Power Factor & APFCPower Factor & APFC

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By: Ravi Shankar Singh

What is power factor…?What is power factor…?

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Power Factor = Active Power (kW)/Apparent Power (kVA)

PF≤1.0Usually P.F is always “Lag” (Inductive)Some time P.F can be “Lead” (Capacitive).

Origin of Low Power FactorOrigin of Low Power Factor

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Electrical Equipment need Reactive PowerInductive loads draw Reactive PowerPhase 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.

Disadvantages of low power factorDisadvantages of low power factor

Inefficient use of Electrical Energy:Overloading of Transformer/Generator;Overloading of Cable, Switchgear, Busbar …Higher temperature due to increased lossesImposes larger kVA demandLimits No. of loads that can be connectedReduced revenue to Electrical UtilitiesPoor Voltage regulation

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Power Factor Power Factor CorrectionCorrection

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Ø2Ø1

V= Line Voltage

I=Active Current

I1

I2

IR(L)

IR(C)

Reactive Current (inductive)

Reactive Current (capacitive)

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Reduction inTransformer Rating

Reduction in KVARDemand

Advantages of P.FCorrection

Reduction in KVADemand

Reduction in LineCurrent

Reduction in Lineloss

Reduction in Cable / Bus-bar

size

Reduction in Switchgear

Rating

Avoid power factor penalties

Reduction in KVADemand

ESTIMATION OF kVAr REQUIRED ESTIMATION OF kVAr REQUIRED for New Electrical Installations for New Electrical Installations

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M M 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.

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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 KvarKvar For UPS- rating of UPS = 50 KVA* 0.7

= 35 KwKvar for UPS = 35 [tan(cos-1(0.70)- tan(cos-1(0.99)]

= 25 KvarKvar For Others & lighting load-Kvar for UPS = 24 [tan(cos-1(0.70)- tan(cos-1(0.99)]

= 17 KvarTotal kvar requirement = (30+104+35+25+17)kvar =211 KvarAssuming 15% design assumption and contigency = 221*0.15=31.65 KvarTotal kvar = 242.65 kvarKavr recommended= 250 kvar

Capacitor req. (c) = Qc/V2(2f)

Hence Capacitor req. for UPF=106*250/(2302

*100)

= 150.51F.

Type of compensationType of compensation

Fixed compensation

Variable compensation(for varying loads)- APFC Svc

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1. Individual compensation2. Group compensation3. Central compensation

- Steady Loads– No load compensation of Induction Motors– No load compensation of Transformers

Disadvantages of fixed capacitorDisadvantages of fixed capacitor

Manual operation(on/off)Not meet the require kvar under varying

loads.Can result leading power factor Cause over voltageMal-operation of relays, diesel generatorsSaturation of transformerPenalty by electricity authority

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•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

Benefits of APFCBenefits 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.

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Automatic Power Factor Automatic Power Factor Correction (APFC):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

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How to Improve Power Factor Without How to Improve Power Factor Without Causing Harmonic Problem ?Causing Harmonic Problem ?

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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 “fR” do not coincide with predominant harmonics.

Network With Harmonic Network With Harmonic FiltersFilters

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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

Lin

ear

Loa

d

BUS

M

GRID

ZT

Equivalent Load Impedance “ZL”

ZN

L

C

Specification of capacitors in APFCSpecification 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

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Selection of switching equipmentSelection 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

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Harmonics and parallel resonanceHarmonics and parallel resonance

H=Kp ± 1 (converter) where k= 1,2,3,4,……. p= pulsating indexHigh Harmonics current produces high harmonics

voltages.When harminics current frequency and parrellel

resonance become equal than corrosponding harmonics voltage produces over current in capacitor.

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Series reactorSeries reactor

XT= Xc/h2

Supress high inrush current to safe value at time of capacitor switching.

Improve voltage waveformReactor should be able to carry 135%of rated

contineous current.Discharge VTTo discharge voltage of capacitor

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TYPES OF CAPACITOR TECHNOLOGIESTYPES OF CAPACITOR TECHNOLOGIES

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MPP - METALLISED POLYPROPYLENE

MD - MIXED DIELECTRIC

FF/ALL PP - FILM - FOIL OR ALL POLY

PROPELENE

MD -XL - MIXED DIELECTRIC LOW LOSS

METALISED POLYPROPELENE CAPACITORMETALISED POLYPROPELENE CAPACITOR

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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

MIXED MIXED DIELECTRIC TYPEDIELECTRIC TYPE

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MD - MIXED DIELECTRIC

PP FILM, FOIL AND PAPER ARE USED

TO FORM CAPACITOR WINDING

PP FILM

FOIL

PAPER

FILM FOIL OR APPFILM FOIL OR APP

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FILM FOIL OR APP - ALL POLY

PROPELENE

METAL LAYER IS PLACED IN -

BETWEEN PP FILM TO FORM

CAPACITOR WINDING

PP FILMFOIL

PP FILM

FILM FOIL OR APPFILM FOIL OR APP

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FILM FOIL OR APP - ALL POLY

PROPELENE

METAL LAYER IS PLACED IN -

BETWEEN PP FILM TO FORM

CAPACITOR WINDING

PP FILMFOIL

PP FILM

MIXED DIELECTRIC - LOW MIXED DIELECTRIC - LOW LOSSLOSS

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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

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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

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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

APFCAPFC28

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Power factor correction in Power factor correction in harmonics enrich environmentharmonics enrich environment

percentage of Non linear loads in an installation becomes greater than 20% of connected load.

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Conventional capacitor

N/w Harmonics

Parallel resonance

Current amp

Overloading cap

Voltage distortion

Cap failure

solutionsolutionUse 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

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COMPONENTSCOMPONENTS33

CONTROLLERCONTROLLER34

REACTORREACTOR35

DRY TYPE RESIGN EMBADED

Circuit DiagramCircuit Diagram

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THYRISTER CONTROLLED VAR STATCOM