1010 Basics of Transformer Cm

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TRANSFORMER CONDITION MONITORING

BASICS of TRANSFORMER CM

1. Introduction to TRANSFORMER MAINTENANCE

2. TEMPERATURE SENSING

3. VIBRATION MONITORING

4. PARTIAL DISCHARGES (ACOUSTIC EMISSION)

5. MOISTURE MONITORING

6. GAS MONITORING DGA

7. Examples of SYSTEM SOLUTIONS

8. ENDING









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Ver. 2011-12-01 [email protected] : 00:01Page: 4 of 80; Part 10.1 Basics of TRANSFORMER CM

TYPES OF TRANSFORMER FAULT

• Phase-ground faults - from winding to core or winding totank

• Phase-phase faults - between windings• Interturn faults - between single turns or adjacent layers

of the same winding• Arcing contacts• Local hotspots caused by shorted laminations• External faults causing thermal or mechanical damage• Overloads


TYPES OF TRANSFORMER FAULT

• Low level internal partial discharges (moisture ingress or design problems)

• Bushing faults (internal to the tank)• Tapchanger faults (often housed in a separate

tank)• Terminal faults (external to the tank, but inside

the transformer zone)


Role of the Transformer

No Transformer No Power Delivery

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Impact of Transformer Failure

No Power Delivery = Loss of Revenue $$$Power may have to be purchased to meet

contractual obligations $$$Direct Replacement Cost $$$

Bad Publicity & Environmental Damage


Typical Utility Transformer Fleet

Approx 60% are >35yo(End of Life region)

Approx 8% are <10yo

(Design Flaw Region)


Transformer Failure

There are 3 types of Transformer Failure: 1. Sudden/unexpected due to outside

influences 2. Design flaw3. End of Life

Failure risk can be reduced by monitoring the Transformer Condition

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Predicted End of Life Failure Rate

Failure distribution for a fleet of Transformers installed between 1964 and 1992

Significant Rise in

# of Failures

Source: William H Bartley & Rowland I James Jr.


Transformer Users’ Pain{ evaluation from beg of 2000’s }

There were typically 730 transformer fire and explosions per year in the USA.

Many experts anticipate that this number to go up from 1% at beginning of 2000’s to 2% after 2010.

The emphasis on renewable will put more burden on the existing Transformers


Why do Transformers Explode?A growing concern for Corporate Risk Managers and Insurance Companies

Transformers are considered by Corporate Risk Managers and Insurers as the most critical equipment inside plants because of • the large quantity of oil • in contact with high voltage elements.

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Why do Transformers Explode?Loose international transformer norms and lack of regulation

The Norm IEC 76 only includes basic electrical measurements and does not cover mechanical design or protection. By comparison, pressure vessels have to comply with adequate rules and controls. Such directives do not exist for transformers that have proven to be more dangerous


Why do Transformers Explode?Transformer electrical and mechanical protection limits

• Pressure Relief Valve inadequacy: pressure gradients developed during low impedance faults are too fast for mechanical devices. All transformers that have exploded have been protected with Pressure Relief Valves.



• Buchholz and Rapid Pressure Relay inefficiency:• Transformer electrical protections are not

designed to react to sharp pressure gradients. • During the 62 Transformer Protector tests, the

Buchholz always failed to detect any gas and oil movement or pressure variation.

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Electrical Breaker opening time:• the best breaker technology trips in 50 ms• far too late to prevent the explosion, • which occurs 10 to 50 ms after the low

impedance fault.

Additionally, the tank pressure

keeps increasing after breaker opening



Transformer Monitoring can Mitigate……

1 Transformer / FAILURE

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Varioussystems


Temperature Monitor• Every 6° to 8° C rise in operating temperatures,

the expected life of the transformer will go down by half

• These temperature build-ups cause localized area of high heat and paper damage, followed by events of partial discharge .

• One needs to have a long term trending of the operating temperature inside the transformer.

• Should be performed distributed temperature sensing of all the windings

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Overtemperature Monitoring

Two temperatures must be monitored:

> Winding temperature (‘WT’) - this can rise rapidly, without much of an increase in oil temperature

> Oil temperature (‘OT’) - this can rise slowly to a critical point without an unacceptable windingtemperature increase


Typical alarm and trip levels(dependent on asset management policy)

• winding alarm - 90ºC to 110º C• winding trip - 110ºC to 135ºC• oil alarm - 80ºC to 95ºC• oil trip - 95ºC to 115ºC• Oil trip may be disabled if transformer is

readily accessible by maintenance crews – on the grounds they can visit sub and may beable to remedy problem this is a controversial practice.


