Transformer  Reliability  

Garth  Cuthbert  Nov  2015  

A  prac'cal  approach  to  achieving  life  expectancy  

Transformer  Reliability  

3  x  1000  kVA  OFW  1ph  11,000–800  Volts  In  service  since  1915  

What  contributes  to  reliability?  

Preven'on  /  Mi'ga'on  “Bow'e”  

What  contributes  to  failure?  •  Overload,  Overvoltage,  Overtemperature  

•  Natural  ageing  processes  -­‐  Entropy  •  Unexpected  and  unplanned  operaPng  events  •  Human  error  

Transformer  Failure  Cause  

Miss-­‐Applica*on  

10%  

Design  Deficiency  

40%  

OEM  Workmanship  

5%  

Transporta*on  Damage  25%  

Maintenance    Error  10%  

Opera*ng    Error  10%  

Miss-­‐Applica*on  

10%  

Design  Deficiency  

20%  

OEM  Workmanship  

15%  

Transporta*on  Damage  

5%  

Maintenance  Error  30%  

Opera*ng  Error  20%  

1970-­‐1980   2005-­‐2015  

Failure  Rate  2.5  per  100     Failure  Rate  0.5  per  100    

RCM  -­‐  Reliability  Centered  Maintenance  

•  Based  on  known,  probable  failure  modes,  both  evident  and  hidden  

•  OpPmizes  ongoing  maintenance  costs  vs.  replacement  costs  while  maximizing  availability  

•  Creates  a  baseline  and  record  of  criPcal  equipment  metrics  from  start-­‐up,  during    warranty  period,  through  operaPng  events  resulPng  in  an  accurate  and  informed  assessment  of  current  condiPon  and  risk  

•  Predicts  and  miPgates  the  evoluPon  of  latent  failures  

What  needs  maintenance  and  how  frequent?  

IEEE  C57.93  -­‐  Guide  for  Installa*on  and  Maintenance  of  Liquid-­‐Immersed  Power  Transformers  

Manufacturer’s  Opera*on  and  Maintenance  Manual  

Component    or  FuncPon  

Typical  IEEE  C57.93  and  OEM  Recommended  Maintenance  AcPon  

RCM  Best  PracPce/Strategy  

Dehydrator  Leak  Free  Tank  and  Coolers  

ConnecPons    

R1M  InspecPon:  Note/Record  Abnormal  IndicaPon  

R1Y    Infrared  Thermographic  Survey  

R1M  InspecPon:  Note/Abnormal  IndicaPon  

R3Y  Auto  Dehydrator  conPnuously  monitored  with  self  checking  failsafe  design.  

Air  bladder  equipped  conservator  

Galvanized  air-­‐liquid  coolers  

Double  walled  water-­‐liquid  heat  exchangers  with  integrated  leak  detec*on  

External  Inspec*on  

Early  detecPon  of  common  faults  before  serious  damage  or  failure  occurs.  Poor  connecPon  of  HV  bushing  and  evidence  of  compromised  flow  in  two  coolers      

Infrared  Thermographic  Survey  

Indica*on  Gauges  Liquid  Level  Liquid  Temp  Winding  Temp  Gas  AccumulaPon  

Bushing  Liquid  Level  

R1M  InspecPon:  Note  Abnormal  IndicaPon  Record  levels  and  temperatures  in  staPon  records  

R1M  InspecPon  Note  Abnormal  IndicaPon  R3Y  Intelligent  Transformer  Monitor  (ITM)  –  non  mechanical  (RTD)  oil  temperature  inputs,  

conPnuously  monitored  with  self  checking  failsafe  design  and  remote  oil  temperature  data  

Component    or  FuncPon  

Typical  IEEE  C57.93  and  OEM  Recommended  Maintenance  AcPon  

RCM  Best  PracPce/Strategy  

Controls  Fan  FuncPon  

R1M  InspecPon:  Confirm  Auto  and  Manual  FuncPonality  

R1M  InspecPon  Confirm  Auto  and  Manual  FuncPonality  R3Y  ITM  Control  outputs  to  fan  circuits  with  self  checking  funcPonality  

Indica*on  and  Control  –  Func*onal  Verifica*on  

Some  failure  modes  are  extremely  difficult  to  detect  and  even  more  difficult  to  quanPfy  contribuPon  to  end  of  life.  

These  tend  to  be  design  and  workmanship  related.    

A  robust  purchase  specificaPon  supported  by  strong  QA  oversight  of  the  supplier  through  commissioning  will  detect  acPve  and  potenPal  problems.  

This  image  was  presented  online  as  representaPve  of  a  manufacturer  quality  standards!  

