What part of the IDG keeps the Generator turning at a constant speed of 12,000 rpm?

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Multiple Choice

What part of the IDG keeps the Generator turning at a constant speed of 12,000 rpm?

Explanation:
Keeping the generator at a fixed speed is the job of the Constant Speed Drive. The IDG uses this drive to hold the generator’s rotor at about 12,000 rpm, even as the engine speed varies. The drive does this with a hydraulic fluid coupling that damps speed changes: when the engine speeds up, the coupling slips a bit and transmits less effective torque to the generator; when the engine slows, it transmits more torque to keep the generator turning at the same rate. This constant rotor speed is what keeps the electrical frequency stable (roughly 400 Hz for a 4-pole generator). The voltage regulator controls voltage, not speed, and a gearbox alone wouldn’t compensate for engine-speed fluctuations.

Keeping the generator at a fixed speed is the job of the Constant Speed Drive. The IDG uses this drive to hold the generator’s rotor at about 12,000 rpm, even as the engine speed varies. The drive does this with a hydraulic fluid coupling that damps speed changes: when the engine speeds up, the coupling slips a bit and transmits less effective torque to the generator; when the engine slows, it transmits more torque to keep the generator turning at the same rate. This constant rotor speed is what keeps the electrical frequency stable (roughly 400 Hz for a 4-pole generator). The voltage regulator controls voltage, not speed, and a gearbox alone wouldn’t compensate for engine-speed fluctuations.

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