Temperature vs life

• Economic gains are possible from short time overloads - “life used” calculations may permithigher temperatures for short periods, but WTtrip needs to be more complex or monitored

• 110 ºC winding hot spot temperature gives‘standard’ 20-25 year life of insulation

• Roughly every 7 ºC increase in temperaturedoubles the rate of loss of life for paper in oilinsulation

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END WINDING TEMPERATURE SENSING

By incorporating fiber-optic sensors into transformer windings temperature data can be used to monitor for hot spots within the transformer and to provide ratings based on safe operating temperatures. Alternatively, a fiber-optic cable can be installed after the windings have been wound on the core, or fiber-optic point sensors can be placed at strategic locations.


FO Cable part of Distributed Temperature Monitoring









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Varioussystems


How about Vibration monitoring

There are significant differences in the low frequency vibration signal amplitudes and frequency content, dependent on the degree of winding looseness.


Low frequency vibration measurement..... symptoms:

I. Detection of significant difference in low frequency response,

II. Shift of existing resonance, III. Creation of new resonance, IV. Change in shape of various plots would potentially

indicate mechanical or electrical problem with I. the winding and II. transformer core

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Vibration Severity Criteria for Transformers{velocity sensor data - Eng units: ips }

Started with the following overall levels.0.25-.50 ips-…Minor

0.50-.75 ips-… Intermediate Watch list (further investigate)

0.75-1.0 ips-… Serious Look for oil leaks, hot metal gasses and increasing sound levels.

1.00 ips or greater-…Critical Oil leaks, gas generation rates and hot spots.


Vibration Severity Criteria for Transformers {velocity sensor data - metric units: mm/s }

Started with the following overall levels:

4,5 – 9,0 mm/s-…Minor

9,0-13,5 mm/s -… Intermediate Watch list (further investigate)

13,5-18,0 mm/s -… Serious Look for oil leaks, hot metal gasses and increasing sound levels.

> 18,00 mm/s -…Critical Oil leaks, gas generation rates and hot spots.


Vibration Severity CriteriaAlarm Parameters for Transformers [ips]

Nominal Freq / Hz Frequency / Hz Label Name Warning Alert Danger

5 to 115 Sub-sync 0.05 0.1 0.25

120 115 to 125 One Times 0.25 0.5 1.0

125 to 235 1st Odd 0.1 0.2 0.3

240 235 to 245 Two Times 0.15 0.25 0.5

245 to 355 2nd Odd 0.1 0.2 0.3

360 355 to 365 Three Times 0.15 0.25 0.5

365 to 375 3rd Odd 0.1 0.2 0.3

480 375 to 485 Four Times 0.1 0.2 0.3

485 to 1000 Hi End 0.1 0.2 0.3

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Vibration Severity CriteriaAlarm Parameters for Transformers [mm/s]

Nominal Freq / Hz Frequency / Hz Label Name Warning Alert Danger

5 to (2*fLINE – 5) Sub-sync 0.9 1,8 4,5

2*fLINE(2*fLINE – 5) to (2*fLINE + 5) One Times 4,5 9,0 18

(2*fLINE + 5) to (4*fLINE – 5) 1st Odd 1,8 3,6 5,4

4*fLINE(4*fLINE – 5)

to (4*fLINE + 5) Two Times 2,7 4,5 9,0

(4*fLINE + 5)to (6*fLINE – 5) 2nd Odd 1,8 3,6 5,4


to (6*fLINE + 5) Three Times 2,7 4,5 9,0

(6*fLINE + 5) to (8*fLINE – 5) 3rd Odd 1,8 3,6 5,4


to (8*fLINE + 5) Four Times 1,8 3,6 5,4

(8*fLINE + 5) to 1000Hi End 1,8 3,6 5,4


Where to measure the vibrationsHIG H SIDE

SIDE #2

SIDE #4

H ILO

25C

X X

X

X

SIDE #3

LTC

X XX

X

Eight readings ~ Approx 1,6 m from “bottom of core”, and 45 cm from corner

Shell Form


Where to measure the vibrations

High Voltage Side

Side 1L Side1R

Side 2L

Side 2R

Side 3R

Side 4R

Side 3L

Side 4L

0.15@240

0.09@360 0.22ips

0.9ips

0.05ips

Overhead View of Transformer

Snd=80db

AE=35Cts

Snd=78db

AE=30Cts

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8. ENDING


Major Failure Mechanisms

Aging of paper

Moisture in oil

Looseness –movement of the windings


For the Aging of PaperThe occurrence of PD reveals the existence of dielectric insulation problems within the circuit breaker and the windings. Typically the higher the emitted power and frequency of occurrence, the higher the chance of failure by dielectric breakdown. PD can be measured:

- On-Line or - Off-Line.

