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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.