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Power Distribution System Power Factor Improvement BY INSTALLING CAPACITORS ON DISTRIBUTION SYSTEM Prof. Dr. Suhail Aftab Qureshi 1 WHAT IS POWER FACTOR? Power Factor is the ratio of ACTIVE POWER to the TOTAL POWER (apparent power): Power Factor = Active Power P = Total Power S S = Total power of Generator (or used) P = Power consumed in the load (active power) Q = Reactive power stored in magnetic field. Or wasted power 2 WHAT IS POWER FACTOR? Vectorial Representation: P S P.Q Φ j=90o Load Q S Generator Total power = S = VI = (units = KVA) Active power = P = VI CosΦ = (units = KW) Reactive power= Q = VI SinΦ = (units = KVAR) V = Voltage : Volts V I = Current : Ampere Φ Φ = Physical displacement of V&I I Power Factor = CosΦ 3 WHAT IS LOW POWER FACTOR? P P.F. = S If the ratio of active power (P) to total power (S) is less than one (unity) then the power factor is low, which means total power is not being consumed. Example: S = 100KVA S = 100KVA P = 80KW P = 100KW Generator Generator P.F = 0.8 P.F = 1.0 Q = 60-KVAR Q = 0 4 WHAT IS LOW POWER FACTOR? The above example clearly indicates that a generator of total power of 100-KVA will supply maximum of 80-KW of active power to a load with P.F. = 0.8 and the same generator will supply maximum of 100-KW of active power to load with P.F = 1.0. 5 HOW TO IMPROVE THE POWER FACTOR ? The power factor can be improved by supplying KVAR to the loads (inductive type) “Capacitor is source of KVARs” Therefore the power factor of connected load can be improved by installing power factor improvement capacitors/capacitor banks 6 HOW TO IMPROVE THE POWER FACTOR ? LOAD LOAD LOW POWER FACTOR CAPACITOR LOAD LOAD IMPROVED POWER FACTOR Fig.I 7 KVA AND KW SAVING COSΦ2 = 0.9 KVA (Saving) = S(KVA)1 – S(KVA)2 Vectorial representation of P.F Improvement. 1&2 refer to before and after improvement of P.F. 8 KVA AND KW SAVING COSΦ2 = 0.9 KW (Saving) = P1 – P2 9 POWER FACTOR IMPROVEMENT BY CAPACITOR BANK WAPDA KWh KVARh CONSUMER KW KW KVAR KVAR METERS LOAD WAPDA KWh KVARh CONSUMER KW KW KVAR METERS LOAD Power Factor Improvement by Installation of Capacitor 10 CAPACITOR DISADVATAGES OF LOW POWER FACTOR • For a given power to be supplied, the current is increased. • The current thus increased in-return causes increase in copper losses (PL=I2R) and decrease in the efficiency of both apparatus and the supply system, which results in overloading and hence burning of the associated equipment. 11 DISADVATAGES OF LOW POWER FACTOR 3. Copper losses in transformers also increases. 4. Generators, transformers, switches, transmission lines and other associated switchgear becomes over-loaded. 5. Voltage regulation of generators, transformers and transmission lines increases. 6. Hence, cost of generation, transmission and distribution increases. 12 NATURAL POWER FACTORS o CEILING FAN 0.5 TO 0.7 o CABIN FAN 0.5 TO 0.6 o EXAUST FAN 0.6 TO 0.7 o SEWING MACHINE 0.6 TO 0.7 o WASHING MACHINE 0.6 TO 0.7 o RADIO 0.9 o VACUUM CLEANER 0.6 TO 0.7 o TUBE LIGHT 0.5 TO 0.9 o CLOCK 0.9 o ELECTRONIC EQUIPMENT 0.4 TO 0.95 13 NATURAL POWER FACTORS o NEON SIGN 0.5 TO 0.55 o WINDOW TYPE AIR CONDITIONER 0.62 TO 0.85 o HAIR DRYERS 0.7 TO 0.8 o LIQUIDISER 0.8 o MIXER 0.8 o COFFEE GRINDER 0.75 o REFRIGERATOR 0.65 o FREEZER 0.7 o SHAVER 0.6 o TABLE FAN 0.5 TO 0.6 14 NATURAL POWER FACTORS o MERCURY VAPOUR LAMP O.4 TO 0.6 o INDUSTRIAL INDUCTION MOTOR: ◘ NO LOAD O.18 ◘ 25% FULL LOAD 0.56 ◘ 75% FULL LOAD 0.81 ◘ 100% FULL LOAD 0.85 ◘ 125% FULL LOAD 0.86 o COLD STORAGE O.76 TO 0.80 o CINEMAS 0.78 TO 0.80 o METAL PRESSING O.57 TO 0.72 15 NATURAL POWER FACTORS o OIL MILLS O.51 TO 0.59 o WOOLEN MILLS O.70 o POTTERIES 0.61 o CIGARETTE MANUFACTURING 0.80 o FOUNDRIES 0.59 o STRUCTURAL ENGINEERING 0.53 TO 0.68 o CHEMICALS 0.72 TO 0.87 o MUNICIPAL PUMPING STATIONS 0.65 TO 0.75 o OIL TERMINALS 0.64 TO 0.83 o ROLLING MILLS 0.60 TO 0.72 16 NATURAL POWER FACTORS o PLASTIC MOLDING 0.57 TO 0.73 o FILM STUDIOS O.65 TO 0.74 o HEAVY ENGINEERING WORK 0.48 TO 0.75 o RUBBER EXTRUSION AND MOLDING 0.48 o PHARMACEUTICALS 0.75 TO 0.86 o OIL AND PAINT MANUFACTURING 0.51 TO 0.69 o BISCUIT FACTORY 0.60 o LAUNDRIES 0.92 o FLOUR MILLS 0.61 o GLASS WORKS 0.87 17 NATURAL POWER FACTORS o IRRIGATIONS