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Preferred Bipole III route. • Bipole I and II both use interlake transmission corridor. • About 75% of the province generating capacity is carried over this corridor.
A  Preliminary  Look  at  the   Feasibility  of  VSC  HVDC   Technology  in  Manitoba   M.  Mohaddes,  M.  Rashwan,  R.  Ostash   TransGrid  SoluFons   D.  Jacobson,  P.  Wang   Manitoba  Hydro    

IEEE 2011 Electrical Power and Energy Conference

Manitoba  System  –  HVDC  Bipoles   • Bipole I and II both use interlake transmission corridor Preferred Bipole III route Bipole I & II route

• About 75% of the province generating capacity is carried over this corridor • Both Bipole I and II terminate at Dorsey converter station • Bipole III (2000 to 2500MW) improves system reliability by adding a new line and converter station • Bipole III termination electrically close to Dorsey converter station

IEEE 2011 Electrical Power and Energy Conference

Plans  for  the  HVDC  Bipoles   •  Bipole  III   –  Present  plan  to  use  convenFonal  LCC  HVDC  technology  

•  Bipoles I and II –  Future plans to eventually replace the HVDC valves

•  Preliminary feasibility studies to investigate VSC HVDC –  Fast-­‐growing  raFngs   –  Possibility  to  operate  with  overhead  lines   –  Reduced  losses  due  to  change  in  VSC  topology  from  PWM  to  mulF-­‐ level   –  For  these  reasons,  becoming  possible  to  consider  VSC  technology   instead  of  convenFonal  LCC   IEEE 2011 Electrical Power and Energy Conference

Manitoba  System  &  VSC  Studies   •  How  would  using  VSC  instead   f   network MHoac BP1the  nBP2 LCC  affect   eed  for   1854 MW 2000 MW BP3 synchronous  condensers?   2000-2500 MW Synch condensers: •  Synchronous   condensers   3x300 MVAr

Synch condensers: 4x250 MVAr

6x160 MVAr

–  Large  capital  costs   –  Require    lots  of  maintenance  

Riel 500 kV

Dorsey 500 kV

Three 230kV •  Feasibility Studies compared ties to SK VSC and LCC in terms of:

Transient  Stability  Scenarios:   Two ties to ON 1. All  Bipoles  LCC  (present   plan)   –  Need for synchronous condensers 2. BP3  VSC  /  BP1  and  BP2  LCC   Manitoba 3. BP3  and  BP2  VSC  /  BP1  LCC   –  Performance of interconnected US D602F G82R R50M L20D future system 500kV line 4. All  Bipoles  VSC   IEEE 2011 Electrical Power and Energy Conference

Study  Models/Methodology   •  Four  Key  Faults:  

BP1 1854 MW

3 HVDC inverters very near each other, a single disturbance –  Solid  3PF  at  inverter   can cause sudden temporary loss of –  Remote  3PF  at  inverter  large HVDC infeed

–  Solid  3PF  at  recFfier  

BP2 2000 MW

–  DC  line  fault  (LCC  and  VSC)  

•  Main  focus  of  study   results  

Result: Frequency dip in southern system ac network

–  Southern  system  frequency   response   IEEE 2011 Electrical Power and Energy Conference

BP3 2000-2500 MW

MH ac network

Study  Results:  3PF  at  Rec  or  Inv   •  Not  much  difference  in  system   BP1 1854 MW response  whether  the  Bipoles   Low AC voltage at use  VSC  or  LCC   •  Low  AC  voltage  at  rec  or  inv  =   minimal  power  transfer,   regardless  of  type  of  DC   technology  

BP2 2000 MW

BP3 2000-2500 MW

rec or inv leads to minimal DC power transfer

•  In  all  cases,  large  southern   system  frequency  dip  due  to   temporary  loss  of  large   amount  of  power  infeed  in  the   southern  system  

MH ac network

Result: Frequency dip in southern system ac network same for VSC or LCC

IEEE 2011 Electrical Power and Energy Conference

Study  Results:  VSC  Advantage    –  Remote  Inverter  Faults   VSC  without  Riel  syncs  gives   be`er  performance  than  LCC   with  Riel  syncs   Why?  Because  VSC  does  not   fail  commutaFon  like  LCC     The  more  LCC  links,  the  more   power  temporarily  lost  =   more  underfrequency  

Better voltage performance with VSC

Dorsey  voltage    

0.3 Hz better underfrequency with VSC

Dorsey  frequency  

~2 cycles

BP1  Power  

BP2  Power  

Blue: VSC no Riel syncs Green: LCC with Riel syncs

Less power loss with VSC (no comm fail)

