DGA (dissolved-gas analysis) on Oil-Paper Transmission Cable Systems, including Extruded Cable Terminations and

Transformers

Nirmal Singh, DTE Energy Electric, Detroit, MI, US

CIGRE SCB1 Meeting, October 9-12, New Delhi, India

nirmal.singh@dteenergy.com

1

Outline

• Taped cable types in brief, covered for DGA

• Aging of paper & dielectric fluid and general DGA considerations

• Sampling, analysis & interpretation

• DGA methods, including EPRI’s

• Termination vs. splices vs. cables vs. risers

• DGA of HPFF/HPGF/SCFF cable systems

• General DGA guidelines for cables/Transformers

• DGA of fluid-filled extruded cable terminations

• Cable vs. transformer, DGA-wise

• Case histories of cables/transformers

2

Skid Wires

Outer Shielding

Moisture Barrier Carbon Tapes

Conductor Shielding

Binder Tapes

Typical HPFF cable

Cable Types Covered for DGA

3

PIPE COATING

STEEL PIPE

PRESSURIZED FLUID

SKID WIRES

INSULATION SHIELD

INSULATION

CONDUCTOR SHIELD

CONDUCTOR

Cross-section of HPFF/HPGF cable

Sectional view of submarine SCFF cable with key components

Condition & Life Considerations

• Life of a cable is primarily governed by the condition of the impregnated taped insulation, provided the fluid pressure and integrity of the steel pipe/sheath are maintained

• Of the two insulating components, namely, paper and fluid, the latter is quite stable up to about 140oC (absence of oxygen helps). However, paper degrades under thermal stresses

• As paper ages, its mechanical properties are reduced. During thermal aging of paper, carbon oxides (2 key DGA gases), moisture and minute amounts of methane and hydrogen are evolved. In addition, paper loses its initial DP (degree of polymerization) value and produces furans that readily dissolve in the dielectric liquid, its Copper No. increases – opposite of DP, but like furfural

• These traditional (mechanical) & non-traditional (DP, furans, copper no.) properties enable us to estimate cable life well for cables & transformers

4

Condition & Life Considerations………

• The dielectric fluid is affected by general contamination –moisture, oxygen and particulates. The impact of such external factors can be readily measured by a series of electrical (DF@100oC, BD) and chemical (moisture, peroxide, IFT)

• As for other fluid-filled equipment, the cable fluid offers a convenient means to assess the condition of the cable through various fluid quality tests and, most importantly, via Dissolved-Gas Analysis that is being increasingly recognized as the most viable and cost-effective diagnostic test for cable systems/transformers

• DGA responds well as a diagnostic test for cables and transformers that are advancing in age and, as such, require better condition/life assessment in the present climate of fiscal restraints worldwide

5

Principles of DGA

• Operation of fluid-involving cables/transformers yields several gases:

• H2, CO2, CO & hydrocarbon gases evolve from fluid & paper under thermal & electrical stresses, chemical stresses (rusting) can also generate H2

• CO2 & CO evolve predominantly from paper

• Such gases remain dissolved in the fluid, hence term dissolved. Loose all semblance of gas

• Depending on the cable condition, the type, concentration & distribution of these dissolved gases vary, giving clues to its condition

Basically, DGA consists of quantitatively identifying such gases, relating to equipment condition

6

DGA Steps

• Sampling, proper tools & written procedures – sampling errors are often made in the field

• Chemical Analysis, periodic reconditioning of GC columns, calibration, occasional cross-checking of accuracy & precision using standard gas-in-oil solutions

• Interpretation

Effectiveness of DGA is critically dependent on these three sequential steps

Both individual gas levels and the entire gas pattern are important for proper interpretation; availability of extensive lab/field data properly generated is invaluable, including exposure to cases relating gasing problems revealed through the opening of cable systems & transformers

7

DGA Interpretation

• Knowledge of operating history is essential, any failures, makeup fluids, some of the saturated hydrocarbon gases might have come with the original fluid, even as a carbon dioxide blanket – specially for HPFF cables

• Keen Knowledge of equipment, design, operation, any repairs, additions, components and materials

• Operation of taped transmission cables yields several gases. Depending on the cable condition, the individual levels & distribution of these gases vary, giving clues to its condition

• Acetylene is the single most important gas, followed by hydrogen; former absent in vast majority of operating cables; ratios of C2H6/C2H4 and CO2/CO are also important, but may not be a show-stopper

• Sound Cables show minimal gases

8

Interpretation continued……..

• Both individual gas levels & the entire gas pattern “as a whole” are important along with certain ratios

• Depending on the cable system condition, gas limits are classified into four categories: normal, acceptable, concern & action levels; these levels correspond to increasing order of severity & are associated with progressively ascending gas concentrations

• Normal & acceptable condition requires routine attention

• In concern level, the concentration of gases, particularly C2H2, H2 and the C2H4/C2H6 & CO/CO2 ratios are high enough to necessitate close monitoring through DGA

9

Interpretation continued…..

Action level condition requires immediate investigation into high gas levels & how and why of their formation. It includes high DGA frequency, location of source, additional fluid tests with focus on moisture/DF/BD, understanding of cable line profile, heavy vehicular traffic, degassing, stoppage of fluid circulation for forced-cooled HPFF lines, DGA history, addition or loss fluid, history of any companion circuit, inspection & any repairs. Consult with internal & external experts. Importance & nature of the equipment involved also govern the action plan(s); termination failures are safety hazard, requiring prompt attention. The ultimate action is utility’s call

10

Unique Features of DGA

• High measurement accuracy

• High sensitivity to electrical/thermal stresses, distinguishing each stress

• Low detection limits with readily available, relatively low cost chemical equipment

• Apparently higher sensitivity than PD measurements, exceedingly more economical approach & better understood – users can readily rate to DGA - (over 1 million annual DGAs)

• Once formed, dissolved gases stay in place, accumulative process, not intermittent like corona activity, unless the fluid moves

• Can locate a problem source through fluid movement, often done successfully for HPFF cables

• Potential for remaining life assessment via carbon oxides, as they evolve during paper aging – a thermal phenomena

• Sampling on energized transformers and HPFF/HPGF cables, but not terminations & SCFF cables; the bottom of 345 kV, and even that of 230 kV HPFF terminations can be sampled, albeit with due care – has been done on several occasions

11

DGA Shortcoming & Challenges

• A potential problem source will generate gases, precise problem location with respect to various dielectric media involved is often hard to define, some can be harmful to various degrees, others almost innocuous (e.g. in pipe fluid)

• Unless properly followed, one cannot say when the gas generation started – it can increase, stabilize; on-line monitoring can help

• The upper limits of various gases cannot be properly defined nor expressly sought (too many factors involved), failure location activity can also complicate matters; DGA is both science & art (to some extent), lab & massive field data helpful, with good operational history of the system

• Because of its low solubility, the upper limit of hydrogen is more easy to identify, remembering repairs at 50 psi for HPFF cables

12

DGA of Terminations vs. Splices

• The confined nature of the limited termination fluid requires a different sampling procedure to cover the entire termination length

• The gas limits and distribution for terminations are markedly different from that of cables

• Use both top & bottom valves, when available

• First sample bottom valve, followed with 2 samples from the top valve, 1-3 gallon interval, depending on the volume

• If only top valve is available, take first sample with appropriate drainage, followed by 2 additional samples as the fluid is drained, to cover the entire

• Terminations tend to yield much more acetylene, splices much less acetylene but more hydrogen - HPFF cables; SCFF splices can give appreciable acetylene, much less hydrogen

