This presentation based on conventional transformer diagnosis techniques which is dissolved gas analysis. In the technique included topics such as Key Gas Method, Gas Ratio Methods, Duval's Triangle, Effect of Stray Gassing in DGA, Partial Discharge Identification using DGA.

1. Shantilal Shah Government Engineering
College, Bhavnagar
ELECTRICAL ENGINEERING
CONDITION MONITORING
GUIDED BY:-
ASST.PROF.P.R.KAPADEEYA
PREPARED BY:- HARDIK RATHOD (140430109052)

2. Conventional
Diagnosis Technique
DISSOLVED GAS ANALYSIS

3. Contents:-
1. Introduction of Dissolved Gas Analysis
2. Key gas method
3. Gas ratio methods
4. Duval’s Triangle
5. Effect of Stray Gassing in DGA
6. Partial Discharge Identification using DGA

4. 1.Introduction:-
 In 1928, Buchholz published the method of diagnosis of fault
in a transformer by testing the gases that evolve rapidly
during the failure of oil-filled transformers.
 Subsequently, it was realized that slowly developing faults
within a transformer would produce gases which will remain
dissolved in oil. As a result such faults could be detected by
analyzing the gases dissolved in oil.

5. 1.Introduction:-
 Hence, DGA monitoring has become a common tool for
condition monitoring of transformers. it is possible to
distinguish faults such as partial discharge, corona, thermal
heating, and arcing in transformers as well as in other oil-filled
equipment.

6. 2.Key Gas Method:-
Gas (ppm) <4 years of service 4–10 years of
service
>10 years of service
Hydrogen (H2) 100–150 200-300 200-300
Methane (CH4) 50-70 100-150 200-300
Ethane (C2H6) 30-50 100-150 800-1000
Ethylene (C2H4) 100-150 150-200 200-400
Acetylene (C2H2) 20-30 30-50 100-150
Carbon monoxide
(CO)
200-300 400-500 600-700
Carbon dioxide
(CO2)
3000-3500 4000-5000 9000-12000
This method is based on the correlation of key gases generated with the fault
type.

7. 2.Key Gas Method:-
Key gases Nature of Fault
Methane (CH4) and Ethane (C2H6) Gradual overheating
CO2 or CO or both Transformer overloaded or operating hot
Ethylene (C2H4) Hot spots in overheated joints, core bolts,
etc
Carbon monoxide (CO) Overheating involving cellulose
insulation
H2 Corona discharge, electrolysis of water or
rusting
H2, CO2 or CO Corona discharge involving cellulose or
severe overloading

8. 3.Gas Ratio Methods:-
 Gas ratio methods are based on correlation of ratio of fault
gas concentrations with incipient fault types. These methods
are convenient, reliable for fault diagnosis, independent of
transformer capacity, and can be computer programmed.
Other Interpretation Techniques:-
 Dornenburg Ratio Method
 Roger’s Ratio Method
 IEC Ratio Method

9. Dornenburg Ratio Method:-
 This method is capable of determining mainly three fault
types: viz. thermal decomposition, corona or low intensity
partial discharge, and arcing or high intensity partial
discharge. This method uses four gas ratios R1(CH4/H2),
R2(C2H2/C2H4), R3(C2H2/CH4), and R4(C2H6/C2H2).

10. Roger’s Ratio Method:-
 Roger’s ratio method is an improvement over Dornenburg
method. It has been found to provide accuracy often higher
than 80 % for dissolved gas analysis. This technique considers
two of the four ratios introduced by Dornenburg, viz. CH4/H2,
C2H2/C2H4, and in addition considers two new ratios, viz.
C2H4/C2H6, and C2H6/CH4.

11. 4.Duval’s Triangle:-
 In the 1970s it was identified that the gas ratio methods has a
disadvantage that some DGA results may not fall within the
ratio codes and hence the diagnosis could remain unresolved.
 To overcome this problem, a graphical method was proposed
by Duval in 1974

12. 4.Duval’s Triangle:-
The original Duval’s triangle is shown in Fig.(a) and the
revised version is shown in Fig.(b) Six different fault classes
were diagnosed using the original triangle method

13. 4.Duval’s Triangle:-
Fault code Fault Type Fault code Fault Type
a High energy arcing PD Partial discharge
b Low energy arcing,
Tracking
D1 Low energy discharge
c Corona discharge D2 High energy
discharge
d Hot spots, T<200 C DT Mixture of electrical
and thermal
faults
e Hot spots,
200 C<T<400 C
T1 Thermal faults, T<300
C
f Hot spots, T>400 C T2
T3
Thermal faults, 300
C<T<700 C
Thermal faults, T>700
C

14. 5.Effect of Stray Gassing in DGA:-
 The mineral oils that are in use in transformers do not
produce measurable amount of gases at temperature below
300 C. However, some insulating oils are stated to be ‘‘stray
gassing’’ type.
 Such oils produce significant amount of H2 and CH4 at
temperatures as low as 100 C at the beginning of their service
life. It occurs in the first year of the service life of such oil and
is in general a nonrecurrent process. The gas concentrations
of H2 and CH4 reach a plateau after some time in service.
 These values must be taken into account for such oil types to
avoid misinterpretation of DGA results.

15. 6.Partial Discharge Identification
using DGA:-
 Low Energy partial discharges produce small amount of gases
and causes little damage to the transformer insulation which
in many cases is the detection limit for DGA.
 Thus low energy PDs may not be detected by DGA unless such
PD activity is intense or occurring over a long period of time.

16. 6.Partial Discharge Identification
using DGA:-
 As a result, DGA is more suited for the determination of onset
of the next stage of PD activity, i.e., when PD starts to cause
damage to paper insulation. Damage or carbonization of
paper insulation requires relatively higher energy and hence
detectable amount of gases in DGA analysis are found for
high energy PDs.

17. REFERENCE:-
1. Recent Trends in Condition Monitoring and Transformers by
Sivaji Chakravorti, Debangshu Dey, Biswendu Chatterjee.

18. THANK YOU