Presentation on theme: "Power Factor Correction Capacitors"— Presentation transcript:
1Power Factor Correction Capacitors Selection & Applications Of Power Factor Correction Capacitor For Industrial and Large Commercial Users Ben BanerjeePower Quality Solution Group
2Agenda Power Factor Fundamental The Need for Power Factor Correction Effects of Harmonics: TPF & DPFCorrection Alternatives & Capacitor LocationsPF Rate, Capacitor Sizing, & ROICapacitor Applications To MotorsCapacitor Switching EquipmentOther Application Issues* Steady State VAR Correction* Dynamic VAR CorrectionStandards & Codes
4ACTIVE & REACTIVE POWERS Most plant loads are Inductive and require a magnetic field to operate:MotorsTransformersFlorescent lightingThe magnetic field is necessary, but produces no useful workThe utility must supply the power to produce the magnetic field and the power to produce the useful work: You pay for all of it!These two types of current are the ACTIVE and REACTIVE components
5Power Factor Fundamental Definitions:Working /Active Power: Normally measured in kilowatts (kW). It does the "work" for the system--providing the motion, torque, heat, or whatever else is required.Reactive Power: Normally measured in kilovolt-amperes-reactive (kVAR), doesn't do useful "work." It simply sustains the electromagnetic field.Apparent Power: Normally measured in kilovolt-amperes (kVA). Working Power and Reactive Power together make up apparent power.
6Power Factor:The Beer Analogy Mug Capacity = Apparent Power (KVA)Foam = Reactive Power (KVAR)Beer = Real Power (kW)kVARReactivePowerkVAApparentPowerBeer (kW)Mug Capacity (KVA)Power Factor =kWActivePowerCapacitors provide the Foam (KVAR), freeing up Mug Capacity so you don’t have to buy a bigger mug and/or so you can pay less for your beer !
7Power Factor Fundamental Power Factor : A measure of efficiency. The ratio of Active Power (output) to Total Power (input)A power factor reading close to 1.0 means that electrical power is being utilized effectively, while a low power factor indicates poor utilization of electrical power.Power Factor = Active (Real) Power Total Power = kW kVA = Cosine (θ)= DISPLACEMENT POWER FACTORTotal Power (kVA)Active Power (kW)Reactive Power(KVAR)
8LEADING AND LAGGINGIRICIRVILOADILICGLKVARCKWKVARL2
9LEADING AND LAGGING KW KVAR (LAG) KW KVAR (LEAD) KW KVAR (LAG) KW INDUCTION MOTOROVER-EXCITEDSYN. MOTOR2
10Typical Uncorrected Power Factor (Use only as a Guide)
13Why do we care about Power Factor? In Industrial Facilities, Mostly Induction Motor loadsEnergy Efficient Motors not optimized for PFLow power factor is caused by oversized or lightly loaded induction motorsLow power factor results in:Poor electrical efficiency!Higher utility bills **Lower system capacityOn the Supply Side, Generation Capacity & Line LossesPower Factor Correction Capacitors (PFCC) provide an economical means for improving Energy utilization
14Why do we install Capacitors? BeforeAfterIn this example, demand was reduced to 8250 kVA from kVA.1750KVA Transformer Capacity Release.The power factor was improved from 80% to 97%Power Factor CorrectionCapacitors offload the utility grid by supplying the reactive power required by inductive loads. Power factor is improved by reducing the reactive power component. Capacitors provide the reactive power required by inductive loads.The installation of capacitors will improve the power factor from the point of connection back to the source as shown. In this example, the load is kVA at a power factor of 80%. This results in demand for 8000 kW of active (real) power and 6000 kVAR of reactive power. With the installation of a capacitor in figure 2 (b) most of the reactive power is supplied locally and the power supply sees a power factor of 97%.Since the power supply provides reduced reactive power with the installation of power factor capacitors, peak currents are reduced. Power factor capacitors are rated in kVAR. Power factor capacitors help bring the network current in phase with the network voltage by supplying leading current to effectively cancel lagging inductive current. Reactive energy is continuously swapped between the capacitor and inductive load.The result of improved power factor is reduced utility demand resulting in lower utility demand bills, released system capacity and lower system losses.
