STG-3 Series 2

Starting mode of STG-3 Series 2

During start, STG-3 Series 2 receives power from onboard batteries or an external ground power source. In this mode it works as a DC electric motor and accelerates the APU rotor through the drive. The starting phase is short and uses high current, so the condition of contactors, cables, batteries, ground power connection and start control relays is important. If the APU does not accelerate correctly, the fault is not always inside the starter-generator itself.

Generator operation of STG-3 Series 2

After successful start, the automatic start system removes starter power. The running APU then drives STG-3 Series 2 mechanically, and the unit changes to generator mode. In this mode it supplies 28.5 V DC to the onboard electrical network and can support aircraft systems or charge batteries, depending on the aircraft circuit. Voltage regulation works through external regulator and generator control equipment, so brush condition, commutator surface and field circuit should be checked together.

STG-3 Series 2 installation and maintenance points

STG-3 Series 2 has forced air cooling, with airflow supplied by the onboard system. The brush-commutator assembly is one of the main service points. The unit uses aviation copper-graphite brushes of MGS-7 type. Brush wear, spring pressure, commutator condition and signs of overheating should be checked during maintenance. Series 2 is generally treated as an improved version of the earlier STG-3 series, while remaining interchangeable by mounting points where approved by documentation.

Identification and ordering of STG-3 Series 2

Before ordering STG-3 Series 2, the nameplate, aircraft type, APU type and maintenance documentation should be checked. It is better to confirm whether the request is for a new, overhauled or serviceable unit, and what documents are required with delivery. For correct selection, provide the aircraft type, installed APU, current unit marking and photos of the data plate if available. The product is also known under alternative designations STG-3 Series 2, STG-3 2nd series and СТГ-3 2-й серии.

Related equipment in this system: APD-9V, PSG-15 / PSG-15M, RMO-16. These positions are linked by system function and are not presented as interchangeable.