GSR-ST-12/40A

GSR-ST-12/40A and the DC power system

GSR-ST-12/40A is a brushed DC starter-generator with shunt and series field windings. Its documented MiG-29 installation uses the machine as a generator: it supplies the DC network while the aircraft accessory gearbox provides mechanical drive. The presence of starter windings in the design does not mean that this particular aircraft uses the unit to crank its main engines. This distinction separates the machine's construction from its function in the installed electrical system.

Installation on the accessory gearbox

The generator is installed on the KSA-2 aircraft accessory gearbox. The same assembly carries the GP21-3 integrated drive-generator, but the two units serve different electrical circuits and are not replacements for one another. In the MiG-29 power system, two 15SCS-45B batteries provide an emergency DC source when normal generation is unavailable. The generator, its mechanical drive and the reserve source therefore perform separate functions within the overall power-supply arrangement.

GSR-ST-12/40A magnetic system and housing

A tubular steel housing supports six main poles with shunt field windings and six interpoles. Three main poles also carry single-turn series windings associated with starter operation. Access windows in the housing expose the commutator and brush assembly for inspection. The pole system, armature and current-collection components form an electromechanical unit; voltage regulation is a separate system function rather than a property of the housing or brush gear alone.

Brush assembly and service dimensions

Six reaction-type brush holders are attached to the housing through insulating components. Each holder carries three spring-loaded brushes, giving eighteen brushes in the assembly. Brush dimensions and the specified wear heights are listed separately in Technical Details. These values describe different conditions: the minimum height for a scheduled inspection is not the same as the critical wear limit. Commutator condition, brush movement and spring contact are relevant to the operation of this current-collection system.

Electrical output and related equipment

The generator belongs to the 12 kW DC class. Output voltage, load current, shaft-speed range, field current and environmental limits are grouped in Technical Details for direct reference. Other machines in the generators and starter-generators category cover different drive and electrical requirements. Background information about the aircraft is available in the neutral MiG-29 reference. Installation approval remains specific to the aircraft configuration and complete unit designation.

Machine type: Brushed DC starter-generator
Documented aircraft: MiG-29
Installed function on MiG-29: DC power generation
Mechanical installation: KSA-2 aircraft accessory gearbox
Rated voltage: 28.5 V
Rated power: 12 kW
Rated load current: 400 A
Shaft-speed range: 4,000–9,000 rpm
Field current: 1.9–15 A
Ambient temperature: −60 to +60 °C
Mass: 32 kg
Housing: Tubular steel housing with brush-access windows
Main poles: 6
Interpoles: 6
Field windings: Shunt; single-turn series windings on 3 main poles
Brush holders: 6 reaction-type holders
Brushes per holder: 3, spring-loaded
Total brushes: 18
New brush dimensions: 8 × 20 × 31 mm
Minimum brush height at 100-hour inspection: 20 mm
Critical brush height: 17 mm
Emergency DC source in MiG-29 installation: Two 15SCS-45B batteries

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