15Harmonics Displacement Power Factor Total Power Factor Effects of Harmonics on Capacitors
16Linear vs Non-LinearUntil recently, most electrical equipment drew current in a “linear” fashion:Today, many electrical loads draw current in a “non-linear” fashion:viCurrent (i) & Voltage (v) are both “Sinusoidal”Current (i) is periodic, but not “sinusoidal”vi
18Time vs Frequency f1 + f3 + f5 + f7 = Time Domain Frequency Domain 60 Hz+f3180 Hz+f5300 Hz+f7420 Hz=
19Total Harmonic Current Distortion Is Same As Total Demand Distortion (TDD)+=åITDDh241100L%3
20Total or True Power Factor (TPF) (DPF) x(Harm Coefficient)KWDPF == Cos fKVA1Harm Coefficient =1 + TDD2Total or True Power Factor has two components – displacement power factor and harmonic power factor. However, harmonic PF is not a term used today. We call it the harmonic coefficient.The product of these two values equals the true PF.TPF = Total or true power factorDPF = Displacement power factorHarm coefficient = Harmonic power factor = Cos d
21Total Power Factor Example VFD ( Six Pulse )DPF = .95TDD = 90% ( No Line Reactor)Harm coefficient =TPF = .95 x = .70611= .7433In this example we’ll use a PWM VFD that has no DC bus choke or input line reactor. Typically these drives can cause 90 to 120% TDD.PWM VFD have diode rectifiers so the DPF is .95 or better.When the harmonic coefficient is calculated using 90% THD(I) the factor is The total PF is
22Applying Capacitors: Caps at Motors or at SWBD / MCC: Disadvantage: If Drives are present anywhere, the harmonic currents they produce can flow back to the point of lowest impedance: the capacitor!This will cause premature failure of the capacitor.MVFDMMMM
23How Harmonics Affect Capacitors Capacitors are naturally a low impedance to high frequencies:Caps absorb harmonicsCaps do not generate harmonicsAs capacitor absorbs harmonics, the capacitor heats upReduced life expectancyVoltage harmonics stress the capacitor dielectricParallel combination of capacitors with motor or transformer can cause resonance condition
24ResonanceThe second and potentially more serious concern, is network resonance. When capacitors are added to the network, they set up a parallel resonance circuit between the capacitors and the network inductancesThe installation of standard capacitors can magnify harmonic currents on the network
26Resonant Point likely to amplify dominant harmonic (typically 5th) Capacitor ResonanceResonant Point likely to amplify dominant harmonic (typically 5th)Harmonic current components that are close to the parallel resonance point are magnified. The magnified current can cause serious problems such as excessive voltage distortion, nuisance fuse and breaker operation, overvoltage tripping of drives and insulation breakdown within motors, transformers and conductors.5th harmonic typically dominates on three phase networks.Magnification of Harmonic Current when Standard Capacitor are Added to the Network
27Power Factor Correction With Harmonics: De-tuning a network:“Force” the resonant point away from naturally occurring harmonics4.2 Harmonic (252 Hz)I<h5>ZIh5fAWe control the impedance of these two elementsfffff13579
29Most utilities penalize for bad Power Factor... If the consumer does not correct the power factor, the utility may have toBuild more power plantsInstall New/ Large transformersUse larger utility cables/ Wires, Switchgear,etc.Many different rate structures across the country. Typically, penalties are imposed for PF < 95%.Thousands of Customers across the country are currently unaware that they are being penalized for low power factor!!!