13

Gases measured, their Generation & what they Indicate

• Gas generation is a thermodynamic phenomenon - electrical activity simply exposes a macro- fluid volume to localized, elevated temperatures. Depending on the level/intensity, range of temperatures /fluid nature and duration/covrage of this activity, a large number of gases such as hydrogen, carbon oxides, methane, lower (C1s) and higher hydrocarbon gases (C2s, C3s)……….requiring higher energies to evolve, are generated

• Paper essentially yields carbon oxides, fluids the rest

• Depending on the problem faced by the cable(or transformer), the type, distribution & concentration of the evolved gases vary – giving a handle on the nature of the problem

• Considering that several fluids of differing chemical nature and viscosities are involved in taped cables, we measure 16 gases. The four isomers of butane add 4 to this total. The starting material for polybutene fluid is isobutylene gas, hence this measurement. Moreover, this large number helps identify the extent of any contamination of original pipe fluid in some HPFF cables, where it has been observed

14

Indications by Main Gases

• Acetylene is the single, most important gas for diagnosis by DGA; generated only if any electric arc (visible, if eye could see it, howsoever, feeble) is involved. Any severity short of arc formation will not form acetylene, as demonstrated by earlier EPRI work

• Hydrogen is related to very mild corona activity. Large concentrations of Hydrogen are possible in HPFF cables, observed. Rusting situations can lead to hydrogen, demonstrated. Can also evolve from metals (where it is absorbed) from previous manufacturing processes or welding

• Ethylene & ethane are basically related to electrical activity, which falls between the levels of acetylene and hydrogen. Of the two, ethylene requires higher level of electrical energy. In addition, thermal activity also contributes. Propylene & propane follow the same pattern, except higher energy levels are involved. Ethylene is invariably associated with the presence of acetylene. Ethylene is higher than ethane in unsatisfactory situations, an important lesson

15

Indications by Main Gases…..

• Carbon dioxide & monoxide are related to thermal activity in paper. The latter is also associated with electrical activity on paper. The concentrations CO2 are much higher than that of CO, 4-10. If CO level is higher than the CO2, a problem is indicated, another important lesson. We rarely see CO/CO2 ratio > 1

• Methane is related to low level thermal activity

• Isobutylene is predominantly encountered in polybutene fluids & is related to thermal activity and possibly mechanical action of pumps. Being a higher hydrocarbon gas, it requires greater energy level compared to lower hydrocarbons

• Again, while individual gases may be important, one has to look at the pattern as a whole, one cannot generally go with one gas – the levels involved are also important, when looking at ratios or otherwise

• Gas trending is of utmost importance, so is previous DGA history 16

Dry Paper

Time (hours) C. Monoxide (ppm) C. Dioxide (ppm)

0 nd 0.83

5 2.77 1.11

34 13.22 1.21

52 14.77 0.94

75 14.38 0.75

144 15.91 0.7

172 13.06 0.72

196 16.94 0.67

212 17.43 0.69

Impregnated Paper

0 7.0 1.0

72 7.4 1.2

80 8.0 1.1

96 10 1.6

128 12.8 2.7

Gas Generation Under Electrical Stress for Dry & Impregnated Paper showing Carbon Oxides Evolution, in Nitrogen 2.5 kV Applied to Sphere-Plane 34 mils Total Paper Thickness2.75 in. Sphere Diameter

17

Gas Concentration at Saturation Level in Dielectric Fluids at 40oC and 200 psig in Thousands ppm

Gas Cosden 0EG Chevron DO100 Cosden 6EG Cosden 15EG

Nitrogen n/a 1,575 1,830 4,261

Hydrogen 1,341 1,404 1,188 812

C. Monoxide 2,197 2,134 2,313 2,416

C. Dioxide 14,382 12,473 13,017 8,522

Methane 6,425 5,626 13,117 4,894

Ethane 27,953 37,953 33,259 26,334

Ethylene 24,503 23,571 20,441 12,817

Acetylene 14,282 19,176 13,882 10,287

18

Sampling Methods

• Glass Syringes, starting with 100 cc, now 30-50 cc, expensive, cleaning cost, inconvenient to ship, develops leaks after repeated use

• Stainless Steel, hard to clean, opaque, hydrogen can get adsorb into metal, particularly stainless steel

• Open beaker, long given up, loses several low solubility gases such as hydrogen & CO in particular

• EPRI cells, EPOSS (EPRI Pressurized Oil Sampling System) up to the late 1990s (8 in. glass tube, 1.5 in. dia, heavier metallic fittings, expensive), since then EDOSS vial – both based on headspace principle & equally accurate

19

Shortcomings of ASTM method for HPFF cables

• Compared to the traditional transformer oil, cable fluids differ markedly in viscosity, chemical type, often 3-4 different types of fluid are involved in the same cable

• Higher viscosities of cable fluids render their field sampling difficult, all the more in winter months, OK for SCFF

• Fluids in operating cables have exceedingly high levels of Nitrogen than their transformer counterparts, resulting in bubble formation in the sampling device to which some key gases escape. Bubbles tend to become larger with time due to de-pressurization from the high original pressures

• Lack of automation, could lead to human errors

• Two-step operation, where sampling and analysis devices are not the same

• Reliance on mercury, a hazardous material

20

Shortcomings Continued……………

• Extraction efficiency problems, when gas content is low (typical in transformers) or high (as often can be for cables)

• Relatively large sample (50-100 cc), which some systems such as transformer bushing & extruded cable terminations, cannot readily afford

• Repeated use of sampling devices can lead to leaks, their scrupulous cleaning is also time-consuming

• Traditional devices do not offer long storage

• Heavier, bulkier and expensive sampling system; does not lend to transport in large numbers

21

Bubble Formation in Syringe Sampling

22

23

EDOSS (EPRI Disposable oil Sampling System) Method

• Based on a unique, custom-made sampling system, which also serves as the analysis vessel, nothing seemingly comparable in the market. Utilizes commercially available equipment (headspace analyzer with a 50-sample carrousel, gas chromatograph) with some modifications

• Advantages

– Requires small sample volume 5/6 cc; suitable for low fluid volume equipment

– Light, easy-to-apply in the field, fast, easy shipment and inexpensive sampling system for HPFF and SCLF cable systems (and transformers); HPGF cables require a steel cylinder. Caters for a wide viscosity range, no plastic tubing/valves, no undesirable bubble formation

– Automated, cost-effective analysis system, no human errors

– Long shelf - life of evacuated vials, (~2 months), easy/permanent labeling

Power Transformers

Cables

Terminations

Filter

3-way valve

Needle assembly

Vial coupler

EDOSS vial

Fluid flush

Pump

EDOSS Sampling Schematics for Transformers, HPFF Cables & Extruded Cable Terminations, including Vial Box

24

Box of 18 vials

HPFF 345-kV Splice Sampling

25

General Gas Limits for HPFF/HPGF/SCFF Cable Systems

• The suggested gas limits are based on field (bulk of which is on HPFF cables) and lab data & relate to normal, acceptable, concern and action levels, along with two gas ratios

• These limits should not be signify firm gas limits and are meant to provide general guidelines. As more experience is gained, they would be modified – in a way, they represent a “living document” with a sound foundation. The upper gas limits cannot be well defined nor sought due to several factors in play

• These limits vary significantly depending on the accessories and the very type of cable. This is understandable due to design differences and, in particular, the amount of fluid involved

