{"id":2513,"date":"2026-09-10T07:01:04","date_gmt":"2026-09-10T07:01:04","guid":{"rendered":"https:\/\/speed-reducer-gearbox.com\/gas-turbine-auxiliary-planetary-reducer-compact-power-overview\/"},"modified":"2026-09-10T07:01:04","modified_gmt":"2026-09-10T07:01:04","slug":"gas-turbine-auxiliary-planetary-reducer-compact-power-overview","status":"publish","type":"post","link":"https:\/\/speed-reducer-gearbox.com\/en\/gas-turbine-auxiliary-planetary-reducer-compact-power-overview\/","title":{"rendered":"Gas Turbine Auxiliary Planetary Reducer: Compact Power Overview"},"content":{"rendered":"
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Gas turbines \u00a1\u00aa whether in power generation, offshore platform duty, or industrial process driving \u00a1\u00aa require a compact, reliable gearbox to drive their auxiliary systems from the main shaft at the correct speed. The accessory gearbox on a gas turbine distributes power from the high-speed turbine spool, typically 3 000 to 30 000 rpm depending on turbine size, to the fuel control unit, lubrication oil pump, hydraulic pump, starter motor, and electrical generators, each of which requires a specific speed. Planetary gearboxes within the accessory gearbox achieve the required speed ratios in the most compact, lightest format available \u00a1\u00aa critical constraints in aero-derived industrial turbines where weight and envelope are primary design drivers inherited from the aircraft application.<\/p>\n

Gas Turbine Auxiliary Drive Requirements<\/h2>\n

Each auxiliary system on a gas turbine has a specific speed requirement that must be met precisely: the fuel control unit requires a constant speed proportional to engine speed for flow metering; the oil pump requires minimum pressure at idle and rated flow at full power; the starter motor requires a speed range to accelerate the turbine to self-sustaining speed. These different requirements are served by different gear ratios from the accessory gearbox, all driven simultaneously from the same turbine spool shaft. The accessory gearbox planetary stages are compact, lightweight, and designed to the same reliability standards as the turbine itself \u00a1\u00aa since an accessory gearbox failure means a turbine shutdown.<\/p>\n

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\n\n\n\n\n\n\n\n\n\n
Auxiliary System<\/th>\nRequired Speed<\/th>\nTurbine Speed<\/th>\nRequired Ratio<\/th>\nNotes<\/th>\n<\/tr>\n<\/thead>\n
Fuel control unit<\/td>\n3 000 rpm<\/td>\n15 000 rpm<\/td>\n5:1 step-down<\/td>\nSpeed-proportional metering<\/td>\n<\/tr>\n
Lube oil pump<\/td>\n3 000\u00a8C6 000 rpm<\/td>\n15 000 rpm<\/td>\n2.5:1\u00a8C5:1<\/td>\nPressure controlled by bypass<\/td>\n<\/tr>\n
Hydraulic pump<\/td>\n1 500\u00a8C3 000 rpm<\/td>\n15 000 rpm<\/td>\n5:1\u00a8C10:1<\/td>\nActuator control pressure<\/td>\n<\/tr>\n
Permanent magnet generator<\/td>\n12 000\u00a8C24 000 rpm<\/td>\n15 000 rpm<\/td>\n0.8:1\u00a8C1.6:1<\/td>\nBrushless VF or constant frequency<\/td>\n<\/tr>\n
Starter motor drive mode<\/td>\n0\u00a8C3 000 rpm<\/td>\n0\u00a8C3 000 rpm<\/td>\nReversible planetary<\/td>\nBack-drives turbine from motor<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Ratios are illustrative for a medium industrial gas turbine at 15 000 rpm rated spool speed.<\/p>\n<\/div>\n

Weight and Compactness as Design Drivers<\/h2>\n

In aero-derived industrial gas turbines including the GE LM2500 and LM6000 series used extensively in Australian LNG facilities, offshore platforms, and power stations, the original aircraft design heritage means the accessory gearbox is engineered to the same weight density targets as aviation hardware. Every kilogram of accessory gearbox weight adds cost in the original engine unit and adds to the crane capacity required for installation or maintenance. Planetary gearing achieves the highest torque-to-weight ratio of any gear architecture, which is why it is the universal choice for high-performance accessory gearbox applications. The AB060 high-precision planetary series<\/a> demonstrates the torque density achievable in a compact planetary format applicable to auxiliary drive applications in high-speed industrial turbine installations. The AF060 flange output planetary<\/a> provides an alternative in a flange-mount configuration suited to accessory unit integration.<\/p>\n

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High Speed Gear Quality and Noise<\/h2>\n

Gas turbine accessory gearbox planetary gears operate at input speeds of 5 000 to 30 000 rpm \u00a1\u00aa far above any standard industrial planetary gearbox application. At these speeds, the gear mesh frequency reaches 2 000 to 10 000 Hz, which falls in the audible frequency range and produces the characteristic high-pitched whine of gas turbine operation. Surface finish on gear tooth flanks must be below Ra 0.2 micrometres to minimise the micro-pitting and transmission error that generates this noise. Gear tooth profile corrections \u00a1\u00aa tip relief, lead crowning, and profile crowning \u00a1\u00aa are applied to each individual gear pair to minimise loaded transmission error at the specific operating speed and torque of each accessory gearbox stage.<\/p>\n

Turbine Start Sequence and Reverse Drive<\/h2>\n

During turbine start, the starter motor drives the turbine spool through the accessory gearbox in reverse \u00a1\u00aa the motor is the input and the turbine spool is the output, exactly reversing the normal power flow direction. The accessory gearbox planetary stages must transmit this reverse torque without damage while the turbine accelerates from rest to self-sustaining speed. For an LM2500-type turbine, self-sustaining speed is approximately 3 000 rpm; the starter motor drives the spool from 0 to 3 000 rpm in 30 to 60 seconds at a torque that may reach 2 to 3 times the rated continuous output torque. The planet gears and planet pin bearings must withstand this start cycle repeated thousands of times over the turbine service life. The EPT right-angle precision planetary<\/a> series provides right-angle output configurations applicable to starter motor integration on small gas turbine auxiliary gearboxes, while the PGV planetary gearbox<\/a> offers a reference for high-speed precision planetary drive performance in turbomachinery auxiliary applications.<\/p>\n

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Frequently Asked Questions<\/h2>\n
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\n1. What material are gas turbine accessory gearbox planetary gears made from?+<\/span><\/summary>\n
Aerospace-grade accessory gearbox gears use 9310 or 8620 case-hardening steels with a carburised and ground case depth of 0.9 to 1.3 mm, giving surface hardness of 58 to 62 HRC and core hardness of 32 to 40 HRC. Shot peening of tooth roots adds compressive residual stress for fatigue resistance. For industrial non-flight gas turbine accessory gearboxes, 17CrNiMo6 or 18CrNiMo7-6 to AGMA or DIN specifications provides equivalent performance at lower material cost.<\/div>\n<\/details>\n
\n2. How long does a gas turbine accessory gearbox planetary gearbox last between overhauls?+<\/span><\/summary>\n
Aero-derived industrial gas turbines typically have accessory gearbox overhaul intervals of 20 000 to 30 000 hours, aligned with the engine hot section inspection interval. The accessory gearbox is disassembled, cleaned, inspected dimensionally against limits defined in the engine manufacturer’s Component Maintenance Manual, and rebuilt with replacement parts for any worn or out-of-tolerance components. Life-limited parts with a calculated cycle limit are replaced regardless of apparent condition.<\/div>\n<\/details>\n
\n3. What oil system does a gas turbine accessory gearbox use?+<\/span><\/summary>\n
Gas turbine lubricating oil is a synthetic ester-based oil typically meeting MIL-PRF-23699 or equivalent, designed for operation from minus 54\u00a1\u00e3C cold start to 200\u00a1\u00e3C hot bearing zones. This same oil lubricates the accessory gearbox planetary gears and bearings. The oil system delivers oil at 3 to 5 bar pressure through a jet to each gear mesh and bearing, with the return oil draining by gravity back to the tank and passing through a filter and cooler before recirculation.<\/div>\n<\/details>\n
\n4. Can the gas turbine start if the accessory gearbox has a partial failure?+<\/span><\/summary>\n
Depends on which component fails. A failed oil pump within the accessory gearbox will prevent starting because the turbine lubrication system loses pressure, triggering a pre-start interlock. A failed accessory such as a hydraulic pump or generator may allow a degraded-mode start if the interlock system permits. A catastrophic accessory gearbox gear failure that jams the accessory drive pad typically prevents engine rotation and the accessory gearbox must be repaired before starting.<\/div>\n<\/details>\n
\n5. Are planetary gearboxes always used in gas turbine accessory gearboxes?+<\/span><\/summary>\n
Gas turbine accessory gearboxes use a combination of gear types: bevel gears to change the power takeoff direction from the spool shaft to the accessory mounting face, followed by spur or helical gear trains to distribute to each accessory pad at the correct speed. Planetary stages are used where a high ratio is needed in a compact coaxial format \u00a1\u00aa for example, the starter motor drive requires a high step-down ratio to allow the starter motor to fit within the accessory gearbox envelope. Not all accessory gearboxes use planetary stages; simple spur gear trains serve the lower-ratio applications.<\/div>\n<\/details>\n<\/div>\n
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Speak with a Planetary Drive Specialist<\/h3>\n

Share your torque requirement, ratio, and application environment \u00a1\u00aa our team at Condell Park NSW returns a sized recommendation and stock check within one business day. No obligation.<\/p>\n

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ADDRESS<\/div>\n

27 Harley Crescent
Condell Park NSW 2200<\/div>\n

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PHONE<\/div>\n

+61 2 9708 3322<\/p><\/div>\n

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EMAIL<\/div>\n

sales@speed-reducer-gearbox.com<\/p><\/div>\n<\/div>\n

Send Enquiry →<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

Gas turbines \u00a1\u00aa whether in power generation, offshore platform duty, or industrial process driving \u00a1\u00aa require a compact, reliable gearbox to drive their auxiliary systems from the main shaft at the correct speed. The accessory gearbox on a gas turbine distributes power from the high-speed turbine spool, typically 3 000 to 30 000 rpm depending […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-2513","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/posts\/2513","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/comments?post=2513"}],"version-history":[{"count":0,"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/posts\/2513\/revisions"}],"wp:attachment":[{"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/media?parent=2513"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/categories?post=2513"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/en\/wp-json\/wp\/v2\/tags?post=2513"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}