Dga Analysis For Transformer Condition Monitoring

LIFE MANAGEMENT OF TRANSFORMERS AND REACTOR BY DGA ANALYSIS

Transformer Maintenance:-A Combination of actions carried out to return

an item to, or restore it to, an acceptable condition.

Preventive Maintenance:- Maintenance carried out at predetermined intervals, or to other prescribed criteria and intended to reduce the likelihood of an item not meeting an acceptable condition (i.e. Condition Monitoring)

Various methods of preventive Maintenance:•SFRA •Tan♪ •DGA •Infrared Thermography

DISSOLVED GAS ANALYSIS • IMPORTANCE OF TRANSFORMERS IN THE SYSTEM

• Importance Of Oil In Transformer 1) Provides Insulation 2) Acts as the Cooling Media 3) Dissolves moistures and gases as the result of Deteriotion of insulation 4) May extinguish Arc during Fault*

THE DGA INCLUDES:-Oil Sampling -Analysis -Results Interpretation

Taking Out OIL SAMPLE

Use GOOD Syringe, The Test Results are as Good as Syringe

Do Not use small sampling port on side of drain valve.

Always FLUSH Drain valve Before taking samples

Also Flush The tube and Syringe

Do not pull back on the syringe barrel – apply slight Resistance and allow fluid pressure to fill syringe

Syringe should not have any Bubble Initially ,which may form later, if so do not let them release

GENERATION OF FAULT GASES

CAUSES OF GENERATION OF GASES GASES ARE SHOWN ACCORDING TO MAJOR (MINOR) BASIS

PARTIAL DISCHARGE (CORONA) PYROLYSIS (THERMAL HEATING) ARCING

▬►LEAST INTENSITY AND ENERGY ▬► SEVERE INTENSITY AND MORE ENERGY ▬► MOST SEVERE INTENSITY AND HIGHEST ENERGY

NOTED POINTS 2) LEFT STRIP SHOWS GASES DUE TO PARTIAL DISCHARGE 4) THE GRAPH IS NOT IN SCALE AND IS INDICATIVE ONLY 6) SMALL AMOUNT OF H2,CH4 AND O2 ARE FORMED BY NORMAL AGING 4)

DECOMPOSITION OF INSULATION (CELLULOSE) STARTS NEARLY AT 100ºC

SOLUBILITY OF GASES IN OIL RELATIVE SOLUBILITY AS THE FUNCTION OF OIL TEMPERATURE

Analysis Types - Total combustible gas analysis - Multi-gas analysis I) Total Combustible Gas Analysis • Includes Gases Like • Quantity of gases are measured in part per million (ppm) •Standards Used in this seminar@ IEEE C-57-104-1991 @ IEC 60599[12] PAPER 18

FOUR CONDITION BASED GAS ANALYSIS ( BASED ON IEEE-C 57-104-1991 Std Table 4)

IEEE C57-104-1991 STANDARD

CONDITION I : Indicates Satisfactory operation CONDITION II : May indicate presence of fault CONDITION III : Indicate excessive decomposition of Oil/Insulation, Check gas generation per day** CONDITION IV : Continued operation could result in failure.

Action Based on Total Dissolved Combustible Gas Analysis (TDCG) (BASED ON IEEE C 57-104-1991 Table-5)

BUT REMEMBER……..

1) THERE IS NO ‘QUICK AND SURE’ INTERPRETATION

2) ONLY ON THE BASIS OF DGA NEVER MAKE DECISION B’COZ WRONG SAMPLING,MISHANDELING, EASY CONTAMINATION,MIS-LABELING

3) THE RATE OF RISE OF GAS/ SUDDEN RISE OF GAS IS MORE IMPORTANT THA THE AMOUNT OF GAS (EXCEPT ACETELYNE C2H2) 4) THERFORE WE REQUIRES PROPER RECORD OF DGA 5) AN INCREASING GAS GENERATION RATE INDICATES A PROBLEM OF

