Adil Abdalrahman, ABB Power Grids, HVDC, 2016-11-24 ... · PDF fileAdil Abdalrahman, ABB Power Grids, HVDC, 2016-11-24 Experiences from SSTI-studies in ... 700 MW VSC HVDC transmission

HVDC2014-009991

© ABB GroupDecember 3, 2016 | Slide 1

Adil Abdalrahman, ABB Power Grids, HVDC, 2016-11-24

Experiences from SSTI-studies inHVDC projects

HVDC2014-009991

Contents

§ General

§ Approach for SSTI Studies

§ SSTI Screening Study

§ SSTI Detailed Study

§ Examples from HVDC projects (SSTI and SSCI)

§ Ferroresonance

HVDC2014-009991

General§ General

§ Approach for SSTIStudies

§ Screening study

§ Detailed study

§ Examples from HVDCprojects (SSTI andSSCI)

§ Ferroresonance

HVDC2014-009991

Steam Turbines

|

Steam turbine-generator shafts aremore susceptible to torsional interactiondue mainly to the fact that they haveseveral torsional frequencies in thesubsynchronous range.

HVDC2014-009991

Definition of SSO, SSR, SSTI

§ SSO – Subsynchronous Oscillation

Problems related to SSO:

§ SSR – Subsynchronous Resonance:passive elements (seriescompensated lines)

§ SSTI - Subsynchronous TorsionalInteraction: active elements (powersystem controls e.g. HVDC,SVC/STACOM, high speed governor,PSS)

§ SSCI - Subsynchronous ControlInteraction: interaction between powerelectronic control systems, e.g. ofHVDC or DFIG WTG, and seriescompensated line. Purely electricalphenomenon (not related tomechanical shaft system)

HVDC2014-009991

SSTI with LCC HVDC

GeneratorRotatingExciterHP-IP

Turbine

HVDCControls

Idc

w

Ig

a

Vg

LPTurbine

HVDC2014-009991

SSTI with VSC HVDC

HVDC2014-009991

Torsional stresses and fatigue

§ The increasing speed perturbations cause torsionalvibrations in the shaft structure of the generator

§ Torsional stresses and fatigue of the shaft whenthe fatigue limit of the shaft material is exceeded.

Fatigue limit: limitng value of the cyclic stress towhich shaftcan be subjected such that practically nocumulative fatigue damage.Cycles: cycle to crack initiation

HVDC2014-009991

Approach forSSTI Studies

§ General

§ Approach for SSTIStudies

§ Screening study

§ Detailed study

§ Examples from HVDCprojects (SSTI andSSCI)

§ Ferroresonance

HVDC2014-009991

Approach for SSTI Studies

§ SSTI Screening Study based on UIF factor

§ Detailed SSTI Studies based on damping torque analysis

§ Design Subsynchronous Damping Controller (SSDC), if necessary

§ Verification of SSDC by time domain simulation, verification inFactory System Test and during commissioning

HVDC2014-009991

SSTI ScreeningStudy

§ General


§ Screening study

§ Detailed study

§ Examples from HVDC projects(SSTI and SSCI)

§ Ferroresonance

HVDC2014-009991

Screening study

2

1 ÷÷ø

öççè

æ-=

Gin

Gout

Gen

HVDC

SCSC

MVAMWUIF

MWHVDC = the rating of the HVDC systemMVAGen = the rating of the generator under studySCGin= the system short circuit capacity at the HVDC commutating bus with the generatorunder study being in serviceSCGout = the system short circuit capacity at the HVDC commutating bus without thegenerator under study being in service

§Low possibility of interaction if UIF < 0.1

§For a purely radial case SCGout is zero and thus UIF is equal to 1 times the ratio of HVDC togenerator rating (e.g. when the first generator has just been synchronized during Black Startof an AC grid via HVDC-Light link)=>UIF=1 if the generator is of the same size as the HVDC

Unit interaction factor, UIF:

