Vaisala Optimus OPT100 - Calculating Relative Moisture Saturation Inside Transformer; Total Gas Pressure Measurement

Property Output unit(s) Description
Gas ratios for:
• CH
4
/H
2
• C
2
H
2
/C
2
H
4
• C
2
H
2
/CH
4
• C
2
H
6
/C
2
H
2
• C
2
H
4
/C
2
H
6
• CO
2
/CO
Ratio Ratio is calculated from 24 h average values of
the gases
2.3.1 Total gas pressure measurement
Total gas pressure (TGP) is measurement parameter introduced in software version 1.12.0. Total
gas pressure is the total dissolved gas pressure of the sampled oil volume, measured by the
DGA monitor as part of its normal measurement cycle. The primary use of the TGP parameter
is to determine if there is an air leak into a sealed transformer. In case of a leak, majority of the
dissolved gases are nitrogen and oxygen, and the proportion of fault gases in the pressure
value is negligible. The pressure trend of the dissolved gasses gives reliable indication of leak,
as nitrogen is the dominant component, and it is not formed or consumed in reactions inside
the transformer.
From software version 1.13.0 onward TGP measurement results (current value and 24 hour
average) are available through output protocols, and TGP measurement can be used for gas
alerts. TGP has its own separate graph view on page Measurements > Total gas pressure.
2.3.2 Calculating relative moisture saturation inside transformer
DGA monitor measures relative oil moisture (%RS) inside its
cabinet. The temperature of the moisture sensor location does not represent the
temperature inside the transformer tank or inside the oil circulation pipes.
Additionally, oil sampling through the steel pipes changes the oil temperature.
As relative moisture saturation is strongly temperature dependent, the %RS
measured and output by DGA monitor is not equal to %RS inside the
transformer tank.
CAUTION!
However, DGA monitor does output both the measured %RS and the temperature where it was
measured. To calculate the %RS in the true temperature inside the transformer, use the
following equation.
%
RS
T2
= % RS
T1
× 10
A T2 − T1
T1 + 273.15 × T2 + 273.15
%RS
(T1)
Relative moisture saturation output by DGA monitor
T1 Temperature of the in-oil measurement chamber inside DGA monitor
T2 Temperature at location where new relative moisture saturation is needed at
A -1662.70
OPT100 User Guide M211858EN-U
14