MA-025
–
DGA 900 Operator Guide
–
Rev 2.0
12-Apr-19
Page 88 of 92
Table E-1: Main Tank: Gas Level Alarms
µL/L or
ppm
Hydrogen
(H2)
Methane
(CH4)
Acetylene
(C2H2)
Ethylene
(C2H4)
Ethane
(C2H6)
Carbon
monoxide
(CO)
Carbon
dioxide
(CO2)
TDCG
IEEE STD
Condition 1
100
120
1
50
65
350
2500
720
1)
Set alarms to the following only if the measurements taken are
LESS THAN
the above values.
(C2H2 is set slightly higher to avoid spurious alarms)
Caution
100
120
2 or 4*
50
65
350
2500
Alarm
120
144
3 or 6*
60
78
420
3000
*
To avoid spurious alarms on the DGA 900, C2H2 Caution and Alarm limits should be set no lower than 2
and 3 ppm respectively.
2)
Set alarms to the following only if the measurements taken are ABOVE the IEEE Condition 1 values.
Measured Value * yyy% = ppm caution/alarm value)
Caution
Value *120%
Value
*120%
Value *120%
Value
*120%
Value
*120%
Value *120%
Value
*120%
Alarm
Value *150%
Value
*150%
Value *150%
Value
*150%
Value
*150%
Value *150%
Value
*150%
Note: The values cited in this table assume that no previous tests on the transformer for dissolved
gas analysis have been made or that no recent history exists. If a previous analysis exists, it should
be reviewed to determine if the situation is stable or unstable.
Note: See the example in Section E.8 at the end of this Appendix.
E.4
Main Tank: Gas Rate Of Change Alarms
Set the Rate of Change (ROC) alarms to the following values listed in Table E-2 for the most
critical gases:
▪
Daily Rate of Change (ROC) alarms
–
if oil volume is
unknown
Table E-2: ROC alarms (key gas values)
ppm /
day
Hydrogen
(H
2
)
Methane
(CH
4
)
Acetylene
(C
2
H
2
)
Ethylene
(C
2
H
4
)
Ethane
(C
2
H
6
)
Carbon
monoxide
(CO)
Carbon
dioxide
(CO
2
)
TDCG
Caution
-
-
0.5
0.5
-
2
-
2
Alarm
-
-
1.0
1.0
-
5
-
8
▪
Daily Rate Of Change (ROC) alarms
–
if oil volume or weight is
known
If the oil volume is known, the severity of defects based on ROC depends on the volume (or
weight) of oil contained in the transformer. For instance, a 1 ppm/day gas increase in a
large transformer (80,000 l oil) means a ROC of 80 ml/day of such gas. In a smaller
