Generator Harmonic Issues

Generator Harmonic issues explained

Harmonic distortion increases the rms value of the output voltage and thus creates issues on Diesel Generator regulation.
This is based on the rms value of sinusoidal voltage.
What is more, the high time constant of the flux variations in the windings makes precise corrections difficult.

Harmonics can increase the rms current, which in turn, will cause a temperature rise in generator windings.

Amplification of the harmonics will cause a number of consequences:
As a result, an increase in voltage distortion (THDU, normally limited to 5%) on the upstream busbars during Diesel Generator power.Generator Harmonics Issues
Also, reduction in the input power factor lower than 0.8.
Equally, will subsequently reduce the load capacity of the generator.
Solution is to locate and remove the cause of the harmonic distortion upstream.

Harmonic sub-transient reactance

Harmonic sub-transient reactance X”d of a generator is calculated ar approximately 10 to 12%.
This compares to the 3 or 4% for the short-circuit voltage of a transformer.
In other words, the output impedance of a Diesel Generator is 2 to 4 times higher than that of a transformer.
Each harmonic order lHk, a sinusoidal current k times the fundamental frequency, is amplified.
When compared to normal operation on utility power with the output impedance of the transformer.

How to cure Harmonic issues with Diesel Generators?

First Option is to Oversize the Diesel Generator
A classic solution to avoid the effects of harmonics is to oversize the Diesel Generator.
This increase in power makes it possible to handle the temperature rise in coils, to ensure correct regulation and to obtain a higher output impedance.
Should the Genset be supporting a UPS power system, then the power rating of the diesel generator must be 2 times greater than that of the UPS. (eg: 2:1 ratio)
500kVA UPS will require a 1000kVA Diesel Generator Power source.

Contact Power Continuity for more information
Call on 0845 055 8455

Power Continuity and Powercontinuity are registered Trade Marks.

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