What is tribology consultancy?

Tribology consultancy involves expert analysis and advisory services for lubricating oils, grease, transformer oil, and coolants to optimize equipment performance and reliability.

What industries does TriboTech serve?

TriboTech serves TSOs, DSOs, wind farm operators, data centers, solar parks, and industrial operators across Northern Europe.

How quickly can TriboTech respond to emergencies?

TriboTech offers 24/7 emergency support for critical infrastructure with analysis results typically within 48 hours.

Are TriboTech's diagnostic tools free to use?

Yes, all TriboTech diagnostic tools are 100% free to use with no registration required. This includes all 7 Duval Triangles, 5 Pentagon variants, and IEC 60599 ratio analysis. The tools are IEEE C57.104-2019 and IEC 60599:2022 compliant.

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Duval Fault Code Library

What D1-H, T3 or S actually means: every fault code our DGA tools can emit, with baseline severity, recommendations, and the exact clause in the standard or paper that defines it.

Generated from TriboTech's central fault-code registry — the same single source of truth our calculators and report pipeline use, with clause-level provenance on every entry.

Electrical discharge

Partial discharge and low-/high-energy discharge faults, including the 2022 oil ("-H") vs paper ("-P") splits.

PD — Partial Discharge

Medium

Low-energy electrical discharge (corona type) in gas bubbles or voids.

Recommendations: Monitor gas evolution rate. Corona PD is usually benign, but watch for the X-wax → thermal-runaway path (IEC 60599:2022 §5.9); sharpen concern for instrument transformers, where near-instant breakdown can occur.

Possible causes

Gas-filled cavities from incomplete impregnation
High humidity in paper
Oil supersaturation or cavitation

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Triangle 3b Triangle 4 Triangle 5 Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 3 Pentagon 4 Pentagon 4b Unified Pentagon

Standards:IEC 60599:2022

D1 — Low-Energy Discharge

High

Low-energy electrical discharge (sparking, partial arcing).

Recommendations: Investigate for loose connections or floating potentials. D1→D2 escalation is an immediate-action trigger (TB 771 §3.7).

Possible causes

Sparking/arcing between bad or floating-potential connections
Discharges between clamping parts, bushing and tank
Tracking in wooden blocks, insulating beams or winding spacers
Breakdown of oil; selector breaking current

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Pentagon 3 Pentagon 4

Standards:IEC 60599:2022

D1-H — Low-Energy Discharge in Oil

High

Applies to: Mineral oil

D1 discharge located in oil ("-H" = Huile/oil, NOT high energy).

Recommendations: Locate the discharge source. Note TB 771 places arcing in oil only in the lesser-concern group; escalation to paper (D1-P) or to D2 raises priority.

Emitted by:Triangle 1 Triangle 3b Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 4b Unified Pentagon

D1-P — Low-Energy Discharge in Paper

High

Applies to: Mineral oil

D1 discharge located in paper insulation — strictly more dangerous than D1-H (paper carbonises).

Recommendations: Higher priority than D1-H: discharge in paper degrades solid insulation. Corroborate with CO/CO2/furans.

Emitted by:Triangle 1 Triangle 3b Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 4b Unified Pentagon

Standards:CIGRE TB 771

D2 — High-Energy Discharge

Critical

High-energy electrical discharge (arcing) with power follow-through.

Recommendations: Immediate action. High-energy arcing threatens winding and insulation integrity — de-energise and inspect.

Possible causes

Flashover, tracking or arcing of high local energy / power follow-through
Short circuits between windings, ground, bushings and tank
Closed loops between adjacent conductors around the main magnetic flux

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Pentagon 3 Pentagon 4

Standards:IEC 60599:2022

D2-H — High-Energy Discharge in Oil

Critical

Applies to: Mineral oil

D2 arcing located in oil ("-H" = Huile/oil).

Recommendations: Immediate action. Confirm location; arcing in oil can migrate to paper.

Scope variations

Scope variations
Scope	Class	Baseline severity	What changes	Source
Mineral oil	Fault	Critical	D2 arcing located in oil ("-H" = Huile/oil).	Defined in:Duval & Buchacz 2022 Pt I, p.21
Mineral oil · OLTC (in-tank)	Fault	Critical	In in-tank (MR) OLTCs, D2-H-region gas is frequently contamination from normal switching, not a main-tank arc.	Defined in:Duval & Buchacz 2022 Pt I, p.21 (MR in-tank D2-H contamination)

Emitted by:Triangle 1 Triangle 3b Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 4b Unified Pentagon Triangle 2

D2-P — High-Energy Discharge in Paper

Critical

Applies to: Mineral oil

D2 arcing in paper insulation — strictly more dangerous than D2-H.

