DEAR SIR,

In our captive power plant there are six frame 9e gas turbine generator & two 28 mw steam turbine generators. My question is on which bases it is decided to trip gas or steam turbine or only generator should trip on the occurrence of fault.

& also can anybody explain me on which fault only generator should trip & on which faults both generator & gas (or steam) turbine should trip & why.

As per my knowledge turbine & generator both should trip on reverse power operation to avoid the damage to the turbine. But in our cpp there is no tripping for turbine on reverse power operation. So can anybody explain me why this type of disition taken.

 

You need to ask the designers of the power plant and the packagers of the Frame 9E and steam turbine why they made the decisions they did.

As an owner/operator, once the plant is out of warranty and/or is not under LTSA or CSA, you are free to modify its operation as you see fit (hopefully after some due diligence).

Reverse power is many things to many different prime movers. It's not so bad for single-shaft heavy duty gas turbine, but it's destructive for steam turbines and reciprocating engines. Some steam turbines can't even stand positive power flows below some level. I've seen 600 MW steam turbines that trip on "reverse power" at 120 MW because the cooling effect of the steam flow is too low at loads less then approximately 120 MW, so the "reverse power" relay is set to trip the steam turbine (and steam turbine generator breaker) below 120 MW.

Again, these kinds of questions, while seemingly general in nature, can be very complicated when taking plant operation into account. Load balance with certain transformer schemes; load sharing; tie-line considerations. All of these things and more can influence a lot of these seemingly simple decisions.

Lastly, there is a certain French packager of GE turbines which will do just about anything a Customer asks them to do (unlike GE which is pretty staid and "conservative"). Some of the control schemes they have implemented have just been, well, uh, gee, um, er, unusual.

To say the least!