What are the THD (Total harmonic distortion) in case of Softstarter ATS48?
Generally speaking, the current THD caused by soft starter is not significally high, ATS48 generates current harmonics only during the acceleration/deceleration phase, in steady state (when the thyristors are full conducting) they are negligible with the starter bypassed.
Softstarters conform to the following norm:
IEC 60947-4-2: Low-voltage switchgear and controlgear - Contactors and motor-starters - AC semiconductor motor controllers and starters,
which states, concerning harmonics:
Subclause 22.214.171.124.2 of IEC 60947-1:2007 applies with the following addition:
Because no significant harmonic emissions are produced in the FULL-ON state, tests are not
required on those controllers or starters which run only in the FULL-ON state or which are
by-passed by a mechanical switching device after completing a start, for example, Forms 2 and 3 and certain Form 1 controllers or starters.