Understanding DGA Techniques & Interpretations Presentation

Understanding DGA
Techniques and
Interpretations
P R E S E N T E D B Y
WEB I NAR June 2017

2
Agenda
1. Formation of Gases
2. Types of Faults
3. Fault Identification
4. Diagnostic Methods
Overview
5. DGA Diagnostic Tools
6. DGA Examples

3
01
Formation of Gases
in Transformers

4
Monitoring of Gases in Transformers
As insulating material
breaks down due to
stress, gases form and
dissolve in the
transformer oil
Levels and
combinations of the
gases formed are used
to detect pending or
occurring faults
DGA is the leading tool
to assess transformer
condition and is now a
universal practice
Dissolved Gas Analysis

Which Gases are Generated?
Eight key gases in transformer oil
are associated with fault conditions.
DGA detects the level of gases
indicative of various faults that may
lead to transformer failure.
EthyleneC2H4
MethaneCH4
EthaneC2H6
HydrogenH2
AcetyleneC2H2
Carbon MonoxideCO
Carbon DioxideCO2
OxygenO2
5
INSULATING OIL

8
Types of Faults
Abbreviations Descriptions
PD Partial Discharges
D1 Discharges of Low Energy
D2 Discharges of High Energy
T1 Thermal Fault, t < 300 °C
T2 Thermal Fault, 300 °C < t < 700 °C
T3 Thermal Fault, t > 700 °C

9
Fault Types
PD Partial discharges of the
corona-type
Discharges in gas bubbles or voids
trapped in paper
D1 Discharges of low energy
Partial discharges of the sparking-type
(Inducing carbonized punctures in paper)
Low-energy arcing, inducing surface
tracking of paper & carbon particles in oil
D2 Discharges of high energy
High Energy Arcing or Flashovers
(including Short Circuits)
T1 Thermal faults of
temperatures <300 °C
Overloading or Blocked oil ducts (Evidenced
by paper turning Black/Brown)
T2 Thermal faults of temperatures
between 300 and 700 °C
Defective contacts and/or welds (including
high Circulating currents)
Evidenced by Carbonization of paper and the
formation of carbon particles
T3 Thermal faults of
temperatures >700 °C
Large circulating currents in tank and core
Short circuits in laminations (Evidenced by
formation of carbon particles)
Metal coloration (800 °C) or metal fusion (>1000 °C)

10
Fault Severity
Most severe faults
1. Faults D2 in paper and in oil
(high-energy arcing)
2. Faults T2-T3 in paper (>300 °C)
3. Faults D1 in paper (tracking,
arcing)
4. Faults T3 in oil (>700 °C)
Less severe faults
1. Faults PD/D1 in oil (sparking)
2. Faults T1 in paper (<300 °C)
3. Faults T2 in oil (<700 °C)
4. Are difficult to find by
inspection
A fault in paper is generally considered as more serious than a fault in
oil because paper is often placed in a HV area (windings, barriers)

11
03
Fault Identification
by Gas Type

12
Indication / Faults H2 CO CO2 CH4 C2H2 C2H4 C2H6 O2 H2O
Cellulose aging
Mineral oil decomposition
Leaks in oil expansion systems,
gaskets, welds, etc.
Thermal faults – Cellulose
Thermal faults in oil
@ 150 °C - 300 °C
TRACE
@ 300 °C - 700 °C
TRACE
@ 700 °C
Partial Discharge TRACE
Arcing ●
Fault Identification Chart

13
06
Diagnostic Methods
Overview

14
Diagnostics Methods Summary
Comparison Among: Key Gas Method (KGM), Doernenburg Ratio Method (DRM), Rogers Ratio Method (RRM), IEC
Ratio Method (IRM), and Duval Triangle Method (DTM)
Type Method Fault Types Gases Involved
KGM
Uses individual gas concentrations,
easy to implement, very conservative
PD, arcing, overheated oil, overheated
cellulose
CO, CO2, H2, CH4,
C2H2, C2H4, C2H6
DRM
Uses four gas concentration ratios
(CH4/H2, C2H2/C2H4, C2H2/CH4,
C2H6/C2H2) to indicate three fault
types, uses specified concentration
limits to differentiate between faults
Thermal decomposition, PD, arcing
H2, CH4, C2H2,
C2H4, C2H6
RRM
Uses three gas concentration ratios
(C2H2/C2H4, CH4/H2, C2H4/C2H6)
PD, arcing, low temperature of thermal
fault, thermal <700 °C, thermal >700 °C
H2, CH4, C2H2,
C2H4, C2H6
IRM
Similar to RRM but excludes the
C2H6/CH4 ratio, indicates six fault
types, uses specified concentration
limits to differentiate between faults
PD, low energy discharge, high energy
discharge, thermal faults <300 °C, between
300 and 700 °C, and greater than 700 °C
H2, CH4, C2H2,
C2H4, C2H6
DTM
Uses triangular map to indicate six
faults, does not identify a normal
state
PD, low energy discharge, high energy
discharge, thermal faults <300 °C, between
300 and 700 °C, and greater than 700 °C
CH4, C2H2, C2H4

15
Results are shown in the following Table
The diagnostic tools
have been tested to
determine the accuracy
of each method in
predicting a fault.
Based upon a database
of over 100 test cases
within the IEC data
bank indicating the
gases observed with a
physical inspection of
the type of failure.
Performance was
separated into –
“No Diagnostics”,
“Wrong Diagnostics”
and “Unresolved
Diagnostics”

16
% Correct
Diagnoses
% Unresolved
Diagnoses
% Wrong
Diagnoses
KGM 42% 0% 58%
RRM 62% 33% 5%
DRM 71% 26% 3%
IRM 77% 15% 8%
DTM 96% 0% 4%
KGM = Key Gas Method
RRM = Rogers Ratios Method
DRM = Doernenburg Ratios Method
IRM = IEC Ratios Method
DTM = Duval Triangle Method

17
04
DGA Diagnostic Tools
Procedures and Methods

18
Standards and Guidelines
IEEE Std. C57.104 2008
IEEE Guide for the
Interpretation of Gases
Generated in Oil Immersed
Transformers
IEC 60599-2015
Mineral Oil Impregnated Electrical
Equipment in Service: Guide to the
Interpretation of Dissolved and Free
Gas Analysis

19
Diagnostic Tools for DGA
Analysis Tool
Reference Standard
IEEE C57.104-2008 IEC 60599-2015
TCG Procedure ✔
TDCG Procedure ✔
Key Gas Method ✔
Doernenburg Ratios ✔
Rogers Ratios ✔
Basic Gas Ratios (IEC Ratio) ✔
Duval Triangle ✔
CO2/CO Ratio ✔ ✔
O2/N2 Ratio ✔
C2H2/H2 Ratio ✔

20
Key Gas Method
Key Gas Method
Considered as a modification of the
TDCG procedure.
Permits a tentative determination of
possible fault types empirically
determined from a transformer’s
unique gas profile.
Focuses on which gas is the largest
portion of TDCG (the “key” gas).
Useful for benchmarking in the normal
range, and to confirm diagnoses in the
warning range.
Limitations
High tendency to return inconclusive
results.
If a severe fault occurs and involves the
paper insulation, all gases will be high
yet insufficient to register a fault if
using the specified values according to
the standard.

21
Key Gas Method
Key Gas Method (IEEE Std. C57.104-2008)
Key Gas Fault Type Typical Proportions of Generated Combustible Gases
C2H4 Thermal oil
Mainly C2H4; Smaller proportions of C2H6, CH4, and H2;
Traces of C2H2 at very high fault temperatures
CO Thermal oil and cellulose
Mainly CO; Much smaller quantities of hydrocarbon;
Gases in same proportions as thermal faults in oil alone
H2
Electrical Low Energy Partial
Discharge
Mainly H2; Small quantities of CH4; Traces of C2H4 and C2H6
H2 & C2H2
Electrical High Energy
(arcing)
Mainly H2 and C2H2; Minor traces of CH4, C2H4, and C2,H6;
Also CO if cellulose is involved

Key Gas Levels
22
Condition 1= normal
Condition 4= highest alarm level

24
Rogers Ratios / Basic Gas Ratios
Rogers Ratios /
Basic Gas Ratios
Similar to Doernenburg ratios.
Suggests five to six general fault
types via three ratios from five
fault gases.
Limitations
Ratios generated often yield results
not falling into any of the suggested
fault types.

25
Rogers Ratios
Concentration of Dissolved
Gas
Key Gas
L1
Concentrations
(ppm)
Hydrogen (H2) 100
Methane (CH4) 120
Carbon Monoxide
(CO)
350
Acetylene (C2H2) 35
Ethylene (C2H4) 50
Ethane (C2H6) 65
Ratios for Key Gases – Rogers Ratios Method
Case
Ratio 2 (R2)
C2H2/C2H4
Ratio 1 (R1)
CH4/H2
Ratio 3 (R3)
C2H4/C2H6
Suggested Fault Type
0 <0.01 <0.1 <1.0 Normal
1 ≥1.0 ≥0.1, <0.5 ≥1.0
Discharge of low
energy
2 ≥0.6, <3.0 ≥0.1, <1.0 ≥2.0
Discharge of high
energy
3 <0.01 ≥1.0 <1.0
Thermal fault, low
temp <300 °C
4 <0.1 ≥1.0 ≥1.0, <4.0 Thermal fault, <700 °C
5 <0.2 ≥1.0 ≥4.0 Thermal fault, >700 °C

