Question 1

What is IEC 60599 used for?

Accepted Answer

IEC 60599:2022 governs interpretation of dissolved and free gases in mineral-oil-filled electrical equipment in service — primarily power and distribution transformers. The standard defines the three-ratio method (R1, R2, R3) and reference fault classifications used worldwide.

Question 2

What do R1, R2, and R3 stand for?

Accepted Answer

R1 = C2H2 / C2H4 distinguishes electrical from thermal faults — high values indicate arcing. R2 = CH4 / H2 indicates fault temperature; low values point to partial discharges. R3 = C2H4 / C2H6 refines thermal-fault temperature classification — higher values mean hotter faults.

Question 3

How does IEC 60599 relate to the Duval Triangle?

Accepted Answer

Both interpret the same fault-gas data but in different geometries. IEC 60599 uses three ratios with discrete fault-code thresholds; Duval triangles map fault chemistry into a continuous coordinate space. They are complementary diagnostics — agreement increases confidence; disagreement warrants closer inspection.

Question 4

What does the "NS" (Not Significant) result mean?

Accepted Answer

NS is returned when one or more denominator gases is below the standard’s detection threshold, making the ratio unreliable. The fault may still be real — additional samples, lower-LOD analytical methods, or absolute-concentration screening are typically the next step.

Question 5

Does this tool work for natural ester or synthetic ester oils?

Accepted Answer

No. IEC 60599 thresholds apply to mineral oil only. For natural ester (FR3, MIDEL eN) use IEEE C57.155 / CIGRE TB 443; for synthetic ester (Midel 7131) use IEC 61203:2025. TriboTech’s Duval Pentagon page covers alternative-fluid variants directly.

Code	Fault Type	Temperature Range	Severity
PD	Partial Discharges	< 150°C (cold plasma)	Medium
D1	Discharges of Low Energy	Variable (arc)	High
D2	Discharges of High Energy	> 3000°C (arc core)	Critical
T1	Thermal Fault	< 300°C	Medium
T2	Thermal Fault	300-700°C	High
T3	Thermal Fault	> 700°C	Critical

Code	Fault Type	Temperature Range	Severity
PD	Partial Discharges	< 150°C (cold plasma)	Medium
D1	Discharges of Low Energy	Variable (arc)	High
D2	Discharges of High Energy	> 3000°C (arc core)	Critical
T1	Thermal Fault	< 300°C	Medium
T2	Thermal Fault	300-700°C	High
T3	Thermal Fault	> 700°C	Critical

IEC 60599:2022 Ratio Analysis

Gas Concentrations (ppm)

Zone Visualization

About IEC 60599:2022

About the IEC 60599:2022 Ratio Method

The Three Ratios

Fault Types

Important Notes

References