Advanced	
  Research	
  Projects	
  Agency	
  for	
  Energy,	
  U.S.	
  Department	
  of	
  Energy...
Contents	
  
Purpose	
  and	
  Scope	
  .....................................................................................
Purpose	
  and	
  Scope	
  
	
  
Electricity	
  is	
  dynamic	
  –	
  supply	
  must	
  meet	
  demand	
  that	
  changes	...
ability	
  to	
  change	
  the	
  way	
  that	
  power	
  flows	
  through	
  the	
  transmission	
  grid	
  using	
  hard...
substation	
  equipment;	
  and	
  High	
  Voltage	
  Alternating	
  Current	
  (HVAC)	
  power	
  transmission	
  control...
 
Fig.	
  1.	
  Breakeven	
  
distance	
  for	
  HVDC	
  
transmission	
  lines	
  
HVDC	
  becomes	
  cost	
  
competitiv...
HVAC	
  Power	
  Transmission	
  Controllers	
  (PTC)	
  can	
  control	
  impedance,	
  voltage	
  and	
  phase	
  and	
 ...
Shunt	
  Compensators	
  	
  
Shunt	
  devices	
  are	
  used	
  to	
  control	
  transmission	
  voltage,	
  reduce	
  re...
Thyristor	
  Controlled	
  Series	
  Capacitors	
  (TCSC)	
  are	
  a	
  family	
  of	
  equipment	
  that	
  provides	
  ...
and	
  change	
  the	
  shape	
  of	
  the	
  grid	
  by	
  actuating	
  line	
  switching	
  hardware	
  or	
  by	
  cont...
Value	
  Analysis	
  of	
  Power	
  Flow	
  Control	
  
	
  
Power	
  flow	
  control	
  benefits	
  the	
  entire	
  tran...
flow	
  control,	
  defines	
  the	
  associated	
  benefits	
  and	
  costs,	
  and	
  identifies	
  the	
  stakeholders	...
make	
  the	
  most	
  difference.	
  In	
  addition,	
  they	
  can	
  increase	
  the	
  flexibility	
  and	
  adaptabil...
enables	
  dynamic,	
  autonomous	
  response	
  and	
  eliminates	
  risks	
  associated	
  with	
  other	
  central-­‐co...
uncertainty	
  has	
  the	
  potential	
  to	
  exacerbate	
  transmission	
  congestion	
  as	
  the	
  penetration	
  of...
reduce	
  the	
  overall	
  cost	
  to	
  serve	
  remote	
  load	
  by	
  30-­‐50%.	
  The	
  most	
  economic	
  generat...
HVDC	
  collection	
  systems	
  enable	
  a	
  new	
  design	
  paradigm	
  for	
  renewable	
  energy	
  generation	
  s...
Summary	
  of	
  Power	
  Flow	
  Control	
  Technology	
  Value	
  
	
  
One	
  power	
  flow	
  control	
  technology	
 ...
stakeholders	
  are	
  often	
  involved	
  in	
  technology	
  investment	
  decisions,	
  and	
  a	
  level	
  of	
  agr...
The	
  beneficiaries	
  of	
  a	
  change	
  in	
  power	
  flow	
  control	
  will	
  often	
  be	
  temporary	
  and	
  ...
Table	
  3.	
  Overview	
  of	
  beneficiaries	
  as	
  a	
  result	
  of	
  power	
  flow	
  control	
  improvements	
  i...
•

•

•

effects	
  of	
  the	
  technology.	
  Data	
  sharing	
  at	
  a	
  high-­‐level	
  will	
  enable	
  deeper	
  ...
Benefits of power flow control
Benefits of power flow control
Benefits of power flow control
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Benefits of power flow control

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Describes a future in which the transmission grid can be controlled to optimize the use of cost-effective, clean generation resources while providing high-quality, reliable power. Summarizes the research that the Advanced Research Projects Agency - Energy (ARPA-E) is undertaking into hardware and software technologies that could significantly change the ability to control the flow of electricity in the power grid.

This analysis is intended to describe potential benefits of a flexible transmission system achieved through power flow control technologies. Specifically, it categorizes the benefits of power flow control technologies and defines the impact of technologies used for power flow control. It also makes recommendations for further studies and analyses on power flow control.

Written by ARPA-E interns Lotte Schlegel and Chris Babcock under the guidance of Josh Gould.

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Benefits of power flow control

