we run a GE Gas turbine mark IV 30MW.

Auxiliary motor overload alarm (C105) came up, there was power outage. It was observed that the gas turbine tripped on transformer lockout trip alarm (c0167) and this was traced to cooling fan motor 88FC01.

Please can u explain how the trip in the cooling water motor could lead to transformer lockout?

Thanks for the anticipated response..

chudy

 

chudy,

Have you used the Trip History Display to determine what the cause of the trip was? It was most likely the transformer lockout, NOT the cooling water pump motor.

MOST everything that trips the turbine does so through the L4T rung, and it's various sub-rungs (L4PRET, L4POST, L4PST, etc.). Only if the aux motor overload alarm (usually L49X) was in one of those rungs to drive L4T to a logic "1" while the turbine was running would the turbine trip because of an aux motor overload (via software, that is).

It is GE's philosophy (not necessarily the philosophy of those who packaged GE turbines (like John Brown, Alsthom, Thomassen, BHEL, etc.)) to sacrifice an auxiliary motor to keep the turbine running--meaning that an aux motor overload was not normally used to trip the turbine on a GE-packaged heavy duty gas turbine. The motor would be allowed to burn up if the operator didn't respond quickly enough to stop the motor or resolve the overload condition to keep the turbine running. Aux Motor Overload wasn't a start-check permissive, and it wasn't a trip--on GE-packaged machines unless the owner demanded it (which wasn't very intelligent) or someone modified the logic to make it so (again, not very intelligent).

There is a hardware trip, shown on 04G of the Mark IV Speedtronic elementary. Someone may have wired the input to this circuit--but it's not likely, though stranger things have happened.

If the cooling water fan motor failed, and the L.O. Header temperature was high (above 175 deg F, usually) then the turbine would be tripped on high-high L.O. temp. But not usually because the cooling water fan motor tripped. There is usually more than one cooling water fan motor, and if one trips it doesn't usually result in high-high L.O. Temp (unless it was already very high to begin with--there should be a high L.O. Header temp alarm at 165 deg F).

Since you seem to have confused cooling water pump (usually 88WC01) and cooling water fan (88FC01 is usually a cooling WATER <b>fan</b>), is it possible the transformer cooling fans/pumps are in the aux motor overload string and a high transformer oil temp tripped the turbine.?.?.?

Please write back to let us know what you find after a more proper examination of the alarms and logic.