Steam Turbine hydraulic pump logic

hi, we have Alstom steam turbine and the hydraulic power for CV and Stop valve is provided by a set of hydraulic pumps, via a trip block.

When the machine trips or shutdown the logic does not stop the hydraulic pump automatically and it should be manually stopped. My question is, what might be the reason that Alstom kept the pump running after trip or shutdown. infact, there is no auto-stop command for hydraulic pumps and only time they are stop in auto is when there is fire detection signal.

I checked with other stations using different manufacturers and in almost all of them, the hydraulic pump is left running after trip.

I recall similar logic with Ansaldo/Siemens ST, where automatic sequence doesn't stop the hydraulic pumps after trip and normal shutdown.

"The turbine is tripped only if AT LEAST 2 of the solenoid valves are de-energized " according to Alstom O&M manual

Look at the start/shutdown sequences for this plant for better overview

Any time!
Phil Corso,

Rizwan Siddiqui is referring to the hydraulic pumps which supply pressure/flow to operate the stop and control valves. Usually, for a steam turbine, the hydraulic fluid is NOT mineral oil-based, but is some type of fire-resistant formula (because a leak of mineral oil-based hydraulic fluid spraying on a HOT steam turbine control valve can ignite and result in a nasty fire--and worse).

The L.O. Pumps (including the DC motor-driven Emergency L.O. Pump, or as some new steam turbines have: an AC motor-driven Emergency L.O. Pump powered by an inverter getting its power from a set of batteries).

MANY steam turbines have manual controls for the hydraulic system--an operator must start them, and an operator must shut them down. Some owners have requested automatic controls for the hydraulic system (pumps; vapor extractor; coolers; heater(s); etc.). But, due to decades of practice, many OEMs (Original Equipment Manufacturers) have continued doing things the same way--again: for decades, and into the 21st century.
thanks guys.. let me add here ...

for our steam turbine, the source of oil for lift oil, hydraulic oil and lube is one tank. the lift oil and hydraulic oil takes it suction from lube oil header. the hydraulic system comprises of pair of pumps, a trip block (with pilot solenoids) and then it goes to control valves and stop valves. The trip block is a hydraulically operated. a set of three trip solenoid valve energizes/denergizes to activate the trip block, which allows the passage of high pressure oil toward servos on Control valve. when unit trip/shutdown the trip block de-activate.

For siemens and GE gas turbines that I have worked on, for unit startup, the sequence would start the hydraulic pumps, builds the pressure and operates fuel control valves, and when unit trips or shutdown the pumps stops automatically after preset time, about 15~30 minutes. so there is an auto-stop signal from trip/shutdown logic.

contrary to this, for steam turbines, in most of the cases the auto start of hydraulic pump is there. but not auto-stop. my question is for auto stop logic of hydraulic pump.

I recall working with AE units, with parker servo valves, and there hydraulic pressure was actually need to assist/ensure fast closure of the governor. There it was understandable, that the hydraulic pumps must continue to run after trip/shutdown.

however with our Alstom unit this not the case. the Control valve actuators are single acting and the closure is only from spring force. So, having hydraulic pressure after CV closure incase of trip/shutdown has not point.

only thing which comes to my mind is that hydraulic oil should circulate through the system for cool down, does it make sense.

I will share the hydraulic system P&ID tomorrow.

sorry gentlemen for delayed response.. a bit busy with annual shutdown.