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Electrical PD diagnostic techniquesPD measuring circuits according to IEC 60270

a) coupling device in series with the coupling capacitor b) measurement at a bushing tap

Components:AC voltage source U, optional blocking impedance Z, coupling capacitor CK, measuring impedance Zm, a measuring instrument M and generalized test object Ca.

[König, 1993]

frequently used circuit in test laboratories

often applied in on-site/on-line PD investigations


Electrical PD diagnostic techniquesPD Measuring Impedance for Bushing Tap Installation

500 kV Transformer Bushing

Decoupling of PD signals from the bushing tap

in a wide frequency range up to 30 MHz

Lower cut-off frequency < 60 kHz

Additional voltage signal for phase-resolved

measurements

Superimposed PD and test voltage signal

Very fast and safe over-voltage protection

TNC-socket for signal output

Special feature for continuous PD monitoring

(IP 68)


Electrical PD diagnostic techniquesAdvanced solution: ACOUSTIC EMISSION added

Acoustic methodElectromagnetic (UHF) method

measuring system

Sound field (acoustic wave)

Piezo-Sensor

PD (partial discharge)

)))))) ))))))

)) ) )) )

) ))) ))

measuring system

))) Electromagnetic wave

example sensor „monopole“

Key characteristics:

non-destructive on-line application of the sensors (no bushing tap necessary)immunity against a wide range of disturbing signals on-site (e.g. corona)

no apparent charge information is delivered so far PRPD patterns possible short arrival timesgeometric PD location possible

very low attenuation in oil and solid insulationsignal attenuation depends on PD site

very low noise level („faraday´s cage“)in principle immun against electric noises

non-destructive on-line application of the sensors (no bushing tap necessary)immunity against a wide range of disturbing signals on-site (e.g. corona)

no apparent charge information is delivered so far PRPD patterns possible short arrival timesgeometric PD location possible

very low attenuation in oil and solid insulationsignal attenuation depends on PD site

very low noise level („faraday´s cage“)in principle immun against electric noises

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IEC 62478 - IEC Proposal, now already Draft level"Non-conventional PD-measurements"

In the past few years, there has been the development of many so-called non-conventional PD measurement methods. Partial discharges (PD’s) generate pressurewaves, sound, light and electromagnetic waves. These physical effects can be detectedby different sensors and so there is the possibility to detect PD’s with non-conventionalmethods besides the conventional electrical measurement. The main method for PDmeasurement is electromagnetic (HF/VHF/UHF) and acoustic measurements. Also,there have been a lot of papers published using these methods. Therefore, IEC TC42 hasin the meeting of September 1st, 2005 in Beijing, decided to proceed with this new workitem called “Measurement of PD’s by electromagnetic (e.g. UHF) and acoustic methods”and to form a new working group for this task. (......)

The task of this new WG is to collect all the used applications of these methods tocompare them with each other and to look at their frequency range. Anotherdifferentiation of the measuring technique is if it is a narrow bandwidth or a wide bandfrequency measurement technique. This work will also include the use and thetechniques of the different sensors, their frequency range and their sensitivity. Also, itwill investigate the issue of the methods, the possibility of PD location and if acalibration or in minimum a sensitivity check is possible. The WG will start with theelectromagnetic methods and after finishing will move forward to the acousticmethods.


System Check for UHF (on transformers)

Performance Check • Functional check of the whole measuring path including sensors and partial discharge (PD)

acquisition system• not necessarily transmission of electromagnetic waves through the test object , „one-port“

solutions are possible

Sensitivity Check • Emission of electromagnetic waves into the test object necessary and known distance between

sensors and injection location • Pulse Generator injection necessary to determine relation between the apparent charge (pC)

and measured quantities (e.g. V,W,J) through simultaneous measurement • „one-port“ solutions might be possible in relation to the wave length (for compact objects, not

for extended objects)


Instruments classification based on Bandwidth

Frequency Domain Measurement Time Domain Measurem.Class

Mode Zero Span Full Spectra Ultra Wide Band

FrequencyBand

PDPattern

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Advanced tools for PD monitoring – Electromagn. PD TestsCone-shaped active drain valve UHF-sensors

for the decoupling of electromagnetic PD signals

from the inner of an oil-paper-insulated

transformerPD-signals in the UHF frequency range

(mainly 300 MHz – 1 GHz)

sensors support „Performance/Sensitivity Check“ (high-frequency test impulses can be injected

with additionally integrated electrode)

sensor head is grounded (for lower frequencies)sensor application at oil valves, which are

available e.g. for oil filling or draining (liquid

tightness is tested for 120°C warm oil with 5 bar compression)

