Download - automatic power factor controller
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