26
CO2 vs. CO Ratio
CO2/CO
Ratio
Thermal
decomposition state
<3 Excessive
>7 Normal
<10 Normal
>10 Excessive
This ratio may be used as an
indicator of thermal
decomposition of cellulose.
Levels should exceed minimum values
for the ratio to be valid
• CO > 500 ppm
• CO2 > 5,000 ppm
Best used as a complement to other
diagnosis methods for a more accurate
assessment
CO2/CO

27
O2/N2 Ratio
O2/N2
At equilibrium, the O2/N2 ratio is
close to 0.5, reflecting air
composition. (This takes into
account the relative solubility of
O2 and N2)
An O2/N2 ratio of less than 0.3 is
generally considered to indicate
excessive O2 consumption,
meaning O2 is consumed more
rapidly than it is replaced by
diffusion.
This ratio may be used as an
indicator of oil oxidation
and/or paper aging. It is best
when combined with other
methods.
Dissolved O2 and N2 may be found in oil:
• As the result of contact with the
atmosphere in the conservator of an
air-breathing transformer.
• Via leaks in sealed equipment.

28
TCG & TDCG Procedures
Focuses on monitoring Total Combustible Gas
and Total Dissolved Combustible Gas levels.
TDCG
The sum of all combustible
gases that are dissolved in the
insulating oil.
H2+CH4+C2H2+ C2H4+C2H6+CO
Total Dissolved Combustible Gas
Limitations
May detect high TCG or TDCG
concentrations suggesting a fault is
present, when these generation rates
are actually stable for the transformer.
Do not offer any value regarding the
fault type, so it is recommended to
combine them with other diagnostic
tools.
TCG
The sum of all combustible gases
reported as a % of the transformer
gas space.
H2+CH4+C2H2+ C2H4+C2H6+CO
Total Combustible Gas %

29
TCG Procedure
TCG
level in %
TCG Rates
%/day
Sampling
Intervals
Operating
Procedures
Condition 1 <0.5
<0.01 Annually
Continue normal operation.
0.01 ~ 0.3 Quarterly
>0.03 Monthly
Exercise caution.
Analyze for individual gases.
Determine load dependence.
Condition 2 >0.5 ~ <2.0
<0.01 Quarterly Exercise caution.
0.01 ~ 0.3 Monthly
>0.03 Monthly
Condition 3 >2.0 ~ <5.0
<0.01 Monthly Exercise extreme caution.
Plan outage.
Advise manufacturer.
0.01 ~ 0.3 Weekly
>0.03 Weekly
Condition 4 >5.0
<0.01 Weekly
Exercise extreme caution.
Plan outage.
0.01 ~ 0.3 Daily Consider removal from service.
Advise manufacturer.>0.03 Daily

30
TDCG Procedure
TDCG level
in ppm
TDCG Rates
(ppm/day) 1
Sampling
Intervals
Operating
Procedures
Condition 1 <720
<10 Annually
Continue normal operation.
10-30 Quarterly
>30 Monthly
Exercise caution.
Condition 2 721 to 1,920
<10 Quarterly Exercise caution.
10-30 Monthly
>30 Monthly
Condition 3 1,921-4,630
<10 Monthly Exercise extreme caution.
Plan outage.
10-30 Weekly
>30 Weekly
Condition 4 >4,630
<10 Weekly
Exercise extreme caution.
Plan outage.
10-30 Daily Consider removal from service.
Advise manufacturer.>30 Daily

31
C2H2/H2 Ratio
C2H2/H2
A C2H2/H2 ratio higher than
2.0 to 3.0 in the main tank
indicates possible OLTC
contamination.
Best used in combination
with other diagnosis
methods.
OLTCs (On-Load Tap Changers)
produce gases corresponding to
discharges of low energy (D1).
The pattern of oil decomposition in the
OLTC differs from the pattern of oil
decomposition in the main tank resulting
from low energy discharges.
If oil or gas contamination
(communication) exists between the OLTC
and the main tank, an incorrect diagnosis
of the main tank may result.

32
Doernenburg Ratios Method
Doernenburg
Ratios Method
Suggests three general fault types
based on the calculation of four
ratios based on five key gases.
Limitations
Ratios generated often yield results
not falling into any of the three
suggested fault types.

33
Doernenburg Ratios
Concentration of Dissolved Gas
Key Gas
L1 Concentrations
(ppm)
Hydrogen (H2) 100
Methane (CH4) 120
Carbon
Monoxide (CO)
350
Acetylene (C2H2) 35
Ethylene (C2H4) 50
Ethane (C2H6) 65
Ratios for Key Gases – Doernenburg Ratio Method
Suggested
Fault
Diagnosis
Ratio 1
(R1)
CH4/H2
Ratio 2 (R2)
C2H2/C2H4
Ratio 3 (R3)
C2H2/CH4
Ratio 4 (R4)
C2H6/C2H2
Oil
Gas
space
Oil
Gas
space
Oil
Gas
space
Oil
Gas
space
Thermal
Decomposition
>1.0 >0.1 <0.75 <1.0 <0.3 <0.1 >0.4 >0.2
Corona (Low
Intensity PD)
<0.1 <0.01 Not Significant <0.3 <0.1 >0.4 >0.2
Arching (High
Intensity PD)
>0.1
<0.1
>0.01
<0.1
>0.75 >1.0 >0.3 >0.1 <0.4 <0.2

34
Summary of the Ratio Methods
One drawback of these
ratio methods is that no
diagnosis can be given in
a significant number of
cases, “Dead Zones” - fall
outside defined zones.
The Basic Gas Ratio,
Rogers Ratios, and the
Dornenburg methods
all use the same 3 basic
gas ratios:
Depending on the values
of these gas ratios, codes
or zones are defined for
each type of fault
CH4/H2
C2H2/C2H4
C2H6/C2H4

36
Duval Triangle Method
The Triangle, developed empirically in the
early 1970s, and is used by the IEC.
Based upon the 3 gases (Methane (CH4),
Ethylene (C2H4), and Acetylene (C2H2)
corresponding to the increasing energy
levels of gas formation.
One advantage of this method is that it
always provides a diagnosis, with a low
percentage of wrong diagnoses.
There are no indeterminate diagnostics
using the Triangle method.
High Quality
Application
01
CH4
02
C2H4
03
C2H2

37
The Duval Triangle: (per IEC 60599 Guidelines)
PD = Partial Discharges
D1 = Discharges of low energy
D2 = Discharges of high energy
T1 = Thermal fault, < 300 °C
T2 = Thermal fault, >300 °C and <700 °C
T3 = Thermal fault, >700 °C
DT = Discharge or Thermal
indeterminate zone
Gas percentages add to 100%
- 2 gases indicates problem
- 3rd gas confirms

38
Triangle Method FAQ’s
01
They are based on a
large number of cases
of faulty transformers in
service which have
been inspected visually.
How have fault zones been
defined in the Triangle?
02
The root cause of the
failure was determined
and matched to the
DGA data.
03
The Triangle was tested
with all these cases and
correctly identifies the
zone that matches the
root cause of failure at
a very high percentage.

39
Triangle Method FAQ’s
In the Triangle method, why not use
Hydrogen (H2) rather than Methane
(CH4) to represent low energy faults?
01
CH4 provides better overall
diagnoses for all types of faults
02
H2 diffuses much more rapidly than
hydrocarbon gases from transformer oil.
This will affect gas ratios using H2 but
not those using hydrocarbon gases.

40
Using the Triangle Method
STEP 1
If, for example, the DGA
lab results are:
Methane, CH4 = 100 ppm
Ethylene, C2H4 = 100 ppm
Acetylene, C2H2 = 100 ppm
STEP 2
First
calculate:
CH4 + C2H4 + C2H2 = 300 ppm
STEP 3
Then calculate the relative % of each gas:
Relative % of CH4 = 100/300 = 33.3 %
Relative % of C2H4 = 100/300 = 33.3 %
Relative % of C2H2 = 100/300 = 33.3 %
To verify that the calculation was done
correctly, the sum of these 3 values should
always give 100%, and should correspond
to only one point in the triangle
These values are the triangular coordinates to
be used on each side of the triangle.

41
DUVAL TRIANGLE (IEC 60599-2007-05)
ZONE FAULT INDICATION
T1 Thermal fault, ≤300 °C
T2 Thermal fault, >300 °C, ≤700 °C
T3 Thermal fault, >700 °C
D1 Discharges of low-energy
D2 Discharges of high-energy
DT
Combination of thermal faults
and discharges
PD Partial discharge

42
The calculation of
triangular coordinates can
easily be done manually,
or with the help of a small
algorithm or software
For those familiar with
computer graphics, it is
also possible to develop
a software displaying the
point and the fault zones
graphically in the triangle
Software from vendors
is available and MS
Excel worksheets can be
found on the web.

43
07
DGA Diagnostics
Examples

44
Example #1 Gas Levels
Reading Acetylene Methane Ethylene
1 0.4 118 105
2 0.8 120 110
3 1.1 130 117
4 1.1 148 120
C2H4 C2H2 CH4
47.00% 0.18% 52.82%
47.66% 0.35% 51.99%
47.16% 0.44% 52.40%
44.59% 0.41% 55.00%

45
Duval Triangle analysis shows
T2 fault condition (in range of
300-700 ⁰C) increasing in
direction of T3 ( greater than
700 ⁰C)
Duval Triangle as shown in the IEC 60599 Gas Guide.
Example #1 Results

Understanding DGA Techniques & Interpretations Presentation

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