Recommendations: Immediate action, highest discharge priority. Paper carbonisation is likely — corroborate with CO/CO2/furans.

Emitted by:Triangle 1 Triangle 3b Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 4b Unified Pentagon

Thermal faults

Overheating and thermal faults by temperature band, plus the mixed discharge/thermal zone.

T1 — Thermal Fault < 300 °C

Medium

Thermal fault below 300 °C.

Recommendations: Monitor loading and cooling. Low-temperature thermal faults rarely need immediate action.

Possible causes

Overloading in emergency situations
Restricted/blocked oil flow in windings
Stray flux in clamping beams of yokes

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Triangle 3b Pentagon 1 Pentagon 1 (improved)Pentagon 3

Standards:IEC 60599:2022

T2 — Thermal Fault 300–700 °C

High

Thermal fault between 300 °C and 700 °C.

Recommendations: Refine with Pentagon 2 / Triangle 5 to separate oil-only heating from paper involvement. Check CO/CO2.

Possible causes

Defective bolted or gliding contacts (e.g. aluminium busbar)
Defective selector-switch contacts (pyrolytic carbon)
Circulating currents between yoke clamps, bolts and laminations
Abraded insulation between adjacent conductors in windings

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Triangle 3b Triangle 5 Pentagon 1 Pentagon 1 (improved)Pentagon 3

Standards:IEC 60599:2022

T3 — Thermal Fault > 700 °C

High

Thermal fault above 700 °C. Location (oil vs paper) must be resolved.

Recommendations: Mandatory corroboration: an unlocated T3 must be refined via Pentagon 2 / Triangle 5 toward the C-codes, with a CO/CO2/furan check (TB 771 App E.1). Escalate if paper carbonisation is indicated.

Possible causes

Large circulating currents in tank and core
Minor circulating currents in tank walls (high uncompensated magnetic field)
Shorting links in core steel laminations

Causes source: IEC 60599:2022, Table A.1, p.25

Emitted by:Triangle 1 Triangle 3 Triangle 3b Triangle 5 Pentagon 1 Pentagon 1 (improved)Pentagon 3 Pentagon 4

Standards:IEC 60599:2022

T3-H — Thermal Fault > 700 °C in Oil

High

Applies to: Mineral oil

T3 thermal fault in oil only ("-H" = Huile) — lesser concern than paper carbonisation.

Recommendations: Oil-only high-temperature faults are tolerable if stable (TB 771 §3.6 p.21: 3,500-440,000 ppm C2H4 reported in ~20 inspected cases of stable T3-H faults). Trend and confirm no paper involvement.

Emitted by:Pentagon 2 Pentagon 2 (improved)Pentagon 4b Unified Pentagon

Standards:CIGRE TB 771

O — Overheating of Oil < 250 °C

Medium

Overheating of oil below 250 °C (NOT oxidation). Light paper browning is possible.

Recommendations: Review loading and cooling. Distinct from oxidation — do not teach oxidation physics downstream.

Emitted by:Triangle 4 Triangle 5 Pentagon 2 Pentagon 2 (improved)Pentagon 4 Pentagon 4b

O-T1 — Overheating / T1 (unified)

Medium

Applies to: Mineral oil

Unified-pentagon merger of O and T1 (bands declared practically equivalent; 50 °C nuance: O <250 °C vs T1 <300 °C).

Recommendations: Treat as low-temperature overheating; monitor loading and cooling.

Emitted by:Unified Pentagon

DT — Discharge + Thermal Mixture

High

Mixed discharge-and-thermal zone (Duval "D+T"). Not an IEC Table-1 fault.

Recommendations: Resolve the dominant mechanism with a pentagon before acting. Severity defaults to the max of the components.

Emitted by:Triangle 1 Triangle 3 Triangle 3b

Standards:CIGRE TB 771

Stray gassing

Low-temperature gas formation that is not a damage fault — and behaves differently in ester fluids.

S — Stray Gassing

Low

Stray gassing of oil (< 200 °C, non-damage fault).

