dissolve gas analysis

8/8/2019 Dissolve Gas Analysis

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DISSOLVED GAS ANALYSIS

Used to find electrical & thermal fault in

transformer Fault can be found at incipient stage

Remedial measure can be initiated to avoidmajor damage to transformer

FORMATION OF GAS

Degradation of solid & liquid insulation Faults in transformer Gases gets dissolved in oil till saturation



DGA - Tool for Quality Check

DGA - Quality check during procurement of new transformers.

DGA - before & after heat run test or fast transient test or high

voltage test.

Abnormal increase in gas concentration after factory test indicate

manufacturing / design defect in transformer.

Defect can be rectified before shipment & installation at site.



DGA

Extraction

of

gases from oil

Analysing

for

key gases

Interpretation

of

results

Methane

Ethane

Ethylene

Acetylene

Hydrogen

Carbon monoxide

IS ratio

Key gas method

Rogers ratio

Rate of rise of key gas



CHARACTERISTIC TRANSFORMER FAULTS

ELECTRICAL FAULTS

Sl Type of faults & cause Major gases

1 High energy discharge (Arcing) Methane

* SC in winding Hydrogen

* Breakdown between windings Acetylene

* Breakdown through the oil between bare

conductors

2 Low energy discharge (High energy partial Hydrogen

discharge) Acetylene

* Bad contact action of connection to metallic Methane

parts

* Continuous sparking at breaks

* Discharges between selector contacts



CHARACTERISTIC TRANSFORMER FAULTS

THERMAL FAULTS

Sl Type of faults & cause Major gases

1 Thermal fault of low temperature <150oC Hydrogen

* General conductor overheating Methane

Ethylene

2 Thermal fault of medium temp. 300 to 700oC Hydrogen

* Local over heating of core due to circulating Methane

current Ethylene

* Bad contacts

3 Thermal fault of high temperature >700oC Hydrogen

* Loacl over heating of core due to circulating Methane

current Ethylene

* Bad contacts Acetylene



Sampling of transformer oil

SAMPLING CONTAINER

Perfectly cleaned & Dried Free from dust & moisture Airtight Glass or Metal or Plastic cans

SAMPLING POINT

Bottom valve Sample in actual contact with body Forced cooled TR-Circulate pump for 30 min

Sampling under energized condition



SAMPLING

•Equipment

•Test Requisition form•Method



GENERAL PRECAUTIONS

Avoid sampling in rainy or foggy weather

Protect sample from direct light

Avoid moisture & dust contamination

Cotton waste & other fibrous materials

should not be used

Use the sampling containers exclusively for

transformer oil sampling

dissolve gas analysis

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