HVDC2014-009991

Screening Study, example of scenario

HVDC2014-009991

Screening Study, typical result data

MachineContingency

Level Outage ID UIF

Unit 1

N-0 0.0081

N-1 Line 1 1 0.0092

N-2 Line 2 2 0.0875

N-3 Line 3, 1 0.2274

Unit2

N-0 0.0000

N-1 Line 1 1 0.0000

N-2 Line 2 2 0.0002

N-3 Line 3 2 0.0013

N-4 Line 4 1 0.0999

N-5 Line 5 1 0.2804

N-5 Line 6 1 0.2804

N-5 Line 7 1 0.2804

N-5 Line 8 1 0.2804

N-5 Line 9 1 0.2279

Unit 3

N-0 0.0000

N-1 Line 1 1 0.0000

N-2 Line 2 2 0.0002

N-3 Line 3 2 0.0012

N-4 Line 4 1 0.0955

N-5 Line 5 1 0.2682

N-5 Line 6 1 0.2682

N-5 Line 7 1 0.2682

N-5 Line 8 1 0.2682

N-5 Line 9 1 0.2270

HVDC2014-009991

§ General


§ Screening study

§ Detailed study

§ Examples from HVDC projects(SSTI and SSCI)

§ Ferroresonance

Detailed SSTIStudy

HVDC2014-009991

Damping torque analysis: total (net) damping

Rotor MechanicalSystem, Gm

Electrical Model ofMachine andTransmission System(including HVDC),Ge

DwDTm

_+

DTe

= ∆∆

= − ∆

= ( ) = {∆∆

}

For stable operation: + ≥ 0

≥ 0( ℎ )

§Impact of the turbine control loop (governor) is neglected, hence∆ =0

§This system is asymptotically stable as long as the Nyquistcurve for the open-loop frequency function ( ) ( )doesnot encircle the point -1

§Mechanical dynamics are passive for all frequencies:Re ( ) = ≥ 0 − 90 ≤arg ( ) ≤ 90

§A sufficient criterion for stability is that the electrical dynamicsalso are passive: −180 ≤arg ( ) ( ) ≤ 180, whichimplies that the Nyquist curve cannot encircle -1

§Thus, it’s desirable that Re ( ) = ≥ 0 for all allfrequencies

§ The mechanical damping ispositive and can compensate anegative electrical damping in acertain frequency range

§D is the electrical damping and maynot be positive for all frequencies.

§Stability can be guaranteed if ≥ 0at and in the neighbourhood of thetorsional frequencies irrespective ofof the mechanical damping.

HVDC2014-009991

Mechanical damping

§ Low at low torsional frequencies and high towardsynchronous frequency

Sources

§ Dissipation forces of windage

§ Bearing friction

§ Material hysteresis damping

§ Steam/gas/water forces on the turbine blades

§ Steam damping increases with load

§ Gas damping is a more complicated function

HVDC2014-009991

Strategy for SSTI study using damping torque analysis

§ Mechanical damping is independent of the networkconditions

§ If the level of electrical damping with HVDC is as good asor better than the electrical damping without HVDC, thentorsional stability is assured

§ Add SSDC, if necessary

HVDC2014-009991

Small signal analysis: Model for calculation of electricaldamping

Rotor MechanicalSystem

Electrical Model ofMachine andTransmission System(including HVDC)

dw + D w wos

Te +DTe_

+

÷ø

öçè

æDD

=wTeDe Re

Obtaining an analytical expression for transfer function of De is complicated as it shall include all dynamics fromthe generator, a.c. network and HVDC as well as its feedback control system. Therefore, De computation isperformed using a time-domain simulation with programs such as PSCAD where the complete system with thegenerator, a.c. network and HVDC is modelled.

