Gas Turbine Accessory Drive

The accessory drive gear, located at the compressor end of the gas turbine, is a gearing assembly coupled directly through a flexible coupling to the turbine rotor. Its function is to drive each gas turbine accessory at its proper speed. In addition, it contains the system main lube oil pump.

Contained within the gear casing are the gear trains which provide the proper gear reductions to drive the accessory devices at the required speed, with the correct torque values. Accessories driven by the gear include : the main lube oil pump and the main hydraulic supply pump. Lubrication of the gear is from the turbine's pressurized bearing header supply.

For ease of maintenance and inspection, the gear casing is split at the horizontal plane into an upper and lower section. Interconnected shafts are arranged in a parallel axis in the lower casing. Three of the shafts are located on the same horizontal plane as the casing joint. The gear consists of four parallel axis, interconnected shafts arranged in a casing which provides mounting pads for the various driven accessories. With the exception of the lube oil

Pump and hydraulic supply pump shaft, all the shaft center lines are located on the horizontal joint of the accessory drive casing. Numbers are assigned to the various shafts in the "Gas turbine equipment publications chapter" according to their function and therefore their speed. The gear casing is made of cast iron and split at the horizontal joint to facilitate assembly. The lower half casing has a closed bottom with opening for lube oil pump suction and discharge lines and casing drain line.

All of the shafts are connected together by single helical gears which are shrunk to the shafts after the teeth are cut. It is possible, in some instances to remove individual gears which may have been damaged in service, and to replace them with new gears.

This operation, however, should be performed at the factory so that the required precision may be maintained. All of the shafts located on the horizontal joint are contained in babbitt-lined steel-backed journal bearings with integral thrust faces which are split on the horizontal joint of the casing.

The thrust faces of the bearings maintain the shafts in their proper axial location and the necessary thrust clearance is preset at the factory. The shafts which are not on the horizontal joint are contained in babbitt-lined, steel-backed, non-split bushings with integral thrust faces. Their thrust clearance is likewise preset at the factory.

The main lubricating oil pump is located on the inboard wall of the lower half casing of the accessory drive gear. 
Accessory Drive

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