28 September 2021
ATS48 total distortionProduct Line:
Schneider Electric does not have measured values of harmonics produced by softstarters.
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 18.104.22.168.2 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.
22.214.171.124 Harmonics and commutation notches
The test values and procedures are given in 126.96.36.199.5.
188.8.131.52.5 Harmonics and commutation notches
No requirement, the test levels are under study for the future."
So, no special considerations or filtering are required for soft start applications.
This is the reason why we do not make tests for that.
Anyway, in the past some calculations were done to estimate it.
ATS48 generates significant current harmonics only during the acceleration/deceleration phase, in steady state (when the thyristors are full conducting) they are negligible THD<2% and 0% with the starter bypassed.
The harmonics level is difficult to calculate accurately because depends on the impedance of the all installation and it varies with the motor load (power factor is not constant).
The following maximum values, are typical for a general case (during ACC/DEC only):
Row 5 : 20% of fundamental
Row 7 : 14% of fundamental
Row 11 : 9% of fundamental
Row 13 : 6.7% of fundamental
Higher rows are practically negligible.
Some tests were done for Row 3, unfortunately not for nominal load : less than 10% can appears with a low power factor.