HVDC2014-009991

SSDC

§ SSDC integrated with the HVDC control

§ Controls may be located far away from the machines

§ Transfer function: typically HP + lead/lag + LP and anegative gain

§ Input: Typically frequency of the ac commutatingvoltage/rotor speed (LCC) or Upcc (VSC)

§ Output: modulation of the control angle, α (in LCC)

: modulation of the voltage reference (in VSC)

HVDC2014-009991

Typical for tubine-generator model

§Required for multi-massmodel

HVDC2014-009991

§ General


§ Screening study

§ Detailed study

§ Examples from HVDC projects(SSTI and SCCI)

§ Ferroresonance

Examples fromHVDC projects(SSTI and SCCI)

HVDC2014-009991

Example 1

÷øö

çèæ

DD

=wTeDe Re

§ 800 MVA generator unit, radially

connected to the HVDC link follwing

N-3 contingency (UIF=0.23), rectifier

side

§ Negative damping around the

torsional frequency 19.6 Hz

§ Subsynchronous damping controller

(SSDC) shall be be added.5 10 15 20 25 30 35 40 45 50

-0.5

0

0.5

1Electrical Damping

De

(pu/

pu)

Freq (Hz)

Reference Case without HVDCCase C1: with HVDC

220 MW LCC HVDC Link

HVDC2014-009991

Example 1: SSDC action

5 10 15 20 25 30 35 40 45 50-0.5

0

0.5

1Electrical Damping

De

(pu/

pu)

Freq (Hz)

Reference Case without HVDCCase C1: HVDC Without SSDCCase C1: HVDC with SSDC

§SSDC increases the electrical damping by adding acontribution to the firing angle α

HVDC2014-009991

Example 1: SSTI time domain verification

SSDC Reg: OFF ON

HVDC2014-009991

Example 2

700 MW VSC HVDC transmission link

Electrical damping for 375 MVA generator, black startingconverter operates as rectifier

§ 375 MVA thermal generator radiallyconnected to the HVDC link duringblack start (active power is approx. 0.53pu) e.g. when the black startingconverter is in Frequency& Voltagecontrol

§ The subsynchronous torsionalfrequencies for the unit are; 16.4Hz,24.9Hz and 33.2Hz.

§ SSDC was needed in order tomaintain the necessary electricaldamping margin for frequencies aboveapproximately 25Hz

HVDC2014-009991

Example 2

Electrical damping verification by time domain simulation

Electrical Damping Verification in Time Domainfor the torsional frequency 24.9 without and withthe SSDC activated.

Electrical Damping Verification in Time Domainfor the torsional frequency 16.4 Hz without andwith the SSDC activated.

HVDC2014-009991

Example 2

Electrical damping verification by time domain simulation

Electrical Damping Verification in Time Domain for the torsionalfrequency 33.2 Hz without and with the SSDC activated.

HVDC2014-009991

Fenno-Skan 2

§ 800 MW and 500kV HVDC interconnector between Finland (Rauma) andSweden (Dannebo). Total length of DC OHL+cableof 303 km, Pole 2 ofFenno-Skan HVDC transimission link.

§ Converter stations are located near Nuclear powerplants Olkiluoto in Finland and Forsmark in Sweden.

§ During FST SSTI the electrical damping was verifiedfor Olkiluoto 1/2-3 and Forsmark 1/2-3 generatorunits using one mass model models (frequencydomain) and multi-mass models (time domain)=>quite challenging FST set-up due to the complexity ofmachine models, total four turbine generators.

§ SSTI also verified during system tests at site

Generator rated power: Forsmark 1 (990 MW),Forsmark 2 (1,120 MW) and Forsmark3 (1,170 MW)Olkiluoto 1 (860 MW), Olkiluoto 2 (860 MW).