PUMPS O.62 TO 0.80 o REPAIR SHOP, AUTOMATIC LATHE, 0.6 WORKSHOP, SPINNING MILLS, WEAVING MILL o WELDING SHOP 0.5 TO 0.6 o HEAT TREATMENT SHOP, STEEL 0.65 TO 0.8 WORKS, ROLLING MILLS o TEXTILE 0.65 TO 0.75 o CEMENT 0.8 TO 0.85 o OFFICE BUILDING O.8 TO 0.85 18 ADVANTAGES OF POWER FACTOR IMPROVEMENT PFI Capacitor’s addition, thus can be viewed in two lights. i. Adding capacitor, releases circuit capacity for more load or relieves the overloaded circuit. The capacitor KVAR per KVA of load increase is of particular interest as this establishes the average cost of supplying each additional KVA of load. This cost can be compared with the cost per KVA of increasing the transformer or supply circuit rating and would justify the application of capacitors. 19 ADVANTAGES OF POWER FACTOR IMPROVEMENT ii. Capacitors applied to given load reduce the I2R losses in the supply circuit. For a 70 percent power factor load with 40-KVAR of capacitors added for each 100 KVA of circuit capacity, the I2R loss will be 59% of its former value. The losses are not only reduced in the circuit in which the capacitors are applied but in all the circuit back to and including the source generator. 20 ADVANTAGES OF POWER FACTOR IMPROVEMENT Automatic Power Factor improvement capacitors or capacitor banks applied on the load end of circuit, with lagging power factor (more than 95% loads), have particular effects, one or more of which may be the reason for the application. • Improves the power factor at the source. • Reduces system losses as current in conductors decreases. 21 ADVANTAGES OF POWER FACTOR IMPROVEMENT 3. Improves voltage level at the load. 4. Decreases KVA loading on the source. 5. Reduces investment in system facilities per KW of load supplied. 6. Eliminates low power factor penalty imposed by WAPDA. 22 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Disadvantages of Low Power Factors. The disadvantages of low power factor are summarized below:- In transmission/distribution lines, it is only in phase component of line current, which is active in the transmission of power. When P.F is low, then in phase (active) component is small but the reactive component is large, hence unnecessarily large current is required to transmit a given amount of power. Large reactive component means, large voltage drop, and hence greater Cu-losses with the results that regulation is increased and efficiency is decreased. Supply authorities usually bound to maintain the voltage at consumer’s terminal within prescribed limits, for which they have to incur additional capital cost of tap changing gear on transformers to compensate for the voltage drop. Hence the supply authorities penalize the industrial consumers for their low P.F by charging increased tariff for KVA maximum demand in addition to useful KW charge. Obviously it is advantageous for the consumer to improve his load P.F. 23 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM How to Improve the Power Factor. Power factor can be improved by supplying KVAR to the Inductive load. Different techniques to improve the P.F are given below:- § With Synchronous Motors § With Capacitors Synchronous motors are not commonly used in distribution network for P.F improvement because it requires regular maintenance & also expensive. This method is mostly used to raise P.F of system having large Induction Motor loads. Also it is difficult to install at In distribution system, Capacitors are the most common method for power factor correction as it is the least expensive & almost maintenance free. 24 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Power Factor Correction with Capacitors. Capacitor is a source of KVARs i.e it provides a static source of leading reactive current. It is desirable to add capacitors in the load areas supplying the lagging component of the current. There are two types of Capacitors according to their mode of installation. i. Series Capacitors ii. Shunt Capacitors Series Capacitors have some draw backs because all load current will flow through capacitors, so if the load is more then we need big capacitor, further it boost the voltage at the point of installation. Shunt Capacitors are more suitable for installation on distribution feeder as it produce a uniform voltage boost per unit of length of line, out of its point of installation. Therefore, it should be installed as far out on distribution system as practical, close to the loads requiring the KVARs.Shunt Capacitor can be viewed in two lights. Adding Capacitors releases circuit capacity for more load, and adding capacitors relieve over loaded circuits. 