If the hydrogen purity falls below a certain level (approximately 80% depending on the manufacturer's recommendations). Is the load reduced by logic?

What are the results? Some people claim to have encountered such a situation in a steam turbine?

 

Hopefully an alarm someone pays attention to.

"If hydrogen gas remains in any area in a concentration from 4% to 75% (the lower and upper flammability limits) in air, then the atmosphere in that area is flammable". Page 3, Hazards when Purging Hydrogen Gas-Cooled Electric Generators, https://www.osha.gov/sites/default/files/publications/shib012216.pdf

 

DISCLAIMER: I don't have personal experience with GE-design steam turbines, ONLY GE-design heavy duty gas turbines. AND I don't have any logic diagrams/programs/application code to refer to at this moment.

On the GE-design heavy duty gas turbines I worked on the hydrogen control panels had a switch: MANUAL/AUTO. There would be Process Alarms generated by the turbine control system based on measurements of sensors mounted in the hydrogen control panel that were connected to the turbine control system. The normal mode of operation (the machine running and producing power) was for the MANUAL/AUTO switch to be in AUTO. IF I RECALL CORRECTLY when the amount of air in the generator reached something like 80% the turbine control system would initiate a unit shutdown (orderly unloading, opening of the generator breaker, and fired shutdown to zero speed) and when the unit reached zero speed a purge of the hydrogen in the generator would commence. (This was done at zero speed to prevent mixing of the hydrogen with the CO2 used to force the hydrogen out of the generator casing.)

The MANUAL/AUTO switch, when in MANUAL, would prevent the automatic purge, but not the shutdown. SOME plants choose to operate like this against the recommendation of the OEM and other knowledgeable personnel in order to prevent automatic purging based on some "false" event.

Trained operators and their supervisors should NEVER let the hydrogen purity get to 80% while the unit was running. There are ways to increase the amount of scavenging (the name for the process of always venting a little of the gas (hydrogen/air) out of the generator to try to increase the hydrogen purity). If there's not enough hydrogen available for increased scavenging then
the machine should be shutdown and appropriate action taken to remedy that (get more hydrogen) and to troubleshoot and resolve the hydrogen purity problem.

In the past, the hydrogen purity of the hydrogen in the bearings was monitored to check for low purity--as that would be the area that would first experience low purity. It was required to manually switch valving in the hydrogen control panel to monitor the hydrogen purity in the generator casing, as it should always be higher than in the bearing areas where seal oil is flowing (air most commonly enters a hydrogen-cooled generator entrained in the seal oil used to keep the hydrogen from leaking out of the generator along the shaft near the bearing area). (The generator casing--and hydrogen side seal areas--is under pressure, which prevents air from leaking IN to the generator.)

To the best of my knowledge, GE-design steam turbines have nearly the same control and protection scheme for hydrogen-cooled generators as used by the gas turbines. BUT, that's a SWAG (Scientific Wild-Arsed Guess) and I have been wrong in the past and I will be wrong in the future.

AGAIN, the hydrogen purity in the generator should NEVER be allowed to reach anything near 80%, even if that means shutting down the machine because there is no hydrogen available to continue operation and scavenging.

The only CERTAIN way to know for sure what happens when hydrogen purity gets low is to read the manuals and have a look at the application code running in the turbine control system. GE now uses (or at least they were using) hydrogen control panels made by third-party companies and I'm not sure exactly what or how they work in conjunction with the Mark* turbine control system to monitor, control and protect a hydrogen-cooled generator.

Anyway, interesting that a robotics student is interested in hydrogen-cooled generator operation.... Hmmmm.....