Our seal oil system on our generator has a differential in head pressure of approx. 9 feet or about 3.5 PSI. the GE manual states to set the differential alarming switch to 2.5PSIDP. Our problem is that is we have a 3.5PSI differential in head pressures, then there would be a drastic loss in seal oil before the alarm would come in..Right? But with the other systems the GE manual specifically notes if head pressure needs to be accounted for as related to the center line of the turbine.

 

GE instructions are known not to be the most complete or accurate instructions.

If I understand the posting, the answer would likely depend on the configuration of the piping on this particular generator. I would think that head pressures would have to be considered.

But, I'm not sure I understand the configuration from the original posting.

 

The 3.5 PSI head differential is the difference between the turbine center line and the enlargement tank, both of which are full of oil during normal operation. Keep in mind the specific gravity of the oil will effect the calculated head pressure difference. Today I took static readings of the reference lines and compared them to the machine gas pressure and the seal oil header pressure, no head pressure and came up with the same pressure with the head added to the reference pressures. I am mostly surprised that this machine has been in operation for over 40 years and no one has caught this before.

 

I'm at a Siemens 501G site. Here, I "zero out" the head on the transmitters so that it doesn't affect the actual value.