• Again, of all gases, acetylene is the single most important gas

Some unusual DGA cases for HPFF cable systems follows the guidelines

26

27

Gas concentration limits for splices and cable runs of static HPFF cables

GasNormal

Range (ppm)

Acceptable

(ppm)Concern level (ppm)

Action level

(ppm)

Hydrogen (H2) 0 – 1,000 < 10,000 10,000 – 100,000 300,000 +

Acetylene (C2H2) 0 < 5 5 – 15 15 +

C. Monoxide (CO) 0 – 4`00 < 500 500 – 1,000 1,000 +

C. Dioxide(CO2) 0 – 1,000 < 5,000 5,000 10,000 +

Methane (CH4) 0 – 400 < 1,000 1,000 –4,000 4,000 +

Ethane (C2H6) 0 – 300 < 500 500 – 1,000 1,000 +

Ethylene (C2H4) 0 – 100 < 200 200 – 500 500 +

Propane (C3H8) 0 – 500

Isobutylene (C2H8)

Polybutene Fluids 0 – 1,500 < 5,000 5,000 – 10,000 10,000 +

Alkylbenzene Fluids 0 – 100 < 500 500 – 1,000 1,000 +

Mineral Oils 0 – 200 < 1,000 1,000 – 2,000 2,000 +

Oxygen (O2) 0

Nitrogen (N2) 0 – 80,000

Gas Ratios 1

CO2/CO 5 – 10 > 1 0.75 – 1 < 0.5

C2H6/C2H4 8 – 10 > 1 0.75 – 1 < 0.5

(1) Ratios only apply to gas concentration levels larger than 50 ppm for carbon oxides

and larger than 20 ppm for hydrocarbons

28

Gas concentration limits for terminations of HPFF cables

(1) Ratios only apply to gas concentration levels larger than 50 ppm for carbon oxides

and larger than 20 ppm for hydrocarbons

Gas

Normal Range

(ppm)

Acceptable

(ppm)

Concern level

(ppm)

Action level

(ppm)

Hydrogen (H2) 0 – 1,000 < 1,500 1,500 – 10,000 10,000 +

Acetylene (C2H2) 0 < 30 30 – 150 150 +

C. Monoxide (CO) 0 – 300 < 300 300 – 2,000 2,000 +

C. Dioxide(CO2 0 – 1,000 < 5,000 5,000 – 10,000 10,000 +

Methane (CH4) 0 – 400 < 1,000 1,000 – 4,000 4,000 +

Ethane (C2H6) 0 – 300 < 500 500 – 1,000 1,000 +

Ethylene (C2H4) 0 – 100 < 200 200 – 500 500 +

Propane (C3H8) 0 – 500

Isobutylene (C2H8)

Polybutene Fluids 0 – 1,500 < 5,000 5,000 – 10,000 10,000 +

Alkylbenzene Fluids 0 – 100 < 500 500 – 1,000 1,000 +

Mineral Oils 0 – 200 < 1,000 1,000 – 2,000 2,000 +

Oxygen (O2) 0

Nitrogen (N2) 0 – 80,000

Gas Ratios 1

CO2/CO 5 – 10 > 1 0.75 – 1 < 0.5

C2H6/C2H4 8 – 10 > 1 0.75 – 1 < 0.5

Gas concentration limits for self-contained cable splices

Gas

Normal Range

(ppm) Acceptable (ppm) Concern level (ppm)

Action level

(ppm)

Hydrogen (H2) 0 – 600 < 1,000 1,000 – 3,000 3,000 +

Acetylene (C2H2) 0 1- 5 5 – 10 25 +

C. Monoxide (CO) 0 – 300 < 500 500 – 1,000 1,000 +

C. Dioxide(CO2 0 – 1,000 < 5,000 5,000 – 10,000 10,000 +

Methane (CH4) 0 – 400 < 1,000 1,000 – 4,000 4,000 +

Ethane (C2H6) 0 – 300 < 500 500 – 1,000 1,000 +

Ethylene (C2H4) 0 – 100 < 200 200 – 500 500 +

Propane (C3H8) 0 – 500

Isobutylene (C2H8)

Polybutene Fluids 0 – 1,500 < 5,000 5,000 – 10,000 10,000 +

Alkylbenzene Fluids 0 – 100 < 500 500 – 1,000 1,000 +

Mineral Oils 0 – 200 < 1,000 1,000 – 2,000 2,000 +

Oxygen (O2) 0

Nitrogen (N2) 0 - 80,000

Gas Ratios 1

CO2/CO 5-10 > 1 0.75 – 1 < 0.5

C2H6/C2H4 8-10 >1 0.75-1 <0.5

(1) Ratios only apply to gas concentration levels larger than 50 ppm for carbon oxides and larger than 20 ppm for hydrocarbons

29

Gas concentration limits for terminations of self-contained cables

Gas

Normal Range

(ppm)

Acceptable

(ppm) Concern level (ppm)

Action level

(ppm)

Hydrogen (H2) 0 – 1,000 < 2,000 2,000 – 5,000 5,000 +

Acetylene (C2H2) 0 – 2 < 5 5 – 50 50 +

C. Monoxide (CO) 0 – 300 < 500 500 – 1,000 1,000 +

C. Dioxide(CO2 0 – 1,000 < 5,000 5,000 – 10,000 10,000 +

Methane (CH4) 0 – 400 < 1,000 1,000 –4,000 4,000 +

Ethane (C2H6) 0 – 300 < 500 500 – 1,000 1,000 +

Ethylene (C2H4) 0 – 100 < 200 200 - 500 500 +

Propane (C3H8) 0 – 500

Isobutylene (C2H8)

Polybutene Fluids 0 – 1,500 < 5,000 5,000 – 10,000 10,000 +

Alkylbenzene Fluids 0 – 100 < 500 500 – 1,000 1,000 +

Mineral Oils 0 – 200 < 1,000 1,000 – 2,000 2,000 +

Oxygen (O2) 0

Nitrogen (N2) 0 – 80,000

Gas Ratios (1)

CO2/CO 5 – 10 > 1 0.75 – 1 < 0.5

C2H6/C2H4 8 – 10 > 1 0.75 – 1 < 0.5

(1) Ratios only apply to gas concentration levels larger than 50 ppm for carbon oxides and larger than 20 ppm for hydrocarbons

30

Gas concentration limits for HPGF cables (200 psi nitrogen)

GasNormal Range

(ppm) (1)

Acceptable (ppm)

Concern Level(ppm) 1

Action Level(ppm) 1

Hydrogen (H2) 0 – 75 < 700 700 – 2,200 2,200 +

Acetylene (C2H2) 0 < 0.07 0.07 - 0.4 0.4 +

C. Monoxide (CO) 0 – 15 < 75 75 – 150 150 +

C. Dioxide(CO2 0 – 75 < 150 150 – 350 350 +

Methane (CH4) 0 – 30 < 75 75 – 300 300 +

Ethane (C2H6) 0 – 15 < 40 40 – 75 75 +

Ethylene (C2H4) 0 – 80 < 15 15 – 40 40 +

Propane (C3H8) 0 – 36

Isobutylene (C2H8)

Polybutene Fluids 0 – 100 < 350 350 - 750 750 +

Alkylbenzene Fluids 0 – 10 < 40 40 - 100 100 +

Mineral Oils 0 – 20 < 80 80 – 200 200 +

Oxygen 0

Gas Ratios 2

CO2/CO 5 – 10 > 1 0.75 – 1 < 0.5

C2H6/C2H4 8 – 10 > 1 0.75 – 1 < 0.5

(1) Gas concentrations must be multiplied by the ratio of cable operation pressure in psi to atmospheric pressure in psi. The numbers given in this table have already being corrected

(2) Ratios only apply to gas concentration levels larger than 40 ppm for carbon oxides and larger than 10 ppm for hydrocarbons

31

DGA schedule for splices and terminations

Accessory Normal Concern Action

Splice 2 to 4 years,

depending on cable

voltage class

6 months to 1

year

Establish whether or not the

splice is the source of gas.

