Speed Matching Gears

Applied designs include a variety of gear configurations. The two most common configurations are parallel-offset and epicyclic designs. Parallel-offset gears require larger skids for equipment mounting, but otherwise provide reliable, economic service and easy maintenance. Epicyclic gears permit gas turbine shafting to operate on a common centerline with its driven load and have lower gear mechanical losses and less oil flow requirement than a parallel shaft design. Epicyclic gears are often recommended for larger ratios where double reduction parallel offset gears would otherwise be required. Larger gas turbine models, which rotate at low enough speed, are designed for direct shaft coupling to 50 and 60 Hz power generators to eliminate losses associated with speed changing gears.

Figure 10-36 shows an epicyclic gear unit. The unit is designed for continuous-duty operation at output speeds of 1,800 rpm for 60 Hz service and 1,500 rpm for 50 Hz service. This gearbox unit has built-in accessory pads that drive the starter, lube pump, and liquid fuel pump (when required). Figure 10-37 shows a reduction drive assembly.

Fig. 10-36 Epicyclic Gear Unit. Source: Solar Turbines

Fig. 10-35 Illustration of Typical Nozzle Vane Showing Isotherms. Source: General Electric Company

Fig. 10-36 Epicyclic Gear Unit. Source: Solar Turbines

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