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©2008 Siemens Energy, Inc. All Rights Reserved

Power TransformersDissolved Gas Analysis

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Siemens Energy, Inc., T&D Service SolutionsPower Technologies International (PTI) 0-2

ü DGA allows to detect the presence and severity of faults:• Air leaks• Hot metal faults• Arcing and partial discharges

ü DGA may help to indirectly detect root cause of faults in:• Windings (short circuits, insulation failure)• Cleats and leads (high contact resistance, loose contacts)• Tanks (ground problems, circulating currents)• Tap changer (resistive contacts, leaks into main tank)• Core (magnetic flux problems)• Oxidation of materials (mostly CO, CO2)

Gases in Transformer OilApplication

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The eight key gases dissolved in transformer oil which are associated withfaulty conditions are:

Acetylene(C2H2)

Oxygen (O2)

CarbonDioxide (CO2)

CarbonMonoxide (CO)

Ethylene(C2H4)

Hydrogen(H2)

Methane(CH4)

Ethane(C2H6)

Gases in Transformer OilKey Gases

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Gases in Transformer OilGas Parameters

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Gases in Transformer OilTypical Chromatography

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n IEEE Std. C57.104.2008 IEEE Guide for the Interpretation of GasesGenerated in Oil Immersed Transformers [OUT-DATED]

n IEEE PC57.104 Draft xx (Under Revision) - Guide for the Interpretation ofGases in Oil Immersed Transformers

n IEC 60599-1999 Mineral Oil Impregnated Electrical Equipment in Service:Guide to the Interpretation of Dissolved and Free Gas Analysis

Gases in Transformer OilNational and International Standards

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Gases in Transformer OilKey Gases

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Gases in Transformer OilIEEE Reference Levels

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Gases in Transformer OilIEEE Technique

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Gases in Transformer OilKey Gas Technique

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020406080

100

CO H2 CH4 C2H6 C2H4 C2H2

Thermal Oil and Cellulose Fault

020406080

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Thermal Oil Fault

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40

60

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High Energy Arcing

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40

6080

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Low Energy Partial Discharge

Gases in Transformer OilKey Gas Example

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Gases in Transformer OilGas Ratios ( IEC / Rogers )

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Diagnostic TechniqueReference Standard

IEEE C57. 104-1991 IEEE PC57. 104-2008 IEC 60599-1999

Individual & TDCG guidelines P P

Doernenburg Ratios P

Rogers Ratios P P

Basic Gas Ratios P

Key Gas Procedure P P

TCG Procedure P

TDCG Procedure P P

Duval Triangle P

CO2/CO Ratio P P

O2/N2 Ratio P

C2H2/H2 Ratio P

Gases in Transformer OilComparative Diagnostic Tools

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Gases in Transformer OilComparative Table

Unresolved, %Wrong diagnosis, %Total, %

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IEC 60599 - changes to improve accuracy

Duval Triangle method (from 1970’s)

n Uses three gases only (CH4, C2H4 and C2H2)

Low energy faults >>>> high energy faults

n No possibility of “unresolved” diagnosis

n High % of correct diagnosis

n Plots relative % of CH4, C2H4 and C2H2

Graphical, can show fault evolution over time

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IEC 60599 & Duval

6 Different Fault types

n PD: Partial Discharge (gas bubbles, insulation voids, etc.)

n D1: Low energy discharge (spark, carbon, surface tracking)

n D2: High energy discharge (arcing w/metal fusion, internalflashovers, oil contamination)

n T1: Thermal fault < 300 degC (overload, blocked ducts)

n T2: Thermal fault < 300-700 degC (minor circulatingcurrent, poor contacts)

n T3: Thermal fault > 700 degC (major circulating current intank/core, short circuit or through fault)

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Duval Triangle method

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IEC 60599 & Duval

Issues w-DGA analysis

Lab inaccuracy

n Median IEC in accuracy is 15% @”normal” concentrations

n North American labs appear worse

n For low gas concentrations, median inaccuracy is 30-50%.

n Diagnosis accuracy only 50%, if lab ~~ 30%

Typical DGA levels

n 90% threshold, in-service population > focus on weakness

n 90% rate of DGA evolution > focus on changing conditions

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IEC 60599 & Duval

Typical DGA levels

With “normal” concentration, attempted diagnosis + monitor

*NOT* xfmr in trouble with normal concentration >> trending

IEC 60599 Typical Gas Levels

H2 CH4 C2H2 C2H4 C2H6 CO CO2ppm 60-150 40-110 3-50 60-280 50-90 540-900 5100-13K

/year 35-130 10-120 0-4 30-150 5-90 260-1060 1700-10K

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On Line DGA

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Bring the lab to the transformer.

Gases in Transformer Oil

On line DGA

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Siemens Gas Guard

Gases in Transformer Oil - continued

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n Oil is sampled automatically via closed-loop GC:

- No risk of human intervention

- Repeatable sampling technique

- No atmospheric exposure

n Data is collected up to hourly:

- Resulting in faster, more accuratedetermination of trends

n All 8 fault gases + moisture are monitoredand correlated with oil temperature andload

Gases in Transformer OilOn Line DGA - continued

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Internal inspection revealed severely damaged crimped connection betweenLV cables connecting an LV winding-exit to a bushing.

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