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IEEE WG C57.139Nashville, March 13, 2012

APPLICATION OF DUVAL TRIANGLES 2TO DGA IN LTCs

Michel Duval

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Normal operation of LTCs may involve:

-arc-breaking-in-oil between contacts, producing arcing gases D1.-switching of selectors and valves, also producing sparking discharges D1.-current dissipation in resistors, increasing their temperature and producing hot spot gases T3, T2 or T1.-combinations of the above, producing mixtures of the corresponding gases.

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Faulty operation of LTCs may involve:

-an increase in the resistance and temperature of contacts, with the production of hot spots T3 and T2, and coking on contacts, through carbonization of oil.

-abnormal arcing D2 or D1 on metallic parts of the LTC.

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Examples of LTC failures:(heavy coking in a ABB UZC)

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Examples of LTC failures:(heavy coking in a Federal Pioneer TC546)

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Examples of LTC failures:(moderate coking in a GE LR83)

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Examples of LTC failures:(arcing/short-circuit in a GE LR83)

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Examples of LTC failures:(arcing/short-circuit in a GE LR65)

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To be able to distinguish between normal and faulty operation of LTCs:

-gases formed as a result of normal operation should be identified as precisely as possible under different power operating conditions.

-deviation from normal operation will indicate faulty operation.

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Mostly arcing gases are formed during normal operation of a large majority of LTCs, such as:

-LTCs of the reactive-type in oil or vacuum from:

-Westinghouse: UN, UR, UV series, UTS, UTN, UTT.-Cooper, McGrawEdison: series 394, 396, 494, 550, 995, 996.-General Electric: LR and LRT series.-Reinhausen: RM series.-Allis Chalmers, Siemens: TLH series.-Federal Pacific: TC series.-Ferranti Packard: RT series.

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-also, in LTCs of the resistive-type in oil or vacuum from:

-ABB: UB, UC, UZ series.-Reinhausen: OilTaps C, R, V, Y.-Westinghouse: UTH.-Hyundai: RS series.

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Duval Triangle 2 can be used for all these types of LTCs, with:

-arcing gases D1 appearing on the left side of the Triangle,

-hot spot gases T3, T2 and T1 on the right side.

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The Duval Triangle 2 for LTCs (inspected cases)

Inspected cases of: : Normal operation; : Severe coking; : Light coking; :

“Heating”; : Strong arcing D2; : Arcing D1

Fault zones:

N = normal operationT3 = Thermal faults T > 700°CT2 = Thermal faults 300 < T < 700°CX3 = Fault T3/T2 in progressX3 = abnormal arcing D2D1 = abnormal arcing D1

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HQ Data - All ABB

Ref. for all HQ data: M.Foata

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HQ Data – ABB In-tank cylinder

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HQ Data – ABB Selector switch

UZE change-over selector problem

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Altalink UZCRT

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HQ Data - GE LR83

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HQ Data – Ferranti Packard

Model known to be susceptible to coking in the inverter switch?

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HQ Data – Westinghouse URS

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HQ data - OilTaps V

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OilTaps R

The use of methane in addition to acetylene and ethyleneindicates some normal overheating T1 of the resistorsduring the operation of these LTCs.

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Triangle 2 applied to large databases by J.Dukarm

Siemens Westinghouse

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Triangle 2 applied to large databases by J.Dukarm

McGraw Edison Cooper

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Other types of normal operation

-Some resistive LTCs such as OilTaps Y and M and VacuTaps VV operate normally in either zone N or zone T3 or zone T2, depending on operating conditions.

-The use of methane in addition to acetylene and ethylene allows to distinguish between faulty and normal operation in such LTCs.

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HQ data - OilTaps D:

3 phases - Y 1 phase - ∆ Normal operationof resistors

Faulty operation

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During high power tests, normal (in blue) and faultyoperation (in red) of resistors.

VacuTaps VV:

Ref: R.Frotscher, CIGRE

In service, normal operation of selectors

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Ref: R.Frotscher (Orlando)

VacuTaps VR:Normal operation in zone T2 is probably due to operation of selectors and resistors.

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-A few other resistive LTCs such as OilTaps G and some UZBs of ABB (ref.John Pruente) operate normally in zone X3 (mixture of arc-breaking-in-oil and high-temperature operation of resistors), depending on operating conditions.

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HQ data - OilTaps G:OilTaps G are high-currents application models. Normal gases occur in zone X3 (mixture of arcing and hot spots).

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Different versions of Triangle 2 should therefore be used for some LTCs, indicating the normal zone(s) of operation depending on power operating conditions:

-Triangle 2a and 2b for OilTaps M-Y and VacuTaps VR-VV.

-Triangle 2c for OilTaps G and some UZBs.

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Finally, reactive LTCs of the vacuum-type:

-Arc-breaking activity occurs in the vacuum bottle only. Normal operation in the surrounding oil used for cooling the bottle does not involve sparking of selector or resistor heating.

-Triangle 1 should be used for these LTCs.

Overheating in oil suspectedRef: Paul Boman