Table 1.

Diagnosis using the three-ratio method (IEC 60599) [37].

Fault Type	${\mathit{C}}_2{\mathit{H}}_2/{\mathit{C}}_2{\mathit{H}}_4$	${\mathit{CH}}_4/{\mathit{H}}_2$	${\mathit{C}}_2{\mathit{H}}_4/{\mathit{C}}_2{\mathit{H}}_6$
PD	<0.1	<0.1	<0.2
D1	>1	0.1–0.5	>1
D2	0.6–2.5	0.1–1	>2
T1	NS	>1/NS	<1
T2	<0.1	>1	1–4
T3	<0.2	>1	>4