Ref: New Fenno-Skan 2 HVDC pole with an upgrade of the existing Fenno-Skan 1 pole. Cigre 2012. Available [online]:https://library.e.abb.com/public/a0f7529d389aef26c1257a86002783d6/New%20Fenno-Skan%202%20HVDC%20pole%20with%20an%20upgrade%20of%20the%20existing%20Fenno-Skan%201%20.p

HVDC2014-009991

Fenno-Skan 2 (SSTI verification at site)

§ Two tests were performed at site for SSTI verification in bothsides:

§ Step in current order, 0,1 pu

§ Simulated DC-line faults, with re-start of the DC-link. DC faultexecuted close to nominal power level, starting with tests atminimum and 50% power. The DC-line faults at high power werechosen in order to get enough power changes in the network toinitiate SSTI

§ Oscillations at the torsional mode frequencies were measured atthe converter stations by the SSTI supervision based on deviationin period time of the AC-voltage

Ref: New Fenno-Skan 2 HVDC pole with an upgrade of the existing Fenno-Skan 1 pole. Cigre 2012. Available[online]:https://library.e.abb.com/public/a0f7529d389aef26c1257a86002783d6/New%20Fenno-Skan%202%20HVDC%20pole%20with%20an%20upgrade%20of%20the%20existing%20Fenno-Skan%201%20.p

HVDC2014-009991

Fenno-Skan 2 (SSTI verification at site)

§ Disturbance caused by the tests was to moderate to initiate anysignificant SSTI since:

§ Network configurations during the system tests were fairlystrong, and the corresponding SSDC was activated

§ The damping of the shaft contains both a mechanical part andan electrical part, where the mechanical is the most importantcomponent, and the surrounding network configurationcontributes to the electrical part

§ Conclusion from the tests:

§ The link with its SSTI regulator did not deteriorate the dampingof the torsional frequencies.

Ref: New Fenno-Skan 2 HVDC pole with an upgrade of the existing Fenno-Skan 1 pole. Cigre 2012. Available [online]:

https://library.e.abb.com/public/a0f7529d389aef26c1257a86002783d6/New%20Fenno-Skan%202%20HVDC%20pole%20with%20an%20upgrade%20of%20the%20existing%20Fenno-Skan%201%20.pdf

HVDC2014-009991

Example 4 (SSCI)

Two main issues:

§ Sub-Synchronous Control Interaction (SSCI) can occur between seriescompensated lines and the converter control system.

§ Ferroresonance oscillations can occur between series compensatedlines and the saturable magnetic core of a converter transformer.Transformer saturation occurs due to voltage recovery after a.c. faultsare cleared (Pseudo-inrush)=>inrush currents rich in harmonic contentproduce harmonic voltage amplification through the resonantimpedance of the system.

350 MW Back- to- Back LCC link

A B

HVDC2014-009991

Example 4 (SSCI assessment)

§ Control instability due to SSCI occurs when the a.c. networkresonance frequency matches with converter resonance frequency

§ Assessment approach:

§ Impedance scanning of AC network (including AC filters) forfrequency sweep from 1 Hz to 65 Hz. Impedance was measured onthe converter bus (bus A in the diagram) for different AC networkconfigurations.

§ Driving point impedance of HVDC system as a function of sub-synchronous frequency was measured at the converter bus on side,both for export and import scenarios.

§ Time domain simulation: AC faults and step changes in activepower and dc current

HVDC2014-009991


§ AC network configurations likely to happen in reality:

§ Zero Capacitor Bypassed

§ One Capacitor Bypassed in One Double Circuit

§ One line out in one double circuit

HVDC2014-009991


Results: AC network impedance

Zero Capacitors BypassedOne Capacitor Bypassed in One Double Circuit

One series compensation line out

Series resonance when the systemreactance changes from negative topositive. The resonance frequencies forthe three configurations are 30Hz,34.5Hz and 35.2Hz respectively

HVDC2014-009991


Results: HVDC system impedance (rectifier)

Normal Power Direction (from A to B), 350 MW Normal Power direction (from A to B), 435 MW

Normal Power Direction (from A to B), 35 MW

HVDC2014-009991


Results: HVDC system impedance (inverter)

Reverse Power Direction (from B to A), 350 MW Reverse Power Direction (from B to A), 435 MW

Reverse Power Direction (from B to A), 35 MW

HVDC2014-009991


Results: 3Ph-G. 100ms, <10% rem.Volt. Bus of series compensated lines.(435 MW from A to B, zero cap bypassed).

rectifier inverter

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1000

0

1000

Eco

nv_S

1P1:

