Influence of Harmonics on Aging

@TW: used in Maintenance Guides: DOCA0305 (MTZ with Mic Act), DOCA0099 (MTZ with Mic X), LVPED508016 (NT/NW)

Influence	Appearance	Consequences
Increase in skin effect, proximity effect, iron loss, Foucault/Eddy currents	Change in color of terminals, insulators, and grease Modified display of LCDs	Harmonics cause temperature rise greater than that of the fundamental current
Possible overload of neutral if third-order harmonics and their multiples are present	Distorted waveform	Erroneous current value Nuisance tripping if non-rms control units

The maintenance and installation recommendations according to the harmonics are defined in the following table:

THDi in % of In	Description	Maintenance recommendations	Installation recommendations
≤ 30 %	No notable influence on aging.	Implement the Intermediate program.	No particular recommendation
30 % to 50 %	At 40 % THDI, potential heat generation is approximately 10 % higher, corresponding to 5 % more current.	Carry out more frequent periodic checks.	Standard filtering with an inductor to reduce harmonics
> 50 %	–	Carry out more frequent periodic checks.	If necessary: Oversize the neutral Oversize switchgear Filtering is mandatory

THDi in % of In

Description

Maintenance recommendations

Installation recommendations

≤ 30 %

No notable influence on aging.

Implement the Intermediate program.

No particular recommendation

30 % to 50 %

At 40 % THDI, potential heat generation is approximately 10 % higher, corresponding to 5 % more current.

Carry out more frequent periodic checks.

Standard filtering with an inductor to reduce harmonics

> 50 %

–

Carry out more frequent periodic checks.

If necessary: