Introduction to Power Quality Monitoring

Presented by: Syed Khundmir T Department of Electrical Engineering University at Buffalo khundmir@buffalo.edu

The BEST Group THE BUFFALO ENERGY SCIENCE AND TECHNOLOGY GROUP

-Winter Lecture Series

Prime  reference:  Electrical  Power  Systems  Quality  By  Roger  C.  Dugan,  Mark  F.  McGranaghan,  Surya  Santoso,  H.  Wayne  Beaty  

Introduc)on

• Power  Quality  Monitoring  (PQM)  is  the  process  of  gathering,  analyzing  and  interpre>ng  raw  measurement  data  into  useful  informa>on.  • PQM  is  o@en  done  to  improve  the  system-­‐wide  power  quality    performance.  • Data  usually  measured  is  the  voltage  and  current  but  is  not  limited  to  these  quan>>es.  

Objec)ves

• Characterizing  system  performance  

• Characterizing  specific  problems  

• As  part  of  an  Enhanced  Power  Quality  Service    • As  part  of  Predic>ve  or  Just-­‐In-­‐Time  Maintenance  

Monitoring  as  part  of  a  facility  site  survey

•  Inspec>on  of  wiring  and  grounding  concerns.  

•  Inspec>on  of  equipment  connec>ons.  

• Monitoring  voltage  and  current  characteris>cs  throughout  the  facility.  

 

Determining  what  to  monitor

•  To  know  what  to  monitor,  characteriza>on  of  disturbances  in  the  system  is  required.  

 

•  Extensive  monitoring  of  all  the  different  types  of  power  quality  varia>ons  can  be  very  expensive.  

Choosing  Monitoring  loca)ons

• Cannot  monitor  at  each  and  every  point  in  the  system.  

• Can  be  expensive  and  hard  to  manage  the  data.  

• Measurements  at  some  strategic  loca>ons  should  be  done.  

Permanent  power  quality  monitoring  equipment 1.  Digital  fault  recorders  (DFRs):  •  It  typically  triggers  on  fault  events  and  record  the  voltage  and  current  waveforms  that  characterize  the  event.  • Helps  in  characterizing  disturbances  like  voltage  sags,  during  power  system  faults.  • Can  also  capture  periodic  waveform  for  calcula>ng  harmonic  distor>on  levels.  

Smart  relays  and  Intelligent  Electronic  Device

• Recently,  manufacturers  of  relays  that  monitor  the  current  anyways  are  adding  on  the  capability  to  record  disturbances  and  make  the  informa>on  available  to  an  overall  monitoring  system  controller.  

•  Loca>on  can  be  at  the  feeder  circuits  as  well  as  at  the  substa>on.  

Voltage  recorders

• A  variety  of  voltage  recorders  are  used  to  monitor  voltage  varia>ons  on  distribu>on  systems.  

•  Typically,  the  voltage  recorder  provides  a  trend  that  gives  maximum,  minimum  and  average  voltage  with  a  resolu>on  of  less  than  2seconds.  

In-­‐plant  power  monitors

• Mostly  located  at  the  service  entrance.  

• Captures  waveshape  for  evalua>on  of  harmonic  distor>on  levels,  voltage  profile  for  rms  varia>ons  and  triggered  waveshape  captures  for  voltage  sag  condi>ons.  

• May  also  posses  capabili>es  to  have  transient  monitoring  capabili>es.  

Special-­‐purpose  power  quality  monitors

• Were  developed  for  the  EPRI  DPQ  Project.  •  Simultaneous  voltage  and  current  monitoring  with  triggering  of  all  channels  during  a  disturbance  is  an  important  capability  of  these  instruments.  

Revenue  meters:  •  The  revenue  meters  monitor  the  voltage  and  current  and  these  days,  many  of  the  manufacturers  are  including  advanced  monitoring  that  could  include  recording  of  power  quality  informa>on.  

 

SeEng  monitor  thresholds

•  It  is  important  to  define  the  range  of  condi>ons  that  can  be  considered  normal.  

•  Some  of  the  monitors  have  preselected  thresholds  that  can  be  used  as  a  star>ng  point.  

• Whereas  some  of  the  monitors  come  with  adjustable  thresholds  based  on  the  equipment  specifica>ons.  

Finding  source  of  disturbance

•  First  step  to  iden>fy  source  of  a  disturbance  is  to  correlate  the  disturbance  with  possible  causes.  •  The  general  guidelines  are:  1.  High-­‐frequency  voltage  varia>ons  will  be  limited  to  loca>ons  close  

to  the  source  of  the  disturbance.  2.  Power  interrup>ons  close  to  the  monitoring  loca>on  will  cause  a  

very  abrupt  change  in  the  voltage  whereas  the  ones  far  from  it  will  result  in  decaying  voltage.  

3.  The  highest  harmonic  voltage  distor>on  levels  will  occur  close  to  capacitors  causing  resonance  problems.  

Conclusion

•  Thus,  the  power  quality  monitoring  can  be  effec>ve  only  when  proper  study  is  done  about  the  objec>ve  of  the  monitoring  system  and  source  of  the  problem.  Only  a@er  these  are  known,  we  can  move  forward  to  decide  the  suitable  point  at  which  the  monitors  are  to  be  connected  and  then  assessment  of  the  data  is  done.