Gas Turbine protection information

[MarcoPolo24]

Hallo everybody,

does anybody have or can recommend some document explaining the Gas or STeam turbine protection system, the possible avoided damages ? An example would be : what is the reason for tripping the Turbine, when I have low fuel gas temperature ? Do I get an unstable burning condition and do I have long-term blade-damage ?

Thanks in advance,
Marcus

 

[byrdj]

I only worked Steam but the principles would apply
the "rules" during that time for protection defined three levels;
1) could result in the loss of life
2) could result in loss of equipment
3) could result in increase maintenance

for level 1, events like over speed, the protection was redundant and testable
for level 2, events like loss of lube oil, the protection was manditory
for level 3, events like high vibration, the protection was recomended, but optional

maintaining unit availableity was a high (secondary priority). thus the trip protection was to ensure there was a real need to do so and not have conservitive tripping logic
the impression I get from today's controls with the ease of adding a program instruction is trips are becoming "if in doubt, trip it out"

 

[georgeverghese]

Low fuel gas supply temp may be an indication that the FG has cooled down to become 2 phase vapor and liquid. Incomplete combustion of liquid condensate in the turbine resulting from slug flow in the feed piping and sudden accumulation of liquids in the combustion chamber could lead to a detonation and turbine damage. So a TSLL on FG supply is a machine and personnel safety instrumented barrier against such risks.

 

[NCTHAI]

There is something more than that for change in fuel gas temperature.... normally combustion systems are designed for specific MWI (Modified Wobbe Index). MWI is measure of energy input to the combustion and is dependent on fuel gas temperature and Specific Gravity (In turn fuel composition and hence calorific value). Acceptable variation allowed is 5% from designed value.

General philosophy for protection is explained by @BYRDJ. You need to check the machine specific O&M manual where such things would be described.