  1. 1.           Advanced  Research  Projects  Agency  for  Energy,  U.S.  Department  of  Energy   Benefits  of  Power   Flow  Control   Hardware  and  Software  Technologies   Lotte  Schlegel,  Chris  Babcock  and  Josh  Gould   9/27/2013    
  2. 2. Contents   Purpose  and  Scope  ......................................................................................................................................  3   Characteristics,  Capabilities  and  Technologies  of  a  Flexible  Grid  ................................................................  3   Power  Flow  Control  Technology  Defined  ................................................................................................  4   Hardware  .............................................................................................................................................  5      High  Voltage  Direct  Current  ...............................................................................................................  5      HVAC  Power  Transmission  Controllers  (PTC)  .....................................................................................  7      Software  .............................................................................................................................................  9      Topology  Control  Algorithms  (TCAs)  ..................................................................................................  9   Value  Analysis  of  Power  Flow  Control  .......................................................................................................  11   Identification  of  Value  Propositions  ......................................................................................................  12   Asset  Management  ............................................................................................................................  12   Reliability  and  Security   .......................................................................................................................  13   Congestion  Relief  ...............................................................................................................................  14      Integration  of  renewable  energy  .....................................................................................................  14      Economic  Efficiency  .........................................................................................................................  15   Summary  of  Power  Flow  Control  Technology  Value   ..............................................................................  18   Stakeholders  in  the  Transmission  Grid  Influence  Technology  Investment  Decisions  ............................  18   Conclusion/Next  steps  ...............................................................................................................................  21   References  .................................................................................................................................................  24                     2    
  3. 3. Purpose  and  Scope     Electricity  is  dynamic  –  supply  must  meet  demand  that  changes  by  the  second  in  the  electric  grid.  While   electricity  markets  have  evolved  to  price  supply  dynamically  and  demand  response  systems  have   developed  to  manage  demand  on  a  dynamic  basis,  the  transmission  grid  is  inflexible.  When  the  flow  of   electrons  is  disrupted  by  a  storm,  an  accident,  or  congestion  choking  the  lines  like  cars  on  an  interstate,   it  affects  the  wallets  of  people  and  businesses.    The  electric  transmission  grid  costs  consumers  billions  in   congestion  costs,  is  difficult  and  expensive  to  upgrade,  and  does  not  respond  quickly  to  contingency   events  –  costing  $79  billion  annually  in  power  interruptions  (Hamachi  LaCommare,  2004).  Transmission   infrastructure  in  the  U.S.  is  aging  -­‐  as  of  2008,  70%  of  transmission  lines  and  transformers  are  25  years  or   older  and  60%  of  circuit  breakers  are  30  years  or  older  (DOE,  2008).     The  electric  grid  of  the  future  will  need  to  be  sufficiently  flexible,  responsive,  and  reliable  to  support   variable  generation  resources,  reduce  areas  of  transmission  congestion,  and  respond  quickly  to  system   disruptions  due  to  severe  weather  events.  The  impending  upgrades  to  infrastructure  present  an   opportunity  to  include  technologies  to  improve  resiliency  of  the  grid.  Increasing  the  flexibility  of  the   electric  transmission  grid  can  be  the  cornerstone  to  addressing  all  of  these  challenges.     ARPA-­‐E’s  Green  Electricity  Network  Integration  “GENI”  program  envisions  a  future  in  which  the   transmission  grid  can  be  controlled  to  optimize  the  use  of  cost-­‐effective,  clean  generation  resources   while  providing  high-­‐quality,  reliable  power1.  To  that  end,  ARPA-­‐E  is  funding  research  into   transformative  hardware  and  software  technologies  that  could  significantly  change  the  ability  to  control   the  flow  of  electricity  in  the  power  grid.     This  analysis  is  intended  to  add  to  the  conversation  about  the  benefits  of  a  flexible  transmission  system   achieved  through  power  flow  control  technologies.  Specifically,  it  will  describe  and  categorize  the   benefits  of  power  flow  control  technologies  and  define  the  impact  of  technologies  used  for  power  flow   control.  It  will  also  make  recommendations  for  further  studies  and  analyses  on  power  flow  control.       Characteristics,  Capabilities  and  Technologies  of  a  Flexible  Grid       Historically,  the  electric  grid  was  designed  to  be  a  passive,  one-­‐directional  system.  To  improve  the  grid’s   reliability  and  turn  intermittent  power  sources  into  major  contributors  in  the  U.S.  energy  mix,  the  grid   needs  to  be  designed  and  operated  to  be  smarter  and  more  flexible.  Power  flow  control  is  one  way  to   increase  the  flexibility  and  resiliency  of  the  electric  grid.  Power  flow  is  determined  by  the  impedance  of   a  transmission  line  and  the  difference  in  voltage  at  each  end  (M.I.T.,  2011)2.  Power  flow  control  is  the                                                                                                                           1  More  at  http://arpa-­‐e.energy.gov/?q=arpa-­‐e-­‐programs/geni      From  MIT’s  Future  of  the  Electric  Grid.  “Two  factors  determine  power  flow:  the  impedance  of  a  line  and  the   difference  in  the  instantaneous  voltages  at  its  two  ends.  Impedance  is  the  combination  of  resistance  and   reactance.  Resistance  accounts  for  energy  that  is  lost  as  heat  in  the  line.  It  is  analogous  to  the  physical  resistance   exerted  by  water  on  a  swimmer  or  wind  on  a  cyclist.  Energy  lost  in  this  way  can  never  be  recovered.  Reactance   accounts  for  energy  associated  with  the  electric  and  magnetic  fields  around  the  line.  This  energy  is  analogous  to   2 3    
  4. 4. ability  to  change  the  way  that  power  flows  through  the  transmission  grid  using  hardware  and  software   to  maximize  system  value.  These  technologies  can  change  the  effective  impedance  of  the  network  or   the  sending  and  receiving  voltages  to  influence  the  path  of  electrons  flowing  through  the  transmission   grid.  This  enables  the  ability  to  hold  power  on  a  transmission  line  at  a  certain  level  or  direction.   Electrons  follow  the  path  of  least  resistance  (or  lowest  impedance),  and  the  result  of  changing  the   pathways  of  the  grid  is  to  change  the  way  that  power  flows  through  the  transmission  system.   Specifically,  power  flow  control  can  be  used  to  remove  congestion,  respond  to  contingency  events  (e.g.   loss  of  a  generator  or  transmission  line),  and  mitigate  power  quality  issues.   Power  flow  control  includes  the  faculties  to  control  the  voltage  or  impedance  on  given  major   transmission  lines,  switch  lines  on  and  off,  direct  power  from  one  line  to  another  to  increase  the   capacity  of  a  transmission  route,  provide  voltage  support,  transport  power  efficiently  over  long   distances,  and  quickly  reverse  the  direction  of  power  flow  from  one  area  to  another  in  response  to   contingencies.  A  system  planner  can  optimize  power  flow  on  a  system  by  choosing  among  technologies   to  enable  each  of  these  capabilities  as  appropriate.  In  order  to  fully  integrate  power  flow  control  at  the   system  level,  information  systems,  hardware  technology,  and  human  operators  at  ISOs/RTOs,   generators,  and  transmission  and  distribution  companies  coordinate  to  match  system  supply  and   demand  at  every  moment.  For  instance,  information  (such  as  forecasting  of  weather,  supply  and   demand),  sensors,  communication  devices,  and  control  technology  work  together  to  enable  physical   changes  to  the  transmission  grid.  As  power  flow  control  hardware  technologies  are  added  to  the  system,   coordinated  control  of  the  transmission  grid  will  maximize  the  efficacy  of  power  flow  control  and  ensure   reliability  across  the  system.  Changes  are  likely  required  to  optimize  the  coordination  of  the  grid  with   the  addition  of  power  flow  control  technologies  -­‐  for  instance,  as  variables  and  options  are  added  to  the   system,  either  a  central  operator  with  sufficient  computational  power  to  respond  to  dynamic  grid   conditions  or  coordinated  distributed  control  will  be  necessary  to  ensure  system  optimization.     Power  flow  control  can  increase  reliability  and  resiliency,  optimize  transmission  asset  efficiency  and  help   prioritize  new  transmission  construction  by  increasing  the  capacity  of  the  transmission  grid,  reduce  cost   to  electric  consumers,  facilitate  grid-­‐interconnection  of  generation,  storage,  demand  response,  and   detect  and  minimize  the  impact  of  unforeseen  disruption  events  such  as  extreme  weather.  