Seminario Técnico Pentágono de Duval - Diagnóstico DGA

Practicing DGA

Fault Gas Formation

Note: For faults T3 in paper (C), curve for H2 is a bit higher.

Ref: Duval, TSUG 2013.

2Material Of Dr. Duval

DO NOT REPRODUCE WITHOUT PERMISSION

Occurrence of Faults in Service at CIGRE

Triangle Method

Triangle 4 (using H2, CH4 and C2H6)

Allows to distinguish between:

-Stray gassing of oil at T < 200°C (in zone S)

-Overheating at T < 250°C (in zone O)

-Possible carbonization of paper at T > 300°C, with a probability of 80%, not 100% (in zone C)

-Corona partial discharges (in zone PD).

Triangle 5 (using CH4, C2H4 and C2H6)

Allows to distinguish between:

-Hot spots in oil only at T > 300°C or 700°C (in zones T2 or T3)

-Possible carbonization of paper, with a probability of 90%, not 100%

-For faults O, S, PD, use rather Triangle 4.

Use of Triangles 4 and 5

Triangle 4 should be used only for faults identified first with Triangle 1 as faults PD, T1 or T2, or when there is a high level of H2.

Triangle 5 should be used only for faults identified first with Triangle 1 as thermal faults T2 or T3.

Neither Triangle 4 nor Triangle 5 should be used in case of electrical faults D1 (including sparking PDs) or D2.

When Triangles 4 and 5 do not agree, this often indicates a mixture of faults.

Duval Pentagon 1 (2014):

-The order of gases at the 5 summits of the pentagon corresponds to the increasing energy required to produce these gases, i.e., from H2 to C2H2 counter-clockwise.

Material Of Dr. DuvalDO NOT REPRODUCE WITHOUT PERMISSION

Duval Pentagon 2 (2014):

-Free algorithms for Pentagons 1 and 2 are available from duvalm@ireq.ca.

101010

Detection of Multiple Faults in Transformers:

-First clue is if there is a change in gas pattern. Second clue is if

Triangles 1,4, 5 and Pentagons 1, 2 do not provide the same

diagnosis. This may be an indication of multiple faults.

-this is because each graphical representation is more sensitive to

some gases. For instance, Triangle 4 is more sensitive to H2 and

therefore to faults S or PD than even the Pentagons.

-similarly, Triangle 5 is more sensitive to C2H4 and to faults T3 in oil

than Triangle 1 and the Pentagons.

When to Use the Pentagons and Triangles?-Ask software to indicate for each set of DGA results the fault indicated by Pentagons 1,2 and Triangles 1,4,5 (following the rules for the use of Triangles 4,5).

Display graphically in Pentagon 1 the evolution of DGA points with time. If some of them are in thermal fault zones, switch to Pentagon 2.

When DGA points move with time from one fault zone to another, this means a new fault is appearing. If interested to more precisely identify this new fault, subtract the last gas formation from the new one and add it as DGA point “Delta”.

When the Pentagons and Triangles do not provide the same fault diagnosis for some DGA results, this may indicate multiple faults. If interested to identify them more precisely, display graphically Triangles 1, 4 and/or 5 providing different fault diagnosis (or all of them), in addition to Pentagon 1 or 2.

See examples 19-19 for the interpretation of intermediate mixtures of faults.

121212

Risk of failure vs. type and location of fault

131313

Detection of Low DPs of Paper-CO2, (> 10,000 ppm), CO2/CO (> 20) and furans 2-FAL (> 1 ppm) are

more sensitive than methanol to detect DPs < 400:

Cases of Transformers with Low DPs of Paper

Note: no cases of mechanical failure of paper at low DPs have been reported to CIGRE so far.

161616

90% Typical Concentration Values

at IEC, in ppm

(vs. source)

171717

90% Condition 1 Concentration Values

at IEEE, in ppm

(vs. kV, MVA, age, %O2)

181818

Probability of having a

failure-related event in

service (PFS) in %, vs. the

concentration of all gases

in ppm. T = 90% typical

value; P = pre-failure

value.

CIGRE Gas Concentrations above Typical Values

191919

CIGRE Sampling Intervals between Typical

and Prefailure Concentrations, in ppm

(based on revised condition 1 values in the US of 2010 and

pre-failure values of CIGRE)

202020

CIGRE Sampling Intervals between Typical

and Prefailure Gassing Rates, in ppm/month

(based on gassing rates for condition 1 in the US and pre-

failure gassing rates of CIGRE)

212121

CIGRE Approach Applied to the IEEE

Transformers of 2014

222222

90% Condition 1 Concentration Values

vs. Type of Thermal Fault at CIGRE:

232323

Condition 4 Concentration Values

vs. Type of Fault at CIGRE:

(in ppm, using previous adjustment factors)

242424

Comparison with Cases of High Gas Levels

without Failure at CIGRE:

(in ppm)

252525

#2 - Attempt a fault diagnosis

• Compare lab results or monitor readings with in-house typical values of concentration and gassing rate, or compare with published values (e.g., from IEEE and CIGRE)

• If measured DGA values are above typical values, a fault diagnosis may be attempted

262626

#3a - Evaluate the severity of the fault

•The severity of the fault will depend on:

• The rate of gas formation

• The concentration of gases

• The nature of the fault (electrical or thermal)

• The location of the fault (paper or oil only)

272727

#4 - Actions on the equipment-Increase the frequency of oil sampling

• (as values move from typical values to pre-failure values)

-Determine the dependence of gas formation on load

-Consider complementary tests • (UHF detection of partial discharges, detection of hot spots by infra-red

cameras and acoustic tests)

-For critically located or severely affected equipment, install on-line gas monitors

-For the most severe cases, plan the replacement of the transformer and/or its removal from service and inspection

-Ask for advise of DGA experts

Concentration Limits for Multi-Gas Monitors

Gassing Rate Limits for Multi-Gas Monitors

Fault Detection with Hydrogen Monitors

313131

DGA in LTCs at IEEE:

Triangle 2 for compartment types Triangles 2 for in-tank types

323232

Normal operation zones for in-tank types:

• N or N1 for MR types M and D.

• N or N3 for MR types VR and VV.

• N or N4 for MR types R and V.

• N or N5 for MR types G and UZDs.

• Depending on operating conditions.

• Other DGA examples would be needed for the normal and faulty

operation of these LTCs.

333333

Pentagon 3 for FR3

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