1[k

V]

Eco

nv_S

1P1:

2[k

V]

Eco

nv_S

1P1:

3[k

V]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

0

1

2

P_S1

P1[p

u]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

0

1

2

UD

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

0

2

4

ID_P

1[p

u]IO

RD

_LIM

_S1P

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

ALPH

A_O

RD

_S1P

1A

LPH

A_M

EAS_

S1P1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

50

100

150

Time [s]

GAM

MA_

S1P1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-500

0

500

Econ

v_S2

P1:1

[kV

]Ec

onv_

S2P1

:2[k

V]

Econ

v_S2

P1:3

[kV

]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

0

1

2

P_S

2P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

0

1

2

UD

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

0

2

4

ID_P

1[p

u]IO

RD

_LIM

_S2P

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 150

100

150

ALP

HA

_OR

D_S

2P1

ALP

HA_

MEA

S_S

2P1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

Time [s]

GAM

MA

_S2P

1

HVDC2014-009991

Ferroresonance

§ General


§ Screening study

§ Detailed study

§ Examples from HVDC projects(SSTI and SCCI)

§ Ferroresonance

HVDC2014-009991

Ferroresonance

§ An oscillating phenomenon between a non-linear inductance and acapacitor.

§ Elements needed for a circuit to exhibit Ferroresonance:

§ A non-linear inductance e.g. transformer magnetic core

§ A Capacitance:§ Voltage grading capacitors in HV circuit breakers

§ Conductor interphase capacitance

§ Capacitance to ground of cables or long lines

§ Series capacitor or shunt capacitor banks

§ A voltage or a current source

§ Low losses (less damping)

§ It is not so easy to predict the occurrence of ferroresonance.

§ Ferroresonance results in high voltages and currents, however, thewaveforms are usually irregular in shape.

Introduction

HVDC2014-009991

Study System

System parameters

HVDC back-to-back SystemBUS 1 (400 kV) BUS 2 (400 kV)

Filter BanksPole I

Filter BanksPole I

Filter BanksPole II

Filter BanksPole II

AC System 1 AC System 2

Pole I (P1)

Pole II (P2)

Power flow

Zs Zs

Series compensated line

System Parameters AC System 1 AC System 2

AC Voltage 400kV 400 kVDC Voltage 200 kVDC Power Pole I rated for 500 MW

Pole II rated for 500 MWShort Circuit MVAmin 1 200 MVA 2 500 MVA

Short Circuit MVAmax 3 000 MVA 8 000 MVA

§ Each pole has two 6-pulse converters connected in series on rectifier and inverter side.

§ At the rectifier side, both the poles are connected by 400 kV double-circuit transmissionlines (nearly 225 km in length) having 50% series compensation.

HVDC2014-009991

§© ABB Group

§December 3, 2016 | Slide 43

Fault at Rectifier Side AC BusFor 3-phase to ground fault

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-500

0

500

U -AC

1U -A

C2

U -AC

3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1

0

1

PD_P

1[p

u]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

ALP

HA -P

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 120

40

60

80

Time [s]

GAM

MA -P

1

0.5 1 1.5 2-0.5

0

0.5

1

1.5

Time [s]

ID_P

1[p

u]

20 30 40 50 60 70 80 90 1000

0.1

0.2

0.3

Frequency [Hz]

Spe

ctra

ofID

_P1

[pu]

§(a) Line to neutral ac voltage

§(b) Dc power (p.u.)