Drain fluid to obtain sample

from the cable, both sides if

possible. Consult with experts

before opening the splice.

Cable Run

1 to 2 years, if a

problem has been

identified

6 months to 1

year

Consider changing cable length

in question

Termination 2 to 4 years 6 monthsOpen termination for visual

inspection/ rebuild.

32

Comparison of DGA Results Between MH17139 and Adjoining Manholes, Stephens-Caniff HPFF 345 kV Cable.

Failure took place on June 15, 1988

Gases (ppm) MH17140 MH17139 MH17138

Methane 301 2,078 108

Ethane 153 1,074 78

Ethylene 248 1,387 87

Acetylene 22 147 0.8

Propane 211 309 131

Propylene 163 820 61

Isobutane 114 196 78

n-Butane 81 105 67

t-2-Butene 38 85 31

1-Butene 32 94 22

Isobutylene 667 2,335 406

Hydrogen 2,283 14,278 1,089

C. Monoxide 881 1,055 443

C. Dioxide 851 1,042 711

Nitrogen 154,937 137,391 186,30433

Stephens-Caniff 345 kV, Sampling at the Test Failure (MH17132) and Adjoining Manholes

Date 7/7/1988 7/6/1988 7/7/1988

Gases (ppm) MH17140 MH17139 MH17138

Methane 316 492 369

Ethane 146 155 119

Ethylene 242 337 227

Acetylene 2.1 25 1.4

Propane 228 214 177

Propylene 148 222 148

Isobutane 121 132 115

n-Butane 93 95 85

t-2-Butene 42 56 46.5

1-Butene 34 44 35

Isobutylene 653 870 739

Hydrogen 1616 2,938 708

C. Monoxide 1173 736 659

C. Dioxide 609 424 387

Nitrogen 221,675 98,320 62,74634

DGA & Revealed Damage Extending to Cuter and tapes,138 kV GIS Termination

35

Gases

Methane 169,700

Ethane 20,017

Ethylene 20,063

Acetylene 1,314

Propane 8,993

Propylene 22,330

Iso-butane 9,577

nButane 768

t2Butene 1,059

1Butene 1,886

Isobutylene 123,930

Hydrogen 74,970

C Monoxide 2,078

C Dioxide 1,234

Nitrogen 73,620

Variation of acetylene concentration (average) with time, 138 kV SF6 HPFF Termination

36

HPFF cases involved in major/minor fires, involving different HPFF cables

Year 1990 2001

Gases (ppm) / Location Manhole X Manhole Y Manhole Z

Methane 27,168 862 869

Ethane 7,468 287 283

Ethylene 2,316 83 84

Acetylene 2 0 0

Propane 6,694 822 806

Propylene 4,381 134 131

Isobutane 2,022 107 104

n-Butane 3,228 229 223

t-2-Butene 468 33 34

1-Butene 1,153 67 68

Isobutylene 11,932 607 600

Hydrogen 6,177 9,961 11,783

C. Monoxide 7,746 160 156

C. Dioxide 46,092 1,611 1,650

Nitrogen 72,466 89,040 83,338

37

DGA Results on a 138 kV HPFF Cable System, including its Reservoir, April 23, 1992

Downtown Substation

Gases (ppm) Manhole Phase A Phase B Phase C Reservoir

Methane 158,384 2,708 2,000 2,554 542

Ethane 81,380 9,707 17,685 18,958 13,001

Ethylene 1,431 223 204 219 141

Acetylene 0 0 0 0 0

Propane 44,080 12,817 24,410 24,805 21,157

Propylene 11 24 22 23 20

Isobutane 6,031 1,001 101 1,011 959

n-Butane 3,277 2,830 2,822 2,840 2,568

t-2-Butene 85 91 92 92 83

1-butene 16 23 23 23 21

Isobutylene 470 637 640 645 585

Hydrogen 629 129 232 138 23,207

C. Monoxide 0 14.8 11.3 5.2 0

C. Dioxide 109 279 202 242 99

Nitrogen 33,568 120,693 120,054 120,042 83,296

38

DGA Data on HPFF Pumping Plant Reservoirs, with two rare cases showing Acetylene

Sample Date 1/31/2000 2/22/2005 2/24/2005 09/21/09 4/8/2013 7/10/2014 10/27/2016 5/4/2016 4/18/2017

Methane 138 58,440 860 7,094 0.5 31 14.5 35.5 42

Ethane 62 27,000 2,327 14,121 1.7 43 45.5 21.5 46

Ethylene 38 6.8 1.8 2.5 0.6 91 6.55 23 22

Acetylene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.20 11

Propane 60 17,403 1,608 9,257 4.4 65 70.5 22 60

Propylene 36 75 11 29 1.5 47 21 24.5 51

Isobutane 35 1,162 112 1,202 0.3 67 58.5 2.05 68

n-Butane 42 479 35 1,742 0.3 7.5 12.5 2 7

t-2-Butene 17 18 20 24.5 0 2.6 2.65 0 10

1-Butene 15 5.7 4.8 15.5 0.2 7.2 3.25 3.55 7

Isobutylene 291 1,594 572 4,847 0.9 121 80.5 8 123

Hydrogen 707 82 21 21 58 79 43 0 77

C Monoxide 474 39 15 18 7.8 101 27 24 107

C Dioxide 6,734 160 77 178 117 579 480 130 372

Nitrogen 120,744 132,232 128,132 55,797 132,087 135,662 80,552 113,685

39

High Hydrogen Cases for HPFF Cables

Utility 1* 2a 2b 3 4 5a 5b 6a 6b 7

Date Sampled 4/24/92 10/2/89 6/25/98 6/21/06 3/14/00 3/7/01 10/23/07 10/24/05 7/20/06 5/5/99

Methane 547 3.1 12 14 11 835 880 16 0.5 0.0

Ethane 13,194 1.0 2.3 5.3 7.7 190 185 10 0.9 5.2

Ethylene 143 2.3 0.0 1.4 0.6 15 9.4 2.3 0.7 0.7

Acetylene 0.0 0.0 0.0 0.0 0.0 0.6 0.4 0.0 0.0 0.0

Propane 21,426 1.6 4.8 7.7 16 125 323 23 3.6 24

Propylene 21 2.1 1.1 3.8 6.2 52 57 6.0 3.5 1.0

Isobutane 928 0.0 1.5 10 1.3 419 716 12 44 0.7

n-Butane 2,614 0.0 0.9 3.4 0.8 770 918 1.1 25 4.3

t-2-Butene 86 0.0 0.0 0.0 0.0 609 1,160 0.4 33 0.0

1-Butene 21 0.0 0.0 1.3 0.6 178 216 0.4 57 0.0

Isobutylene 595 0.0 0.0 2.6 9.0 1,245 2,038 214 8,660 14

Hydrogen 24,099 24,056 56,778 59,719 106,137 264,830 450,820 726,550 81,375 110,471