The   following  sections  will  describe  the  technologies  that  enable  power  flow  control  and  the  value  that   power  flow  control  capabilities  afford  to  different  stakeholders  in  the  electric  grid.     Power  Flow  Control  Technology  Defined     Both  hardware  and  software  technologies  have  power  flow  control  applications.  This  analysis  will  focus   on  two  types  of  hardware  technologies  –  High  Voltage  Direct  Current  (HVDC)  transmission  cables  and                                                                                                                                                                                                                                                                                                                                                                                                 the  potential  energy  stored  when  riding  a  bicycle  up  a  hill.  It  is  recovered  (in  the  ideal  case)  when  going  down  the   other  side.  In  an  AC  line  in  the  U.S.,  this  energy  is  stored  and  recovered  120  times  per  second,  and  thus  is  quite   different  from  the  behavior  of  energy  stored  in  devices  such  as  batteries.  The  resistance  of  a  line  is  determined  by   the  material  properties,  length,  and  cross-­‐section  of  the  conductor,  while  reactance  is  determined  by  geometric   properties  (the  position  of  conductors  relative  to  each  other  and  ground).  In  practical  transmission  lines,  resistance   is  small  compared  to  reactance,  and  thus  reactance  has  more  influence  on  power  flow  than  resistance.”   4    
  5. 5. substation  equipment;  and  High  Voltage  Alternating  Current  (HVAC)  power  transmission  controllers  that   use  power  electronics  to  augment  the  existing  AC  grid.  In  addition,  the  capabilities  enabled  by  software   control  algorithms  such  as  topology  control  are  discussed.     Hardware   Hardware  can  efficiently  direct  the  flow  of  power  on  the  grid,  help  stem  energy  losses,  and  enable  the   grid  to  be  more  responsive  and  resilient.  Advances  in  materials  and  engineering  are  decreasing  the  costs   of  power  flow  hardware;  many  of  the  concepts  of  which  have  been  around  for  a  long  time.  The   descriptions  below  include  power  flow  control  technologies  that  already  exist  and  are  in  wide  spread   use  in  the  grid  today,  as  well  as  emerging  technologies  not  yet  in  use  that  show  tremendous  promise  for   power  flow  control  applications.     High  Voltage  Direct  Current  transmission  systems  are  composed  of  one  or  more  DC  transmission   lines  or  cables  between  a  converter  (combined  rectifier  and  inverter),  which  converts  AC  to  DC  or  vice   versa.  The  DC  lines/cables  in  concert  with  the  most  recent  voltage  source  converter  (VSC)  technology   enable  rapid  control  of  the  direction  of  power  flow.  Both  voltage  and  current  source  converters  can   invert  DC  to  a  matching  AC  frequency  of  an  interconnected  AC  grid,  which  affords  HVDC  the  ability  to   connect  two  asynchronous  AC  systems.  DC  poses  fewer  technical  challenges  compared  to  AC  because  it   is  not  necessary  to  match  frequency,  phase  or  voltage.  DC  can  be  configured  as  a  monopolar  (one  cable)   or  bipolar  (two  cable)  system  which  offers  cost  savings  over  tripolar  AC  designs  which  require  one  cable   for  each  of  the  three  phases.  Because  of  this  and  the  lower  line  losses  (30-­‐50%  lower  as  compared  to   AC),  HVDC  transmission  lines  are  the  least  expensive  option  for  transmitting  power  over  long  distances   (Reed,  2012).  HVDC  transformers  have  been  more  expensive  relative  to  HVAC.  The  distance  at  which  a   given  HVDC  line  becomes  more  cost  effective  than  HVAC  at  a  given  voltage  is  the  difference  between   line  and  terminal  costs  including  the  difference  between  losses  (see  Figure  1).  Also,  when  connected   with  an  AC  grid,  HVDC  can  mitigate  power  factor  issues  (current  lagging/leading  voltage)  by  providing   reactive  power  support,  and  can  provide  black  start  capabilities3  with  VSCs.     HVDC  transmission  systems  are  used  to  transport  power  over  long  distances  and  sub-­‐sea.  HVDC  lines   with  VSCs  allow  for  bi-­‐directional  control  of  power  flow  and  can  be  directly  scheduled  and  dispatched.   Bi-­‐directionality  allows  for  the  export  of  energy  from  control  area  A  to  control  area  B  under  certain   conditions,  and  re-­‐dispatch  for  import  of  energy  from  area  B  to  area  A  in  other  scenarios.  One  example   of  bi-­‐directional  flow  is  the  HVDC  cross  channel  2,000  MW  link  that  imports  electricity  to  Britain  from   France  during  much  of  the  year,  but  exports  power  to  France  during  the  summer  when  demand  is  high   or  to  meet  load  during  scheduled  outages.  The  Cross  Sound  Cable  between  Connecticut  and  Long  Island   is  also  bi-­‐directional,  although  power  flows  from  Connecticut  to  Long  Island  for  most  hours  of  the  year.                                                                                                                           3  Black  start  is  the  process  of  restoring  power  to  a  power  plant,  normally  without  relying  on  the  power  of  the   transmission  grid.  Typically  in  the  case  of  a  wider  grid  outage,  black  start  is  provided  in  a  sequence:  a  portable   generator  is  used  to  start  one  power  plant,  the  proximal  transmission  lines  are  energized  and  the  power  used  to   start  the  next  base  load  generator,  and  so  on.  Voltage  Source  Converters  can  be  used  for  black  start  as  they  can   synthesize  a  balanced  set  of  three  phase  voltages.       5    
  6. 6.   Fig.  1.  Breakeven   distance  for  HVDC   transmission  lines   HVDC  becomes  cost   competitive  with  HVAC   over  a  distance  at  which   line  losses  at  a  given   voltage  are  lower  than  a   comparable  HVAC  line.                     Source:  Pike  Research,     2012     HVDC  technology  has  gained  popularity  since  the  mid-­‐20th  century.  Historically,  the  limitations  to  its   practical  use  have  been  the  high  cost  of  the  power  electronics  required  for  the  converter.  Recent   technical  breakthroughs  have  reduced  the  cost  of  power  electronics  and  increased  their  application.   HVDC  is  now  being  deployed  globally,  with  dozens  of  projects  in  the  global  pipeline,  and  is  of  particular   importance  to  integrating  distant,  renewable  energy  generators  such  as  offshore  wind  farms.  When   considering  new  transmission  corridors,  HVDC  is  more  favorable  to  HVAC  because  of  the  smaller   footprint  of  the  transmission  towers.  HVDC  proponents  envision  a  future  in  which  DC  cables  are   embedded  within  the  existing  AC  grid  and  multi-­‐terminal  HVDC  allows  for  a  superimposed  HVDC   network  that  will  help  to  integrate  remote  resources,  improve  system  stability  and  reliability  via  AC-­‐DC   interties,  and  increase  control  of  power  flows  through  the  system.  HVDC  technologies  are  being   developed  by  numerous  vendors,  including  General  Electric  with  funding  from  the  ARPA-­‐E  GENI   program.     GE  Global  Research  is  developing  two  ARPA-­‐E  funded  projects  to     improve  HVDC  technology  –  multi-­‐terminal  HVDC  and  improved  cable   insulation.       The  multi-­‐terminal  HVDC  Networks  with  High-­‐Voltage  High-­‐   Frequency  Electronics  project  is  developing  multi-­‐terminal  HVDC-­‐ compatible  converters  to  improve  the  ability  to  network  HVDC  and     integrate  renewable  energy  into  the  grid.         Nanoclay  Reinforced  Ethylene-­‐Propylene-­‐Rubber  for  Low-­‐Cost  HVDC     Cabling  project  is  developing  low-­‐cost  insulation  for  HVDC   transmission  cables.  Cables  will  be  less  expensive  and  suppress  excess     charge  accumulation,  which  will  protect  the  insulation.           6    
  7. 7. HVAC  Power  Transmission  Controllers  (PTC)  can  control  impedance,  voltage  and  phase  and  hold   power  at  a  desired  level  and  direction  of  flow.  PTC  devices  use  a  combination  of  solid  state  power   electronics  and  other  static  equipment  to  modulate  the  state  of  a  given  AC  transmission  line  by  injecting   and  removing  voltage  and  impedance.  These  coordinated  actions  result  in  controllable  voltage/current   phase  shift  to  manage  real  and  reactive  power  flows,  controllable  line  impedance  to  increase  or   decrease  current,  and  the  ability  to  balance  the  current  phase  between  the  three  phases  of  an  AC   transmission  system.     Historically,  these  capabilities  were  accomplished  by  Flexible  Alternating  Current  Transmission  Systems   (FACTS),  which  employed  similar  power  electronic  devices  in  substations  and  were  typically  large  and   capital  intensive.  Today,  advances  in  technology  are  decreasing  the  cost  and  footprint,  and  increasing   the  reliability  and  operability  of  these  devices,  making  HVAC  PTC  viable  solutions  for  power  flow  control   applications.  Such  devices  are  being  developed  by  several  ARPA-­‐E  GENI  teams,  including  Smart  Wire   Grid,  Varentec,  Oak  Ridge  National  Laboratory,  and  Michigan  State  University.       Phase  Shifting  Transformers   Phase  shifting  transformers  change  the  voltage  phase  angle  between  primary  and  secondary  windings,   changing  the  input  and  output  voltages  of  a  line  and  thereby  controlling  the  active  power  that  can  flow   in  the  line.  Effectively,  they  inject  a  voltage  in  series  with  the  line.  This  enables  control  of  power  flow   between  two  power  systems,  balances  loading,  and  improves  system  stability.       Dynamic  Power  Flow  Controller   Varentec  is  developing  low  cost  transmission  controllers  to   dynamically  control  voltage  and  power  flow  with  ARPA-­‐E  funding.  The   technology  would  enable  early  detection  and  fail-­‐safe  protection  of   the  transmission  grid  to  maintain  its  operating  state.       Magnetic  Amplifier  for  Power  Flow  Control   Oak  Ridge  National  Laboratory  is  developing  an  electromagnet-­‐based   amplifier-­‐like  device  that  will  allow  for  complete  control  over  the  flow   of  power.  The  prototype  device  is  a  low  cost  iron-­‐based  magnetic   amplifier.           Distributed  Series  Reactor   The  Distributed  Series  Reactor  (DSR)  is  a  technology  being  developed  by  Smart  Wire  Grid,  a  startup   based  in  Oakland,  California.  DSRs  are  small,  single-­‐turn  transformers  that  inject  inductance  onto  a   transmission  line.  The  level  of  inductance  is  tunable  to  alter  the  overall  line  impedance  and  thus  the  flow   of  current.  DSRs  are  distributed  along  transmission  lines,  in  all  3  phases,  and  can  communicate  with  each   other  to  form  a  variable  impedance  system.  They  can  also  operate  autonomously  to  alter  flows  at  a   specific  point  on  the  line.  As  such,  the  technology  can  help  to  reduce  congestion  and  balance  power  flow   within  a  system.   7    