View from inside the transformer


Type-Test Cone-shaped active drain valve UHF-sensors

Oil pressure estimation Combined temperature/pressure test









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Alternatives of arrival time based positioning

electro-acoustic

(test laboratory or on-site/off-line)

electromagnetic- acoustic

(test laboratory or on-site, off-line or on-line)

1. Mixed-acoustic methods:

all-acoustic

(test laboratory or onsite, off-line or on-line

with reduced sensitivity)

2. All-acoustic methods:

electrical PD

sensor 1sensor 2sensor 3

t

electrical PD

sensor 1sensor 2sensor 3

tt

)z ,y ,(x s1s1s11S

2S

)z ,y ,(x s3s3s33S

)z ,y ,(x s4s4s4

iS

4S

)z ,y ,(x s2s2s2

1D

2D3D

4D

iD)z ,y ,(x sisisiPD

(x, y, z)

)z ,y ,(x s1s1s11S

2S

)z ,y ,(x s3s3s33S

)z ,y ,(x s4s4s4

iS

4S

)z ,y ,(x s2s2s2

1D

2D3D

4D


(x, y, z)

)z ,y ,(x s1s1s11S

2S

)z ,y ,(x s3s3s33S

)z ,y ,(x s4s4s4

iS

4S

)z ,y ,(x s2s2s2

1D

2D3D

4D


(x, y, z)

schematic view of a transformer tank with acoustic sensors

( ) ( ) ( ) ( )212

12

12

1 Sssss Tvzzyyxx ⋅=−+−+−

( ) ( ) ( ) ( )222

22

22


( ) ( ) ( ) ( )23

23

23


( ) ( ) ( ) ( )212

12

12


( ) ( ) ( ) ( )222

22

22


( ) ( ) ( ) ( )23

23

23


Observation equations:

unknowns x, y, z Input parameters:sensor coordinates, sound

velocity, meas. time difference

sensor 1

sensor 2

sensor 3PD

sensor 1

sensor 2

sensor 3PD

triangulation

Advanced tools for PD monitoring Acoustic PD location


Vibration measurements extended with:sound & AE

High Voltage Side

Side 1L Side1R

Side 2L

Side 2R

Side 3R

Side 4R

Side 3L

Side 4L

0.15@240

0.09@360 0.22ips

0.9ips

0.05ips

Overhead View of Transformer

Snd=80db

AE=35Cts

Snd=78db

AE=30Cts









8. ENDING

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Major Failure Mechanisms

Aging of paper

Moisture in oil

Looseness –movement of the windings


Moisture In Oil

Moisture in oil is destructiveto cellulose, especially in thepresence of oxygen.

Presence of moisture willfacilitate partial discharge.

Fiberoptics moisture sensorcan be a part of a CMsolution









8. ENDING

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Varioussystems


Dissolved Gas Analysis (DGA)

Power Transformers contain insulating oilWhen a fault occurs, the oil breaks down generating gasThese gases dissolve into the oil Fault type/severity are indicated by gases present

Traditional Methods of DGA1. Samples collected manually from Transformers 2. Analysis performed by specialist oil laboratories3. Sample collection to analysis ranges from days -> weeks 4. Performed on an regular (6 – 12 month) basis

Commonly accepted as the most effective method of Transformer Assessment


The most important aspects of DGA

• The type of gas created indicates the nature of the fault.

• The rate of increase in these gases indicate the severity of the fault.

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Oil pyrolysis (Thermal Heating)

R eferences:M . Duval, Elect ra,133, 40 (1990 ).T. V. Oommen, Ga s Generat ion in Power T ra nsformers

HYDROGEN H2

METHANE CH4

ETHANE C2 H6

ETHYLENE C2 H4

ACETYLENE C2 H2

GA

S C

ON

STIT

UE

NTS

250 750 1000 1250 1500 1750500Fault Temperature ( °C )

2000


Cellulose pyrolysis (Thermal Heating)Life of paper ~ Life of transformer

R eferences:M. Duva l, Ele ct ra ,133,40 (1990 ).T. V. Oomm en, Gas Ge ne ra tion in Power Transforme rs

GA

S C

ON

STIT

UEN

TS

200 250 300100 500400

CARBON MONOXIDE CO

CARBON DIOXIDE CO2


The problem with manual sampling...