C. Monoxide 0 38 17 18 116 28 35 40 19 0

C. Dioxide 101 33 14 438 202 740 429 373 296 81

Nitrogen 83,556 7,341 8,907 17,365 12,817 135,370 103,945 47,920 80,662 37,205

*Resevoir, 2-gallon drainage reduced hydrogen to 3000 ppm

40

Hydrogen Profile over time, including the observance of its peak, 138 kV

Sample Date

03/28/95

6/21/06 07/10/07 02/15/10 05/11/10 8/6/2013 9/28/2015

Drainage ---- ----no

drainage4

gallons6

gallons 1 quart 2

gallons2

gallons2

gallonsno

drainage50

gallons100

gallons

0 gallon

s25

gallons55

gallons110

gallons165

gallons0

gallons25

gallons55

gallons110

gallons165

gallons195

gallons

Methane 49 13.5 12 13 13 12 11 12 11 12 11 10.6 9.8 10 10 9.2 9.8 10 10 11 11 11 10

Ethane 23 5.3 5.4 5.2 5.1 6.3 5.7 5.6 5.5 4.5 4.5 3.9 4.2 4.2 4.3 4.1 4.1 4.2 4.5 5.1 5.0 5.0 4.7

Ethylene 12 1.4 1.2 1.3 1.2 1.1 1.2 1 1.1 0.8 0.9 0.8 0.8 0.9 0.8 0.7 0.8 0.8 0.8 0.8 0.8 0.8 0.8

Acetylene 0.0 0.0 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Propane 34 7.7 7.0 6.7 6.8 6.5 5 5.2 5.4 6.6 6.5 6.0 5.3 5.4 3.8 4.0 3.9 5.1 5.1 5.1 4.8 4.9 4.5

Propylene 23 3.8 3.5 3.5 3.6 3.3 2.5 2.8 2.5 3.0 2.9 2.6 2.5 2.4 2.3 2.3 2.3 2.4 2.2 2.2 2.1 2.1 2.1

Iso-butane 2 10 1.8 1.8 1.1 0 0 0 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 0.5 0.4 0.4

n-butane 19 3.4 0.3 0.0 1.0 0.7 0.7 0.6 0.6 3.5 3.5 3.1 0.5 0.5 0.4 0.4 0.4 0.5 0.5 0.5 0.5 0.5 0.5

t-2-butene 2 0.0 0.2 0.0 0.0 0 0 0 0 0.0 0.0 0.0 0.1 0.1 0.1 0.2 0.1 0.2 0.2 0.1 0.1 0.1 0.1

1-butene 6 1.3 1.5 1.5 1.3 0.8 0.6 0.8 0.5 1.2 1.2 1.4 0.6 0.6 0.5 0.5 0.6 0.6 0.7 0.7 0.6 0.7 0.6

Isobutylene 6 2.6 2.9 2.7 2.5 3.7 14 3.4 8.2 2.9 2.9 2.9 5.7 4.7 3.1 3.4 3.4 3.6 3.6 3.9 4.2 4.1 4.0

Hydrogen 45,727 59,719 61,450 61,616 61,988 86,754 85,576 85,101 87,462 86,414108,65

6 95,760 72,982 92,433 95,627 91,460 77,591 75,297 83,437102,52

0 96,647 71,697 60,077

C. Monoxide 19 18 19 20 19.3 12 10 9 12 9.0 10 9.0 9.0 9.1 11 9.4 9.7 9.7 11 11 12 12 11

C. Dioxide 193 438 387 450 423 295 274 284 268 270 263 247 227 237 259 242 237 227 242 254 247 255 237

Nitrogen 24,443 17,365 26605 14825 15269 22,190 18,566 18,045 18,230 18432 21866 16453 17452 17549 20539 14961 17069 14,204 14,053 15,040 13,287 14,473 15,400

41

Follow-up of Hydrogen beyond the Splice, showing Reduction in the Pipe, 138 kV

42

HPGF & SCFF Cable systems

• Due to extensive reliance on HPFF cable systems (nearly 80%) in the US, the GA data on HPGF and DGA on SCFF cable systems are limited, however, both are performed. The success of HPGF/reservoir headspace/hydrogen-cooled generators data supports the application of GA for dry extruded transmission terminations

• The concentration of gases in HPGF cables is significantly smaller due to diffusion/lack of accumulation and limited fluid amount resulting from the replacement by nitrogen. However, the gas pattern follows similar trends in problem/failure situations

• For reasons of much lesser fluid in SCFF cables compared to HPFF ones, the gas levels are much smaller. However, SCFF splices can yield markedly higher levels of acetylene due to any electrical activity occurring in the splice region which has limited fluid compared to HPFF counterparts

43

SCFF Cable Splice Sampling by EDOSS

44

DGA on HPGF and SCFF Cables, 120-138 kV

Gases HPGFHPGF (after

failure SCFF

Methane 0.43 3.29 48.7 59 2.1 20 12

Ethane 0.31 1.063 1.5 8.2 2.3 5 7

Ethylene 0.12 2.564 8.9 44 0.6 4 6

Acetylene 0 0.016 14.4 60 0 3.3 0

Propane 0.33 0.757 0.2 5.4 3.1 5 6

Propylene 0.17 1.516 2.1 18 1.4 3 4

Iso-butane 0.09 0.367 0.6 1.5 0 1 1

n-butane 0.15 0.411 0.02 0.3 0 2 1

Isobutylene 0.60 4.29 6.6 7.2 0 2 3

Hydrogen 56.4 188.5 564.9 219 0 1,359 170

C. Monoxide 32.1 7.5 412.9 11 18 20 8

C. Dioxide 17 31.3 98.7 172 183 98 30

45

DGA on Extruded Cable Terminations

• Recognizing that DGA is applicable to fluid-filled equipment, DGA for extruded cable terminations is being considered

• The high viscosity fluids employed in such terminations (3,500 – 10,000 SUS at 400C) coupled with the limited fluid volume present sampling challenges – and proper sampling is a must. Here EDOSS, with its mentioned low sample requirement and combined with a micropump, is most appropriate & has been consistently utilized to generate DGA data by DTE

• While XLPE cables can yield large amounts of methane & butanes, with some lower concentration of other hydrocarbon gases, it is noteworthy that acetylene & hydrogen do not evolve from XLPE, including the cross-linking process. With experience, one can amply distinguish any common hydrocarbon gases. The contribution of cable insulation to the formation of ethylene and propylene is too minute. Acetylene is the best indicator of potential trouble

• As a result of laboratory and gradually increasing field efforts, significant progress has been made toward the application of DGA to extruded cable terminations, supported by data. A few recent extruded cable termination failures have placed focus on development of diagnostic methods for this accessory and DGA offers a sound option

46

Extruded Cable Termination Sampling by EDOSS combined with a Micropump & narrow Tygon Tubing/fittings

While the bottom termination valve should be used, the sample can be also extracted from the termination top with tygon tubing – it is necessary to cover a few elevations of the termination fluid. The excess fluid can be put back in the termination by the two-way micropump, shown below

Extruded 138 kV Cable Termination Sampling Set-up from Top Utilizing a Micro Pump with a Narrow Tygon Fluid Extraction Tubing at a Test Facility