§(c) Rectifier side α in degrees

§(d) Inverter side ɣ in degrees

0.5 1 1.5 20

50

100

Time [s]

ALP

HA -P

1

20 30 40 50 60 70 800

5

10

15

Frequency [Hz]

Spe

ctra

ofAL

PHA

-P1

§(a) Rectifier side α in degrees

§(b) FFT of α shown in plot ‘a’

§(a) Dc current through Pole I

§(b) FFT of dc current shown in plot‘a’

§ Post fault recovery is not stable

§ Observed 42 Hz frequency component on dc side

FFT

HVDC2014-009991

§© ABB Group


Fault at Rectifier Side AC BusFor 3-phase to ground fault

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-500

0

500

U-A

C1

U-A

C2

U-A

C3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1

0

1

PD

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

ALP

HA -P

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 120

40

60

80

Time [s]

GAM

MA -P

1

0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7-1000

-500

0

500

Time [s]

U-A

C1

U-A

C2

U-A

C3

File: 3phg_Rect_WOctrl

0 10 20 30 40 50 600

100

200

300

400

Frequency [Hz]

Spe

ctra

ofU

-AC

1S

pect

raof

U-A

C2

Spe

ctra

ofU

-AC

3

§(a) Line to neutral acvoltage




§(a) Rectifier side ac bus voltage

§(b) FFT of ac voltage shown in plot‘a’

§ Post fault recovery is not stable

§ Observed 42 Hz frequency component on dc side

§ Observed 8 Hz frequency component on ac side

§FFT

HVDC2014-009991

Ferroresonance

§ Possible options to mitigate ferroresonance

§ Bypass the series capacitor upon detection of ferroresonance

§ It limits the power transfer capability of the system

§ It is not a complete solution just a remedy

§ To install a reactor across the series capacitor

§ Extra cost

ü Best way is to have a supplementary control to damp the ferroresonance.

ü No extra cost for the additional equipment

ü Fast control

Possible solutions

HVDC2014-009991

§© ABB Group


Ferroresonance Damping Controller (FDC)Ferroresonance damping controller principle

Idc αmod

∑ αorderαcontrol

Ferroresonance DampingController (FDC)

HVDC Control

§ The output of the controller is αorder which is generated by adding thealpha modulation signal αmod from the FDC to αcontrol calculated by theexisting HVDC current control

HVDC2014-009991

§© ABB Group


Performance of Damping ControllerThree phase to ground fault at rectifier side

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-500

0

500

U-A

C1

U-A

C2

U-A

C3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1

0

1

PD

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

ALP

HA -P

10 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

20

40

60

80

Time [s]

GAM

MA -P

1

§(a)Line to neutral acvoltage




0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-500

0

500

U-A

C1

U-A

C2

U-A

C3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1

0

1

PD

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

ALP

HA -P

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 120

40

60

80

Time [s]

GAM

MA -P

1

§(a)Line to neutral acvoltage




Plots for Pole I without damping controller Plots for Pole I with damping controller

HVDC2014-009991

§© ABB Group


Performance of Damping ControllerThree phase to ground fault at rectifier side

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-0.5

0

0.5

1

1.5

S1:

ID_P

1[p

u]S

2:ID

_P1

[pu]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-50

0

50

100

150

ALP

HA -P1

ALP

HA -P1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-30

-20

-10

0

10

20

Time [s]

Alp

ha-M

od


§(b) Rectifier side α in degrees

§(c) Modulation signal from the damping controller

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65-2

0

2

Time [s]

S1:ID

_P1

[pu]

S2:ID

_P1

[pu]

20 30 40 50 60 70 80 90 1000

0.1

0.2

Frequency [Hz]Spe

ctra

ofS1

:ID_P

1[p

u]S

pect

raof

S2:ID

_P1

[pu]

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.650

20

40

60

80

100

Time [s]

ALPH

A --W

O--

CN

TRL

ALPH

A --W

--C

NTR

L

20 30 40 50 60 70 80 90 1000

5

10

15

Frequency [Hz]

Spec

traof

ALPH

A --W

O--C

NTR

LSp

ectra

ofAL

PHA --

W--C

NTR

L

§(a) Rectifier side α in degrees

§(b) FFT of α shown in plot ‘a’


§(b) FFT of dc current shown in plot ‘a’

Documents

Adil Abdalrahman, ABB Power Grids, HVDC, 2016-11-24 ... · PDF fileAdil Abdalrahman, ABB Power Grids, HVDC, 2016-11-24 Experiences from SSTI-studies in ... 700 MW VSC HVDC transmission