25 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Power Factor Correction with Capacitors. There are two types of Shunt Capacitors. i.Switched Capacitors ii.Fixed Capacitors Switched Capacitor Switched Capacitors banks are programmable capacitors & can be switched on/off during load cycles by different program settings.Time Clocks, temperature, voltage, current and kilovars controls are common actuators for capacitor switching. Switched Capacitors are usually applied to correct the power factor to 0.97 at peak load (if economical). Each Switched Capacitor bank should save at least 8 KW loss at peak load. 26 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Power Factor Correction with Capacitors. Fixed Capacitors Fixed Capacitor bank are usually applied to correct the power factor to unity at light load (if economical) & permanently connected into the system through fuses. Proposed permanently connected capacitor application should be checked to make sure that the voltage to some consumers will not rise too high during light load periods. Each Fixed capacitor bank should save at least 1 KW loss at light load. These are quite cheap as compared to switched capacitors, therefore, they are often used in distribution network to improve the power factor. 27 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Benefits to Be Achieved by Installing Shunt Capacitors on Power Distribution System. Reactive Power Compensation i.e decrease KVA loading on source, therefore, additional KW loading may be placed without augmenting the existing system. Power Factor Improvement Reduction in Line Current i.e reduce lagging component of circuit current. Reduction in System Losses i.e reduce I2 R power loss & I2X Kilovar losses in the system. 28 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Benefits to Be Achieved by Installing Shunt Capacitors on Power Distribution System. Reduction in Voltage Drop i.e increase voltage level at the load. Reduce Investment in System Facilities per KW of Load Supplied. Advantage No.1 is a direct consequence of installing a shunt capacitor because the same supplies the reactive demand to the load, relieving extra burden to reactive power. Thus due to reactive power compensation all other advantages are automatically achieved. 29 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Power Factor Improvement By Capacitor Bank Before Installation of Capacitor Meters Kwh Kvarh KW KW Load KVAR KVAR G/Station Meters After Installation of Capacitor Kvarh Kwh KW KW Load KVAR G/Station KW KVAR Capacitor 30 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples which Illustrate the Benefits to be Achieved By Installing Capacitors. i. Reactive Power Compensation i.e Decrease in KVA Loading at Source. Assume that a single phase load supplied from a single phase A.C System with supply voltage as 230 Volts has active & reactive power demand as 3000 Watts and 4000 Vars respectively. If we install a shunt capacitors of rating 3000 Vars on the load point, then reactive power equal to 3000 Vars is compensated and directly supplied by the capacitor, leaving behind only 1000 Vars on the system. The Effect is shown by the following calculations. VA burden on the System before installation of Capacitors = ( 3000² + 4000²)1/2 = 5000 VA VA burden on the System after installation of Capacitors = (3000² + 1000²)1/2 = 3162 VA It means that VA burden on the system has been largely reduced due 31 to reactive power compensation. ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples which Illustrate the Benefits to be Achieved By Installing Capacitors. i. Reactive Power Compensation i.e Decrease in KVA Loading at Source. Assume 100 KVA Circuit or piece of apparatus has to carry 100 KVA at various P.F. 60% 70% 140 % Load KVA 130 80% Load P.F 120 90% 110 100 150 0 20 40 60 80 100 CAP. Kvar in % of Circuit KVA 32 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples Illustrating the Benefits to be Achieved By Installing Capacitors. ii. Power Factor Improvement This advantage is obtained as a consequence of reactive power compensation. From the example discussed in (i) above we can conclude as under:- § Power Factor before installation of a shunt capacitor = W = 3000 = 0.6 VA 5000 § Power Factor after installation of a shunt capacitor = W = 3000 = 0.949 VA1 3162 It means power factor has been improved from 0.6 to 0.949. 33 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples which Illustrate the Benefits to be Achieved By Installing Capacitors. ii. Power Factor Improvement. Assume 100 KVA Circuit or piece of apparatus has to carry 100 KVA at various P.F. 100 Circuit P. F % 90% 80% 70% 90 60% Load P.F 80 70 0 20 40 60 80 100 60 CAP. Kvar in % of Circuit KVA 34 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples Illustrating the Benefits to be Achieved By Installing Capacitors. iii. Reduction in Line Current As the reactive power compensation causes reduction in VA burden of the line, so for a system having regulated supply voltage, it can be seen that reactive compensation actually causes reduction in line current. From the data of (i) the values can be calculated as under:- § VA before installing capacitor was = 5000, V = 230 Volts § VA = V x I, Therefore I = (VA/V) = (5000/230) = 21.7 Amps § VA after installing capacitor was = 3162, V = 230 Volts § VA1 = V x I1 Therefore I1 = (VA1/V) = (3162/230) = 13.7 Amps It means that current has been reduced from 21.7 Amps to 13.7 Amps. 35 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples Illustrating the Benefits to be Achieved By Installing Capacitors. iv. Reduction of System Losses Assume that power was supplied through 800 ft. long S/Phase L.T line of Gnat conductor having resistance per mile as 2.11 ohms and capacitor has been installed. The losses can be calculated as under:- § Resistance R = (2.11 x 800)/5280 = 0.32 ohms [ 1 mile = 5280 ft.] § System Losses for one year = 2 (VA)² x0.32 x8760 =2 (5000)²x 0.32 x 8760 without Capacitor (V)² (230)² = 2649527 Watt hours § System Losses for one year with capacitor § =2(3162)²x0.32x8760/(230X230)= § 1059625 Watt hours § %age Reduction in System Losses = (2649527 36 – 1059625 )x 100/2649527 = 60% ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Some Examples Illustrating the Benefits to be Achieved By Installing Capacitors. v. Reduction in Voltage Drop Voltage Drop before and after installing shunt capacitor can be calculated by using the following formulas. § V.D = (R x W) + (Xl x VAR) OR V.D = Ir R + Ix X Without Capacitor V § V.D = (R x W) + (Xl x VAR1) OR V.D = Ir R + Ix X – IcX With Capacitor V Suppose R = 0.64 ohm for S/P circuit Xl = 0.145 ohm for S/P circuit, V = 230 Volts W = 3000 Watt, VAR = 4000 Vars, VAR1=1000 Vars § V.D = (0.64 x 3000) + (0.145 x 4000) = 10.86 Volts Without Capacitor 230 § V.D = (0.64 x 3000) + (0.145 x 1000) = 8.97 Volts With Capacitor 230 Reduction in Voltage Drop = 10.86 – 8.97 = 1.89 Volts 37 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Vectorial Representation of Power Factor Improvement P (KW) After improving P.F from ø1 to ø2, ø2 KVAR is reduced from Q1 to Q2. The ø1 difference in values of KVAR is due S2 Q2 (KVAR) to capacitor, which supply leading (KV A) KVAR (Qc) to partially neutralize the S1 lagging KVAR of the System. (K Q1 (KVAR) VA ) Qc (KVAR) Leading KVAR Supplied by Capacitor is Qc = Q1 – Q2 Qc = P (tan ø1 – tan ø2) Before Capacitor Installation After Capacitor Installation ø1= Power Factor before Improvement ø2= Power Factor After Improvement P = Active Power (KW) at ø1 P = Active Power (KW) at ø2 S1 = Apparent Power (KVA) at P.F ø1 S2 = Apparent Power (KVA) at P.F ø2 Q1= Reactive Power (KVAR) at at P.F ø1 Q2= Reactive Power (KVAR) at at P.F ø2 38 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Effect of Shunt Capacitors on Feeder Voltage Profile The effect of shunt capacitor application on voltage profile of Feeder, where the load is assumed to be uniformly distributed along the Feeder is illustrated in figure as below. Uniformly distributed Load Sub Station Capacitor Rise produced by Capacitor Volts Reference Feeder Profile with