Recommendations: Non-damage fault. Trend against typical values; no action beyond monitoring unless it evolves.

Scope variations

Scope variations
Scope	Class	Baseline severity	What changes	Source
All fluids & contexts	Fault	Low	Stray gassing of oil (< 200 °C, non-damage fault).	Defined in:IEC 60599:2022 §4.3, p.12
Soybean oil (natural ester)	Normal	Normal	Natural-ester stray gassing (C2H6+H2) is a designed signature for a period of weeks to months after energisation — normal/expected.	Defined in:IEC 62770:2024 §4.1 Note 2
Rapeseed oil (natural ester)	Normal	Normal	Natural-ester stray gassing is a designed signature for a period of weeks to months after energisation — normal/expected.	Defined in:IEC 62770:2024 §4.1 Note 2
Sunflower oil (natural ester)	Normal	Normal	Natural-ester stray gassing is a designed signature for a period of weeks to months after energisation — normal/expected.	Defined in:IEC 62770:2024 §4.1 Note 2, p.9

Emitted by:Triangle 4 Triangle 5 Pentagon 1 Pentagon 1 (improved)Pentagon 2 Pentagon 2 (improved)Pentagon 3 Pentagon 4 Pentagon 4b Unified Pentagon

Standards:IEC 60599:2022 IEC 62770:2024

Paper carbonisation

Possible paper carbonisation and its published location refinements (Duval & Buchacz 2023).

C — Possible Paper Carbonisation

HighRequires corroborating analysis

Applies to: Mineral oil

Possible carbonisation of paper > 300 °C (probability, not certainty).

Recommendations: Corroborate before concluding: CO/CO2 ratio and furans (DP). Do not report paper carbonisation on the gas triangle alone.

Emitted by:Triangle 4 Triangle 5 Pentagon 2 Pentagon 2 (improved)Pentagon 4 Pentagon 4b

Standards:CIGRE TB 771

C1 — Carbonisation Between Turns / In Windings

CriticalRequires corroborating analysis

Applies to: Mineral oil

Paper carbonisation between turns or in windings — the hardest location to detect (pre-failure at the lowest gas level).

Recommendations: Highest carbonisation priority. Corroborate with CO/CO2/furans; treat as critical given the low detection threshold (PF 25 ppm).

Emitted by:Pentagon 2

C2 — Carbonisation Outside Windings

HighRequires corroborating analysis

Applies to: Mineral oil

Paper carbonisation outside the windings.

Recommendations: Corroborate with CO/CO2/furans. Less dangerous than C1, more than C3.

Emitted by:Pentagon 2

C3 — Carbonisation In Leads

HighRequires corroborating analysis

Applies to: Mineral oil

Paper carbonisation in leads — least dangerous location (pre-fails at the highest gas level).

Recommendations: Corroborate with CO/CO2/furans. Lowest carbonisation priority, but still a paper fault.

Emitted by:Pentagon 2

C-T1 — Carbonisation × T1 (unified)

CriticalRequires corroborating analysis

Applies to: Mineral oil

Unified-pentagon carbonisation merged with the T1 thermal band.

Recommendations: Corroborate paper involvement with CO/CO2/furans. Highest of the C-Tn set.

Emitted by:Unified Pentagon

C-T2 — Carbonisation × T2 (unified)

HighRequires corroborating analysis

Applies to: Mineral oil

Unified-pentagon carbonisation merged with the T2 thermal band.

Recommendations: Corroborate paper involvement with CO/CO2/furans.

Emitted by:Unified Pentagon

C-T3 — Carbonisation × T3 (unified)

HighRequires corroborating analysis

Applies to: Mineral oil

Unified-pentagon carbonisation merged with the T3 thermal band.

Recommendations: Corroborate paper involvement with CO/CO2/furans.

Emitted by:Unified Pentagon

subzone-4 — Overheating with Paper Browning

Medium

Applies to: Mineral oil

Overheating (O) accompanied by light paper browning — the fourth published 2023 subzone, well separated from carbonisation C1. NOT carbonisation.

Recommendations: Review loading and cooling; light paper browning indicates early cellulose stress. Trend CO/CO2 to confirm it is not evolving toward carbonisation.

Emitted by:Pentagon 2

Contamination flags

Non-normative overlay flags, such as OLTC oil contamination in the main tank.