  8. 8. Shunt  Compensators     Shunt  devices  are  used  to  control  transmission  voltage,  reduce  reactive  losses,  dampen  power   oscillations  and  are  connected  in  shunt  to  a  transmission  line.  A  Static  Synchronous  Compensator   (STATCOM)  is  a  VSC  usually  connected  to  the  grid  through  a  shunt  transformer.  STATCOMs  do  not   require  the  bulk  capacitors  and  inductors  that  are  used  in  the  thyristor-­‐based  Static  Var  Compensators   (SVCs)  which  are  still  in  widespread  use  today.  Instead,  the  STATCOM  generates  reactive  power  entirely   electronically  and  can  act  as  either  a  source  or  sink  of  reactive  power.  The  STATCOM  can  also  exchange   real  power  between  the  grid  and  an  energy  storage  device  connected  at  its  DC  terminals.  VSCs  based  on   Insulated-­‐gate  bipolar  transistor  (IGBT)  technology4  have  much  faster  switching  times  than  other   compensator  technologies,  which  makes  them  particularly  useful  for  dynamic  voltage  support  and   power  factor  correction.       A  STATCOM  does  not  affect  power  flow  on  a  transmission  line  directly.  However,  by  using  local  shunt   reactive  power  injection  to  change  the  voltage  profile  of  a  transmission  line  (e.g.  support  voltage  at  the   midpoint  of  a  long  line),  it  can  enable  a  line  to  be  loaded  more  heavily  (e.g.  to  thermal  limits)  without   exceeding  steady  state  stability  margins  or  voltage  drop  limits.  In  contracts,  a  power  flow  controller  is   connected  in  series  with  a  transmission  line  and  has  the  ability  to  force  a  change  in  power  flow  on  the   line,  essentially  by  introducing  a  controllable  voltage  in  series  with  the  line.   Series  Compensators   A  Static  Series  Synchronous  Compensator  (SSSC)  is  a  VSC  connected  in  series  with  a  transmission  line.  It   has  the  ability  to  raise,  lower,  or  even  reverse  the  power  flow  on  the  line  by  injecting  a  relatively  small   voltage  in  series.  For  a  wide  range  of  power  flow  control,  only  reactive  power  output  from  the  VSC  is   needed.  However,  additional  control  capabilities  such  as  independent  control  of  real  and  reactive  power   flow,  can  be  obtained  if  a  source/sink  of  real  power  is  connected  to  the  DC  terminals  of  the  VSC.   Currently,  there  are  no  examples  of  SSSC  installations  in  transmission  grids  except  those  installed  as  part   of  the  three  Unified  Power  Flow  Controller  demonstration  projects.       A  stand-­‐alone  SSSC  is  a  more  versatile  (and  potentially  lower-­‐cost)  power  flow  controller  than  a   Thyristor-­‐Controlled  Phase  Angle  Regulating  Transformer  with  a  similar  MVA  rating,  which  is  the  closest   comparable  device.  At  present,  back-­‐to-­‐back  HVDC  is  being  considered  in  some  places  to  solve  loop   flows  and  other  transmission  problems,  but  requires  two  converters  rated  for  full  transmitted  power.  In   most  cases  the  problem  could  be  solved  with  a  single  fractionally  rated  SSSC.                                                                                                                           4  IGBT  technology  is  a  power  semiconductor  device  that  forms  an  electronic  switch.  They  are  high  efficiency,  fast   switching  and  can  handle  high  voltages  and  current  when  many  devices  are  stacked  in  parallel.     8    
  9. 9. Thyristor  Controlled  Series  Capacitors  (TCSC)  are  a  family  of  equipment  that  provides  a  controllable   capacitance  (or  in  some  cases,  an  inductance)  connected  in  series  with  a  transmission  line  to  reduce  (or   increase)  the  total  reactance  of  the  line.     Unified  Power  Flow  Controllers  (UPFCs)   UPFCs  provide  the  functionality  of  both  shunt  and  series  compensators.  They  control  real  and  reactive   power  flow  and  provide  voltage  support  for  the  connecting  bus5.  Historically,  UPFCs  have  taken  up   significant  space,  been  very  expensive,  and  required  the  construction  of  large  transformers.  There  are   only  three  operational  UPFCs  in  the  world,  each  of  which  was  tailored  to  meet  a  particular  utility’s   problem.  However,  grid  operators  are  largely  uncomfortable  with  the  series  compensation  capabilities   of  UPFCs,  and  as  a  result  these  operating  modes  are  rarely  used,  leaving  the  UPFCs  to  operate  largely  as   a  STATCOM  (for  more,  see  Marcy  UPFC  case  study  in  this  document).  Moreover,  the  company  that  built   the  UPFCs  –  Westinghouse  –  was  acquired  by  Siemens,  which  no  longer  sells  or  supports  the  devices.  An   ARPA-­‐E  team  from  Michigan  State  University  is  building  a  transformer-­‐less  UPFC  which  addresses  these   issues  and  can  control  power  flows  from  intermittent  resources  including  wind  and  solar  resources.       Transformer-­‐Less  Unified  Power  Flow  Controller     Michigan  State  University  is  developing  a  power  flow  controller  to     improve  the  routing  of  electricity  from  renewable  sources  through  existing   power  lines.  The  UPFC  will  eliminate  the  need  for  a  transformer  and     construction  of  new  transmission  lines.  It  will  optimize  energy  transmission       and  h elp  reduce  transmission  congestion.     Software   Advancements  in  computing  and  data  communications  can  optimize  grid  operations,  match  power   delivery  to  real-­‐time  demand,  and  find  effective  ways  to  manage  sporadically  available  renewable  power   sources  and  grid-­‐level  power  storage.     Topology  Control  Algorithms  (TCAs)  are  a  network  solution  to  optimally  activate  (close)  and   deactivate  (open)  transmission  lines  to  decrease  the  cost  of  the  transmission  system.  This  is  based  on   the  counter-­‐intuitive,  but  demonstrated,  phenomenon  that  closing  a  congested  pathway  improves  the   overall  system  flow6.  TCAs  are  integrated  into  software  that  controls  the  grid’s  hardware  infrastructure,                                                                                                                           5  Real  power  is  power  delivered  to  the  end  user  to  do  work  (measured  in  watts).  Reactive  power  is  current   energizing  the  system  components  (measured  in  volt-­‐amperes  reactive-­‐  VAR).     6  Closing  a  congested  pathway  can  open  the  electric  flow  at  the  system  level.  This  has  been  demonstrated  by  ISOs   and  researchers,  including  the  Brattle  Group,  Argonne  National  Labs,  and  a  team  from  Texas  A&M.  To  illustrate   this  concept  a  team  from  Texas  A&M  showed  that  when  a  50MW  line  was  dropped  in  a  3-­‐line,  3-­‐generator  system,   the  feasible  cost  to  serve  load  dropped.  This  concept  is  demonstrated  in  the  diagrams  below:   9    
  10. 10. and  change  the  shape  of  the  grid  by  actuating  line  switching  hardware  or  by  controlling  the  HVAC  PTC   devices  listed  above.  The  net  effect  of  changing  the  shape  of  the  grid  is  to  change  the  way  that  power   flows  through  the  transmission  system.     TCAs  are  not  a  new  concept;  they  have  been  employed  by  operators  of  wireless  ad-­‐hoc  networks  for   radios  (since  1970’s)  and  computers  (since  1990’s)  by  optimizing  the  transmission  power  of  each  node   to  improve  signal  flow  in  the  network.  For  the  electric  power  industry,  recent  advances  such  as  phasor   measurement  units  (PMUs),  low-­‐latency  communication  systems,  and  the  reduced  cost  and  improved   speed  of  computer  processors  allow  for  TCAs  to  be  an  effective  solution  for  power  flow  in  the   transmission  grid.  TCAs  are  being  developed  through  the  ARPA-­‐E  GENI  program  by  Texas  A&M  and   Boston  University.     Automated  Grid  Disruption  Response  System   Texas  A&M  is  developing  a  Robust  Adaptive  Topology  Control  (RATC)     system  designed  to  detect,  classify,  and  respond  to  grid  disturbances   by  reconfiguring  the  grid  to  maintain  economically  efficient,  reliable     operations.  The  system  would  help  to  prevent  outages  and  minimize   the  time  it  takes  for  the  grid  to  respond  to  interruptions,  and  make  it     easier  to  integrate  renewable  resources  into  the  grid.                 Transmission  Topology  Control  for  Infrastructure  Resilience  to  the   Integration  of  Renewable  Generation   Boston  University  is  developing  a  technology  that  helps  grid  operators   manage  power  flows  and  integrates  renewable  resources  by  optimizing  the   transmission  system.  The  system  would  have  the  capability  of  turning  power   lines  on  and  off  to  manage  transmission  congestion,  increase  use  of   renewable  resources,  and  improve  system  reliability.  The  fast  optimization     algorithms  would  enable  near  real-­‐time  change  in  the  grid.                                                                                                                                                                                                                                                                                                                                                                                                     10    
