (similar to power sensitive PSSs) will easily react to low frequency dynamics, e.g. load flow changes.A ”leading” type of controller will have adverse impact on high frequency dynamics.

Best compromise: A leading controller with feedback from voltageangle difference. A sharp low pass filter is needed.

In practice the ”ABB approach” may be the best solutionApplying phase-locked loops for tracking critical modes.

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Proposed TCSC controller

..on the two 420 kV lines to Sweden

..with feedback from voltage angle difference, either from local measurements or using remote signals from PMUs.

3s1 + 3s

1+1.06s1+ 0.2s( )2 K

1+0.12s+0.01s2

-0.03

-0.01

X4040-4041

θ4030

θ30117

+

-

Gain andlow pass filter

Wash outfilter

Phase compensation”Lead”

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Performance of TCSCResponse to fault in Hasle

0 5 10 15 20 25 30500

600

700

800

900

1000P OWR 4041 TO 30117 CKT 1

Time [sec.]

[MW

]

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Performance of TCSCResponse to fault in Hasle

0 5 10 15 20 25 300.1

0.12

0.14

0.16

0.18

0.2DELTAANGLE

Time [sec.]

Vol

tage

ang

le d

iffer

ence

[rad

.]

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Performance of TCSCResponse to fault in Hasle

0 5 10 15 20 25 30-0.03

-0.025

-0.02

-0.015

-0.01XOUT

Time [s ec.]

Rea

ctan

ce [p

.u.]

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Performance of TCSCDamping comparisons

PacDyn PSS/E

Mode: 0.34 Hz 0.57 Hz 0.34 Hz 0.57 Hz

Base Case: 1.4 % 2.4 % 2.4 % 4.1 %

With TCSC: 4.4 % 4.3 % 5.1 % 4.2 %

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Performance of TCSCResponse to tripping of Petäjäskoski-Letsi

0 4 8 12 16 20700

800

900

1000

1100

1200

Time [sec.]

[MW

]

P OWR 4041 TO 30117 CKT 1

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Performance of TCSCResponse to tripping of Petäjäskoski-Letsi

0 4 8 12 16 20-0.03

-0.025

-0.02

-0.015

XOUT

Time [sec.]

Rea

ctan

ce [p

.u.]

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Controlled shunt compensation

Main results from linear analysis

Transfer function residues (Bshunt,i θi ) Mode shapesFrequency responses Damping ratio computation with P(SWE-NOR) Bshunt,i feedback

Interpretation of results

SVC control design

Simulation results and performance assessment

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Modal and frequency analysis

Transer function residue calculation of (Bshunt,i θi ) mainly for 400 kV buses (0.34 Hz)Modeshapes for bus voltage angle (θi)

Frequency responses:Bshunt,i PFIN-SWE , Bshunt,i PNOR-SWE

Power variation in a Finland-Sweden and a Norway-Sweden 400 kV AC line in response to modulation of the bus shunt susceptance at selected AC buses (mainly 400 kV buses)

Daping ratio computation with PNOR-SWE Bshunt,i feedback (0.34 Hz)

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Transfer function residues and mode shapesPower system stabilizers deactivated at OLG

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

residue Bshunt,i-->TETA(i): 0.34 Hz

Power system stabilizers deactivated at Olkiuoto

0

0.2

0.4

0.6

0.8

1

1.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

mode shape for TETA: 0.34 Hz

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Buses ordered by residue magnitudes

1 MP4 # 4163 21 AN4 # 4202 41 SK-HVDC #599902 MP4APU1 # 4166 22 MU4 # 4223 42 KR.SAND #540223 MP4APU2 # 4167 23 KR4 # 4220 43 STOKKEL3 #540824 LI4 # 4170 24 VYBORG42 # 4249 44 ASV400 #705075 OL42 # 4168 25 YL4 # 4230 45 TSO400 #705156 RAF4 # 4164 26 VH4 # 4111 46 KYV400 #706097 RA4 # 4162 27 HU4 # 4140 47 BJS400 #705148 RADC4 # 4165 28 VB4 # 4240 48 BJS400B # 25149 UL4 # 4161 29 SEVZATEZ #60323 49 HVE400 #70520

10 OL4 # 4160 30 SEVZAT2 #60324 50 GOR400 #7059211 FOR4 # 4171 31 AJ4 # 4110 51 HCV400 #7051812 IN4 # 4180 32 AP4 # 4130 52 ISH400 #7052113 ES4 # 4181 33 VJ4 # 4120 53 AVV400 #7050814 TO4 # 4112 34 KI4L # 4041 54 KRUSEB.4 #3040315 TM4 # 4190 35 NI42P # 4074 55 ARRIE..4 #3040216 HI4 # 4211 36 VJ4E # 4124 56 SEGE...4 #3041217 KA4 # 4150 37 PR4 # 4030 57 SÖDERÅ.4 #3041418 LS4 # 4203 38 PS4 # 4031 58 BARSEB.4 #3040419 HY4 # 4200 39 ISOVA.V4 #30111 59 KARSTO3 #5523220 NJ4 # 4201 40 PI4 # 4050

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Frequency response and damping

Power system stabilizers deactivated at Olkiluoto

0

1

2

3

4

5

6

7

8

9

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

freq.resp. Bshunt,i-->P(NOR-SWE): 0.34 Hz

Power system stabilizers deactivated at Olkiuoto

0

0.5

1

1.5

2

2.5

3

3.5

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

daping ratio (%) , feedback P(NOR-SWE)-->Bshunt,i: 0.34 Hz

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Effects of deacivated/active stabilizers at Olkiluoto on frequency response

Power system stabilizers deactivated at Olkiluoto

0

1

2

3

4

5

6

7

8

9

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

freq.resp. Bshunt,i-->P(NOR-SWE): 0.34 Hz

Power system stabilizers active at Olkiluoto

0

0.2

0.4

0.6

0.8

1

1.2

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

freq.resp. Bshunt,i-->P(NOR-SWE): 0.34 Hz

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Effects of deacivated/active stabilizers at Olkiluoto and SVC-locations on damping

SVC location (gain p.u./p.u.) Damping (%) AJ4 HU4 PR4 0.34 Hz 0.58 Hz - - - 0.33 2.09 50 - - 1.99 2.68 - 50 - 1.64 2.70 - - 50 2.06 2.47 50 50 - 2.73 3.12 - - 100 2.86 2.66

Deactivated stabilizers at Olkiluoto

50 50 50 3.50 3.27 - - - 2.84 2.49 50 - - 4.22 3.07 - 50 - 4.02 3.11 - - 50 4.45 2.87 50 50 - 4.86 3.51 - - 100 5.17 3.07

Active stabilizers at Olkiluoto

50 50 50 5.55 3.67

Sbase = 100 MVA

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Interpretation 4

Residue computation (Bshunt,i θi ) is an efficient way of finding candidate busesFrequency response information of the Bshunt,i PNOR-SWE transfer functions can be used to rank the candidate buses for SVC placement.Large 400 kV nodes in Finland are good choices for SVC placement when damping of 0.34 Hz oscillations is considered

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Design of SVC controllers

Start with design of the primary voltage control loop of the SVC:

Simple proportional (or proportional + integral + reactive droop) controllers are usedEnsures robust control and high bandwidth

Additional stabilising control loops can be addedThe preliminary conclusion is that the voltage control loop by itself provides sufficient damping!

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SVC voltage control loopFrequency response: Vref Vb

0.20.40.60.81.

0.1 1. 10. 100.

-180

-135

-90

-45

0

0.1 1 10 100Frequency [rad/s]

Magnitude

Phase angle

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Performance of SVCResponse to fault in Hasle

0 5 10 15 20 25 30500

600

700

800

900

1000P OWR 4041 TO 30117 CKT 1

Time [sec.]

[MW

]

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Performance of SVCResponse to fault in Hasle

0 5 10 15 20 25 30-2

-1.5

-1

-0.5

0

0.5

1

1.5

2VARS 4119 [AJS H 9.0000] [1 ]

Time [sec.]

SV

C re

activ

e po

wer

[100

Mva

r]

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Performance of SVCResponse to fault in Hasle

0 5 10 15 20 25 301

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08VOLT 4110 [AJ4 400.00]

Time [s ec.]

Vol

tage

[400

kV

]

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Performance of SVCDamping comparisons

PacDyn PSS/E

Mode: 0.34 Hz 0.57 Hz 0.34 Hz 0.57 Hz

Base Case: 1.4 % 2.4 % 2.4 % 4.1 %

With SVC: 5.9 % 4.1 % 7.3 % 4.7 %

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Summary of analysis

Two low damped inter-area modes of concern (at around 0.34 Hz and 0.57 Hz).

These modes can be efficiently damped by either controlled shunt (SVC) or series (TCSC) compensation devices if placed on strategic locations.

Shunt compensation (SVC)...

Series compensation (TCSC)…

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Preliminary conclusions

Damping control with shunt compensation:Promising results with SVC at strategic locations.

Transfer function residue and frequency response calculations can be used to find good locations for SVC

Damping control with series compensation:Transfer function residue and frequency response computations can be used to find good locations for TCSC

Control design much more complex than for SVC