PFC units sizing in steel factory harmonics environment: a case study

This paper deals with PFC units design related problems in case of installation in harmonics rich environments: in particular the paper contains an overview of sizing approach used in a real case of PFC units design for installation in a steel factory where new PFC units installation has been necessary after a fault with catastrophic consequences for the existing ones. The document contains a report on stresses calculation on PFC units due to harmonic currents generated by non linear loads installed in the above mentioned plant. Plant load, estimated to be around 80 MVA, is formed by a big amount of small loads fed by power converters: this is a big disturbance source for the installation in terms of harmonic content. In particular, due to the usual lack of real harmonics contents data availability, main issue has been the process of definition of a generic harmonic distortion for installed loads, based on power converters installed and literature available data on power converters spectra and its on field verification for PFC optimal design, with three measurement campaigns aiming to verify real harmonic distortion and series and parallel resonance risk. This kind of problem is really actual and, most of all, is constantly growing also in other industries, not only in steel factories where harmonics content has always been a key problem. Now, due to the continuous increase of power converter usage and equipment power consumption, and mostly to the increase of equipment disturbances sensitiveness, to avoid potentially tragic faults, a deep measurement campaign is the key solution at PFC units design stage, also considering the usual lack of data on installation harmonic distortion. The experience described in this paper constitutes the first detailed example of on-field verification of harmonic disturbances effects on two 8.4 Mvar, 13 kV PFC units in a harmonics critical environment aiming first of all at a detailed fault analysis (referred to pre-existent PFC units- ) and then to a correct new unit design. In the paper the different design stages and related issues are described, including: installation network analysis, load analysis, harmonic distortion evaluation, PFC units stresses analysis, PFC units sizing, on field stresses verification. This work highlights the strong need for deep measurements campaigns in harmonics rich industrial environment as the only way, in addition to a correct distortion pre-analysis aiming to a careful PFC design strategy to prevent potentially catastrophic faults.