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 smallsampling port onside of drain valve.

Always FLUSH Drain valve Before taking samples

Also Flush The tube and Syringe

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

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

GENERATION OF FAULT GASES

CAUSES OF GENERATION OF GASES

PARTIAL DISCHARGE (CORONA)

PYROLYSIS (THERMAL HEATING)

ARCING

▬►LEAST INTENSITY AND ENERGY

▬► SEVERE INTENSITY AND MORE ENERGY

▬► MOST SEVERE INTENSITY AND HIGHEST ENERGY

GASES ARE SHOWN ACCORDING TO MAJOR (MINOR) BASIS

NOTED POINTS1) LEFT STRIP SHOWS GASES DUE TO

PARTIAL DISCHARGE

2) THE GRAPH IS NOT IN SCALE AND IS INDICATIVE ONLY

3) 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 OILRELATIVE 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)

CONDITION I : Indicates Satisfactory operationCONDITION II : May indicate presence of faultCONDITION III : Indicate excessive decomposition of Oil/Insulation, Check gas

generation per day**CONDITION IV : Continued operation could result in failure.

IEEE C57-104-1991 STANDARD

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

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 THAN 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

BUT REMEMBER……..

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

IEC 60599 STANDARD

ROGERS RATIO METHOD OF ANALYSIS

USES 3 RATIOS AS

THIS METHOD IS FOR FAULT ANALYSING AND NOT FOR FAULT DETECTION

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 paper3) 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:-

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

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

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

4) Top oil Temperature should be noted always while taking oil sample.

5) Failure of transformer due to moisture is the most common cause.

Moisture distribution in paper

↑ Comparison of moisture distribution in paper and oil

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

SUMMARY

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-out

@ The DP Indicates the Residual life of the Transformer.

Date of test CO CH4 CO2 C2H4 C2H6 C2H2 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/C2H4CH4/H2

C2H4/C2H6

0

1.55

3

Code 0 2 2

Result 8 Fault over Temp range 700c

QUERIES