1. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 1 POWER FACTOR CORRECTION WITHIN INDUSTRIAL SITES EXPERIENCES REGARDING PQ AND EMC IBERDROLA DISTRIBUCIÓN ELÉCTRICA F. Ferrandis

2. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 2 Industrial Compensation vs Distribution Network Compensation Common practice both in distribution networks and industrial facilities...... But different reasons... Utilities: Technical (system capacity, efficiency, voltage drops), economic (line losses, infrastructure costs) Customers: Avoid penalties, existing space

3. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 3 Industrial Compensation vs Distribution Network Compensation... And also different problems... Utilities: Tipically maintenance problems (capacitors & circuit breakers) Customers: Serious problems caused by their own capacitor banks –Harmonics –Others: voltage variations; interharmonics; high frequency surges; EMC problems

4. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 4 Customer facilities: problems in reactive power compensation at MV/HV Might be the cheapest for Q > 1 MVAr Usually: –Without regulation –Always connected –Connection through fuses (no circuit breakers) Predominantly reactive system  very little damping  higher resonance at high order frequency Two common configurations: –Capacitor banks connected directly at the PCC –HV customers with capacitor banks connected at MV busbars

5. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 5 Customer facilities: problems in reactive power compensation at MV/HV Harmonics can affect the whole system More complex behaviour, considering the whole distribution network Problems: –Different configurations  Variable resonances  problems with harmonics (itself & other sources) –Switching of single capacitor banks without limiting inductances  discharges onto substation capacitor bank  stressed circuit breakers, damages...at the PCC...

6. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 6 Customer facilities: problems in reactive power compensation at MV/HV LC system with very low damping Bigger capacitor banks and non-linear loads (compared with MV public grids) Problems: –Untuned: very strong connection transients –Tuned: attraction of harmonics from the network Arc furnaces: L-C filters overload due to interharmonics –Both: resonance variation due to capacitor installations without further studies...at MV busbars...

7. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 7 Customer facilities: problems in reactive power compensation at LV Most frequent, commercial products up to 1000 kVAr –Standardised, untuned (1.3·I nominal ) –Oversized, untuned (1.5·I nominal ) –Tuned (with reactors) Commonly automatic banks –High number of switching operations –Multiple configurations When loads with PF < 0.7  larger capacitor banks compared with S tranformer  low frequency resonance Great % disturbing loads  harmonic currents increase Summation laws for harmonics: worse than in MV grids

8. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 8 Customer facilities: problems in reactive power compensation at LV Problems in capacitor banks: –overloads due to harmonics in untuned capacitor banks: by a resonance circulation of high order harmonics –disturbing loads with good PF (e.g. non controlled rectifiers) –coexisting tuned & untuned capacitor banks –high temperature in tuned capacitor banks due to inductance losses –stressed contactors

9. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 9 Customer facilities: problems in reactive power compensation at LV Problems in other equipment units: –control or switching failures due to harmonics –transformer overheating: resonance, harmonic currents –EMC: control system failures due to radiated fields

10. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 10 Customer facilities: problems in reactive power compensation at LV CASE STUDY 1: OVERHEATING PROBLEMS IN MV/LV TRANSFORMER After installing a 3rd. order filter to reduce harmonic content  20ºC decrease in transformer!!! Before:After: Problems in other equipment units:

11. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 11 Customer facilities: problems in reactive power compensation at MV/HV CASE STUDY 2: EFFECT ON THE NETWORK IMPEDANCE...at the PCC... 30 kV customer with 2 MVAr, usually feeded from near substation (Scc=1000 MVA, Q=14 MVAr) Problems (23th harmonic resonance) appeared with auxiliar feeder (Scc=200MVA, Q=0) Different grid configurations  different resonances  No control over the final situation

12. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 12 Customer facilities: problems in reactive power compensation at MV/HV CASE STUDY 3: OVERLOAD OF AN ARC FURNACE WITH L-C FILTER...at MV busbars... Arc furnaces emit interharmonics during initial melting  overload of capacitor bank components L-C filters must be oversized Dumped filters recommended

13. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 13 Conclusions (I) Similar approach: Industrial customers and utilities use capacitor banks to correct PF... but different problems arise –Utilities: mainly switching problems –Customers: harmonic resonances and others (interharmonics, high frequency surges, EMC problems) Several reasons: –HV/MV: Harmonics can affect the whole system. Complex behaviour due to changes in the network impedance –LV: High rate Q capacitor bank / S transformer,, poor PF loads, Great % disturbing loads, different summation laws

14. F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation Barcelona 12-15 May 2003 14 Conclusions (II) Solutions in industrial sites: –Transient switching overcurrent  Transient limitation MV: capacitor banks with reactors LV: usually adapted contactors, occasionally static switches –Capacitor overload  Harmonic current limitation or capacitor oversizing MV & LV: tuned capacitor banks or capacitors of oversized nominal voltage –Harmonic voltage reduction  Filtering MV: pasive filters (L-C or dumped) LV: usually pasive filters, ocassionally active filters