DGA sampling of horizontal terminations by EDOSS in

conjunction with a micro-pump at a Test Facility

EDOSS sampling set-up for a modern 230 kV

termination by micropump and its accessories in

the field

Reversible

Micro pump

EDOSS Vial

47

DGA Results (ppm) on 138 kV and a modern 230 kV Extruded Cable Termination

Case No. 138 kV 230 kV

CH4 11,737 219,309 12,617 223 372 2,084 4,930 248,133 280,867 205,067

C2H6 36 23 37 27 40 44 30 992 1,015 776

C2H4 3.3 5.3 3.6 5.2 4.0 9.5 8 10 21 13

C2H2 0 0 0 0 0 4.0 6 0 2.5* 1.4

C3H8 211 137 227 158 238 14 130 127 112

C3H6 7 6 8 5 10 23 37 50 44

i-C4H10 1,283 768 1,301 884 1,345 11 198 204 216

n-C4H10 864 544 951 763 1,017 19 65 63 55

C4H8 2,275 844 1,534 1,142 1,518 81 9,227 9,713 11,892

H2 13 18 17 32 25 531 30 192 154 141

CO 405 209 232 342 686 677 455 33 25 23

CO2 7,546 11,709 8,646 4,837 6,609 2,863 1,060 1,115 950 883

48* This was examined and no tracking was observed, but all components were not fully dismantled for quick restoration

DGA Data (ppm) on 12 Terminations, with only one showing Acetylene

Sample date August 11, 2014

Sept. 5

2014

Aug. 12,

2014

Sept. 5,

2014

Aug.12,

2014

Location

Circuit 4052 Circuit 3852

1806YJ

(Phase A)

1807YJ

(Phase B)

1808YJ

(Phase C)

1809YJ

(Phase A)

1810YJ

(Phase B)

1811YJ

(Phase C)

1812YJ

(Phase A)

1813YJ

(Phase B)

1814YJ

(Phase C)

1815YJ

(Phase A)

1816YJ

(Phase B)

1817YJ

(Phase C)

Methane 102 8.4 57 11 6.3 7.0 49 52 45 4,156 3,339 4,324

Ethane 18 4.0 11 7.1 8.4 4.9 18 6.9 12 11 10 13

Ethylene 2.7 1.6 9.2 1.2 3.2 1.0 2.6 1.4 2.7 2.9 2.3 2.5

Acetylene 0.0 0.0 7.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Propane 72 32.7 46 46 46 39.7 53 37 48 42 44 69

Propylene 3.8 2.0 3.4 1.9 14.7 2.6 2.6 2.4 3.6 3.5 3.4 8.9

Iso-butane 414 215 359 305 195 250 325 290 274 255 255 358

n-Butane 72 62.3 73 62 56 71.7 52 61 60 55 55 87

t-2-Butene 2.6 2.5 2.6 2.4 10.7 5.6 2.1 2.5 1.1 2.3 2.0 3.0

1-Butene 51 40.0 42 39 41 45.7 39 36 43 33 36 55

Isobutylene 1,466 686 981 985 633 783 1,059 978 996 961 976 973

Hydrogen 0 17 35 0 0 0 22 0 0 20 19 28

C. Monoxide 322 58.3 210 68 48 41.0 230 75 186 205 176 269

C. Dioxide 75,020 9,433 57,900 9,247 6,550 5,684 17,910 10,706 12,692 29,594 25,928 30,154

Oxygen 19,925 19,508 12,957 22,250 22,580 17,711 19,596 16,287 16,895 19,270 81,759 19,098

Nitrogen 108,226 112,643 106,331 101,047 106,201 104,965 109,336 107,162 114,329 108,717 115,134 114,416

Moisture 28.5 26.6 28.3 30.2 27.6 41.1 18.9 24.9 16.2 20.2 28.9

49

Acetylene (ppm) Variations along the Termination Length

Sample date September 5, 2014

Location Circuit 4052

1808YJ (Phase C)

Methane 66 67 69 62 65 66 67 68

Ethane 13 13 13 13 14 13 13 13

Ethylene 9.9 10 10 9.9 10 10 11 10

Acetylene 8.1 8.2 8.5 8.5 8.7 8.7 8.6 8.7

Propane 51 51 50 49 50 51 51 51

Propylene 3.9 3.9 3.9 4.1 4.0 3.9 4.1 4.1

Iso-butane 377 381 379 381 378 384 386 391

n-Butane 80 76 81 84 83 82 83 81

t-2-Butene 2.4 2.5 2.8 2.6 2.5 2.8 2.7 2.6

1-Butene 48 46 47 47 50 49 50 50

Isobutylene 991 995 1001 997 1,011 1,112 1,109 1,113

Hydrogen 31 34 38 34 38 38 37 36

C. Monoxide 229 227 231 224 244 231 229 223

C. Dioxide 59,108 57,984 60,123 59,364 60,001 59,879 60,124 60,328

Oxygen 14,592 12,758 15,052 14,607 15,327 15,233 15,844 14,494

Nitrogen 109,931 105,813 111,766 108,238 113,932 107,838 111,306 109,298

50

Date November, 2014

Location 1808YJ (Ph C) 1806 YJ (Ph A)

Methane 7.4 6.5 35 34

Ethane 2.6 2.8 5.3 5.2

Ethylene 1.3 1.4 1.1 1.2

Acetylene 1.2 1.2 0 0

Propane 27 29 62 63

Propylene 1.9 2.0 3.1 3.2

iso-Butane 333 363 423 415

n-Butane 60 50 75 72

Isobutylene 841 899 1412 1409

Hydrogen 0 0 0 0

C. Monoxide 10 12 52 48

C. Dioxide 11,076 10,466 41,331 38,435

DGA Data (ppm) on Fluid Collected in a bottle for two Phases during Dissection

51

Sampling by EDOSS with a Micropump on the received Terminations

Terminations with the associated cables, as received

at the EPRI Charlotte, North Carolina site

52

Termination Design & the Revealed Carbonization at the Poor Cable Semiconducting transition to the Cable

Insulation during Dissection

Transition points in terminations with acetylene

(left) and without acetylene (right).

Tracking/carbonization due to PD is visible in

termination with acetylene.

Tracking/carbonization observed,

with the elastomeric semiconducting

component of the stress-cone

covering the cable

insulation/insulation screen interface

Tracking/Carbonization

Steep transition &

carbonizationSteep transition

Compression Springs

Stress cone insulation

(molded epoxy)

Stress cone deflector

(molded epoxy coated with

semi conductive layer)

Major seal (semi-

conductive rubber)

Spaces filled with

dielectric liquid

Extruded termination design, including a

magnified view of the stress-cone region

Epoxy spacers

Cable Semi-con Screen

Transition point

53

72 kV HPFF Termination Damage

Stress Cone Movement and Carbonization and Severe Dendrite Formation, 161 kV HPFF termination being used at 138 kV

Tracking on Outer Tape, 138 kV HPFF CableTracking Evidence on Cable Insulation, 138 kV Extruded Metal Stress

Cone Design

Examples of DGA Revealed Damage for HPFF and Extruded Terminations

54

Transformer vs. Cable DGA

55

Transformers vs. Cables, DGA-Wise

• Transformer experience is useful but not a one-to-one substitution due to inherent design, material & operational differences:

fluid pressureelectrical stressesfluid characteristicsdesign & geometryfluid movementgas diffusion/permeationdegree of insulation tightnesscellulosic materialsgas limits

• Transformer guidelines would shutdown otherwise satisfactory cables

56

Transformers vs. Cables, Main Material Differences

• Compared to transformers, high voltage cellulosic cable papers are of high quality, no additives for thermal upgrading (even distilled water is utilized for final washes), only the turn insulation paper comes closer to cable paper

• Transformers have a range of cellulosic materials ranging from turn insulation papers to press boards to ducts to barriers to maple wood……..

