Harmonics, Inter-harmonics, and Sub-harmonics

I knew instinctively what these terms meant, but I never knew the true harmonic terminology until I attended a harmonics training training course recently at The University of Manchester. So if you didn’t know like I did, here’s enlightenment for both of us.

Harmonics: A sinusoidal component of a periodic wave having a frequency that is an integer multiple of the fundamental frequency.

Inter-harmonics: Components with frequencies between two consecutive harmonics or those components whose frequencies are not integer multiples of the fundamental power frequency.

Sub-harmonics: A special subset of interharmonics that have frequency values that are less than that of the fundamental frequency.

Table below illustrate their usage with examples for a 50Hz system.

Note: Information presented here and illustration was taken from the Prof. A. Testa’s power quality course lecture held at the University of Manchester on the 26th Jan 2010. Some information was obtained through email exchange between Prof. V. Katic and I following my attendance of the course. Thank you Gentlemen.

Power System Type Faults

When power systems design engineers or consultants refer ‘Type Faults’, it’s common for young power system engineers ( beginners like me) to assume them referring to power systems fault types (line-line-line fault, line-ground fault etc). However, in actual practice a ‘Type Fault’ is referred to an equipment or system due to its design failures. In other words, Type Faults are failures due to errors in design parameters, calculations, assumptions etc.

The good thing is that I get to learn, and pass it on to someone who wish to learn.

^__^