  11. 11. Value  Analysis  of  Power  Flow  Control     Power  flow  control  benefits  the  entire  transmission  system  as  well  as  transmission  owners,  generators,   operators,  planners,  regulators,  and  consumers.  Transmission  benefits  can  be  numerous  and  diverse,   including:   • • • • • • • • Reduce  energy  transmission  losses   Mitigate  transmission  outages   Defer  and  prioritize  transmission  investments   Increase  transfer  capability  from  one  part  of  the  system  to  another   Reduce  cycling  of  base  load  generators  to  increase  asset  efficiency   Increase  wheeling  of  power  in  and  out     Reduce  loop  flows   Meet  public  policy  goals   Any  one  of  the  technologies  described  above  can  help  to  achieve  these  benefits.  However,  to  maximize   the  benefits  of  power  flow  control  and  to  maintain  system  reliability,  some  system  coordination  is   required  in  order  to  understand  the  system-­‐level  effect  of  the  installation  of  power  flow  control   technologies,  to  plan  for  future  asset  mix,  and  to  optimize  operations  of  the  physical  grid  and  electricity   markets.  Power  flow  control  is  achieved  when  software  technologies  in  concert  with  well-­‐placed   hardware  work  together  to  optimize  the  transmission  system.  Ultimately,  planners,  operators  and   regulators  may  need  to  consider  several  additional  factors  to  realize  the  full  potential  and  system   benefits  of  power  flow  control  technologies,  including:   • • • Market/regulatory  structure  for  wide  area  control  –  to  make  sure  that  market  structure  and   technical  capabilities  are  aligned  to  properly  value  the  benefits  of  power  flow  control  technologies   Software  –  synchronous  access  to  cloud  resources  for  optimized  coordinated  control   Sensors  –  accurate,  real-­‐time,  dispersed  estimation  sensors  to  measure  and  communicate  the   conditions  of  the  electric  grid  in  real  time  and  ensure   This  analysis  does  not  consider  the  many  complementary  technologies  that  would  help  to  maximize   flexibility  and  control  including  PMUs,  advanced  metering  infrastructure  or  distribution-­‐level   technologies,  or  incentives  and  market  structures  that  could  enable  power  flow  control.  The  analysis  is   solely  focused  on  the  high-­‐voltage  transmission  technologies  and  software  applications  described  above.   One  can  think  of  the  value  of  power  flow  control  technologies  in  terms  of  the  total  costs  and  benefits  of   a  transmission  grid  with  power  flow  control  capabilities  as  compared  to  the  total  cost  and  benefits  of   the  system  without  these  capabilities.  However,  one  of  the  difficulties  in  quantifying  the  value  of  power   flow  control  capabilities  is  that  system  optimization  requires  that  there  be  short-­‐term  beneficiaries  of  a   change  in  power  flow,  and  corresponding  entities  that  might  see  a  drop  in  revenue  in  the  short-­‐term,  as   any  change  to  the  physical  constraints  of  the  electric  grid  can  affect  the  price  that  generators  or   transmission  owners  are  paid  for  electricity.  This  analysis  explores  five  distinct  value  streams  of  power   11    
  12. 12. flow  control,  defines  the  associated  benefits  and  costs,  and  identifies  the  stakeholders  and  how  they   might  be  affected  at  a  system  level.   Identification  of  Value  Propositions   Asset  Management     Transmission  infrastructure  in  the  United  States  is  built  to  meet  peak  demand,  which  leads  to  sub-­‐ optimal  utilization  outcomes  at  a  system  level  during  non-­‐peak  periods.  Reliability  standards  and   favorable  FERC-­‐established  rates  of  return  provide  incentives  for  transmission  investment.  At  the  same   time,  much  of  the  existing  transmission  infrastructure  is  reaching  the  end  of  its  useful  life,  and  new   transmission  is  difficult,  expensive,  time-­‐consuming,  and  highly  litigious  to  build.  Transmission  owners   are  also  faced  with  competing  calls  for  capital  to  meet  reliability  and  environmental  priorities.  Research   from  the  Edison  Electric  Institute  shows  that  its  shareholder-­‐owned  utility  members  increased  their   investment  in  transmission  infrastructure,  investing  $11.1  billion  in  2011  and  planning  to  spend  $54.6   billion  through  2015  (Edison  Electric  Institute).  Several  power  flow  control  technologies  could  increase   the  capacity  of  existing  transmission  lines  and  defer  new  investment  in  construction  or  help  prioritize   construction  of  new  lines  to  optimize  the  use  of  the  transmission  grid.  While  increasing  the  capacity  of   transmission  lines  would  produce  system-­‐level  benefits,  ultimately  some  transmission  owners  and   electricity  generators  would  see  lower  revenues  in  cases  where  they  currently  benefit  from  congestion.     HVDC   In  some  scenarios,  power  flow  control  technologies  could  decrease  transmission  losses  and  increase   transmission  utilization.  Most  notably,  HVDC  lines  have  lower  losses  in  transporting  power  over  long   distances,  and  technological  advances  in  insulation  could  increase  this  benefit  further.  For  instance,  GE   Global  Research  is  developing  a  nanoclay  reinforced  ethylene-­‐propylene-­‐rubber  for  low-­‐cost  HVDC   cabling  that  could  bring  down  the  cost  of  HVDC  cable  by  as  much  as  80%.  Such  a  decrease  in  the  cost  of   HVDC  would  lower  the  distance  at  which  HVDC  is  cost  competitive  with  HVAC,  and  increase  its   affordability  as  an  option  for  integration  into  the  AC  grid.     HVDC  requires  smaller  transmission  right  of  ways,  so  new  construction  or  reconductoring  of   transmission  lines  can  be  easier  to  achieve.    This  is  particularly  important  in  heavily  populated  areas,   which  often  suffer  from  transmission  congestion.  In  these  cases,  transmission  planners  may  consider   using  existing  transmission  right  of  ways  to  install  buried  HVDC  cable  to  increase  transmission  capacity   without  permitting  a  completely  new  transmission  pathway.     Power  Transmission  Controllers  and  Topology  Control  Algorithms   HVAC  PTCs  such  as  DSRs  and  STATCOMs  can  increase  the  capacity  of  AC  transmission  infrastructure  and   reduce  the  need  for  a  new  transmission  line,  to  optimize  the  existing  AC  transmission.  Because   repowering  existing  assets  could  be  less  costly,  a  transmission  owner  could  prioritize  capital   expenditures  and  deploy  resources  for  new  transmission  lines  in  parts  of  the  system  where  it  would   12    
  13. 13. make  the  most  difference.  In  addition,  they  can  increase  the  flexibility  and  adaptability  for  grid   operators  to  use  existing  AC  lines.     Topology  control  allows  for  line  switching  to  optimize  economic  efficiency  and  minimize  congestion.  In   some  cases,  employing  topology  control  alone  would  increase  the  utilization  of  transmission  lines  and   defer  the  need  for  new  transmission  construction.  One  common  concern  about  topology  control  is  that   it  might  increase  circuit  breaker  operations  and  maintenance  expenses.  Under  a  scenario  with  topology   control,  circuits  will  be  switched  more  frequently,  but  in  non-­‐fault  conditions  with  much  less  current.   Circuit  breakers  have  a  robust  design  to  deal  with  fault  conditions  are  expected  to  operate  will  in  a   topology  control  case.  However,  equipment  manufacturers  will  need  to  validate  and  support  this  new   use  case.  Circuit  breakers  that  are  old  and  past  warranty  may  be  of  greater  concern  in  than  newer   devices.  While  it  is  thus  possible  that  line  switching  could  increase  the  need  for  maintenance  on   breakers  that  are  used  more  frequently  in  switching  than  static  scenarios,  the  system-­‐level  benefits   should  outweigh  the  costs.     Reliability  and  Security     Where  power  systems  are  designed  to  meet  one  or  two  contingency  extreme  events,  power  flow   control  capabilities  could  help  to  mitigate  the  impact  of  one  or  two  outages  by  providing  alternate   power  flow  paths  to  continue  to  serve  load.  The  economic  impact  of  the  infamous  northeastern  August   2003  blackout  was  estimated  to  be  $4  to  $10  billion  in  the  United  States,  highlighting  the  importance  of   the  electric  grid  in  today’s  economy  (U.S.-­‐Canada  Task  Force,  2004).  Reliability  is  top  of  mind  for  system   operators,  regulators,  policy  makers,  and  businesses  in  the  U.S.  today,  as  reflected  in  the  regional   implementation  of  North  American  Electric  Reliability  Corporation  (NERC)  standards.  Power  flow  control   technology  could  increase  the  flexibility  and  responsiveness  of  the  grid.       HVDC   HVDC  technology  provides  several  reliability  benefits.  Specifically,  a  DC  circuit  breaker  with   instantaneous  response  time  will  allow  for  quick  fault  detection  and  response,  which,  in  conjunction   with  other  power  flow  control  technologies,  can  prevent  a  system-­‐level  problem  and  re-­‐route  power  to   enable  continual,  uninterrupted  service.  Similarly,  directional  switching  of  power  flow  enables  routing   options  post-­‐contingency.  The  ability  to  reverse  power  flow  in  response  to  a  contingency  can  decrease   generation  capacity  requirements  for  ancillary  services.     In  the  case  of  an  HVDC  intertie  between  two  asynchronous  grids,  VSCs  can  provide  black  start  service   from  one  grid  to  another,  significantly  decreasing  response  time  without  the  need  for  reserve   installations  that  would  otherwise  be  idle  much  of  the  year.      Power  Transmission  Controllers  and  Topology  Control  Algorithms   DSRs,  STATCOMs,  and  TCAs  each  provide  reliability  benefits.  DSRs  can  control  potential  transmission   overload  and  bypass  congested  lines,  increasing  transmission  utilization,  decreasing  congestion,  and   thereby  increasing  dispatch  options.  The  built  in  device-­‐to-­‐device  communication  system  in  DSRs   13    
