Transformer Reliability

Transcription

1 Transformer Reliability A prac'cal approach to achieving life expectancy Garth Cuthbert Nov 2015

2 Transformer Reliability 3 x 1000 kva OFW 1ph 11, Volts In service since 1915

3 What contributes to reliability? Preven'on / Mi'ga'on Bow'e

4 What contributes to failure? Overload, Overvoltage, Overtemperature Natural ageing processes - Entropy Unexpected and unplanned operapng events Human error

5 Transformer Failure Cause Maintenance Error 10% Opera*ng Error 10% Miss- Applica*on 10% Opera*ng Error 20% Miss- Applica*on 10% Design Deficiency 20% Transporta*on Damage 25% Design Deficiency 40% Maintenance Error 30% OEM Workmanship 15% OEM Workmanship 5% Transporta*on Damage 5% Failure Rate 2.5 per 100 Failure Rate 0.5 per 100

6 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

7 What needs maintenance and how frequent? IEEE C Guide for Installa*on and Maintenance of Liquid- Immersed Power Transformers Manufacturer s Opera*on and Maintenance Manual

8 External Inspec*on Component or FuncPon Dehydrator Leak Free Tank and Coolers ConnecPons Typical IEEE C57.93 and OEM Recommended Maintenance AcPon R1M InspecPon: Note/ Record Abnormal IndicaPon R1Y Infrared Thermographic Survey RCM Best PracPce/Strategy 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

9 Infrared Thermographic Survey Early detecpon of common faults before serious damage or failure occurs. Poor connecpon of HV bushing and evidence of compromised flow in two coolers

10 Indica*on and Control Func*onal Verifica*on Component or FuncPon Indica*on Gauges Liquid Level Liquid Temp Winding Temp Gas AccumulaPon Bushing Liquid Level Controls Fan FuncPon Typical IEEE C57.93 and OEM Recommended Maintenance AcPon R1M InspecPon: Note Abnormal IndicaPon Record levels and temperatures in stapon records R1M InspecPon: Confirm Auto and Manual FuncPonality RCM Best PracPce/Strategy 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 R1M InspecPon Confirm Auto and Manual FuncPonality R3Y ITM Control outputs to fan circuits with self checking funcponality

11 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!

12 Alarm and Protec*on - Func*onal Verifica*on Component or FuncPon Mechanical Alarms Liquid Level Liquid Temp Winding Temp Gas AccumulaPon Mechanical Trips Liquid Level Liquid Temp Winding Temp Sudden Pressure Pressure Relief Typical IEEE C57.93 and OEM Recommended Maintenance AcPon D3Y Verify IndicaPon D3Y Verify Alarm to Annuciator Display D3Y Verify Trip ProtecPon RCM Best PracPce/Strategy 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

13 Fiber Op*c Winding Temperature Monitors accurately measure the winding hot spot temperature.

14 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

15 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

16 Internal Condi*on Assessment Component or FuncPon RaPo Adjuster Typical IEEE C57.93 and OEM Recommended Maintenance AcPon No recommendapon RCM Best PracPce/Strategy D3Y Exercise the RaPo Adjuster. Measure winding resistance in all posipons InsulaPon Integrity D3Y- D7Y InsulaPon power factor (Doble ) tests including oil and bushings. Core Ground InsulaPon Resistance (Megger ) Winding Resistance Winding RaPo D3Y InsulaPon power factor (Doble ) tests including oil and bushings. D3Y Core Ground InsulaPon Resistance (Megger ) Oil Integrity R1Y- R3Y Oil Tests (1 liter sample) Dissolved Gas Analysis (Oil Syringe) Furan Analysis R2Y Oil Tests (1 liter sample) R6M Dissolved Gas Analysis R2Y Furan Analysis Online DGA Monitoring

17 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.

18 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.

19 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

20 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 years, celebrate achieving 35 years and repre at 40 years.