Hi, all!
I've been asked a question by a former colleague I don't have the experience to answer: When should the Cooldown Oil Pump of a GE-design Frame 5 Model R/N/T be started during turbine start-up/shutdown?
This particular machine has the normal Accessory Gear-driven Main L.O. Pump, and uses an early version of hydraulic ratcheting for Cooldown operation when the unit is at zero speed. The other L.O. Pump is a "small" motor-driven pump--with a 5-HP AC motor and a 5-HP DC motor coupled together to drive the pump. The DC motor provides the Emergency L.O. Pump functionality (88QE). The AC motor is labeled on the L.O. Piping Schematic as the Cooldown Oil Pump, but other documentation provided with the machine (which was re-packaged and re-located to its current site) refers to the AC motor as <i>both</i> the Cooldown Oil Pump (88QC) and the Auxiliary Oil Pump (88QA). The Piping Schematic lists the motor-driven L.O. Pump output as 20 psig at 170 GPM. The Main L.O. Pump rating (on the Piping Schematic) is 360 GPM at 65 psig.
The present sequencing in the turbine control system (not a GE Speedtronic turbine control system) starts and stops the Cooldown Oil Pump as if it were an Auxiliary L.O. Pump: during starting starts at START and shuts down at 95% speed, and during shutdown starts at 94.5% speed and remains on when zero speed is reached and Cooldown starts, until operator selects Cooldown off.
Because the motor-driven oil pump rating is so much less than the Main Oil pump rating, I wonder if it should be running all the way up to 95% speed, and if it should be started at 94.5% speed during shutdown. If I interpret the AC motor's name properly (<i>Cooldown</i> Oil Pump) it would mean the AC motor would run the pump during Cooldown (which it does), and probably during initial starting (but not all the way up to 95% speed), and start at a much lower speed during shutdown. Because the rated output pressure and flow of the motor-driven oil pump is so much lower than the Main L.O. Pump it just doesn't seem to make sense to run the pump at speeds up to and below approximately 95% speed--but, neither does it seem to hurt anything, except that there is apparently a pressure bauble when the motor-driven oil pump starts at 94.5% speed during a shutdown, which sometimes results in a unit trip which can't be explained at this writing.
Another thing to note is that Auxiliary L.O. Pumps usually have output pressures nearer to the Main L.O. Pump pressure, and that helps to establish Trip Oil ("Control Oil) System pressure during starting. The motor-driven L.O. pump on this unit barely has enough output pressure to actuate the Hydraulic Trip Oil pressure switches without pressure from the Main L.O. Pump. So, this isn't a reason for running the motor-driven L.O. pump during a start--except to provide L.O. to the bearings as the unit breaks away from zero speed and during initial acceleration, after which the Main L.O. Pump (a positive displacement, gear pump) should be more than capable of supplying pressure and flow to the bearings. Also, the Trip/Control Oil pressure is taken off the Main L.O. Pump output ahead of a pressure regulator which controls the Trip/Control Oil pressure, so the motor-driven L.O. pump doesn't contribute to Trip/Control Oil pressure at all.
Unfortunately, I don't have access to any old Fuel Regulator or Mark I/Mark II Speedtronic elementaries or Service Manuals for Model R/N/T units, so I don't know how the Cooldown Oil Pump was operated when the unit was new.
So, my question is: What was the original operational philosophy for Cooldown Oil Pumps on GE-design Frame 5 Model R/N/T units?
Hopefully glenmorangie and/or otised can provide some information.... Or, if someone has a similar machine and is in possession of the original Speedtronic elementary and/or the Original Service Manual Starting L.O. System Description for a unit with a Cooldown L.O. Pump rather than an Auxiliary L.O. Pump can take a few minutes and look up what was originally provided for pump operation/control logic.
Thanks in advance for any help!
I've been asked a question by a former colleague I don't have the experience to answer: When should the Cooldown Oil Pump of a GE-design Frame 5 Model R/N/T be started during turbine start-up/shutdown?
This particular machine has the normal Accessory Gear-driven Main L.O. Pump, and uses an early version of hydraulic ratcheting for Cooldown operation when the unit is at zero speed. The other L.O. Pump is a "small" motor-driven pump--with a 5-HP AC motor and a 5-HP DC motor coupled together to drive the pump. The DC motor provides the Emergency L.O. Pump functionality (88QE). The AC motor is labeled on the L.O. Piping Schematic as the Cooldown Oil Pump, but other documentation provided with the machine (which was re-packaged and re-located to its current site) refers to the AC motor as <i>both</i> the Cooldown Oil Pump (88QC) and the Auxiliary Oil Pump (88QA). The Piping Schematic lists the motor-driven L.O. Pump output as 20 psig at 170 GPM. The Main L.O. Pump rating (on the Piping Schematic) is 360 GPM at 65 psig.
The present sequencing in the turbine control system (not a GE Speedtronic turbine control system) starts and stops the Cooldown Oil Pump as if it were an Auxiliary L.O. Pump: during starting starts at START and shuts down at 95% speed, and during shutdown starts at 94.5% speed and remains on when zero speed is reached and Cooldown starts, until operator selects Cooldown off.
Because the motor-driven oil pump rating is so much less than the Main Oil pump rating, I wonder if it should be running all the way up to 95% speed, and if it should be started at 94.5% speed during shutdown. If I interpret the AC motor's name properly (<i>Cooldown</i> Oil Pump) it would mean the AC motor would run the pump during Cooldown (which it does), and probably during initial starting (but not all the way up to 95% speed), and start at a much lower speed during shutdown. Because the rated output pressure and flow of the motor-driven oil pump is so much lower than the Main L.O. Pump it just doesn't seem to make sense to run the pump at speeds up to and below approximately 95% speed--but, neither does it seem to hurt anything, except that there is apparently a pressure bauble when the motor-driven oil pump starts at 94.5% speed during a shutdown, which sometimes results in a unit trip which can't be explained at this writing.
Another thing to note is that Auxiliary L.O. Pumps usually have output pressures nearer to the Main L.O. Pump pressure, and that helps to establish Trip Oil ("Control Oil) System pressure during starting. The motor-driven L.O. pump on this unit barely has enough output pressure to actuate the Hydraulic Trip Oil pressure switches without pressure from the Main L.O. Pump. So, this isn't a reason for running the motor-driven L.O. pump during a start--except to provide L.O. to the bearings as the unit breaks away from zero speed and during initial acceleration, after which the Main L.O. Pump (a positive displacement, gear pump) should be more than capable of supplying pressure and flow to the bearings. Also, the Trip/Control Oil pressure is taken off the Main L.O. Pump output ahead of a pressure regulator which controls the Trip/Control Oil pressure, so the motor-driven L.O. pump doesn't contribute to Trip/Control Oil pressure at all.
Unfortunately, I don't have access to any old Fuel Regulator or Mark I/Mark II Speedtronic elementaries or Service Manuals for Model R/N/T units, so I don't know how the Cooldown Oil Pump was operated when the unit was new.
So, my question is: What was the original operational philosophy for Cooldown Oil Pumps on GE-design Frame 5 Model R/N/T units?
Hopefully glenmorangie and/or otised can provide some information.... Or, if someone has a similar machine and is in possession of the original Speedtronic elementary and/or the Original Service Manual Starting L.O. System Description for a unit with a Cooldown L.O. Pump rather than an Auxiliary L.O. Pump can take a few minutes and look up what was originally provided for pump operation/control logic.
Thanks in advance for any help!