  14. 14. enables  dynamic,  autonomous  response  and  eliminates  risks  associated  with  other  central-­‐control   communications  devices.  The  AC  regulation  function  of  STATCOMs  can  automatically  control   transmission  contingency  conditions  and  prevent  problems  or  decrease  recovery  time.  TCAs  will   optimize  transmission  line  switching  under  normal  and  contingency  conditions  –  bypassing  congested   lines  and  finding  the  optimal  path  to  serve  load.     In  order  to  quantify  the  specific  benefits  of  power  flow  control  technologies  on  a  particular  system,  it   would  be  necessary  to  model  the  grid  response  under  contingency  conditions  using  reliability  software,   and  then  again  with  power  flow  control  technologies  built  in  and  estimating  the  economic  value  of  the   reduction  in  load  loss  (Budhraja,  Mobasheri,  Ballance,  Dyer,  Silverstein,  &  Eto,  2009).       Congestion  Relief     Transmission  congestion  happens  whenever  preferable  or  low  cost  generation  is  unable  to  serve  electric   load  due  to  a  physical  limit  on  the  transmission  system.  Market  efficiency  is  based  on  optimal  economic   operation  of  the  grid  by  dispatching  the  lowest-­‐cost  generation.  Congestion  disrupts  this  process  and   leads  to  dispatch  of  higher  cost  generation  to  meet  demand  in  the  importing  location,  and  exerts   downward  pressure  on  prices  in  exporting  areas.  Reducing  congestion  on  the  transmission  grid  will   reduce  congestion  pricing  for  energy  and  ancillary  services  and  allow  for  economic  dispatch  of   generation  while  balancing  transmission  lines.  At  a  system  level,  the  cost  of  constructing  new   transmission  lines  or  adding  power  flow  control  technologies  must  be  weighed  against  the  benefits  of   doing  so.  Congestion  is  often  a  problem  in  or  around  densely  populated  areas,  where  permitting  new   transmission  lines  can  be  particularly  difficult.  In  these  cases,  there  may  be  a  clear  system-­‐level  benefit   to  power  flow  control  technologies.  Congestion  relief  brings  multiple  benefits  in  terms  of  integration  of   renewable  energy  and  economic  efficiency  of  energy  markets.   Integration  of  renewable  energy   Multiple  renewable  integration  studies  have  validated  the  substantial  system  level  and  societal  benefits   of  increased  renewable  energy  penetration.  Wind  and  solar  energy  generators  reduce  the  system   operating  costs  by  displacing  fuel  expenses  and  deferring  upgrades  to  existing  conventional  generators;   in  addition  to  lowering  generation  fleet  carbon  emissions.  In  the  Western  Wind  and  Solar   Interconnection  Study  (WWSIS),  it  was  found  that  by  tapping  the  large  solar  and  wind  resource  in  the   Western  Connection,  up  to  35%  of  the  required  energy  could  be  delivered  by  renewables  (GE  Energy,   2010).  This  results  in  a  40%  reduction  in  the  annual  system  OPEX.  In  the  Eastern  Wind  Integration  and   Transmission  Study  (EWITS),  a  10%  reduction  in  annual  system  OPEX  was  achieved  by  incorporating  30%   of  the  energy  requirement  from  wind  in  the  Eastern  Connection  (EnerNex  Corporation,  2011).  EWITS   also  calculated  an  18%  reduction  in  CO2  emissions.   The  challenge  to  incorporating  variable,  uncertain  renewable  energy  is  that  the  current  system   infrastructure  and  operational  practices  were  designed  for  dispatch-­‐able  and  predictable  generation   supplies.  However,  renewable  energy  generators,  such  as  wind  and  solar,  are  variable  and  uncertain   (non-­‐perfectly  predictable)  due  to  the  nature  of  wind  and  cloud  coverage.  This  variability  and   14    
  15. 15. uncertainty  has  the  potential  to  exacerbate  transmission  congestion  as  the  penetration  of  renewable   generation  increases.  Conversely,  there  might  be  an  under  supply  of  energy  or  system  frequency   disruption  if  the  renewable  generators  slow  or  stop  production  (due  to  ramping).     To  mitigate  these  challenges,  system  operators  can  require  additional  reserve  capacity  to  supplement   renewables  and  come  online  quickly  to  stabilize  system  frequency  in  the  event  of  ramping  of  the  energy   resource.  Other  generators  must  perform  load  following  to  match  their  output  to  any  changes  in  the   energy  supply-­‐demand  balance.  Furthermore,  local  generators  are  called  upon  in  instances  when   congestion  prevents  renewable  energy  from  serving  the  load.  In  this  case,  current  practice  empowers   grid  operators  to  curtail  renewable  generators  if  their  supply  cannot  be  reliably  transmitted  due  to   congestion  elsewhere  in  the  system.  In  all  these  cases,  the  operation  of  reserve  generators  is  generally   higher  cost  than  the  renewable  generators.  Some  system  operators  have  begun  to  utilize  forecasts  of   renewable  energy  regions  to  aid  in  more  economic  reserve  scheduling  and  transmission  system   operation.  However,  the  accuracy  of  these  forecasts  at  present  is  marginally  better  than  assuming   persistence.  Poor  information  leads  to  inefficient  dispatching  and  un-­‐necessary  cycling  of  conventional   generators  which  is  a  less  efficient  operational  method  that  outputs  greater  emissions  and  more  wear   and  tear  on  the  asset.     These  additional  operational  requirements  of  renewables  are  manageable,  but  lessen  the  total   achievable  system  benefits  due  to  the  increased  demand  for  real-­‐time  reserves  and  inefficiencies  in  the   near-­‐term  asset  scheduling  and  curtailment  practices.  For  example,  the  integration  of  wind  energy  in   ERCOT  is  estimated  to  cost  an  additional  $0.66/MWh  due  to  deployment/operation  of  reserves,  the  cost   of  base  load  cycling,  and  transmission  congestion  (Ahlstrom,  2013).  In  terms  of  capital  outlay  for  reserve   capacity,  it  is  estimated  that  PJM  spends  $3  per  each  additional  MW  of  wind  power  capacity  (The  Brattle   Group,  2013).   The  renewable  integration  studies  have  found  that  these  practices  and  associated  costs  can  be  largely   avoided  if  the  grid  were  flexible  to  compensate  for  the  variable,  uncertain  supply.  Power  flow  control   technologies  can  achieve  sufficient  transmission  system  flexibility  to  lower  renewable  integration  costs,   reduce  congestion,  and  allow  for  even  further  economic  utilization  of  renewable  energy  by  minimizing   curtailment.  In  addition,  a  more  interconnected  and  controllable  transmission  system  will  facilitate  the   network  benefits  of  geographic  averaging  of  renewable  resources  and  more  accurate  wind  and  solar   forecasts.   Economic  Efficiency   Power  flow  control  technologies  can  increase  the  economic  efficiency  of  the  electric  grid  through  lower   losses  and  by  enabling  economic  dispatch  of  transmission  and  generation  assets.  HVDC  devices,  DSRs   and  TCAs  can  be  installed  on  the  existing  transmission  grid  to  allow  for  the  necessary  flexibility  to  lower   integration  costs  through  the  mitigation  of  curtailment-­‐causing  system  bottlenecks  and  congestion.     HVDC   Long-­‐distance  HVDC  installations  improve  market  access  to  remote  resources.  When  congestion  is   appropriately  managed,  HVDC  facilitates  lower  energy  prices.  Lower  line  losses  of  HVDC  can  further   15    
