dear sirs,

is there any difference between slow roll speed and normal turning gear speed for GE 9171 E gas turbines,

during slow roll operation as well as turning gear operation , starting motor comes into picture or separate ratchating device, turning motor provision is there,

it will be help ful if get any reply on the above

 

It's impossible to say from your post what the configuration of your system is, or has been modified to.

Some Frame 9Es were shipped with turning gear motors and gearbox assemblies for cooldown operation to prevent rotor bow. Many were shipped with a cooldown method known as "slow roll" which utilized Aux. L.O. Pump discharge pressure through the torque converter to *maintain* approximately 30-50 RPM during shutdown. As shaft speed is decelerating after a shutdown or emergency trip, when the unit reached approximately 100 RPM a separate oil circuit through solenoid-operated valve, 20TU-2, direct Aux. L.O. Pump discharge pressure into the torque converter (which is permanently coupled to the turbine shaft (no clutch)). This pressure would keep the shaft spinning at about 30-50 RPM as long as the L.O. Header Temperature did not drop below approximately 27 deg C (80 deg F).

When the operator selected COOLDOWN OFF, 20TU-2 would de-energize and the shaft would coast down to zero speed and the Aux. L.O. Pump would stop.

If the unit was at zero speed and it was desired to put the unit on "slowroll" (cooldown operation), the operator would select COOLDOWN ON and the starting motor would start and the torque converter would be pressurized as if during a normal starting sequence to break the shaft away from zero speed (sometimes to 150-250 RPM, the exact value is unimportant). The starting motor would be de-energized and the torque converter de-pressurized and the shaft would begin to decelerate slowly. At approximately 100 RPM 20 TU-2 would be energized to direct Aux. L.O. Pump discharge pressure into the torque converter as above to maintain 30-50 RPM.

With this method, the Aux. L.O. Pump discharge pressure is insufficient to break the turbine and generator shaft away from zero speed. Aux. L.O. Pump Discharge pressure can only assist an already spinning shaft with maintaining approximately 30-50 RPM (as long as L.O. Header Temperature remains "warm"). That's why slowroll speed isn't a fixed value; it varies with L.O. temperature, torque converter adjustment and condition, bearing condition (older bearings = slightly faster speed; newer, tight bearings = slower speed), etc.

Some owners/operators modified their units to add a turning gear motor and gearbox because they deemed the slowroll cooldown method unreliable. Some owners/operators purchased units with a turning gear motor and gearbox for the same reason. In my experience, gas turbine turning gears usually operate at about 6-10 RPM, but I haven't seen very many gas turbine turning gear mechanisms (only two, actually). The speed should be listed on the gearbox or determined from the gear ratios.

I have never seen any kind of ratchet mechanism on a Frame 9E, but that certainly does *NOT* mean there isn't at least one unit out there with some kind of ratchet mechanism.

Your Frame 9E was supplied with Schematic Piping Diagrams ("piping schematics") or P&IDs for all the major systems, including the Starting Means system. The Starting Means system piping schematic/P&ID should have the details of what kind(s) of cooldown mechanism(s) were supplied or added to the unit(s) at your site. The instruction books provided with the unit(s) should also have some description of the cooldown system on your unit(s) and how it operates.

 

Dear Sir,

Thanks for responce,

i have refer to starting means piping schematics for my plant. it shows only one solenoid that is 20 TU 1. there is no other solenoid like 20 tu 2, and more over turning gear motor is shown. so i think there should'nt be slow roll option,

agains thanks for guidance.