This document discusses power factor correction and automatic power factor correction (APFC) systems. It explains that power factor is the ratio of active power to apparent power and can be lagging or leading. Low power factors are caused by inductive loads and non-linear loads. APFC systems use capacitors in automatic steps controlled by a microprocessor to maintain a high power factor under varying loads without manual intervention or risk of overvoltage. This improves efficiency and reduces utility penalties and equipment loading and sizes. The document provides specifications for capacitor selection and switching equipment for APFC systems.

1. Power Factor & APFC By: Ravi Shankar Singh

2. What is power factor…? Power Factor = Active Power (kW)/Apparent Power (kVA) PF≤1.0 Usually P.F is always “Lag” (Inductive) Some time P.F can be “Lead” (Capacitive).

3. Origin of Low Power Factor Electrical Equipment need Reactive Power Inductive loads draw Reactive Power Phase difference between current & Voltage reduces “Displacement PF”. Reactive Power to maintain magnetic fields in Motors. Non-Linear loads reduces “Distortion PF”. True PF, being product of displacement and distortion PF is lower than both. Capacitors can only improve displacement PF.

4. Disadvantages of low power factor Inefficient use of Electrical Energy: Overloading of Transformer/Generator; Overloading of Cable, Switchgear, Busbar … Higher temperature due to increased losses Imposes larger kVA demand Limits No. of loads that can be connected Reduced revenue to Electrical Utilities Poor Voltage regulation

5. Power Factor Correction V= Line Voltage I=Active Current I 1 I 2 I R(L) I R(C) Reactive Current (inductive) Reactive Current (capacitive) 2 1

6. Reduction in Transformer Rating Reduction in KVAR Demand Advantages of P.F Correction Reduction in KVA Demand Reduction in Line Current Reduction in Line loss Reduction in Cable / Bus-bar size Reduction in Switchgear Rating Avoid power factor penalties Reduction in KVA Demand

7. ESTIMATION OF kVAr REQUIRED for New Electrical Installations M 75 HP, (415V, 3ph, compressor pf. 0.7) 75 HP, (415V, 3ph, compressor) 20 HP, (415V, 3ph, Pump, PF =0.70 Lag) Other loads, (total of 25 Kw) 500kVA, 11kV/415V, %Impedance = 4.25% 50 kVA, (440V, 3ph, UPS) Lighting (Load 10kW) M 30 HP, (415V, 3ph, I M pf 0.7) Let us assume that the target Power Factor as desired by the Customer is 0.95. M M

8. Kvar For The Supply Transformer- For 500 kVA transformer, kVAr = 30 kVAr Kvar For Induction Motor- rating of motor = 200 HP x 0.746 = 150 kW Kvar for motor = 150*[tan(cos -1 (0.95)- tan(cos -1 (0.99)] = 104 Kvar Kvar For UPS- rating of UPS = 50 KVA* 0.7 = 35 Kw Kvar for UPS = 35 [tan(cos -1 (0.70)- tan(cos -1 (0.99)] = 25 Kvar Kvar For Others & lighting load- Kvar for UPS = 24 [tan(cos -1 (0.70)- tan(cos -1 (0.99)] = 17 Kvar Total kvar requirement = (30+104+35+25+17)kvar =211 Kvar Assuming 15% design assumption and contigency = 221*0.15=31.65 Kvar Total kvar = 242.65 kvar Kavr recommended= 250 kvar Capacitor req. (c) = Qc/V 2 (2  f) Hence Capacitor req. for UPF=10 6 * 250/(230 2 * 100  ) = 150.51  F.

9. Type of compensation Fixed compensation Variable compensation(for varying loads)- APFC Svc 1. Individual compensation 2. Group compensation 3. Central compensation - Steady Loads – No load compensation of Induction Motors – No load compensation of Transformers

10. Disadvantages of fixed capacitor Manual operation(on/off) Not meet the require kvar under varying loads. Can result leading power factor Cause over voltage Mal-operation of relays, diesel generators Saturation of transformer Penalty by electricity authority

11. varying power demand on the supply system. power factor also varies as a function of the load requirements. difficult to maintain a consistent power factor by use of Fixed Compensation i.e. fixed capacitors. leading power factor under light load conditions(fixed compensation) This result in over voltages, saturation of transformers, mal-operation of diesel generating sets, penalties by electric supply authorities. automatically variation, without manual intervention, the compensation to suit the load requirements. Automatic Power Factor Correction(APFC) system provide this facility. leading power factor will be also prevented. NEED FOR AUTOMATIC POWER FACTOR CORRECTION

12. Benefits of APFC Consistently high power factor under fluctuating loads Prevention of leading power factor Eliminate power factor penalty Lower energy consumption by reducing losses. Continuously sense and monitor load Automatically switch on/off relevant capacitors steps for consistent power factor. Ensures easy user interface Protect under any internal fault Advance µ- relay with communication facility Used MPP-H/MD-XL/FF(APP) type capacitors User friendly, aesthetecally designed enclosure, dust and vermin proof.