30How do utilities charge for Power Factor? Utilities recoup the cost of providing reactive power in different ways…..kVA billing: utility measures and bills every ampere of current including reactive current.kW demand billing with Power factor adjustment: utility charges according to kW demand and adds a surcharge for power factor, typically in the form of a multiplier applied to kW demand.kVAR Reactive Demand charge: A direct charge for use of magnetizing power. (example:$ 4.50/kVAR)Two utilities recently introduced substantial Power Factor PenaltiesTXU (Texas) $ $5.50 per kW Demand to 95% pfTVA (Tennessee) $1.46 per kVAR lagging, $1.14 per kVAR leading (April 1, 2004)
31MOST COMMON POWER FACTOR RATE CLAUSE BILLING KW DEMAND =ACTUAL KW DEMAND X BASE PF/ ACTUAL PF
32Penalty Calculation From Utility Bills In TX BILLING DEMAND (apfa) = KW2 & ACTUAL DEMAND = KW1Due to PF Adjustment, KW2 > KW1*Distribution System Charge = (KW2-KW1) x $3.55 / apfa = M1*Nuclear Decommission Charge = ( KW2-KW1) x $0.044/apfa = M2*Transition Charge = (KW2-KW1) x $0.177/ apfa = M3*Transition Charge = (KW2-KW1) x $0.272 / apfa = M4*Transmission Service Charge = (KW2-KW1) x $1.19 / apfa = M5*Transmission Cost Recov Factor = (KW2-KW1) x $ /apfa =M6Total / Month = M1+M2+M3+M4+M5+M6 = $ / Month
34Capacitor LocationsThree Options for Applying Power Factor Capacitors:A) Fixed individual motors MCCB) Automatic Banks at Main Switch BoardC) De-tuned Automatic Capacitor Bank at Main Switch BoardHarmonic Source e.g. Variable Speed DriveMMMMMABCA
35Fixed Capacitors - Low Voltage Main Benefitpf correctionSide Benefitvoltage supportSmall I2R reductionUsageCorrecting pf on individual loads such as motorsDisadvantagesOvercompensation (correct past unity)Not to be used on non-linear loadsUnable to track minute by minute load changes occurring on non-compensated feeders
36Standard Automatic Capacitor Systems Main Benefitpf correctionSide Benefitvoltage supportSmall I2R reductionUsageCorrecting pf on entire MCC’s or substationsApplication alertNot to be used on non-linear loads
37Anti-Resonant Automatic Cap. Bank Automatic Cap. Bank with a reactors in seriesReactors tuned to 4.2 or 4.4Use where Non-Linear Loads less than 50% of total loads.
38Transient Free De-Tuned Automatic Cap. Banks For sensitive networksSimilar to Anti-resonant Automatic Capacitor System except solid state switchingReactor tuned to 4.2or 4.4Response time < 5 secUse where Non-Linear Loads < 50% of Total Loads.
39Electronic Switch –Transient Free FusesSCR-DiodeDe-tunedInductorL1L2L3Three phase capacitors connected with solid state switching elements which are controlled by a Transient Free ControllerSolid State Capacitor Switching Modules provide reliable, high speed, transient free operation. Each Capacitor switching Module switches up to three capacitor groups (450kVAR) using double phase electronic switches for each three phase capacitor group. Fuses protect the electronic switching elements against short circuit currents.Custom designed Iron Core reactors in the AT6000 de-tune the network, prevent resonance and remove up to 50% of the 5th harmonic. AT6000 is recommended for power factor correction in networks with greater than 15% non-linear loads. For a non-linear load percentage of less than 15%, the standard AT5000 bank is suitable. AT6000 provide the following:Tunes the network below the first dominant harmonic, usually the 5th or 300 HzMay absorb up to 50% of the 5th harmonic current depending on network characteristicsA heavy steel welded yoke to clamp the top and bottom laminations as opposed to traditional bolt through clampingAT5000 vs AT6000 example: suppose a transformer supplies 2000 kW. Of this, 400 kW is used by non-linear devices (AC or DC Drives, power converters etc.) The non-linear load percentage will be greater than 15% (400/2000) and, therefore, an anti-resonant TFRC (AT6000) system is recommended.Capacitors - Heavy Duty Dry Capacitors feature self healing metalized polypropylene film elements provide good heat dissipation resulting in longer lifeElements for 480V networks are rated 590V +10% overvoltage; elements for 600V networks are rated 690V +10% overvoltageUnique open air-element design - modular design