  16. 16. reduce  the  overall  cost  to  serve  remote  load  by  30-­‐50%.  The  most  economic  generation,  including   renewable  generation  resources,  are  often  not  located  in  close  proximity  to  major  load  centers.  To  tap   these  resources,  a  transmission  system  must  be  developed.  For  long  distance  connection,  HVDC   conductors  offer  the  most  value  because  of  5-­‐10%  less  line  loss  than  similar  capacity  AC  conductors   (Bahrman,  2009).  Along  with  the  advantages  of  smaller  transmission  towers  and  no  need  for   intermediate  substations,  lower  line  loss  equates  to  lower  overall  system  cost.  For  a  1000  mile  system   rated  for  6000MW  an  800  kV  HVDC  system  is  $670/MW-­‐mi  less  expensive  than  a  765  kV  AC  system   (Bahrman,  2009).     HVDC  can  be  used  to  route  power  around  a  congested  area  of  the  AC  grid,  bringing  less  expensive  power   or  renewable  generation  situated  at  a  distance  to  market  in  an  area  of  higher  demand.  For  example,  the   Trans  Bay  Cable  delivers  power  from  Pittsburg,  California  to  San  Francisco,  providing  an  alternate  route   for  generation  to  serve  40%  of  the  city’s  peak  energy  needs.  Similarly,  the  Neptune  HVDC  cable  running   from  New  Jersey  to  Long  Island  enables  power  flow  directly  to  Long  Island,  skirting  areas  of  transmission   congestion  in  New  Jersey  and  New  York  and  serving  30%  of  electric  needs  of  Long  Island.     The  bi-­‐directional  flow  capabilities  of  many  HVDC  installations  could  allow  for  the  change  of  flow  to   address  particular  points  of  congestion  where  congestion  stress  points  shift  with  changing  supply  and   load  patterns.  For  example,  the  Cross  Sound  Cable,  a  merchant  transmission  line  between  CT  and  Long   Island,  largely  sends  power  from  CT  to  Long  Island  but  on  occasion  sends  power  the  other  way  in   response  to  changing  conditions.   Back-­‐to-­‐back  HVDC  –AC  intertie  capabilities  enable  ties  between  asynchronous  grids  and  can  thereby   increase  transfer  capacity,  allowing  for  access  to  supply  from  a  contiguous  grid  system  and  decreasing   the  cost  of  reliability  services.  HVDC  that  is  multi-­‐terminal  or  bi-­‐polar  with  bi-­‐driectional  capabilities  will   increase  the  interconnection  further  and  allow  for  economic  dispatch  in  multiple  directions.  For   example,  the  Cross  Sound  Cable  can  send  power  from  Connecticut  to  Long  Island  or  from  Long  Island  to   New  York  depending  on  system  conditions.     With  greater  HVDC  connectivity  of  disparate  renewable  generators  and  loads,  the  negative  system   effects  of  renewable  intermittency  are  largely  displaced.  Using  multi-­‐terminal  HVDC  transmission   systems  with  VSCs  that  allow  bi-­‐directional  power  flow,  system  operators  can  take  advantage  of  varying   geographical  resource  profiles.  For  example,  the  proposed  Clean  Line  Energy  transmission  projects   leverage  periods  of  excess  wind  energy  in  the  SPP  to  deliver  power  to  MISO  or  PJM  (Galli,  2012).  When   SPP  is  not  producing  wind  energy,  MISO  might  be,  or  likewise  PJM  might  be  producing  solar  energy.  By   connecting  large  geographical  areas,  the  average  amount  of  energy  available  to  serve  loads  is  higher  and   more  predictable  than  an  individual  resource  area  alone;  and  HVDC  systems  are  the  most  cost-­‐efficient   manner  to  create  the  connection.  The  geographical  averaging  effect  improves  energy  forecasts  (as   forecast  error  is  smaller  for  larger  geographies),  reduces  the  system  impact  of  ramp  events,  and  thus   reduces  base  load  cycling  and  the  use  of/need  for  reserve  capacity.  Additionally,  a  more  interconnected   transmission  system  allows  for  reserve  capacity  sharing  between  balancing  areas,  which  reduces  the   total  reserves  required  below  that  which  any  single  balancing  area  would  need  to  carry  to  meet  load  and   frequency  regulation  requirements.   16    
  17. 17. HVDC  collection  systems  enable  a  new  design  paradigm  for  renewable  energy  generation  stations.  With   AC  collection  systems,  solar  PV  electricity  is  collected  as  DC  at  each  panel  and  then  converted  to   synchronous  AC  electricity.  For  wind,  generators  produce  asynchronous  AC  electricity,  which  is   converted  to  DC  and  then  to  synchronous  AC  electricity.  If  renewable  generators  were  designed  to   connect  to  an  HVDC  collection  system,  PV  panels  would  not  need  an  inverter  and  wind  turbine-­‐side   converters  would  be  reduced  in  complexity  to  output  DC.  This  not  only  reduces  the  costs  of  developing   renewable  generator  stations  -­‐  by  7%  for  solar  (Goodrich,  2012)  -­‐  it  also  lowers  the  collection  losses   when  there  are  long  feeder  lines  connecting  the  generators  to  the  transmission  system.  Vestas   estimates  a  30%  improvement  in  reducing  energy  losses  for  wind  farms  developed  for  HVDC  collection   instead  of  AC  (Manjrekar).    Power  Transmission  Controllers  and  Topology  Control  Algorithms   DSRs  and  topology  control  algorithms  could  increase  the  flexibility  of  the  transmission  grid  and  thereby   increase  the  economic  efficiency  of  generation  dispatch.  DSRs  allow  operators  to  bypass  congested  lines   by  increasing  capacity  and  distributing  power  flow  among  portions  of  the  AC  grid,  thereby  increasing   transmission  utilization,  decreasing  congestion,  and  allowing  for  economic  dispatch  of  generation.  For   instance,  variable  impedance  devices  such  as  Smart  Wire  Grid’s  DSRs  can  increase  AC  transmission   system  utilization.  A  Smart  Wire  Grid  simulation  of  3,000  modules  on  six  transmission  lines  in  an  eastern   RTO  reduced  the  average  bus  marginal  cost  by  over  6%  in  a  summer  peak  scenario  (Smart  Wire  Grid,   2013).  DSRs  balance  the  load  being  transmitted  across  each  phase  and  allow  for  the  increase  in   transmission  capacity.     Power  flow  control  technologies  designed  to  alleviate  congestion  can  have  a  great  advantage  to  easing   the  integration  of  renewables.  Smart  Wire  Grid’s  DSRs  have  been  demonstrated  to  create  a  variable   impedance  transmission  network  that  allows  power  flow  to  bypass  congested  lines.  A  simulated  study  in   the  Pacific  North  West  found  that  with  an  investment  of  $58  million  (~3000  devices),  the  variable   impedance  system  created  was  able  to  unlock  and  additional  2.8GW  of  wind  energy  by  reducing   congestion  (Smart  Wire  Grid,  2013).  This  benefit  would  be  achieved  without  adding  any  additional   transmission  lines,  and  thus  deferred  significant  investment  for  the  transmission  owners.       Likewise,  this  same  effect  can  be  accomplished  by  optimally  switching  transmission  lines  to  change  the   impedance  characteristics  of  the  transmission  system.  TCAs  can  be  deployed  by  system  operators  to   optimize  their  switching  decisions  based  on  real-­‐time  events  on  the  grid.  TCA  simulations  in  power  flow   modeling  software  has  shown  a  reduction  in  wind  curtailment  instances  from  33%  to  14%  by  switching   lines  (Qiu,  2013).  A  simulation  of  the  impact  of  TCA  using  historical  PJM  data  demonstrated  over  $100M   in  annual  savings  from  congestion  relief  (The  Brattle  Group,  2013).  Again,  these  benefits  were  gained   with  very  little  capital  investment  which  allows  transmission  owners  to  invest  elsewhere  in  their  system.     Other  HVAC  PTC  devices  that  can  provide  voltage  and  frequency  support,  such  as  STATCOMs  and  phase-­‐ shifting  transformers,  have  been  used  to  improve  the  integration  of  wind  and  solar  generators.  These   devices,  which  also  allow  for  power  flow  control,  provide  dynamic  response  to  fluctuations  in  the  power   quality  of  renewable  generators.   17    
  18. 18. Summary  of  Power  Flow  Control  Technology  Value     One  power  flow  control  technology  can  have  multiple  benefits  depending  on  its  application  in  the  grid.   To  understand  the  possibility  of  various  power  flow  control  technologies  at  a  glance,  see  Table  1.   Technical  capabilities  alone  are  not  sufficient  to  achieve  economic  efficiency  of  the  system  with  the   deployment  of  a  power  flow  control  technology.  Market  and  regulatory  barriers  can  prevent  use  of  the   technical  capabilities  even  when  it  would  be  economic,  highlighting  the  need  for  clear  understanding   among  transmission  owners,  system  operators,  and  regulators  of  both  technical  capabilities  and  benefits   of  technology  at  the  system  level.     Table  1.  Power  Flow  Control  Technology  Value  Categories.  Power  flow  control  technologies   can  have  different  or  multiple  benefits  depending  on  their  position  and  application  in  the   electric  grid  –  asset  management,  renewable  integration,  congestion  relief,  economic   efficiency,  and  reliability  and  security.  Classes  of  technologies  that  are  represented  by  one  or   more  of  ARPA-­‐e’s  GENI  technology  teams  are  represented  in  bold  font.     GENI Technology Value Categories X HVDC LCC X X X X X TCSC X X X X X X X X X X X UPFC Real Time X Dispatch & planning X Reduce curtailment X X HVDC VSC Improve Contingency Reliability & Security Ancillary Economic Efficiency Energy Congestion Relief Black start Renewable Integration Improve inter – connection Prioritize or defer new investment Value Asset Management Improve Utilization Power Flow Control Technology Non-GENI Shunt -STATCOM Series - SSSC X X X X X X X X X X PhaseShifting Transformer X X X X DSR X X X X TCA X X X X X X X X X 22   Stakeholders  in  the  Transmission  Grid  Influence  Technology  Investment   Decisions     As  previously  discussed,  quantifying  the  benefits  of  power  flow  control  capabilities  is  particularly   difficult  due  to  the  dynamic  nature  of  the  electric  transmission  grid  and  the  differences  in  benefits  to   individual  stakeholders  as  compared  to  the  overall  system  benefits.  At  the  same  time,  multiple   18    