• Besides the conductor, the inevitable core of transformers also constitutes a heating source, oil often with metal contact

• Transformers experience more heat, and all run close to rated temperature than cables, subject more to hot-spot, vibrations, short-circuit forces, impairment of cooling systems………….

• Accordingly, gas generation is impacted differently

57

Transformers vs. Cables continued……

• HPFF Cables can have a minimum of two fluids (pipe & impregnant), each with widely varying viscosity and often type; viscosity of these cable fluids is significantly higher than that of transformers; SCFF have one low viscosity, with viscosity similar to that of transformers

• Contamination of the original pipe fluid with saturated hydrocarbons has been observed in several earlier cables (late 60-mid 70s) – blanketing or otherwise -Ruled out for transformers & SCFF

• Generally the same sampling & analysis methods; EDOSS is fully applicable• Because of design and material differences, interpretation is markedly

different for the two products, e.g. the TDCG for transformers is typically up to 800 ppm. However, several thousands ppm of hydrogen are not at all uncommon for HPFF cables, making the corresponding TDCG concept irrelevant

• Unlike HPFF cables & splices (but not terminations), transformers can yield much higher ethylene and acetylene levels, even some monomers of butane

• The concept of key ratios generally tends to hold in both cases• Large transformers are design-ordered, and thus designs vary significantly,

unlike cables. While general guidelines have commonality, the observed gas patterns can be equipment - specific, and it should be kept in mind.

58

Transformer Sampling by EDOSS

59

DGA on DTE’s GSUs involved in an EPRI Study

Power Plant STCPP BLRPP GRWPP RRGPP MONPP

Main Unit MU #1 MU #2 MU #3 MU #6 MU #7 MU #1 MU #2 MU #1 MU #2 MU #3 MU #1 MU #2 MU #3 MU #4

Age/MVA 15/190 25/300 27/190 46/370 36/600 23/700 22/700 30/865 49/315 47/360 1/820 33/865 33/865 32/865

Hydrogen 75 19 16 175 29 36 24 83 91 126 13 36 23 52

Methane 177 14 81 24 166 216 212 325 90 455 7 137 17 231

C. Monoxide 545 233 265 471 247 256 413 48 254 1,066 219 465 53 466

Ethylene 29 9.4 7.2 9.2 16 51 19 743 84 1,471 1.2 54 30 126

Ethane 446 6.9 102 13 278 365 106 68 71 314 1.8 111 10.5 156

Acetylene 0.0 0.0 0.0 0.0 0.0 1.4 0.0 5.1 0.0 0.0 0.0 0.7 0.0 0.0

Propylene 125 10 12 16 30 36 22 254 103 1,148 3.8 28 17 60

Propane 877 4.0 95 10 255 229 61 18 42 260 1.6 95 6.7 127

C. Dioxide 15,708 1,639 2,625 6,078 2,062 4,229 5,726 2,156 4,629 24,617 1,619 10,002 2,061 9,103

n-butane 312 1.1 19 2.5 48 48 13 2.3 10 64 0.0 20 1.5 24

Isobutane 60 0.3 5.9 1.9 13 24 6.1 3.9 16 19 3.3 6.5 0.0 7.1

Isobutylene 197 54 34 47 73 282 85 21 628 587 83.5 50 4 43

t-2-butene 17 0.0 1.1 1.6 1.9 2.0 1.3 7.0 7.1 58 0.0 0.0 0.0 2.2

1-butene 37 2.4 2.8 3.7 5.8 7.1 4.2 36 21 226 0.0 5 2.5 9.8

Oxygen 807 960 1,437 683 513 483 627 1,198 1,737 2,032 1,113 3,523 591 799

Nitrogen 93,905 93,595 51,458 85,960 74,558 65,911 76,039 13,858 75,067 86,474 8,300 26,227 106,411 29,923

TDCG 1,272 282 470 692 736 924 774 1,271 589 3,431 241 802 133 1,029

Moisture 34.3 6.5 16.1 51.0 25.3 27.9 15.7 10.3 19.6 30.4 9.8 28.7 7.8 24.1

BD 56.5 51.1 49.8 31.4 57.9 51.3 47.0 50.9 51.1 49.1 51.5 53.0 49.5 48.1

% DF @100C 26.96 1.63 1.67 3.77 1.02 1.104 1.421 0.257 9.59 5.58 0.236 0.418 0.322 0.320

60

330 MVA, 2002, Core Form GSU, with abnormal Hydrogen Concentration, removed

Sample Date 1/16/1311/25/1

312/31/13

1/13/14 1/21/14

1/27/14

2/03/14

2/10/14 2/17/14 3/10/14 3/31/14 4/28/14 5/20/14

Hydrogen 0 1155 1,905 2,156 2,412 2,624 2,901 3,091 3,312 3,682 4,281 4448 4128

Methane 28 2871 4,401 4,897 5,314 5,812 6,312 6,553 7,487 8,679 9,215 9405 9578

C. Monoxide 31 113 119 121 126 131 144 149 158 151 162 156 167

Ethylene 56 3315 4,476 4,819 5,137 5,629 6,075 6,388 7,095 8,419 9,345 9712 9912

Ethane 18 1012 1,564 1,674 1,760 1,888 2,008 2,105 2,339 2,670 3,012 3259 3317

Acetylene 0.6 3.5 5.1 5.8 6.5 7.3 8.2 8.8 9.3 11 14 12 12

Propylene 73 2112 3,088 3,632 3,812 4,001 4,378 4,465 4,912 5,649 6,214 6514 6628

Propane 8.3 215 302 345 357 364 425 445 457 529 575 615 632

C. Dioxide 255 1237 1,445 1,501 1,497 1,442 1,434 1,447 1,444 1,445 1,418 1402 1488

n-Butane 3 23 29 33 35 37 39 42 43 52 55 57 51

Isobutane 2 11 17 21 21 22 23 24 25 24 26 22 24

Isobutylene 54 389 588 662 679 739 787 808 840 951 1,069 1205 1182

Nitrogen 26,620 22,412 27,817 27,713 27,134 27,899 25,631 29,407 30,245 30,456 28,567 30489 29780

Oxygen 1,451 2,365 2,812 1,732 1,864 2,028 1,728 2,328 2,814 1,548 2,248 2215 2459

TDCG 134 8,470 12,470 13,673 14,756 16,091 17,448 18,295 20,400 23,612 26,029 26,992 27,114

61

Sample Date 12/16/11 12/28/11 01/11/12 02/13/12 02/27/12 03/14/12 03/27/12 04/09/12 04/23/12 05/07/12 05/21/12

Winding Temperature (oC) 64 70.2 72.5 74.7 63 69.9 69.5 65 53.5 79

Oil Temperature (oC) 47 51.2 55.8 55.8 45 52.1 53.1 47 71.7 61

Energized Yes Yes Yes Yes Yes

Mwatts 713 734

Mvars 141

MVA

Hydrogen 36 34 22 18 27 22 18 21 47 22 28

Methane 387 381 387 355 341 307 281 255 215 205 163

C. Monoxide 268 271 279 281 274 222 212 211 199 178 141

Ethylene 142 142 149 136 131 124 121 118 111 101 92

Ethane 978 1,012 1,175 1,189 1,161 1,094 1,101 1,089 1,015 975 894

Acetylene 0 0 0 0 0 0 0 0 0 0 0

Propylene 326 348 410 421 445 477 484 491 472 453 439

Propane 993 1,065 1,191 1,274 1,295 1,325 1,356 1,428 1,411 1,365 1,328

C. Dioxide 3,187 3,360 3,145 3,012 2,987 2,880 2,784 2,812 2,715 2,541 2,274

N –Butane 229 247 264 283 312 337 346 358 325 340 332

Isobutane 86 92 97 101 105 112 116 117 113 109 105

Isobutylene 487 491 510 525 543 549 565 584 561 539 526

Nitrogen 61,284 68,147 66,837 58,756 58,547 68,974 67,566 70,142 74,654 72,255 70,707

