IEEE 2011 Electrical Power and Energy Conference

New  Microprocessor  Based  Relay  to  Monitor  and  Protect  Power  Systems  Against  Sub-­‐Harmonics  

K. Narendra, D. Fedirchuk, R. Midence, N. Zhang, A. Mulawarman, P. Mysore, V. Sood

Winnipeg, Manitoba, Canada 5 October 2011

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Outline  •  Introduc.on  •  System  Event  at  Xcel  Energy    •  Event  Analysis  •  Microprocessor  based  relay  hardware  architecture  

•  Sub  harmonic  detec.on  process  •  Principle  of  sub  harmonic  detec.on  •  Opera.ons/Minute  detector  

•  Results  and  discussions  •  Conclusions  

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Introduc.on  •  Wind  power  based  genera.on  is  growing  rapidly  throughout  the  world  

•  Since  wind  farms  are  generally  located  far  away  from  the  load  centers  –  series  compensa.on  is  used  for  economical  reasons  

•  Sub  Synchronous  Resonance  (SSR)  is  a  well  known  phenomena  in  series  compensated  system  and  many  mi.ga.on  techniques  exist  

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Introduc.on..  •  Sub  harmonic  oscilla.ons  due  to  wind  genera.on  interac.on  (controls/system)  impose  new  challenges  to  today’s  electrical  grid.  

•  A  new  event  on  Xcel  Energy  grid  with  wind  generator  interac.on  with  the  series  compensated  transmission  system  lead  to  the  innova.on  of  a  microprocessor  based  sub  harmonic  relay  

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Introduc.on...  •  Sub  harmonics  is  defined  as  the  harmonic  frequency  below  

the  system  frequency  (60  Hz  or  50  Hz)  

•  Natural  frequency  of  series  compensated  transmission  system  is  defined  by  

Where,      fn  =  natural  frequency  (Hz)  

   fsys  =  system  frequency  (60  Hz  or  50  Hz)     Xc  =  series  capacitor  reactance  

  XTOT  =  sum  of  all  the  system  induc.ve  reactance  (transmission  line,    transformer,  generator  sub  transient  reactance  

Note:  

For  compensa/on  between  20%  to  80%,  fn  <  60  Hz  which  is  sub  synchronous  frequency  

fn=  fsys  √Xc  /XTOT  

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System  electrical  dynamics  

Generator  electromagne.c  

dynamics  

current

voltage

Electrical  self  excita.on  or  Induc.on  generator  effect  (IGE)  

Introduc.on….  

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Introduc.on…..  •  SSCI  –Sub  Synchronous  Control  Instability  

–  Interac.on  Between  Power  Electronics  Devices  (Wind  Turbine,  HVDC,  SVC  etc.)  and  Series  Compensated  Transmission  System.  

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Power  Electronic  Devices  

Series  Compensated  Transmission  

System  

Control Signals

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Introduc.on…...  

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System  electrical  dynamics  

Generator  electromagne.c  

dynamics  

Current

Voltage

Turbine  mechanical    dynamics  

Electromagnetic torque

Shaft speed

Torsional  interac.on  

Capacitor  fault  induced  voltage  

Generator  electromagne.c  

dynamics  

Current Turbine  mechanical    dynamics  

Electromagnetic torque

Mechanical  Torque  Amplifica.ons  

Mechanical torque

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System  Single  Line  Diagram  

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1- Breaker 1 & 2 opened for regular system switching procedure

2- CT1,CT2, and W start feeding radially through series capacitor

3- Tripped the CT generator unit

Line 1 345 kV

345 kV

45 MVA

System  Event  

CT1, CT2 - Combustion turbine generators

W - Wind generators – as a single unit

15 MW (20% of total generation)

To the System

To the System

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Event  Analysis  11  

9 Hz & 13 Hz dominant sub harmonics

High speed recording of 3 phase currents captured by the DFR

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Event  Analysis  12  

Slow speed (swing ) recording of one of the phase

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Relay  Architecture  13  

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Relay  Architecture  ..  14  

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Sub  Harmonic  Detec.on  Logic  Diagram  

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Sub  Harmonic  Detec.on  16  

Trip or Alarm: = max (f2, f3, f4, f5, f6, f7) > Lset

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Opera.ons/Minute  Detec.on  17  

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Results  and  discussions  •  RTDS  (Real  Time  Digital  Simulator)  •  COMTRADE  Playback  

– Nominal  sub  harmonic  detector  

– Fundamental  sub  harmonic  detector  – Total  sub  harmonic  detector  – Opera.ons  /  minute  detector  

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Test  Oscillography  Files  19  

Nominal sub-harmonic detector – 5 Hz

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Test  Oscillography  Files  20  

TSHD detector – 5 Hz

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Test  Oscillography  Files  21  

Fundamental sub-harmonic detector – 25 Hz

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Test  Oscillography  Files  22  

Operation/minute detector – 5 Hz and 5 operations/minute

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Results  and  discussions  

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Conclusions  •  The  event  captured  at  the  Xcel  Energy  U.lity  lead  to  the  development  of  a  new  microprocessor  based  sub  harmonic  protec.on  technique.    

•  With  the  increase  use  of  wind  generators  feeding  HV  and  EHV  u.lity  networks,  it  is  necessary  to  ensure  that  sub  harmonic  oscilla.ons  are  monitored,  and  that  the  electrical  grid  is  protected  from  any  resul.ng  detrimental  effects.  

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Conclusions  ..  •  The  performance  of  the  sub-­‐harmonic  protec.on  technique  was  successfully  tested  using  a  Real  Time  Digital  Simulator  (RTDS)    

•  The  tests  demonstrated  that  the  solu.on  is  capable  of  performing  reliably  the  following  func.ons:  – Nominal  sub-­‐harmonic  detec.on  – Fundamental  sub-­‐harmonic  detec.on  

– Total  sub-­‐harmonic  detec.on  – Opera.ons/Minute  detec.on  

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