IEEE 2011 Electrical Power and Energy Conference

BP3  Power  

Study  Results:  VSC  Disadvantage    –  DC  Overhead  Line  Faults  

VSC  without  Riel  syncs  gives   worse  performance  than  LCC   with  Riel  syncs   Why?  Because  VSC  DC  fault   draws  currents  from  AC   system,  looks  like  remote   fault,  causes  other  LCC  to  fail   commutaFon.  Also  longer   restart  Fme.   Response  improves  if  more   bipoles  are  VSC,  less  LCC   bipoles  to  fail  commutaFon  

Blue: VSC no Riel syncs Green: LCC with Riel syncs

Reduction in AC voltage with VSC DC line fault

Dorsey  voltage    

0.3 Hz worse underfrequency with VSC

Dorsey  frequency   BP1  Power  

BP1 LCC comm fail during VSC DC line fault

BP2  Power  

BP2 LCC comm fail during VSC DC line fault

BP3  Power  

VSC longer restart time compared to LCC DC fault

IEEE 2011 Electrical Power and Energy Conference

Findings:  Need  for  Synchronous   Condensers  for  BP3  VSC?   •  Studies  suggest  building  BP3  as  VSC  would  not   require  any  new  synchronous  condensers   –  Save  in  capital  and  maintenance  costs  for  1000  MVAR  of   synchronous  condensers  that  are  needed  if  BP3  is  LCC   –  Must  be  kept  in  mind  that  although  VSCs  can  provide   steady  state  and  dynamic  reacFve  power  support,  cannot   provide  the  inerFa  that  synchronous  condensers  do  

•  The  worst  case  fault  for  the  BP3  VSC  scenario   was  a  VSC  DC  line  fault,  but  sFll  acceptable   system  response  without  any  new  syncs   IEEE 2011 Electrical Power and Energy Conference

Findings:  OperaFon  in  Very  Weak   System  

•  Possibility  of  replacing  all  HVDC  bipoles  with  VSC  in   distant  future   •  How  many  exisFng  synchronous  condensers  could  be   reFred?  No  firm  answer  yet.   –  ReFring  all  syncs  results  in  very  weak  system  (next  nearest  generaFon   quite  far  from  the  inverters)   –  Possibility  of  oscillaFons  between  VSC  and  AC  system  –  started  around   1.6  SCR   –  Idea  to  use  frequency  control  on  VSC  inverter  to  act  more  like   generator  to  stabilize  phase  angle/frequency  in  south   –  Further  study  with  appropriate  VSC  control  models  and  more  system   power  flow  scenarios  needed  to  make  conclusions   IEEE 2011 Electrical Power and Energy Conference

Findings:  MVA  RaFng  of  the  VSC  Links   •  Studies  done  based  on  2432  MVA  raFng,  not  2000   MVA  (due  to  available  PSS/E  VSC  model)   •  SensiFvity  analysis  showed  difference  in  amount  of   VSC  power  lost  during  remote  faults   •  ConsideraFons  regarding  syncs  and  VSC  raFngs:   –  Even  if  all  bipoles  VSC,  may  sFll  want  some  syncs  for  inerFa   –  Higher  MVA  raFng  so  less  power  lost  transiently  during  AC   undervoltage  events,  especially  true  for  more  VSC  links   –  Further  studies  of  VSC  controls:     •  P  priority  over  Q  to  a`empt  to  lose  less  VSC  power   •  VSC  in  frequency  control  to  help  stabilize  Dorsey  frequency   IEEE 2011 Electrical Power and Energy Conference

Conclusions  &  Future  ConsideraFons   •  Bipole  3   – VSC  appears  technically  feasible   – Eliminates  need  for  1000  MVAR  of  new   synchronous  condensers   – VSC  advantage:  remote  faults,  no  comm  fail   – VSC  disadvantage:  DC  line  faults,  longer  restart   Fme,  bigger  disturbance  to  AC  system  than  LCC  

IEEE 2011 Electrical Power and Energy Conference

Conclusions  &  Future  ConsideraFons   •  Bipoles  1  and  2   – VSC  appears  technically  feasible   – How  many  exisFng  synchronous  condensers   could/should  be  reFred  yet  to  be  answered   – System  very  weak  without  any  syncs,  further  study   required  

IEEE 2011 Electrical Power and Energy Conference

The  End  

Thank  You!   Any  QuesFons?  

IEEE 2011 Electrical Power and Energy Conference