A fault can develop and cause failure between samples. A single sample cannot provide rate of change or fault

severity. Human error – sampling & analysis.

These weaknesses are relatively insignificant given:

Transformer catastrophic failure can occur in hours, days or weeks

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Online DGA for a Transformer


Benefits

Online MonitoringMonitoring unit is connected to TransformerUnit automatically samples oil from TransformerGas extracted from oil, concentration measured Oil sample returned to TransformerProcess repeated

Early fault detection

Defer Capital ExpenditureCondition Based Maintenance

Extend Transformer life

Avoid catastrophic failures

Save Money $$$$


Examples of Discrete Monitoring Products

TRANSPORT X*• Portable DGA

• 7 fault gases + moisture• Simple & reliable

TRANSFIX*• Full 8 gas +

moisture on-line DGA

MINITRANS*• Cost-Effective on-line DGA• Discrete gas measurement

(H2, CO, C2H2 + H2O)

MULTITRANS*• Full 8 gas multi tank DGA

TAPTRANS*• Full 8 gas on-line DGA for

main tank & LTC in one unit

HYDRAN M2• On-line Integrated Monitor

• Gas & Moisture in oil• On-line Models/Data storage

Intellix MO150 • Low Cost Transformer

Monitoring System

SIGMA TX* (TBC)Comprehensive

transformer monitoring & modelling

• Full 8 Gas DGA • Bushing/PD/Cooling System/FO hot spot*Kelman Products

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Online DGA for a Transformer

an EXAMPLE.....


Transformer Failure Case StudyNormal DGA

gas levels

Sample Date/Time

Gas

ppm

val

ue


Transformer Failure Case Study

Sample Date/Time

Gas

ppm

val

ue Gases rise over 3 days as fault occurs – sampling frequency automatically

increases

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Transformer Failure Case Study

Sample Date/Time

Gas

ppm

val

ue

Fault severity high -Transformer removed

from service

Fault occurs rapidly over 8 days –manual sampling would not have

been sufficient to detect









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A COMPLEX MONITORING

SYSTEM

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A 300MVA transformer with a DGA systemand a PD On-Line monitoring installed

FARADAY tMEDIC


Product: System 1 Integrated Substation Purpose: Transformer Monitoring and Diagnostics

Chosen KELMAN products

WAN / LAN

Payoff: Typically 5 to 8 years added life expectancy

HYDRAN FARADAY®, tMEDIC or TMCS™ Units

Process:Monitoring

Modbus Ethernet Scanning Display

Exception Alarm Decision SupportSM


TRANSFIX• Full 8 gas (+ moisture)

On-Line DGA

SIGMA TX (TBC)Comprehensive transformer

monitoring & modelling• Full 8 Gas (+ moisture)

On-Line DGA • Bushing/PD/Cooling System/FO hot spot

Recommended products for Power Generation Area

At less than 1% of the initial Transformer cost:both solutions provide the vital information

to protect & maximise Power Station critical assets

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Ethernet

System 1

Perception Express

Minitrans DGA Monitor Minitrans DGA Monitor

PT2PT1

Parámetro Rango

Hidrógeno (H2) 5 – 5,000 ppm

Acetileno (C2H2) 0.5 – 50,000 ppm

Monóxido de Carbono (CO) 2 – 50,000 ppm

Agua (H2O) 1-100% de Humedad Relativa

DGA en Transformadores de Poder


TP1 – 3 x HFCTs ( High Frequency Current Transformers

PDCheck - Techimp

TP2 – 3 x HFCTs ( High Frequency Current Transformers

PDCheck - Techimp

Ethernet

System 1

Descargas Parciales en Transformadores de Poder


UNIT #3PROTECTION SYSTEM / ESD

{ from BINARY OUTPUTS of the M&PS SYSTEM }

Unit 1





A SERVER OFA HS DIAGNOSTIC SYSTEM:

Unit 2 Unit N...

An example with

TRANSFIX from KELMAN

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The Cost of Transformer Failure

A study by The Hartford Steam Boiler Inspection and Insurance Company (HSB)

estimates the cost of Transformer failure at approx

$10,000 per MVA

HSB has been founded in 1866


The Cost of Transformer Failure

A study by The Hartford Steam Boiler Inspection and Insurance Company (HSB)

estimates the cost of Transformer failure at approx

$10,000 per MVA

HSB has been founded in 1866

COST OF PREVENTIONOnline DGA monitoring can cost less

than 1% of the initial Transformer Cost

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Transformer Life Management


Questions

1010 Basics of Transformer Cm

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