Capacitor Feeder Profile without Capacitor Sub Station Distance Voltage Profile of Feeder With & Without Capacitor 39 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Effect of Shunt Capacitors on Feeder Voltage Profile § Capacitors produces a voltage rise because of its leading picofarad current flowing through the inductive reactance of the feeder. § As is seen in the figure, this voltage rise increases linearly from zero at sub station to its maximum value at the capacitor location. § Between the capacitor location & the remote end of the feeder, the rise due to capacitor is at its maximum value. § When the capacitor voltage-rise profile is combined with original feeder profile, the resulting net profile is obtained. § The capacitor has increased the voltage level all along the feeder, resulting also in reduced voltage spread.. 40 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Effect of Shunt Capacitors on Feeder Voltage Profile Proposed permanently connected capacitors should be checked to make sure that voltage to some customers will rise too high during light load periods. Switched capacitor application should be checked to determine that switching the capacitor bank on or off will not cause objectionable voltage flicker. 41 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Effect of Series Capacitor on Feeder Voltage Profile The effect of series capacitor application on voltage profile of Feeder, where the load is assumed to be uniformly distributed along the Feeder is illustrated in figure as below. Uniformly distributed Load Sub Station Series Capacitor Rise produced by Series Cap Volts Reference Feeder Profile with series Cap Feeder Profile without Series Cap Sub Station Distance • The series capacitor produces no voltage effect between the source & the capacitor location and its entire boost effect is between the capacitor location and the remote end of the feeder. 42 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Effect of Voltage Regulator on Feeder Voltage Profile The effect of feeder voltage regulator is shown in figure below Uniformly distributed Load Sub Station Voltage Regulator Rise produced by regulator Volts Reference Feeder Profile with regulator Feeder Profile without regulator Sub Station Distance • Like series capacitor, voltage regulator produces no voltage effect between the source & the regulator location and its entire boost effect is between the regulator location and the remote end of the feeder. 43 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Common Methods of Connecting Capacitors Most common methods of connecting capacitors are as under:- 3-Phase Grounded Wye 3-Phase Ungrounded Wye 3-Phase Delta Single Phase 44 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Common Methods for Connecting Capacitors Fuse Gnd S/P Ground to Ungrounded wye Delta Neutral Grounded wye Grounded Wye & Ungrounded Wye connections are usually made on high voltage circuits, whereas delta & single phase connections are usually made on low voltage circuits. Majority of Capacitor equipment installed on distribution feeders is connected grounded wye. 45 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Common Methods for Connecting Capacitors Grounded wye connection has number of advantages & benefits over Ungrounded wye connection. With grounded wye connection, capacitor tanks/frames are at ground potential. This provides increased personnel safety. Grounded wye connections provides for faster operation of the series fuse in case of a capacitor failure. Grounded capacitors can bypass some line surges to ground and therefore exhibit a certain degree of self-protection from transient voltages & lightning surges. The grounded wye connection also provides a low impedance path for harmonics. 46 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Common Methods for Connecting Capacitors If the capacitors are electrically connected ungrounded wye, the maximum fault current would be limited to three times line current. If too much fault is available, generally 5000 A, the use of current limiting fuses must be considered. 47 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM How Many Capacitors to Install The number of capacitors to install to raise the power factor from one value to another can be computed by using Stander Table. 