13. Automatic Power Factor Correction (APFC): Capacitors grouped into several steps. • Suitable switching devices with coupled with inrush current limiting devices are provided for each step • Power Factor sensed by CT in line side • kVAr required to achieve target PF is computed by the Microprocessor based APFC relay • APFC relay switches appropriate capacitor steps • CT senses improved PF and gives feedback • Thus target PF is achieved

14. How to Improve Power Factor Without Causing Harmonic Problem ? Conventional capacitors should not be used. Capacitors should be replaced by harmonic suppression filters (series combination of suitable series reactor & capacitors) so that, It offers capacitive reactance at fundamental frequency for necessary power factor correction. It offers inductive reactance at all higher order dominant harmonic frequencies to avoid resonance. Its self series resonance frequency “f R ” do not coincide with predominant harmonics.

15. Network With Harmonic Filters No resonance at harmonic frequencies as filter is inductive at such frequencies Harmonic currents flow towards Grid , as it offers least impedance compared to filter Predominantly fundamental current flows through Capacitors Moderate THD(V) in the Bus No harmonic overloading of Capacitors Improvement in Power Factor without Harmonic overload Non Linear Load BUS M GRID Z T Equivalent Load Impedance “Z L ” Z N L C

16. Specification of capacitors in APFC Qkvar Degree Of Protection IP20 Ambient temperature Voltage rise should be ≤ 3.0% [ % Vc = (Q kvar *%X)/(kva)] Voltage rise due to series reactor and harmonics Size of individual capacitor banks (step requirement) Directly connected Discharge Device(Resistor, VT) to discharge the capacitor to reduce voltage to 50 volts within one minute

17. Selection of switching equipment FOR LT Switch- fuse units/CBs/ Thyristers Switch should be quick make and break type Rating of CB, contactors, fuse and cable should be≥130% of capacitor rated current. For automatic switching, each step capacitor should be provided with fuse and contactor. FOR HT Ht capacitor is connected to bus by CB Cb rating should be ≥ maximum operating voltage of circuit Continuous current rating of CB should be ≥ 135% of rated capacitor bank current

18. Harmonics and parallel resonance H=Kp ± 1 (converter) where k= 1,2,3,4,……. p= pulsating index High Harmonics current produces high harmonics voltages. When harminics current frequency and parrellel resonance become equal than corrosponding harmonics voltage produces over current in capacitor.

19. Series reactor X T = Xc/h 2 Supress high inrush current to safe value at time of capacitor switching. Improve voltage waveform Reactor should be able to carry 135%of rated contineous current. Discharge VT To discharge voltage of capacitor

20. TYPES OF CAPACITOR TECHNOLOGIES MPP - METALLISED POLYPROPYLENE MD - MIXED DIELECTRIC FF/ALL PP - FILM - FOIL OR ALL POLY PROPELENE MD -XL - MIXED DIELECTRIC LOW LOSS

21. METALISED POLYPROPELENE CAPACITOR MPP - METALLISED POLYPROPELENE METALISATION HAS BEEN DONE ON ONE SIDE OF POLY PROPELENE FILM AND USED FOR CAPACITOR WINDING ECNOMICAL AND COMPETITIVE DESIGN MPP-S - NORMAL DUTY MPP-H - MEDIUM DUTY PP FILM METALLISED LAYER

22. MIXED DIELECTRIC TYPE MD - MIXED DIELECTRIC PP FILM, FOIL AND PAPER ARE USED TO FORM CAPACITOR WINDING PP FILM FOIL PAPER

23. FILM FOIL OR APP FILM FOIL OR APP - ALL POLY PROPELENE METAL LAYER IS PLACED IN - BETWEEN PP FILM TO FORM CAPACITOR WINDING PP FILM FOIL PP FILM

24. FILM FOIL OR APP FILM FOIL OR APP - ALL POLY PROPELENE METAL LAYER IS PLACED IN - BETWEEN PP FILM TO FORM CAPACITOR WINDING PP FILM FOIL PP FILM

25. MIXED DIELECTRIC - LOW LOSS MD-XL - MIXED DIELECTRIC LOW LOSS PP FILM AND DOUBLE SIDED METALISED FILM ARE USED TO FORM CAPACITOR WINDING PP FILM DOUBLE SIDE METALLISED PAPER

26. Film foil/APP verses Mixed dielectric comparison Film foil/APP Mixed dielectric low dielectric watt loss Film not impregnable More prone to ‘Self healing’ Inferior long term stability Moderate harmonic overload capability High dielectric watt loss Paper impregnable less prone to ‘Self healing’ Superior long term stability Good harmonic overload capability

27. Mixed dielectric verses MDXL Comparison Mixed dielectric MDXL High dielectric watt loss Paper impregnable less prone to ‘Self healing’ Superior long term stability Good harmonic overload capability Lowest dielectric watt loss Combines plus points of MD and APP types Excellent long term stability Superior harmonic overload capability

28. APFC

31. Power factor correction in harmonics enrich environment percentage of Non linear loads in an installation becomes greater than 20% of connected load. Conventional capacitor N/w Harmonics Parallel resonance Current amp Overloading cap Voltage distortion Cap failure

32. solution Use detuned filter circuit Avoid parallel resonance by offering inductive impedance to specific harmonics frequency. The tuning frequency is generally lower than 90 % of the lowest harmonic frequency whose amplitude is significant. Protect capacitors from harmonics over loading Reduces over loading of transformer and other rotating equipments. Prevent current amplification Achieve consistently high power factor. Can be used as fixed or APFC

33. COMPONENTS

34. CONTROLLER

35. REACTOR DRY TYPE RESIGN EMBADED

36. Circuit Diagram

37. THYRISTER CONTROLLED VAR STATCOM