  19. 19. stakeholders  are  often  involved  in  technology  investment  decisions,  and  a  level  of  agreement  among   them  is  necessary  in  order  to  optimize  system  efficiency.     Differences  in  regulatory  structure  among  federal  power  authorities,  investor  owned  utilities,  merchant   transmission  owners,  municipal  utilities,  and  rural  electric  co-­‐ops  lead  to  substantial  differences  in  the   way  certain  groups  assess  power  flow  control  technologies,  even  within  similar  stakeholder  categories.   As  technology  vendors  consider  the  best  value  proposition  and  business  model  for  their  power  flow   control  technologies,  they  should  bear  the  regulatory  environment  and  degree  of  restructuring  of  the   electric  market  in  mind.  For  an  overview  of  influencers  in  the  electric  grid,  see  Figure  2.     Numerous influences on Transmission Owner’s investment and siting decisions ISO/RTO NERC/ coordinating councils $ Tech Transmission Owner Decreasing influence on investment decisions Transmission CAPEX, OPEX, rate recovery FERC PUC Regulatory industry groups Other regulators, NGOs 16   Figure  2.  Overview  of  influencers  in  the  transmission  grid.  A  utility  or   transmission  owner  investing  in  technology  must  be  mindful  and  responsive  to   the  interests  of  multiple  stakeholders  in  the  grid:  the  ISO/RTO  that  dispatches   assets  and  determines  set  points  for  power  flow  control  technologies,  the   regulators  overseeing  investment  and  siting  decisions,  the  bodies  responsible  for   overall  reliability  of  the  electric  grid,  and  other  interested  parties  who  may   intervene  in  a  transmission  case.       The  benefits  of  power  flow  control  technology  to  each  stakeholder  will  vary  by  their  business  model  and   geographic  and  regulatory  situation.  To  better  understand  the  business  models  and  motivations  of   various  stakeholders  in  the  electric  transmission  grid,  see  Table  2.     For  the  most  part,  power  flow  control  will  have  positive  economic  outcomes,  with  the  exception  of   those  stakeholders  who  currently  benefit  from  transmission  congestion  such  as  reserve  generators  and   to  a  slightly  lesser  extent  base  load  generators,  renewable  energy  generators,  and  transmission  owners.   19    
  20. 20. The  beneficiaries  of  a  change  in  power  flow  control  will  often  be  temporary  and  largely  situation-­‐ dependent,  as  market  conditions  will  remain  dynamic  in  a  world  with  power  flow  control.  An  overview   of  how  each  stakeholder’s  situation  might  change  as  compared  to  current  conditions  is  presented  in   Table  3.   Table  2.  Motivations  of  stakeholders  in  the  electric  transmission  grid.  This  table  demonstrates   the  motivations  of  each  stakeholder  involved  in  the  electric  transmission  grid,  including  their   motivations,  inherent  conflicts  and  considerations,  and  a  brief  description  of  their  revenue   model.  While  every  effort  was  made  to  provide  a  comprehensive  overview,  the  differences  in   regulatory  structure  among  federal  power  authorities,  investor  owned  utilities,  merchant   transmission  owners,  municipal  utilities,  and  rural  electric  coops  should  be  considered  when   assessing  the  position  of  each  stakeholder. Stakeholder How do they Conflictsmakeinterest related to of or recover $ Motivation Conflicts & Considerations PFR investment Transmission Owner § Rate of return (~13%) for transmission investment § FERC technology incentive rate § ~11.5% distribution investment § Projects that will be approved or financed –leads to incremental build out of system (relatively short time horizon for utilities dependent on regulated rate of return) § Invest in what they know (wires) rather than new technology § Profit § Incentive towards construction to meet peak - of new transmission lines rather than investment in technology to remove congestion etc. § Regulated: certainty of public benefit case (to rate-base) § Merchant transmission need 20 year, low-risk opportunity ISO/RTO Fees charged to: § Generators § Transmission owners (allocated to states and recovered in rate base) § Reliability (& compliance with standards) § Reduced congestion § Reserve margin § Economic efficiency § Known solutions Split in priority/focus : § Reliability § Economic dispatch § Capacity margins Renewable Generator § Contracts (PPA, tariff) § Bankability § Off-take certainty § Reduced curtailment Base Load Generator § Dispatch § Regulated return (where applicable) § Bankability § Increase utilization § Compliance with regulations § Risk change schedule/dispatch § No compensation for cycling & wear & tear for slow ramping Reserve /peak Generator § Dispatch § Ancillary services § Regulated return (where applicable) § Increase utilization § Ability to access ancillary services revenue streams (where applicable) § Compliance with regulations Risk lowering utilization by removing ancillary service functions FERC § Congressional approval § Recovered from regulated industries § Economic efficiency § Reliability § Policy implementation TO needs to approach FERC with new technology to receive favorable return for new tech solution. Theoretically could change incentive for transmission technology investment over new wires. PUC § Budget set at state level § Recovered from rate payers. § Customer rates § Economic efficiency § Reliability § Policy implementation §Transmission investment on economic benefits accruing to their state rate base vs everyone else in market area § Public perception § Re-election (where applicable) ARPA-E Template   19           20    
  21. 21. Table  3.  Overview  of  beneficiaries  as  a  result  of  power  flow  control  improvements  in  the   electric  grid.   Power flow control technology beneficiaries Benefit is dependent on situation Revenue losses likely in current system Black start Reliability & Security Improve Contingency Ancillary Economic Efficiency Energy Real Time Congestion Relief Dispatch & planning Reduce curtailment Renewable Integration Improve inter –connection Prioritize or defer new investment Value Asset Management Improve Utilization Stakeholders Likely benefit (financial or operational) Transmission Owner ISO/RTO Renewable Generator Base Load Generator Reserve Generator FERC PUC Consumer PFC generally produces beneficiaries…except in cases where stakeholders currently profit off of system inefficiencies   Conclusion/Next  steps       This  document  defined  power  flow  control  and  identified  and  described  technologies  that  enable  power   flow  control.  It  identified  the  benefits  of  power  flow  control  and  how  these  benefits  accrue  to  various   stakeholders  involved  in  the  electric  grid.  It  did  not  perform  a  detailed  analysis  of  system-­‐level  benefits   or  provide  case  studies  quantifying  the  impact  of  power  flow  control  technologies.     As  power  flow  control  technologies  become  more  common  on  the  electric  grid,  further  analysis  will  be   required  to  optimize  their  use  at  a  system  level.  This  should  include:       Technology  case  studies  and  models   • Power  flow  control  technology  case  studies  and  data  sharing  to  document  lessons  learned     For  the  existing  cases  where  power  flow  control  technologies  are  installed  and  operated,  in-­‐ depth  analyses  will  advance  the  understanding  of  the  technical  capabilities,  costs,  and  benefits   of  the  technology.  Where  possible,  case  studies  should  include  quantitative  analysis  of  the   21    
  22. 22. • • • effects  of  the  technology.  Data  sharing  at  a  high-­‐level  will  enable  deeper  understanding  of  the   applications  of  power  flow  control  technologies.  Possible  case  studies  include   o HVDC:      Trans  Bay  Cable  and  its  use  and  effects  on  transmission  congestion    Bi-­‐polar  HVDC  applications  such  as  Cross  Sound  Cable  between  Connecticut  and   Long  Island,  Cross  Chanel  Cable  between  the  UK  and  France   o UPFC:    Marcy  station  UPFC  in  New  York.  What  was  the  economic  (market)  response  to   its  operating  mode  set  points,  before  and  after  installation   o DSR:    Case  study  on  the  Tennessee  Valley  Authority  pilot  installation   Further  describe  and  quantify  the  benefits  of  power  flow  control  technology  to  a  particular   stakeholder   Interested  parties  will  seek  more  information  on  how  the  benefits  of  power  flow  control   technologies  change  the  economics  of  the  system,  particularly  for  cases  where  the  benefits  of  a   power  flow  control  vary  (e.g.,  those  situation  identified  as  “yellow”  in  Table  3–  in  what   situations  are  these  green  and  red?)   Develop  or  identify  a  uniform  model  for  analyzing  transmission  technologies                                       Numerous  stakeholders  expressed  interest  in  a  uniform  grid  model  of  sufficient  size  to  model   system-­‐level  effects  of  combinations  of  technological  installations.   Add  power  flow  control  technology  specifications  to  existing  grid  modeling  software               Recent  modeling  exercises  may  have  been  limited  by  the  technical  specifications  available  to   modelers.  To  the  extent  that  these  set  points  can  be  added  rather  than  programmed  for  each   specific  hypothetical  or  actual  installation,  decision  makers  would  have  more  accurate  models   and  understanding  of  the  effects  of  technological  installations.     System  level  technical  and  market  analyses   • • • Technological  analysis  of  what  is  required  to  enable  power  flow  control  at  a  system  operator   level   Analysis  may  include  modeling  of  optimal  physical  positioning  of  devices  in  the  grid,  reliability   modeling,  and  economic  modeling  of  the  impact  of  increased  transmission  capabilities  and  the   increased  fluidity  of  changing  grid  topologies.   Define  level  of  coordination  and  control  required  within  an  RTO  and  among  regions.                                 In  order  to  increase  the  flexibility  of  the  transmission  and  distribution  grid  and  meet  goals   around  reliability,  integration  of  renewable  electricity  at  the  utility  and  distributed  scale,  energy   efficiency  and  demand  response  capabilities,  we  will  need  some  centralized  control  and   centrally  coordinated  distributed  control.  This  will  provide  quick,  responsive  voltage  support  and   meet  the  changing  needs  of  the  electric  grid.   Consideration  of  market  design  for  a  flexible  transmission  grid                                                                                                                                                           Changing  grid  topologies  can  change  the  economics  of  generator  and  transmission  positioning   22    

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