While I was leaving Jharsuguda for Delhi TMD Engineer informed me that the Dew Point of Instrument Air in TG Hall below Generator was -7.0 degC and asked whether he can fill air to conduct Gas Tightness Test. I told him no and informed him that the Dew Point would increase to positive value at 4.0 Bar pressure required for the Gas Tightness Test. I recommended him to check how much the Dew Point will increase from Dew Point Calculator on this site. I also checked it at 4 barg air pressure and the value is 14.9 degC. Is it ok to fill this air? NO. This is winter season and the temperature of air will go below 14.9 degC resulting into moisture in Generator.
The engineer got confused because I had allowed -7.0 degC Dew Point of Hydrogen taken at atmospheric pressure when the unit was running. I told him that on running unit minimum cold gas temperature was 38 degC and the above Dew Point converted at 3.5 barg Hydrogen Pressure comes to 13.3 degC which is 24.7 degC lower than the Gas Temperature. At that time I had also instructed that in case the unit trips and the cold gas temperature goes below 38 degC the Hydrogen Pressure should be reduced to maintain the Dew Point 20 degC below the cold gas temperature.
If you are dealing with Generators remember that the Dew Point increases with Gas Pressure whether it is air or Hydrogen. The measurement of Dew Point done by Portable Dew Point meter is at atmospheric pressure and you need to convert the measured Dew Point at the Gas Pressure and this online calculator is a handy tool to convert. The converted Dew Point should be atleast 20 degC below the Gas Temperature.
The engineer got confused because I had allowed -7.0 degC Dew Point of Hydrogen taken at atmospheric pressure when the unit was running. I told him that on running unit minimum cold gas temperature was 38 degC and the above Dew Point converted at 3.5 barg Hydrogen Pressure comes to 13.3 degC which is 24.7 degC lower than the Gas Temperature. At that time I had also instructed that in case the unit trips and the cold gas temperature goes below 38 degC the Hydrogen Pressure should be reduced to maintain the Dew Point 20 degC below the cold gas temperature.
If you are dealing with Generators remember that the Dew Point increases with Gas Pressure whether it is air or Hydrogen. The measurement of Dew Point done by Portable Dew Point meter is at atmospheric pressure and you need to convert the measured Dew Point at the Gas Pressure and this online calculator is a handy tool to convert. The converted Dew Point should be atleast 20 degC below the Gas Temperature.