Oxygen 1,897 2,104 1,879 2,215 1,978 3,045 2,457 3,245 2,875 2,978 2,145

TDCG 1,811 1,840 2,012 1,979 1,934 1,769 1,733 1,694 1,587 1,481 1,318

Moisture (ppm) 18.3 16.8 13.9 15.8 9.7 20.1 18.1 14.1 14.5 20.2

Oil Saturation (%) 11.7 10.9 ---- 10.8 9.4 9.0 7.4 8.1

Acid Number (g/mg) 0.024 0.025 0.024 0.024 0.025 0.024 0.025

Disspation Factor @100oC 0.0174 0.0345 0.0369 0.0445 0.0522 0.0567 0.0594

Dielectric Strength (kV),

ASTM D1816, 2mm gap 57.6 61.4 62.5 60.4 61.9 64.3 62.3

Color 1.5 - 2.0 2.0 2.0 2.0 2.0 2.0 2.0

IFT (dynes/cm) 35.1 34.68 34.45 34.12 34.01 34.25 34.13

43-Year, 865 MVA GSU, still not showing concern

62

865 MVA, 1989, Shell Form, Removed and Un-tanked/Dissected in Mexico

Load 650 550 500 630

Sample Date 12/12/03 12/14/0312/16/03 12/17/03 12/18/03

10:15pm 2:15am 4:15am 6:15am 12:00am 11:30pm 3:30am 8:30am 5:00pm

Winding Temp. 38 55 60 55 50 50 45 45 45 46 50

Oil Temp. 35 45 45 40 40 40 40 38 40 38 40

Hydrogen 1,224 1,367 1,633 1,363 1,454 1,579 1,365 1,433 1,470 1,341 1418

Methane 3,415 3,843 4,150 3,915 3,940 4,167 3,876 3,926 4,011 4,029 4004

C. Monoxide 285 263 248 227 247 267 268 228 244 276 282

Ethylene 2,906 3,188 3,375 3,289 3,295 3,407 3,226 3,273 3,337 3,325 3273

Ethane 930 1,038 1,101 1,084 1,081 1,113 1,063 1,080 1,100 1,100 1080

Acetylene 2.6 2.4 1.9 2.0 2.1 2.1 1.8 1.7 1.7 1.7 1.6

Propylene 2,114 2,351 2,437 2,445 2,421 2,466 2,406 2,425 2,470 2,478 2427

Propane 193 215 224 226 222 226 221 223 228 226 221

C. Dioxide 8,450 8,949 9,568 8,920 8,888 9,367 8,661 8,612 8,738 8,640 8365

n-butane 18 20 21 22 21 21 21 21 21 21 20

Isobutane 14 15 15 16 16 16 16 15 16 16 15

Isobutylene 372 412 126 127 125 126 125 127 129 129 126

t-2-butene 109 123 384 387 384 385 385 389 394 392 384

1-butene 335 375 410 415 410 411 421 415 420 428 413

Nitogen 42,716 43,749 50,708 39,803 47,445 39,766 46,409 40,994 39,711 44,509 43163

Oxygen 1,710 1,772 2,916 1,366 1,857 1,391 1,966 1,284 1,075 2,015 1288

TDCG 8,763 9,701 10,509 9,880 10,019 10,535 9,800 9,940 10,163 10,073 10,059

63

Dissection of the Removed 865 MVA GSU without Failure

Winding Damage Occurred within The Innermost Turn of HV Coil Number 28

Damaged Portion of the Inside Turn of Coil 28

In the area of one of the Auxiliary Legs between the B and C Phases, a Localized Hot Spot was Found on the Core 64

General Gas Concentration Limits for Transformers based on DTE Energy Laboratory/Field Data, with

Considerations to Publish Literature

GasNormal Range

(ppm)Acceptable

(ppm)Concern Level

(ppm)Action Level

(ppm)

Hydrogen (H2) 0-150 151-250 251-750 >750

Acetylene (C2H2) 0-3 4- 10 11–20 >20

C. Monoxide (CO) 0 – 200 201-500 501 – 1000 >1000

C. Dioxide (CO2) 0 – 2,000 2001-5000 5,001-10,000 >10,000

Methane (CH4) 0 – 100 101-400 401 –800 >800

Ethane (C2H6) 0 – 100 101-200 201–300 >300

Ethylene (C2H4) 0 – 100 101-200 201–500 >500

Propane (C3H8) 0 – 500

Isobutylene (C2H8) 0 – 50 50-100 101-200 >200

TDGC 0–500 500-2,000 2,001–4,000 >4,000

Oxygen (O2) 750 1,000 2,500 >4,000

Gas Ratios 2

CO2/CO 4 – 10 > 1 0.75 – 1 < 0.25

C2H6/C2H4 2 – 4 4 - 5 < 0.25

(1) With the exception of appreciable amount of acetylene, other gases have to be

looked in relation to others

(2) Ratios only apply to gas concentration levels larger than 50 ppm for carbon

oxides and larger than 20 ppm for hydrocarbons 65

Summary

• DGA is an economical & effective diagnostic test for taped cables and transformers, as shown by its growing worldwide application. Generally better understood, users can readily relate to DGA data

• Acetylene is the single, most important DGA gas for all equipment, so is its increase over time. However, its upper limit, like other gases, cannot be accurately given. A 25 ppm level of acetylene poses concern for a power transformer, 150 for HPFF termination, 50 for a SCFF termination, and 20 ppm for an HPFF splice

• DGA success critically depends on proper sampling, analysis and interpretation. Field sampling is under full control of the user; it is here that most mistakes are made

• DGA behavior of terminations is markedly different from that of splices, cables per se and risers, significantly varies amongst cable types, and DGA offers the most value for all types cable terminations – the limited fluid volume renders this test quite sensitive and quite decisive.

• Cable DGA should not be confused with that of transformers’

• Due to much higher viscosity of HPFF fluids, sampling can present a challenge, all the more in winter – readily overcome by EPRI method(s). Small sample requirement of EDOSS is valuable in many applications

• A keen understanding of cable’s operational history (and construction) is essential for realizing maximum value from DGA, same for transformers. DGA trending is invaluable to monitor the dormant, stable and deteriorating nature of the problem.

• DGA holds great promise for HV extruded cable terminations with fluid & potential for dry ones; provides assessment of crosslinking gases in the former. Based on the high viscosity and limited fluid volume , EDOSS may offer the only viable approach to DGA for fluid-filled terminations. An acetylene level of about 10 ppm poses concern for fluid-filled extruded terminations, requiring close monitoring, more data needed.

• DGA On-line systems & sensors should be considered for oil-paper cables, and extruded cable terminations

• DGA can be equipment-specific. While guidelines are useful, the user should develop his/her own DGA expertise on properly generated-data, as many results can defy accepted norms

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Acknowledgements

• The continuing support of EPRI since the early 1980s and that of over 75 North American and Overseas Utilities in DTE Energy’s DGA efforts is deeply acknowledged

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