Dissolved Gas Analysis

Test standard: ASTM D3612-02, VDE0370-9:1994-06, VDE0370-7:1999-12 Measuring range: 0-10,000 Unit: μl/l (ppm) Sample volume: 5 ml Determined: Dissolved gases in transformer oils H2, O2, N2, CO2, CO, CH4, C2H6, C2H4, C2H2

The analysis of gases present in the transformer oil in dissolved form is carried out with a PerkinElmer Clarus 680 with a TurboMatrix 40 Headspace Sampler, specially developed for this purpose. This analytical procedure is used to evaluate defects in electrical equipment with the aim of initiating countermeasures in good time. Dissolved gas analysis is the most frequently performed method for monitoring transformers. It offers many advantages and not only for the detection of defects:

 

Type of
defect

Cause of defect

Effects, appearance

PD

Partial discharges

Paraffin wax formation on the paper insulation

D1

Low energy discharges

undissolved small carbon particles in the oil, larger holes in the paper insulation

D2

High energy discharges

Carbonisation of the oil, destruction of the paper insulation, molten metal

T1

Thermal defects, temperatures of
up to about 300°C

Oil oxidation, brownish discolouration of paper

T2

Thermal defects, temperatures of 300 to 700°C

increased oil oxidation, carbonisation of paper

T3

Thermal defect,
temperatures of over 700°C

Oil carbonised,
metal discolouration/molten metal

In addition to the values for pollutant gases, the Duval triangle is illustrated in the laboratory report. This allows the visualisation of the type of defect present. At increased concentrations, a summary statement can be generated using this tool.

Example: in a DGA analysis, the following percentages were calculated based on the ppm values: Ethylene (C2H4) = 36.8%, acetylene (C2H2) = 21.1%, methane (CH4) = 42.1%. These values are entered into an isosceles Duval triangle parallel to the sides. The point at which the three lines intersect lies in a field with the types of defect listed in the table. In this way, a conclusion about the type of defect present in the case of example = D1 can be made.

Reference values for which a more frequent analysis is advisable, if exceeded:

Gas component

90% concentration  values in µ/l

Hydrogen

H2

60 - 150

Carbon monoxide

CO

540 - 900

Carbon dioxide

CO2

5.100 - 13.000

Methane

CH4

40 - 110

Ethane

C2H6

50 - 90

Ethene

C2H4

60 - 280

Ethyne

C2H2

3 - 50
(up to 270 for the diverter switch)

Source:

ÖlChecker Winter 2011, page 7