OC — OLTC Oil Contamination

MediumNon-normative

OLTC oil-contamination overlay. Only meaningful for units that HAVE an OLTC; reclassifies rather than ranks, and does not unconditionally suppress a coexisting fault.

Recommendations: Inspection required: Bustamante 2024 §6 notes a high probability of active faults in addition to oil contamination.

Emitted by:Triangle 1 Triangle 2

Normal & procedural (OLTC)

Normal switching-gas zones and procedural codes for on-load tap-changers.

N — Normal OLTC Switching

Normal

Applies to: OLTC compartment

Normal on-load tap-changer switching gas (compartment types).

Recommendations: Expected for OLTC operation. No action.

Emitted by:Triangle 2

N1 — Normal Zone N1 (in-tank OLTC)

Normal

Applies to: OLTC (in-tank)

Additional normal zone N1 for in-tank (MR-architecture) OLTCs, Triangle 2a (CIGRE TB 771 §4.1, Fig. 4.1 p.33 + Table 4.1 p.34, keyed to MR architecture). Not wired to a live tool: no numeric zone boundaries are published (App. Table H.1 p.69 covers Triangles 1/4/5 only), and Triangle 2a additionally needs an OLTC-model input the tool does not collect. Triangle 2a's fault zones are geometrically identical to Triangle 2, which the live tool already covers.

Recommendations: Expected for the relevant MR architecture. No action.

Emitted by:Not yet emitted by a live tool (reference entry).

Standards:CIGRE TB 771

N3 — Normal Zone N3 (in-tank OLTC)

Normal

Applies to: OLTC (in-tank)

Additional normal zone N3 for in-tank (MR-architecture) OLTCs, Triangle 2a (CIGRE TB 771 §4.1, Fig. 4.1 p.33 + Table 4.1 p.34, keyed to MR architecture). Not wired to a live tool: no numeric zone boundaries are published (App. Table H.1 p.69 covers Triangles 1/4/5 only), and Triangle 2a additionally needs an OLTC-model input the tool does not collect. Triangle 2a's fault zones are geometrically identical to Triangle 2, which the live tool already covers.

Recommendations: Expected for the relevant MR architecture. No action.

Emitted by:Not yet emitted by a live tool (reference entry).

Standards:CIGRE TB 771

N4 — Normal Zone N4 (in-tank OLTC)

Normal

Applies to: OLTC (in-tank)

Additional normal zone N4 for in-tank (MR-architecture) OLTCs, Triangle 2a (CIGRE TB 771 §4.1, Fig. 4.1 p.33 + Table 4.1 p.34, keyed to MR architecture). Not wired to a live tool: no numeric zone boundaries are published (App. Table H.1 p.69 covers Triangles 1/4/5 only), and Triangle 2a additionally needs an OLTC-model input the tool does not collect. Triangle 2a's fault zones are geometrically identical to Triangle 2, which the live tool already covers.

Recommendations: Expected for the relevant MR architecture. No action.

Emitted by:Not yet emitted by a live tool (reference entry).

Standards:CIGRE TB 771

N5 — Normal Zone N5 (in-tank OLTC)

Normal

Applies to: OLTC (in-tank)

Additional normal zone N5 for in-tank (MR-architecture) OLTCs, Triangle 2a (CIGRE TB 771 §4.1, Fig. 4.1 p.33 + Table 4.1 p.34, keyed to MR architecture). Not wired to a live tool: no numeric zone boundaries are published (App. Table H.1 p.69 covers Triangles 1/4/5 only), and Triangle 2a additionally needs an OLTC-model input the tool does not collect. Triangle 2a's fault zones are geometrically identical to Triangle 2, which the live tool already covers.

Recommendations: Expected for the relevant MR architecture. No action.

Emitted by:Not yet emitted by a live tool (reference entry).

Standards:CIGRE TB 771

X1 — Under Investigation

Medium

Applies to: OLTC compartment

LTC transitional zone: area still under investigation.

Recommendations: Ambiguous LTC result — resample and trend; do not conclude a fault type yet.

Emitted by:Triangle 2

X3 — Fault in Progress

High

Applies to: OLTC compartment

LTC: fault T3/T2 in progress (mostly) with light coking or increased contact resistance — or severe arcing D2.

Recommendations: Treat as an active LTC fault: inspect contacts; resolve between thermal coking and severe arcing.

Emitted by:Triangle 2

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