INCREASING SEVERITY

NON-COMBUSTIBLE GASES: (N2,O2,CO2)  THESE GASES CAN BE A RESULT OF LEAKAGE  CO2 AND O2 ARE FORMED BY DEGRADATION OF CELLULOSE  N2 IN OIL MAY HAVE COME FROM SHIPPING OF TRANSFORMER BUT SHOULD HAVE CONSTANT LEVEL,INCREASE IN N2 INDICATE POSSIBLE LEAKAGE OR MIS-HANDLING OF SAMPEL

ROGERS RATIO METHOD OF ANALYSIS  USES 3 RATIOS AS

THIS METHOD IS FOR FAULT ANALYSING AND NOT FOR FAULT DETECTION

IEC 60599 STANDARD  IS A POST FAULT ANALYSIS METHOD

 IF GASES USED FOR RATIO ARE LESS THAN 10% OF AMOUNT OF GAS CHROMATOGRAPH DETECT,THE METHOD IS NOT RELIABLE

CARBON DIOXIDE TO CARBON MONOXIDE RATIO CO2 & CO ARE FORMED BY DEGRADATION OF OIL IMPREGNATED PAPER & INCREASES RAPIDELY WITH TEMPERATURE Normally ratio is nearly 7 Not included in Rogers Analysis If the ratio is less than 3 indicates probable paper involvement of electric fault (arcing sparking) Ratio Greater than 10 indicate paper involvement of Thermal fault (Hot-Spot) If suspect arises one should go for Furan analysis

FURANS:

•Useful for estimation of residual life of transformers • Are the family of organic compounds formed by degradations of insulation paper •Changes in furanic number(concentration) are more important than individual number

MOISTURE IN TRANSFORMER OIL EFFECTS Decrease Di-electric strength • • Degrades cellulose (Insulation Paper) • Failure risk •Is the worst enemy of Transformer From where moisture comes in:1) formed by degradation of insulation as transformer ages. 2) Present in the insulation paper 3) Leakages if any (majorly in gasket seals)

Measurement of Moisture (By DGA) -Moisture is measured in ppm -Also expressed as moisture/dry weight i.e M/DW -It can Also be expressed as % Saturation of water in oil (Expressed as the % of moisture in oil compared with the maximum amount of moisture the oil can hold.)

Dissolved Moisture in oil

Fig:- Transformer % Saturation Curve

Important points related moisture in oil:•

A new transformer should have M/DW less than 0.5%

•

When M/DW is reached to 2% a plan should be made for Xmer dry out

•

Never Allow M/DW to go above 2.5% or 30% oil Saturation without transformer dry-out

10)Top oil Temperature should be noted always while taking oil sample. 12) Failure of transformer due to moisture is the most common cause.

↑ Comparison of moisture distribution in paper and oil

 Moisture distribution in paper

SUMMARY  Used to find electrical & thermal fault in transformer  Fault can be found at incipient stage  Remedial measure can be initiated to avoid major damage to transformer  Avoid sampling in rainy or foggy weather  Protect sample from direct light  Avoid moisture & dust contamination  Cotton waste & other fibrous materials should not be used  Use the sampling containers exclusively for transformer oil sampling

✈ Testing

transformer oil periodically once a year as per IS:1866-2000 will improve the performance of transformer & conserve transformer oil

✈ DGA

is a powerful diagnostic tool for predicting internal condition of transformer

@ Rate of rise of gas is more important than amount of gas @ While Taking Sample one should note top oil temperature @ Rogers Ratio Method is for fault analysis (post fault) @ N2 Gas can be act as a key gas for identifying probable leakage or sample mishandling @ The M/DW For a new Transformer should be less than 0.5%

@ Transformer with M/DW Greater than 2.5% must be subjected to dry-ou @ The DP Indicates the Residual life of the Transformer.

Date of test

CO

CH4

CO2

C 2 H4

C 2 H6

C 2 H2

H2

Remark

22.09.07

17

-

115

-

-

-

4

Commissioning value

10.04.08

14

121

315

332

58

1

21

20.08.08

91

262

2100

1698

503

5

189

22.09.08

95

301

2199

1740

555

6

193

Bottom sample

22.09.08

94

303

2201

1755

565

6

195

Top sample

Rogers Ratio C2H2/C2H4 CH4/H2 C2H4/C2H6

0 1.55 3

Code 0 2 2 Result 8 Fault over Temp range 700c

QUERIES