Why Constant Engine Speed Matters on a Generator
The frequency a generator produces is directly proportional to engine speed. If the speed drifts, the frequency drifts with it; for sensitive electronics, any deviation from 50 Hz is a problem.
The frequency of the electricity a generator produces depends directly on engine speed. To produce 50 Hz with a 4-pole alternator, the engine must turn at 1500 rpm. If the speed drops, the frequency drops with it; this creates problems for sensitive electronics and motor loads.
The relationship between speed and frequency
| Number of poles | Speed for 50 Hz | Speed for 60 Hz |
|---|---|---|
| 2 poles | 3000 rpm | 3600 rpm |
| 4 poles | 1500 rpm | 1800 rpm |
| 6 poles | 1000 rpm | 1200 rpm |
What does frequency deviation cause?
- Motor loads: When frequency drops, motor speed drops, more current is drawn for the same work, and heating increases.
- Electronic devices: Power supplies are designed for a specific frequency range; deviation reduces efficiency.
- Synchronization: Frequency match is mandatory for systems that will run in parallel with the grid.
The problem with a mechanical throttle lever
A mechanical lever holds its position by friction. Under the generator's own vibration that friction eventually becomes insufficient and the lever creeps. The operator corrects the speed, and after a while it creeps again. On long runs this means a continuous monitoring burden.
What does electronic speed control provide?
Because the servo actuator holds the commanded position, vibration does not disturb the setting. The speed is set once and stays there. It should be emphasized that the system does not replace the engine's own governor: the governor holds speed steady through load changes, while the electronic control sets the governor's target speed. The two work together.
For the full treatment of this subject: Electronic Speed Control on Diesel Engines