dissolved gas analysis
TRANSCRIPT
DISSOLVED GAS ANALYSIS OF TRANSFORMER OIL
Mrs. Harsha Shah
Insulation Division
DISSOLVED GAS ANALYSIS OF TRANSFORMER OIL
OIL PRODUCES GASES UNDER THERMAL / ELECTRICAL STRSS.
TYPES OF GASES AND RATE OF PRODUCTION DEPENDS ON NATURE AND EXTENT OF STRESS RESPECTIVELY.
PROVEN TO DETECT INCIPIENT FAULT. FACILITY AVAILABLE, NEEDS EXPERTISE
FOR INTERPRETATION OF RESULTS.
DGA
• One of the most important technique to indicate the health of a transformer.
• Analogous to blood testing of Humans to detect various Bio-Logical Abnormalities. However, unlike diagnosis of blood, rules are not clearly established for DGA.
• DGA, An Art & not A Science and interpretation of results much depends on one’s documented experience.
GAS EVOLUATION PROCESS
PRESENCE & QUANTITY OF GASES DEPENDS ON : TYPE /AREA OF FAULT SOLUBILITY & DEGREE OF SATURATION OF
VARIOUS GASES TYPES & RATE OF OIL CIRCULATION TYPE OF OIL PRESERVATION KINDS OF MATERIALS IN CONTACT WITH FAULT
Sampling And Labeling ProcedureSampling
• Dry Weather, avoid contamination• Clean, dry, leak proof glass or stainless
steel container.• Equipment operating normally• Take safety precautions.• Sample bottle must be full without any air
trap completely sealed and should be properly labeled.
LABELLING PROCEDURE
A] IDENTIFICATION OF TRANSFORMER
1. LOCATION
2. MAKE
3. SERIAL NUMBER / TRANSFORMER
NUMBER
4. TRANSFORMER RATING
5. VOLTAGE RATIO
B] HISTORICAL INFORMATION
1. DATE OF COMMISSIONING
2. DATE OF LAST OIL FILLING
3. DATE OF LAST OIL FILTRATION/ DETANKING / TOPPING UP / TRANSFORMER REPAIRS
4. DATE OF SAMPLING
5. OIL VOLUME IN SYSTEM
6. ANY ABNORMALITY IN WORKING
C] OPERATIONAL
1. LOAD ON DUTY : MAX & MIN
2. OIL TEPERATURE : MAX & NORMAL
D] PREVIOUS TEST RESULTS
1. TEST REPORT NO. & DATE IF TESTED AT ERDA
2. TEST RESULTS INCLUDING DATE OF TESTING
IF TESTED IN OTHER LAB
FREQUENCY OF SAMPLING
NEW TRANSFORMERS
FIRST DGA TEST : BEFORE HEAT RUN TEST ON TRANSFORMER
SECOND DGA TEST : AFTER HEAT RUN TEST ON TRANSFORMER (2&24 HRS)
THIRD DGA TEST : BEFORE ENERGIZING TRANSFORMER (B.M.)
FOURTH DGA TEST : WITHIN THREE MONTHS OF SERVICE
IN-SERVICE TRANSFORMERS ANNUALLY AS A ROUTINE CKECKING BEFORE (LATEST DATA) & AFTER FILTRATION
(FRESH B.M.)/TOPPING UP
TRANSFORMERS AFTER OVERHAULING,
REPAIRS, MAINTANANCE BEFORE ENERGISING TRANSFORMER WITHIN THREE MONTHS OF SERVICE
Detection Sensitivity Limit
Sr.No.
Gas DetectionSensitivity
(ppm)1. Hydrogen 52. Oxygen 503. Nitrogen 504. Hydrocarbons 15. Carbon Oxide 25
Interpretation of Results
• Ensure that gas concentrations are high enough to warrant further investigation.
• Gas being present even in normal operating condition without any fault being present.
• Gases might have formed on the occasion of previous faults or during repairs by brazing, welding etc., and not completely removed.
• Since gases are produced in normal ageing also, the service duration of the oil has to be taken into account.
PERMISSIBLE LIMITS OF DISSOLVED GASES IN OIL
OF A HEALTHY TRANSFORMER
GAS <4YRS IN PPM) 4-10 YRS (PPM) >10 YRS (PPM)
H2 100-150 200-300 200-300
CH4 50-70 100-150 200-300
C2H2 20-30 30-50 100-150
C2H4 100-150 150-200 200-400
C2H6 30-50 100-150 800-1000
CO 200-300 400-500 600-700
CO2 3000-3500 4000-5000 9000-12000
Diagnosis of Health of A Transformer / Fault
1. Benchmark Results
2. Permissible Limit
3. IS Ratio Method
4. Muller’s Ratio Method
5. Key Gas Method
6. TCG Content
7. Rate of Rise of Gas
Code of range of ratios
C2H2C2H4
CH4H2
C2H4C2H6
< 0.1 0 1 00.1 – 1 1 0 01 – 3 1 2 1>3 2 2 2
BEFORE & AFTER HEAT RUN TEST
EXISTING METHOD OF INTERPRETATION
NOT SUITABLE FOR NEW TRANSFORMER INITIALLY SMALL QUANTITY OF GASES
DISSOLVED IN OIL DURATION OF TEST IS VERY SHORT VERY SMALL RISE IN GAS CONCENTRATION
NEW GUIDELINE
NEW GUIDELINE IS SUGGESTED BY CIGRE WORKING GROUP FOR THE INTERPRETATION OF DGA RESULTS BEFORE & AFTER HEAT RUN TESTS.
