power factor correction within industrial sites

1F. Ferrandis_SP_ALPHA 2_BLOCK 2_Paper 35_Presentation

Barcelona 12-15 May 2003

POWER FACTOR CORRECTION WITHIN INDUSTRIAL SITES

EXPERIENCES REGARDING PQ AND EMC

IBERDROLA DISTRIBUCIÓN ELÉCTRICAF. Ferrandis



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



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



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



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...




• 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...



Customer facilities: problems in reactive power compensation at LV

• Most frequent, commercial products up to 1000 kVAr– Standardised, untuned (1.3·Inominal)– Oversized, untuned (1.5·Inominal)– Tuned (with reactors)

• Commonly automatic banks– High number of switching operations – Multiple configurations

• When loads with PF < 0.7 larger capacitor banks compared with Stranformer low frequency resonance

• Great % disturbing loads harmonic currents increase• Summation laws for harmonics: worse than in MV grids




• 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




• 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




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:




CASE STUDY 2: EFFECT ON THE NETWORK IMPEDANCE

...at the PCC...

0,001

0,01

0,1

1

10

100

1000

10000

0 5 10 15 20 25 30Harmonic order

Impe

danc

e (o

hms)

Network configuration 1

Network configuration 2Network configuration 3

• 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




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



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 Qcapacitor bank / Stransformer,, poor PF loads, Great % disturbing loads, different summation laws



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

power factor correction within industrial sites

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