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What is HP speed? and difference HP & LP speed?
Hi GE,
HP and LP refer to 'High-Pressure' and 'Low-Pressure' shafts, and speeds. The pressures are "relative" pressures, one turbine operating at a higher pressure than the other, which is called the "low pressure" turbine (shaft).
Some GE-design gas turbines have multiple shafts that spin at independent speeds. The pressures of the hot combustion gases flowing through the turbine sections (HP section and LP section) of the two shafts are different, thus the naming convention (instead of, say, Shaft 1 and Shaft 2, or Shaft A and Shaft B, or Shaft 0 and Shaft 1, or Shaft X and Shaft Y).
The HP shaft is usually directly connected to the axial compressor, and the LP shaft is usually directly connected to the "load"--a centrifugal compressor, or a pump, or a generator. The HP shaft, driving the axial compressor, needs to operate at the speed range the axial compressor is designed to operate in. The LP shaft, driving the load, needs to operate at the speed the load requires.
The control system is configured and programmed to operate the two shafts independently and simultaneously. Most newer two-shaft GE-design heavy duty gas turbines have a variable nozzle section upstream of the LP turbine section that helps control HP speed (yes; HP speed), and LP speed is controlled by varying fuel. (Yes; there is some interaction between fuel control and HP speed, but the basic control philosophy for GE-design two-shaft heavy duty gas turbine controls presumes there is very little interaction, and it actually works very well (the presumption, and the control philosophy!).
Hope this helps!
By the way, some gas turbines (usually aircraft- or aero-derivative gas turbines) have three shafts (HP, IP (Intermediate Pressure), and LP). Usually, the IP shaft speed is controlled by the engine itself (though it's monitored by the control system), and the LP still drives the load. (The IP shaft is sometimes positioned inside the HP shaft.)
There are also some large steam turbines which have multiple shafts, and, they are also denoted by the relative pressures at which they operate.
HP and LP refer to 'High-Pressure' and 'Low-Pressure' shafts, and speeds. The pressures are "relative" pressures, one turbine operating at a higher pressure than the other, which is called the "low pressure" turbine (shaft).
Some GE-design gas turbines have multiple shafts that spin at independent speeds. The pressures of the hot combustion gases flowing through the turbine sections (HP section and LP section) of the two shafts are different, thus the naming convention (instead of, say, Shaft 1 and Shaft 2, or Shaft A and Shaft B, or Shaft 0 and Shaft 1, or Shaft X and Shaft Y).
The HP shaft is usually directly connected to the axial compressor, and the LP shaft is usually directly connected to the "load"--a centrifugal compressor, or a pump, or a generator. The HP shaft, driving the axial compressor, needs to operate at the speed range the axial compressor is designed to operate in. The LP shaft, driving the load, needs to operate at the speed the load requires.
The control system is configured and programmed to operate the two shafts independently and simultaneously. Most newer two-shaft GE-design heavy duty gas turbines have a variable nozzle section upstream of the LP turbine section that helps control HP speed (yes; HP speed), and LP speed is controlled by varying fuel. (Yes; there is some interaction between fuel control and HP speed, but the basic control philosophy for GE-design two-shaft heavy duty gas turbine controls presumes there is very little interaction, and it actually works very well (the presumption, and the control philosophy!).
Hope this helps!
By the way, some gas turbines (usually aircraft- or aero-derivative gas turbines) have three shafts (HP, IP (Intermediate Pressure), and LP). Usually, the IP shaft speed is controlled by the engine itself (though it's monitored by the control system), and the LP still drives the load. (The IP shaft is sometimes positioned inside the HP shaft.)
There are also some large steam turbines which have multiple shafts, and, they are also denoted by the relative pressures at which they operate.
