Electrical power system frequency conversion is required when a load differential exists between a power supply and the equipment being powered. At the very least, equipment designed to operate at a different frequency than the power available will run inefficiently and in a worst-case scenario may become damaged or not work at all.
Because the European power grid operates at 50Hz and North America’s at 60Hz, problems can arise when equipment manufactured in one location is used in another.
That’s why it’s critical to convert generator frequencies as needed.
There are three primary methods to convert power frequency: varying engine speed, using a frequency converter, or employing a variable speed generator.
Vary Engine Speed to Change Generator Frequency
Today’s generator engines are connected directly to an alternator to produce electricity. By changing a generator’s revolutions per minute (rpm), the frequency output (Hz) is changed as per this formula:
Number of magnetic poles (P) * engine (N) rpm ÷ 120 = generator frequency (f)
Or, more concisely:
P*N/120=f
Therefore, to produce 60Hz output, a 3-pole generator requires an engine speed of 2200 rpm. However, reducing engine speed to 2000 rpm results in an output frequency of 50Hz. A 2-pole generator with an engine speed of 3600 rpm produces a 60Hz output frequency, and reducing the speed to 3000 rpm drops the output frequency to 50Hz.
Use a Frequency Converter
You may, however, be using a fixed-speed generator. In that case, you’ll need to use a frequency converter to change the generator’s alternating current (AC) frequency. A rectifier converts the AC output to direct current (DC) which an inverter then converts back into the desired AC output frequency. Originally, frequency converters were belt-driven electromagnetic components but now use solid-state technology.
While a frequency converter can be used, as noted above, to address the problem of equipment manufactured in one part of the world being used in another, there are additional applications. Rail systems typically use 100Hz power and aircraft use 400Hz which also demands 50Hz/60Hz frequency conversion. So, in the latter example, frequency conversion allows passengers to use/charge their electronic devices while in flight.
Employ a Variable Speed Generator
The newest method for frequency conversion uses a variable speed generator set. Unlike changing generator rpm from one fixed speed to another to change frequency or using a converter to change frequencies, this method – also known as a variable-frequency drive (VFD) – allows a generator to spin at varying speeds while still producing the same frequency output.
Wind turbines employ this technology to allow ever-changing wind speeds to produce the same output. Plus, decoupling speed from output means these generators are significantly lighter than their traditional counterparts.
Market penetration, however, is still relatively small as its electronic components are not robust enough for the harsh elements and environments which are typical of large-scale industrial projects far removed from the power grid.
Face it: In a variety of situations for varying reasons, generator frequency conversion is going to be of paramount importance.
In particular, you want to avoid the needless problems that will occur when frequency output doesn’t match equipment specifications. The time is now to determine which frequency conversion strategy (or strategies!) will be best for you.
For more than 25 years, Depco Power Systems has been selling new, used, and rebuilt generators and engines. Contact us today so we can help you with your power generation needs.