TABLE -4 GAS CONCENTRATION IN OIL B.H.R.T.MIN. DETECTION SENSITIVITY OF EQUIPMENT(Sd) MAX.PERMISSIBLE VALUE OF GASES (X1)
S.NO. GAS Sd PPM (V/V) (X1) PPM (V/V)
1. CO2 10.0 200.0
2. CO 5.0 80.0
3. H2 2.0 15.0
4. CH4 0.1 2.5
5. C2H6 0.1 2.0
6. C2H4 0.1 2.0
7. C2H2 0.1 1.0
Maximum Analytical Spread (Sa)
Sa (x) = 0.1 (x)1 + 2 Sd (x)
x = ANY GAS
(x)1 = ORIGINAL QUANTITY OF GAS X
Sd (x) CAN BE TAKEN FROM TABLE - 4
DIFFERENCE IN CONC. OF ANY GAS BHRT & AHRT IS LESS THAN Sa OF GAS - TR. IS HEALTY.
No. Criteria Range 1 Range 2
1. (C2H2)2 – (C2H2)1 <Sa (C2H2) <Sa(C2H2)
2. 1/t {[H2)2] – (H2)1 +
{[CH4)2 – (CH4)1] +
{[C2H4)2 – (C2H4)1] +
{[C2H6)2 – (C2H6)1]} +
<2 ppm (v/v)/hr. <5 ppm (v / v) hr
3. 1/t [(CO)2 – (CO)1] < 5 ppm (v/v) / hr. < 25 ppm (v / v) hr
4. 1/t [(CO2)2 – (CO2)1] < 20 ppm (v/v) / hr.
< 100 ppm (v / v) hr
5. (C2H4)2 – (C2H4)1
(C2H6)2 – (C2H6)1
< 1 ppm (v/v) / hr. < 3 ppm (v/v) / hr.
• Here t is duration of heat run test in hours, (X)2 and (X)1 are
concentrations of gas X, after and before the test.
• 5 th criteria may only be used if increase in gas concentration of C2H4
& C2H6 BHRT & AHRT are > 10 Sa
INTERPRETATION
• All in Range 1 – No Thermal fault
• One or more are > Range 1 < Range 2 – Fault caused by Load current or Leakage flux * Close monitoring required for oil during service.
• One or more are > Range 2 –*more analysis during heat run test.
FAULT DIAG:THERMAL FAULT OF HIGH TEMP(700oC)FAULT OBSERVED:HOT SPOT IN ONE OF THE
CONNECTING LEADS HAVING JOINT
3.64 MVA, 22.5/1.73 kVDATE OF COMM. 5-2-88RATIOS : 0 2 2H2 1049CH4 6986C2H2 1476C2H4 39998C2H6 6462CO 40773CO2 94998
No Sign of any abnormality from out side.
Fault diagnosis : Thermal Fault
Observation : Presence of hot sport in one of
the connecting leads having joint
F.DIAG:THERMAL FAULT OF MED.TEMP(3000C-7000C)FAULT OBSERVED:BOLT ON STAMPING OF
TRANSFORMER WINDING GOT MELTED
3.22 MVA, 22.5/1.73 kVDATE OF COMM. 28-5-82RATIOS : 0 2 1H2 45CH4 296C2H2 4C2H4 2228C2H6 1292CO 68CO2 1458
No Sign of any abnormality from out side.
Fault diagnosis : Thermal Fault
Observation : Top as well as bottom metallic bolts used to hold stamping of the
transformer winding got melted.
FAULT DIAG : ELECTRICAL DISCHARGESF.OBSERVED:ELECTRICAL SPARKING ON H.T.LEADS
18.4 MVA, 33/0.173 kVDATE OF COMM.OCT `76RATIOS : 1 0 2H2 2113CH4 319C2H2 408C2H4 469C2H6 82CO 1632CO2 4190
Fault diagnosis : Electrical discharges
Observation : Electrical discharges on high
voltage leads inside the main tank
was observed. The wooden planks
used to isolate HV leads clearly
show sign of electrical discharges.
F.DIAG:ELECTRICAL DISCHARGES OF LOW ENERGYF.OBSERVED:WINDING FAILURE
33 kVDATE OF COMM. 1984RATIOS : 2 0 2H2 240CH4 26C2H2 202C2H4 51C2H6 3CO 199CO2 64
Fault diagnosis : Presence of severe electrical
discharges
Observation : Total winding was damaged
significantly
Thank you