Overview
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Replace with overview of 4 IDGs, APU gen, external power, bus structure.
Four engine-driven Integrated Drive Generators (IDGs) — one per engine — produce 115 V AC, 400 Hz, 3-phase, 90 kVA each. An APU generator (same rating) and two external power inputs round out the AC sources. Each generator feeds its dedicated AC main bus through a Generator Circuit Breaker (GCB); bus tie breakers permit cross-tying.
Architecture
Sources:
IDG = Integrated Drive Generator
GCB = Generator Circuit Breaker
BTB = Bus Tie Breaker
TRU = Transformer Rectifier Unit
Aircraft Zones — Side View
Components
| IDGs (Generators) | 4 × 90 kVA, 115/200V AC, 400Hz, 3-phase |
| APU Generator | 1 × 90 kVA, ground & in-flight |
| External Power | 2 receptacles (Ext Pwr 1, Ext Pwr 2) |
| Main AC Buses | 4 (one per engine generator) |
| Transfer Buses | AC Transfer L, AC Transfer R |
| Standby Bus | AC Standby + DC Standby |
| TRUs | 4 (Transformer Rectifier Units) |
| Main Battery | 1 × 36 Ah Ni-Cd, 24 V DC |
| APU Battery | 1 × 36 Ah Ni-Cd |
| Hot Battery Bus | Always energized from battery |
Bus Logic
- Normal: Each AC main bus powered by its respective IDG. Bus ties open.
- Single Generator Loss: Bus ties auto-close to restore power from adjacent gen.
- All Generators Lost: APU gen if available; else essential loads on standby bus from battery (limited duration).
- External Power: Ground only — connects to both transfer buses.
Failures & Abnormals
CAUTION — IDG Disconnect — Irreversible
Once the IDG is disconnected on the ground via the cockpit switch, it cannot be reconnected in flight. Maintenance action required.
Limits
- IDG oil temp: see EICAS
- Battery limited duration on standby buses
Notes / Personal
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User notes.