IEC 61000-4-7 defines a method for calculating harmonics and interharmonics based on a 12 cycle window, and then further defines several aggregations of those values.
The groups are used to consolidate harmonics back into 60Hz-wide bands, and interharmonics into 55 Hz wide bands without any finer detail, for rough characterizations.
The subgroups are used to provide a wider band for harmonics, accounting for modulation due to load and system variations, and to avoid including harmonic sidelobes into interharmonic data.
An understanding of these groupings is important for maximizing recorder memory, and avoiding having too much detail to analyze.
This White Paper Includes: