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What is the pressure drop calculation for the loss in air pressure during Generator air tightness test and what is the allowable drop?
Refer to the OEM manual for your specific generator.
> What is the pressure drop calculation for the loss in air pressure during
> Generator air tightness test and what is the allowable drop?
The basic formula is:
L=238(V/H){[(P1+B1)/(273+T1)]-(P2+B2)/(273+T2)]}
Lh=3.38La
Where:
L = gas leakage
Lh = equivalent hydrogen leakage
La = gas leakage using air in the generator
H = duration of test in hours
V = volume of gas system in cubic feet
B1 & B2 = initial and final barametric pressure (inches of mercury)
P1 & P2 = initial and final generator gas pressure (inches of mercury)
T1 & T2 = initial and final generator gas temperature (degrees C)
The generator OEM manuals normally have the equations and further explanations.
What is allowable varies a bit. A reasonable value for a tight system with a system volume of 2500 cu ft is 350 cfd. However, higher leakages are acceptable under certain conditions. For example, a test at the end of an outage conducted as a very rough check with the unit not yet on turning gear will be substantially higher than the same unit once it is on gear with the seal oil system warm. But it can give a quick indication of gross problems when compared to similar data for similar units or past data for the same unit. This is one reason that a quick air test is often done on removing a unit from service. Obviously it is desirable to return a unit from an outage in better condition than when it was taken off for maintenance.
thank you for your reply! We are currently struggling to hold pressure on CO2, leaking about 1 psi per hour. The formula above is meant to relate air to hydrogen. Do you know if there is a relationship out there for co2 and hydrogen? I want to swap to hydrogen but I expect the rate to be way too high since the leak rate on co2 is so drastic. I have an older westinghouse 110MW generatorHello sir,
at my plant we used to run the test for half day, usually during night shift, so that in the morning we have the result and can either work on finding the leakage or start filling the gen with hydrogen.
don't forget to isolate scavenging and h2 analysers prior to the test. (Those are continuous flow to the vent!)
Also we find to have better result without cooling water running (if possible) because cooling water temp will cause the air in the gen to expand or contract.
Even if the formula is made to compensate this effect, it's better if you don't experience it.
i'll check the omm to find the official instruction
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