Diesel Generator Frequency – Explained

Diesel generator frequency is the Electrical frequency, measured in Hertz (Hz), which describes the number of times that the current alternates, or changes direction, each second. This can be seen in an alternating current sine wave graph on an oscilloscope display, each complete wave being caused by one complete rotation of the magnets. For example, if a complete sine wave is completed 50 times every second, then the frequency is 50 Hz. The higher the frequency, the more cycles are competed per second.

Here in the UK & Europe all diesel generators are 50hZ. (the US it’s 60 times per second, so in the US it’s therefore 60Hz for diesel generators)

A generator that is continuously running should have a frequency that matches the required frequency of the appliances that it supplies. A standby generator’s frequency should equal the mains frequency, which is 50 Hz in Europe, Asia and most other countries, and 60 Hz in the Americas and a few other countries. Power Continuity have a generator power calculator in the Apple App store, free to download and use to work out your power frequencies.

Should you want to get bogged down in tech speak, then ‘fill your boot’s’ with this:

A generator induces an electrical current by rotating powerful magnets inside a coil of wire. As the opposite poles of the magnets pass through the coil, the changing magnetic field causes electrons to move backwards and forwards between individual atoms, generating an alternating current and creates the frequency. So there we have it. Simples.

For us in the real world, Generator frequency is worked out using the following equation:
f = (N x P)/120 where:
f is the generator frequency
N is speed in RPM (revolutions per minute)
P is the number of magnetic poles

The generator needs to run at the correct speed (RPM) in order to produce the desired frequency. To calculate this the above formula can be rearranged as follows:
N = (f x 120)/P

If the generator’s speed is fixed then a frequency convertor may need to be fitted to allow the frequency to be adjusted.

Diesel generator frequency – Why is it important?

The frequency of a diesel generator depends on maintaining a continuous 1500 rpm. If 1500 rpm is maintained that the output will be 50hZ continually which is required to power UK equipment. There is a small tolerance window below 50Hz although it is generally speaking average of continuous 50Hz is the norm Diesel generator frequency – What could cause the frequency to fall or drop? Issues can happen, such as the ‘Perfect Storm’, the unexpected and not planned for.

Here are the most unlikely to watch out for that can happen:

  • Generator may have a sudden restricted fuel flow (filters suddenly blocking between service intervals)
  • Contaminated fuel deliveries
  • Water leaking into the fuel supply – leaking roof
  • Sediment in the fuel tank
  • Faulty alternator
  • Faulty AVR
  • Leaking fuel hoses

Worst case – generator can shut down completely on low frequency. If that happens check all of the above and get a fuel quality test before restarting. Always have written copies of all service visits, generator testing, load bank records.

Power Continuity handles all generator servicing & maintenance.
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