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le 2: The recommended value was achieved (Ref Table:I) desired less than 9 ppm value of water content was
after two cycles of evacuation and dry-air purging. achieved.
Time of Reading Dew Temp. of RH (%) The processed oil within the tanker was then poured
Point Insulation 2.47 through filter machine in the main tank of the Transformer
Initial Reading on receipt (oC) kept under continuous vacuuming.
of Main Tank – 24.12 (oC)
After completion of – 10.61 26.79
inspection & repairing
– 6.99 38.96 3.92
After completion of
installation of accessories – 20.92 36.47 5.96
After Vacuum (24 hours) & – 21.04 26.55 3.33
Dry Air purging – 1st cycle
30.30 2.65
After Vacuum (60 hours) &
Dry Air purging – 2nd Cycle
Figure 4: Under vacuum oil filling
Relative Humidity: defined as the amount of water Additional benefits of using Dry-Air
vapour present in air expressed as a percentage of the Generator plant
amount needed for saturation at the same temperature.
i. Breathable dry air should be continuously supplied
Measured RH values were displayed directly by high into the transformer while the access cover is being
end Vaisala make Dew Point Meter (DM70), used in this removed for inspection or fitting accessories by
installation process. However, if this facility is not available, human involvement.
the same can be calculated from respective Dew Point &
Temperature of the condensate. ii. With the help of Dry-Air we can maintain positive
pressure inside main tank which can identify the
The formulae for converting Relative Humidity from Dew leakages during installation stages. This has helped us
Point are as follows: to minimize the chances of leakage which would have
been visible after oil filling or after commissioning.
RH = (T + 273)4.9283(D + 273) 10-0.32286 {-12.0702 - [2705.21 / (D+273)] +
SITE ACCEPTANCE TEST
[2937.4 / (T + 273)]} PARAMETERS
RH: Relative Humidity; Following Site Acceptance Test results are the reflection
of efficacy of the entire dehydration process.
T: Ambient Temperature (OC)
Table 3: Comparison of Tan-Delta value between Factory
D: Dew-Point Temperature (OC) Acceptance Test & Site Acceptance Test
Oil Filling Test Measured Voltage Tan Delta Tan Delta
Mode Between (kV) (%) in FAT (%) in SAT
Handling of Insulating Oil is also extremely difficult in this
weather condition. However, we have managed that with UST HV+IV/TER 5 0.129 0.152
one MS-fabricated Oil Tank with 10 KL capacity and one UST HV+IV/TER 10 0.131 0.147
Oil Filtration Plant with 4500 LPH capacity to handle the GSTg HV+IV/E 5 0.213 0.251
total oil quantity of 67 KL. Avoided repetitive handling of GSTg HV+IV/E 10 0.270 0.339
oil which eventually deteriorates the quality of the Oil. GST HV+IV/TER+E 5 0.173 0.194
At first Mineral Transformer Oil, conforming IEC: 600296
and IS: 335 was treated within the tanker by circulation contd.
through the Filter Machine. The oil was processed until
43
after two cycles of evacuation and dry-air purging. achieved.
Time of Reading Dew Temp. of RH (%) The processed oil within the tanker was then poured
Point Insulation 2.47 through filter machine in the main tank of the Transformer
Initial Reading on receipt (oC) kept under continuous vacuuming.
of Main Tank – 24.12 (oC)
After completion of – 10.61 26.79
inspection & repairing
– 6.99 38.96 3.92
After completion of
installation of accessories – 20.92 36.47 5.96
After Vacuum (24 hours) & – 21.04 26.55 3.33
Dry Air purging – 1st cycle
30.30 2.65
After Vacuum (60 hours) &
Dry Air purging – 2nd Cycle
Figure 4: Under vacuum oil filling
Relative Humidity: defined as the amount of water Additional benefits of using Dry-Air
vapour present in air expressed as a percentage of the Generator plant
amount needed for saturation at the same temperature.
i. Breathable dry air should be continuously supplied
Measured RH values were displayed directly by high into the transformer while the access cover is being
end Vaisala make Dew Point Meter (DM70), used in this removed for inspection or fitting accessories by
installation process. However, if this facility is not available, human involvement.
the same can be calculated from respective Dew Point &
Temperature of the condensate. ii. With the help of Dry-Air we can maintain positive
pressure inside main tank which can identify the
The formulae for converting Relative Humidity from Dew leakages during installation stages. This has helped us
Point are as follows: to minimize the chances of leakage which would have
been visible after oil filling or after commissioning.
RH = (T + 273)4.9283(D + 273) 10-0.32286 {-12.0702 - [2705.21 / (D+273)] +
SITE ACCEPTANCE TEST
[2937.4 / (T + 273)]} PARAMETERS
RH: Relative Humidity; Following Site Acceptance Test results are the reflection
of efficacy of the entire dehydration process.
T: Ambient Temperature (OC)
Table 3: Comparison of Tan-Delta value between Factory
D: Dew-Point Temperature (OC) Acceptance Test & Site Acceptance Test
Oil Filling Test Measured Voltage Tan Delta Tan Delta
Mode Between (kV) (%) in FAT (%) in SAT
Handling of Insulating Oil is also extremely difficult in this
weather condition. However, we have managed that with UST HV+IV/TER 5 0.129 0.152
one MS-fabricated Oil Tank with 10 KL capacity and one UST HV+IV/TER 10 0.131 0.147
Oil Filtration Plant with 4500 LPH capacity to handle the GSTg HV+IV/E 5 0.213 0.251
total oil quantity of 67 KL. Avoided repetitive handling of GSTg HV+IV/E 10 0.270 0.339
oil which eventually deteriorates the quality of the Oil. GST HV+IV/TER+E 5 0.173 0.194
At first Mineral Transformer Oil, conforming IEC: 600296
and IS: 335 was treated within the tanker by circulation contd.
through the Filter Machine. The oil was processed until
43