Component    or  FuncPon  

Typical  IEEE  C57.93  and  OEM  Recommended  Maintenance  AcPon  

RCM  Best  PracPce/Strategy  

Mechanical  Alarms    Liquid  Level    Liquid  Temp  Winding  Temp  Gas  AccumulaPon  

Mechanical  Trips  Liquid  Level  Liquid  Temp  Winding  Temp  Sudden  Pressure  Pressure  Relief    

D3Y  Verify  IndicaPon  D3Y  Verify  Alarm  to  Annuciator  Display  D3Y  Verify  Trip  ProtecPon  

D3Y  Calibrate  and  Verify  IndicaPon  D3Y  Verify  Alarm  to  Annuciator  D3Y  Verify  Annuciator  Self  Monitoring  FuncPonality  Redundant  ITM  Alarm  

outputs  to  annuciator  with  self  checking  funcPonality  and  self  calibraPon  design  

Fiber  Op*c  Winding  Temperature  Monitors  Integrated  data  systems  

Alarm  and  Protec*on  -­‐  Func*onal  Verifica*on  

Fiber  Op*c  Winding  

Temperature  Monitors  accurately  measure  the  winding  hot  

spot  temperature.    

Typical  insulaPon  degradaPon  due  to  conPnuous  operaPon  at  or  

above  thermal  raPngs  

Oil  and  Winding  Temperature  records  would  provide  limited  informaPon  on  condiPon  and  

failure  probability  

Every  transformer  is  equipped  with  temperature  indicaPon  

 and  every  transformer  experiences  some  degree  of  temperature  

related    loss  of  life  

Mechanical  failure  due  to  cumulaPve  effect  of  magnePc  forces  subjected  during  external  

through  faults  

 SophisPcated  monitoring  and  test  programs  capable  of  

predicPng  failure  with  reasonable  confidence  are  available  

 Cost  prohibiPve  for  GSU  applicaPons  considering  <  1  in  10,000  will  fail  due  to  through  

fault  duty          

RaPo  Adjuster  

InsulaPon  Integrity  

Oil  Integrity  

No  recommendaPon  

D3Y-­‐D7Y  InsulaPon  power  factor  (Doble®)  tests  including  oil  and  bushings.  

Core  Ground  InsulaPon  Resistance  (Megger®)    Winding  Resistance  Winding  RaPo  

R1Y-­‐R3Y  Oil  Tests  (1  liter  sample)  Dissolved  Gas  Analysis  (Oil  Syringe)  Furan  Analysis  

D3Y  Exercise  the  RaPo  Adjuster.  Measure  winding  resistance  in  all  posiPons  

D3Y  InsulaPon  power  factor  (Doble®)  tests  including  oil  and  bushings.  

D3Y  Core  Ground  InsulaPon  Resistance  (Megger®)  

R2Y  Oil  Tests  (1  liter  sample)  R6M  Dissolved  Gas  Analysis  R2Y  Furan  Analysis  

Online  DGA  Monitoring  

Internal  Condi*on  Assessment  

Component    or  FuncPon  

Typical  IEEE  C57.93  and  OEM  Recommended  Maintenance  AcPon  

RCM  Best  PracPce/Strategy  

Dissolved  gas  analysis  (  DGA  )  is  widely  used  to  detect  incipient  faults  in  transformers.  UnPl  recently  it  involved  period  sampling  of  the  transformer’s  oil  and  lab  analysis  with  interpretaPon  by  chemists  and  transformers  specialists.    

Available  online  DGA  monitors  have  advanced  significantly  with  diagnosPc  output  data  and  display,  user  set  points  for  alarm  and  trip  funcPons  for  each  different  fault  type.  One  manufacturer  even  calculates  and  displays  diagnosPc  uncertainty.    

A  fiber  opPc  winding  temperature  monitor  coupled  with  a  online  DGA  monitor  provides  the  transformer  owner  with  the  means  to  operate  a  transformer  to  its  full  capacity  raPngs  with  confidence.  The  impact  of  any  planned  or  unplanned  overload  is  easily  recognizable  and  quanPfied.  

The  real  Pme  aspect  of  both  devices  can  provide  input  and  feedback  to  generaPon  opportunity  decisions  and  or  asset  management  decisions.    

ApplicaPon  to  Generator  Step  Up  Transformers  

Fiber  OpPc  Winding  Temperature  Monitor  

1.  Any  transformer  >  15  MVA  2.  Transformers  connected  to  single  unit  generator  

capacity  above  nominal  transformer  capacity  3.  Transformers  required  to  provide  emergency    

connecPon  for  mulPple  generators  

Online  DGA  Monitor  

1.  Any  transformer  >  30  MVA  2.  Any  transformer  connecPng  generaPon  or  

source  voltage  above  16kV  3.  Any  transformer  with  an  on  load  tapchanger  

Aspire  to  operaPng  your  GSU  transformer  for  100+  years?  Think  again!    

Technology  currently  being  developed  will  radically  change  connecPon  between  energy  sources  and  the  electrical  grid.  Look  for  it  in  5  years!  

Aim  for  a  GSU  transformer  life  of  25-­‐30  years,  celebrate  achieving  35  years  and  rePre  at  40  years.