Transformer Oil and Gas Analysis - IEC Standards

Under normal operating conditions, oils should not produce gases. However, as energy (thermal or electrical)  increases, the oil can not withstand such conditions and decomposes generating gases.

International standard IEC 60422 has been prepared by IEC Technical committee 10: Fluids for electrotechnical applications. 

List of IEC Norms

IEC 60156: Insulating liquids – Determination of the breakdown voltage at power frequency –
Test method
IEC 60247: Insulating liquids – Measurement of relative permittivity, dielectric dissipation factor
(tan δ ) and d.c. resistivity
IEC 60296: Fluids for electrotechnical applications – Unused mineral insulating oils for
transformers and switchgear
IEC 60475: Method of sampling liquid dielectrics
IEC 60666: Detection and determination of specified anti-oxidant additives in insulating oils
IEC 60814: Insulating liquids – Oil-impregnated paper and pressboard – Determination of
water by automatic coulometric Karl Fischer titration
IEC 60970: Methods for counting and sizing particles in insulating liquids
IEC 61125: Unused hydrocarbon-based insulating liquids – Test methods for evaluating the
oxidation stability
IEC 61619: Insulating liquids – Contamination by polychlorinated biphenyls (PCBs) – Method
of determination by capillary column gas chromatography
IEC 62021-1: Insulating liquids – Determination of acidity – Part 1: Automatic potentiometric
titration
ISO 2049: Petroleum products – Determination of colour (ASTM scale)
ISO 2719: Determination of flash point – Pensky-Martens closed cup method
ISO 3016: Petroleum products – Determination of pour point
ISO 3104: Petroleum products – Transparent and opaque liquids – Determination of kinematic
viscosity and calculation of dynamic viscosity
ISO 3675: Crude petroleum and liquid petroleum products – Laboratory determination of
density – Hydrometer method
ASTM D971-99a: 2004 Standard test method for interfacial tension of oil against water by the
ring method

 Ref: IEC 60599 - International Standard

Why are Oil and Gas Analysis Important?

The insulating oil in a transformer says a great deal about the actual condition of the transformer as well as its remaining lifetime. Accurate information about the oil makes it possible to anticipate potential failures and put in place a precisely targeted maintenance and/or replacement plan.

Ref - http://www.laborelec.be/

How it works?

Sampling > Analysis > Interpretation > Recommendation

Insulating Oil Analysis

Analyse	Norms
Tension de rupture après filteration	CEI 60156
Tension de rupture	CEI 60156
Gaz Buchholz	CEI 60567
Couleur et apparence	ISO 2049
Soufre corrosif	CEI 62535 / ISO 5662
Soufre corrosif (après traitement à la résine)	CEI 60296
DBDS	CEI 62697
Degré de polymérisation	CEI 60450
Densité	ISO 3675
Facteur de dissipation	CEI 60247
Gaz dissous	CEI 60567
Furannes	CEI 61198
Gazage	CEI 60628
Inhibiteur (DBPC)	CEI 60666
Indice de neutralisation, l'acidité	CEI 62021-1
Stabilité à l'oxydation	CEI 61125
PCB	CEI 12766-2 / 61619
Résistivité	CEI 60247
Sédiments et les boues	CEI 60422
Viscosité	ISO 3104
La teneur en eau	CEI 60814

Note:

Gas formation is the consequence of an energy dissipation process.

Gas generation rate is a measurement of energy dissipation.

Transformer Oil Classification

Good Oils:
NN 0,00 - 0,10
IFT 30,0 - 45,0
Color Pale Yellow
OQIN 300 - 1500

Proposition A Oils:
NN 0,05 - 0,10
IFT 27,1 - 29,9
Color Yellow

OQIN 271 - 600

Marginal Oils:
NN 0,11 - 0,15
IFT 24,0 - 27,0
Color Bright Yellow
OQIN 160 - 318

Bad Oils:
NN 0,16 - 0,40
IFT 18,0 - 23,9
Color Amber
OQIN 45 - 159

Very Bad Oils:
NN 0,41 - 0,65
IFT 14,0 - 17,9
Color Brown
OQIN 22 - 44

Extremely Bad Oils:
NN 0,66 - 1,50
IFT 9,0 - 13,9
Color Dark Brown
OQIN 6 - 21

Disastrous Oils:
NN 1,51 or more
Color Black

Where	IFT - Interfacial Tension
	NN - Neturalisation Number
	OQIN - Oil Quality Index

Ref: http://www.satcs.co.za

Generated Gases

Hydrogen (H2)
Methane (CH4)
Ethane (C2H6)
Ethylene (C2H4)
Acetylene (C2H2)
Carbon Monodixe (C0)
Carbon Dioxide (CO2)

Origin of Gases

Oil	Oxidation
	Pyrolysis (overheating)
	Partial discharges
	Arcing

Cellulose    Decomposition at working temperature (100°C - 110°C)

                  Pyrolysis (Overheating)

                  Partial Discharges

Gas Formation Mechanism

With high temperature, chemical bonds break forming free radicals that recombine to form small and large molecules (gases, waxes).

Gas Evolution With Temperature

Gases Generated During Breakdown of Dielectric Oil

Gases Generated During Breakdown of Cellulose Insulation