40Rule Of Thumb For PFCC Applications * When Non-Linear Loads < 15% Of Total LoadsSelect Standard Automatic Cap. Bank* When Non-linear Loads >15% But < 50% Of Total LoadsSelect Anti-Resonant (Detuned) Auto. Cap. Bank* When Non-Linear Loads > 50% Of Total LoadsSelect Active Harmonics Filter For VAR Correction* When Transformer KVA To Cap. KVAR Ratio < 3Select Anti-Resonant ( Detuned) Auto. Cap. Bank* When Soft-Starters are present, select Detuned Auto. Cap. Bank
42Cyclical Loads & Loads With Dynamic VAR Movements CAUSESWELDING OPERATIONSLARGE HP MOTOR STARTINGPROCESS LOADS (i.e. MIXERS, CRUSHERS, CHIPPERS, SHREDDERS)ARC FURNACESRESULTING INVOLTAGE FLICKERVOLTAGE SAGSPOOR POWER FACTORINABILITY TO START MOTORS2
43Active Filter (AHF)For Power Factor Correction For System where Non-Linear Loads > than 50% of Total Loads.When Fast VAR Movements NecessaryAHF-New breed of power quality productHarmonics cancellationPower factor correctionVAR compensationResonance eliminationIndependent or simultaneous modes of operation
44Active Harmonics Filter Electronic filtering up to the 50th harmonicI sourceI loadPowersourceNon-linearloadActiveHarmonicConditionerI conditioner
45Hybrid FiltersCombination of passive & active technologies+
47HVC Banks – General Marriage of two technologies Fixed capacitor banks and AHFAuxiliaries: MV/LV SWGR2
48Cyclical Loads & Loads With Dynamic VAR Movements CAUSESSOLUTIONSWELDING OPERATIONSLARGE HP MOTOR STARTINGPROCESS LOADS (i.e. MIXERS, CRUSHERS, CHIPPERS, SHREDDERS)ARC FURNACESAPPLICATION OF:HYBRID VAR COMPENSATION (HVC)DYNAMIC VAR INJECTION ON PER CYCLE BASISPASSIVE/ACTIVE SYSTEM ARRANGEMENTWITH INRUSH OR DE-TUNED REACTORSCUSTOM-ENGINREERED FOR SPECIFIC SITE, NETWORK, LOAD CHARACTERISTIC NEEDSRESULTING INVOLTAGE FLICKERVOLTAGE SAGSPOOR POWER FACTORINABILITY TO START MOTORS2
49CAPACITOR APPLICATIONS AT MOTOR TERMINAL > Motor Overload Protection > Re-closure Issue – Jogging , Reversing, Inching , Plugging Applications
50Capacitor At Motor Terminal Motor Over Load Protection Issue
51Motor Self-Excitation Voltage Influenced By Capacitor Ratings
54Multi-Energy Power System of the Future ? Hospital with cogeneration (1.5 MW)SubstationFeederResidential photovoltaic system (6 kW)Utility-owned Photovoltaic site (500 kW)Small wind turbine (10 kW)Factory with natural gas fuel cell (100 kW to 5 MW)Residential Fuel cell (7 kW)Utility-owned wind turbine site (1 MW)4
55Utility & Customer Owned Solar Power System Working In ParallelCos Ø2= 0.55Cos Ø1= 0.891000 KW3000 KW1537 KVAR1818 KVA1537 KVA
56Key Questions to ask Customer For Capacitor Applications Are you being charged for poor power factor by your utility (ask for a copy of their electric bill - kW, kVA, Power Factor)?Do you have a large number of drives, rectifiers or other harmonic generating equipment? Do you have nuisance tripping of overloads ?Do you have welders, chippers, or other large cyclical loads?Do you have problems with voltage sags or “flicker”? How sensitive is your equipment to these power issues?Do you have capacity issues on any of your substations?Do you have HID lighting or critical processes with low tolerance to “brownouts”?Have you been experiencing poor weld quality?Do you have Soft Starters in the System?Do you have Motors subject to reversing, jogging, inching, or plugging?
57Capacitor Standards NEMA CP-1 for Shunt Capacitors UL 810 Standard for CapacitorsNFPA 70, National Electrical CodeIEEE Standard 399, Power System AnalysisANSI / IEEE Standard 18, Shunt Power CapacitorsIEEE Standard 141, Recommended Practice for Electrical Power Distribution for Industrial Plants
58Other Capacitor Application Issues NEC & NEMA :* The Ampacity of Capacitor Circuit Conductors shall not be less than 135% of rated Capacitor Current* Breaker Rating based on 135% Rated Capacitor Current* Fuse Rating based on 165% Rated Capacitor Current for Class R Time Delay* Fusible Switch Rating based on 165% Rated Capacitor Current
59Capacitor Operating Environment Issues Capacitor When Properly Applied Will Have Long Life.Conditions that affect the Life of Capacitor:* Ambient Temp. < 46Deg C or 115Deg F* Case Temp. of Capacitor < 55Deg C or 131 Deg F* Shunt Capacitor designed to operate at 110%Rated Voltage.* Avoid sustained Over Voltage* High System Harmonics
60Summary of Benefits: Reduced Power Costs: Off-load transformers Since Capacitors supply reactive power, you don’t pay the utility for itDepending up on location of Cap. Bank, Line Loss can be reduced.You can calculate the savingsOff-load transformersDefer buying a larger transformer when adding loadsReduce voltage drop at loadsOnly if capacitors are applied at loads(minimal benefit at best)A2