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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
§ Approach for SSTI Studies
§ 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
§ Approach for SSTI Studies
§ 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
§ Approach for SSTI Studies
§ 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
Example 4 (SSCI assessment)
§ 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
Example 4 (SSCI assessment)
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
Example 4 (SSCI assessment)
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
Example 4 (SSCI assessment)
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
Example 4 (SSCI assessment)
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
§ Approach for SSTI Studies
§ 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
§December 3, 2016 | Slide 44
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
§(b) Dc power (p.u.)
§(c) Rectifier side α in degrees
§(d) Inverter side ɣ in degrees
§(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
§December 3, 2016 | Slide 46
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
§December 3, 2016 | Slide 47
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
§(b) Dc power (p.u.)
§(c) Rectifier side α in degrees
§(d) Inverter side ɣ in degrees
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
§(b) Dc power (p.u.)
§(c) Rectifier side α in degrees
§(d) Inverter side ɣ in degrees
Plots for Pole I without damping controller Plots for Pole I with damping controller
HVDC2014-009991
§© ABB Group
§December 3, 2016 | Slide 48
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
§(a) Dc current through Pole I
§(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’
§(a) Dc current through Pole I
§(b) FFT of dc current shown in plot ‘a’