ECN Forum Forums Technical Discussion Electrical Theory and Applications operation of 225kVA static UPS - ISSUES WITH HARMONICS

Dear All,
please, we have an electrical power supply installation to one unit of Balanced Power Plus 225kVA static UPS machine and two 75kW pumps. All three equipment are supplied power from the same busbar. We propose to install dual soft start panel to replace the existing dual star-delta panel that is presently used to power the pumps from the 415V LV busbar. The pumps are 3-phase.

However, we will like to know if we are going to be experiencing problems with harmonics when the pumps are running after we have installed the soft-start panel. We wish to know if this panel upgrade will cause an increase in the Total Harmonic Distortion (in current and voltage) and what the effect on the UPS will be. Also, we will like to know if there are equipment that we can install that will limit the THD to acceptable values (for the UPS) when the pumps are running.

Do treat as urgent and thanking you for your co-operation and support.

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Quick question...
A 225kVa UPS is a double conversion device and rather immune to terrible input power. Are you concerned about THD PoCo penalties?
Other than a active injection filter, voltage and current distortion will vary too much at startup and full load to be resolved by a static or tunned filter. Personally I wouldn't worry much about the UPS.
The UPS has already been exposed to mild/moderate surge and transients with the wye/delta starters. The EFI MOV's are typically the weakest link on the input of most UPS's.