Detection and Interpretation of faults in a transformer using DGA

1. FAULT
INTERPRETATION FOR
POWER
TRANSFORMER USING
DISSOLVED GAS
ANALYSIS

2. IMPORTANCE OF TRANSFORMERS IN A POWER
SYSTEM
• ONE OF THE MOST IMPORTANT
COMPONENT OF A POWER SYSTEM
• STEPPING UP AND DOWN OF VOLTAGE
• VERY EXPENSIVE
• TRANSPORTATION OF TRANSFORMER
IS VERY TEDIOUS AND TIME TAKING
PROCESS.
• fault in a transformer can have a huge
repercussion
• as the number of old transformers and of
those that are difficult to operate in
overload conditions is on the rise, it is
important to detect incipient faults in a
transformer and forecast and prevent
failures

3. Classification of faults in a Transformer
• Partial Discharge (PD)
• Discharges of Low energy (D1)
• Discharges of High energy (D2)
• Thermal fault, (T1)
• Thermal fault, (T2)
• Thermal fault, (T3)
• Thermal & Electrical fault (DT)

4. • Partial Discharge (PD): The temperature plays a less important role in the
chemical reaction occurring in the PD since the vapour temperature in the
discharge zone is not higher than 60150°C. Hydrocarbon cracking in the partial
discharges occurs as a result of excitation of molecules and their subsequent
dissociation by collision with high energy electrons, atomic hydrogen, ions and
also free radicals. It often generates large amounts of hydrogen.
• Discharges of Low energy (D1): Partial discharges of the sparking type,
inducing pinholes, carbonized small punctures in paper. Low energy arcing
results in surface tracking of paper or the formation of small amount of carbon
particles in oil.
• Discharges of High energy (D2): Discharges in paper or oil, with power follow-
through, resulting in extensive damage to paper or large formation of carbon
particles in oil, metal fusion, tripping of the equipment and gas alarms.
• Thermal fault (T1): These types of faults occur below . These are evidenced
by paper turning brownish (> 200 °C) or carbonized (> 300 °C).

5. • Thermal fault (T2): These types of faults occur in between to
. These are evidenced by carbonization of paper, formation of
carbon particles in oil.
• Thermal fault (T3): The high temperature faults whose temperature
is more than falls in this kind of fault. These are evidenced by
extensive formation of carbon particles in oil, metal coloration (800
°C) or metal fusion (>1000 °C).
• Thermal & Electrical fault (DT): Sometime both thermal and
electrical fault occurs inside the transformer. These faults accelerate
the decomposition of dielectric fluid and solid insulation.

6. FORMATION OF GASES IN THE
TRANSFORMER OIL
• ALL ELECTRICAL DEVICES GIVES OFF WASTE HEAT
AS A BYPRODUCT
• HEAT THEREFORE , RISE IN TEMPERATURE
• OVERLOADING
• MOISTURE
• POOR QUALITY OIL OR PAPER
(insulating meterial)

7. DIAGNOSTIC METHODS
• Key Gas
• Rogers ratio
• Dornenberg
• logarithmic nomograph
• IEC ratio
• Duval triangle

8. IEC RATIO
• This method is widely used as a guideline and
a standard for diagnosis of the transformer
fault.This approach consist of three gas ratios
and ten fault cases are identified
corresponding to the suggested fault diagnosis
method.However these faults are mainly
categorized from the original fault types
TH,DA and PD.

9. Dornenberg Method
• This method utilizes the gas concentration from ratio of CH4/H2, C2H2/CH4,
C2H4/C2H6 and C2H2/C2H4.
• If at least one of the gas concentrations exceeds twice the values for limit
L1(see table 7) and one of the other three gases exceeds the values for
limit L1, the unit is considered faulty .
Table 7

10. ROGER’S RATIO METHOD
This method takes into consideration industrial
experience , laboratory tests and further
theoretical assessment. It follows the same
procedure as Dornenburg method except for the
three ratios (R1,R2 and R5).

11. The Duval Triangle method:
• Micheal Duval in 1973.
• Concentration of methane ,ethylene and acetylene in percentages .
• Plotted on a triangular chart (subdivided different fault regions ).
• Should not be applied unless the gas concentrations are well above the detection limit,
because of the relative inaccuracy of gas-in-oil concentration measurements at low
concentrations.
The faults which are detected by Duval triangle are expressed as follows;
1. Partial Discharge (PD) 2.Discharges of Low energy (D1) 3.Discharges of High energy
(D2) 4. Thermal fault (T1) 5.Thermal fault (T2) 6.Thermal fault, (T3) 7. Thermal &
Electrical fault (DT)
Figure 3.1 Classical Duval’s Triangle

12. Various faults produce certain gases and the percent of some gases have been found to
indicate fault types, such as overheated oil and cellulose, corona in oil and arching in oil.
The diagnostic interpretations applying various gases are given below in the Table 4.1.
KEY GAS RATIO METHOD

13. Nomograph Method
• This method was developed by J. O. Church.
• It combines the fault gas ratio concept with the Key Gas
threshold value to improve the accuracy of fault diagnosis.
• It provides both a graphic presentation of fault-gas data
and the means to interpret its
significance.