48 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM How Many Capacitors to Install 49 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM How Many Capacitors to Install 50 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM How to Select a Location Of Capacitor to be Installed The application of shunt capacitor to a distribution feeder produces a uniform voltage boost per unit length of line, out to its point of application. Therefore it should be installed as far out on distribution system as practical, close to load requiring the Kvars. Many Factors influence the location of Capacitor such as the circuits in plant, the length of the circuits, the variation in load, the load factor, type of motors, distribution of loads, constancy of load distribution. The maximum loss reduction on a feeder with distributed load is obtained by locating capacitor banks on the feeder where the capacitor kilovars is equal to twice the load kilovars. This principle holds whether one or more than one capacitor bank is applied to a feeder. 51 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles There are several major factors which must be considered during the design phase of a power factor correction capacitor application. i. Fundamental Protection Principles § Safety of all personal who are required to work near or with the equipment should be of prime importance. § Capacitors should be connected to system through fuses so that a capacitor failure will not jeopardize system reliability or result in violent case rupture. § To assure that the proper fuse protection is provided, the installed capacitor fuse ratings are listed in standard Tables. 52 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles ii. Capacitor Tank Rupture • Capacitor tank rupture will occur if the total energy applied to capacitor under failure conditions is greater than the ability of the capacitor tank to withstand such energy. • Tank rupture curves are essential for correct selection of fuse link for over current protection of any capacitor installation. • Fuse selection should be based upon the coordination of the fuse link maximum clearing curve and the high voltage capacitor tank rupture curve 53 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles iii. Ventilation • Although very efficient power capacitors do consume power and generate heat. This heat must be adequately ventilated when enclosed or exposed to higher than normal ambient temperature. iv. System Voltage • Capacitors are designed for operation on 50 or 60 Hz sine wave power lines at a specific voltage, which is mentioned on the unit name plate. • However, they are normally designed to operate at over voltages of 10% without damage to the capacitor. The Kvar output of the capacitor increases as square of the applied voltage. KvarE2 = Kvar (E2)² (E1)² 54 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles iv. System Voltage § For example 450 Kvar, 11 KV capacitor will supply 492 Kvar at 11.5 KV. KvarE2 = 450 (11500)² (11000)² KvarE2 = 492 55 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles v. Harmonics Distortion • Capacitors are designed to operate on sine wave current with limited amount of harmonics. • Typical applications that may cause harmonics current problems are arc furnaces, saturable reactors, rectifies and solid state motor controls. • Capacitors are usually designed to operate 135% of rated Kvar. This includes any increase due to over voltage as well as that due to harmonic currents. • The total rrms current equal to (I60)2 + (I2)2 + (I3)2 + ------+ (In)2 where n = harmonic number 56 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Protection Principles vi. Discharge Resistor • When the line voltage is removed from a power capacitor, the danger exists that, even days later, under certain conditions, the unit would retain extremely high charge. • To eliminate this hazard, all power capacitors contain internal discharge resistors. This resistor assembly will reduce the terminal voltage from line voltage to 50 V within 5 minutes of de- energization for capacitor rated higher than 1200 V ac and within 1 minute for capacitors rated less than 1200 V ac. vii. High Frequency Charging Current • High frequency charging currents can result in blown fuses. • The use of series reactors & special switches are sometimes required to reduce these currents to safe levels. • Proper installation of lightening arresters will ensure the 57 protection of capacitor equipment from lightning surges. ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Example of Capacitor Applications on 11 KV Feeder 11 KV Ex-Quality Feeder Before Installing Capacitor After Installing Capacitor • Peak Current = 198 Amps • Peak Current = 188.9 Amps • Power Loss = 99.6 KW • Power Loss = 87.4 KW • A.E.L = 376752 KW • A.E.L = 330852 KW • %Power Loss = 3% • %Power Loss = 3% • %A.E.L = 2% • %A.E.L = 2% • % V.D = 6.1% • % V.D = 4.9% Benefits Achieved • Current has been reduced from 198 to 188.9 Amps. • Power loss has been reduced from 99.6 to 87.4 KW with Net Savings are 12.2 KW. • A.E.L has been reduced from 376752 to 330852 KWH with Net Annual Savings are 45900 KWH. • % V.D has been reduced from 6.1% to 4.9% 58 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM Why the Line Staff is reluctant to put the capacitor in Circuit. It has been experienced that on tripping of the feeder, the man at the Grid Station tries to get the feeder held/energized without getting the capacitor discharged fully, the result of which is that the feeder does not hold. The line staff is also not bothered about the discharge of capacitor as well as solid earthing of the capacitor. The residual charge at the capacitor point do not allow the feeder to hold and thus the line staff always disconnect the capacitor in the first instance and then forget to get intact into the circuit. 59 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM 11 KV CAPACITOR JUDGEMENT FACTORS (Minimum kW Saving) The following are the judgment factors in terms of kW saving accrued from the application of capacitors which indicate their feasibility. Capacitors Rural Urban Fixed Capacitors (Saving at Off-Peak) 450 KVAR 1.2 KW 1.2 KW 950 KVAR 1.6 KW 1.6 KW Switched Capacitors (Saving at Peak) 450 KVAR 8.7 KW 4.9 KW 950 KVAR 10.4 to 11 KW 5.6 to 6 KW 60 ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM 11 KV CAPACITOR JUDGEMENT FACTORS Size of the fixed capacitor, to be installed on a feeder, should be estimated at off peak load. If off peak load of the feeder is not available, then 1/3rd of the peak load may be taken for calculation purposes. Size of the switched capacitor, to be installed on a feeder, should be estimated at peak load of the feeder. 61 WAPDA CASE (STUDY PERFORMED BY KEL) § Practical demonstration was performed in presence of Chief Engineer ELR (Energy Loss Reduction), and Managing Director Power, WAPDA. § Sites selected: § 3-locations at Shalimar Grid Station § Average release in (KVA) = 18% § Average release in capacity (KW) = 23% CONTINUED 62 WAPDA CASE (STUDY PERFORMED BY KEL) § Results were then presented, in a presentation, to the Chairman WAPDA in the presence of Member Power, Member Finance, number of G.M’s and Chief Engineers. § The Demonstration was appreciated. CONTINUED 63 WAPDA CASE (STUDY PERFORMED BY KEL) § As a test case Garden Town Grid Station was assigned for feasibility study. The following were the results: § Net saving claimed by KEL = 3.2 MW § Approximate pay back period = 16/17 Months § Net saving to WAPDA in 3 years = Rs. 1,11,73,000.00 64 AEB - MULTAN Tariff KVA KVAR Investment Penalty Payable Saving Reqd. Charged Period (Month) B-2 161527 211752 63527100 8962835 7 B-3 45365 60779 18233700 1632199 11 B-4 - - - - - C-1(a) - - - - - C-1(b) 6358 7629 2288700 138128 17 C-2(a) - - - - - C-2(c) 2073 4224 1267200 208163 6 Total 215323 284384 85316700 10941325 8 65 MULTAN REGION Study Peformed By WAPDA AEB Multan (Year 1990-91) — KVA savings : 2,15,323 — KVAR required : 2,84,384 — Investment : Rs. 8,53,16,700.00 — Penalty charged : Rs. 1,09,41,325.00 — Pay back period : 8 months (only based on penalty) 66 AEB - FAISALABAD Payable KVA KVAR Penalty Tariff Investment Period Saving Reqd Charged (Month) B-2 80718 99929 29978700 6995970 2 B-3 25869 30812 9243600 766316 12 B-4 1796 4116 1234800 4704 263 C-1(a) - - - - - C-1(b) 915 1591 47730 85152 6 C-2(a) 09 139 41700 13283 3 C-2(c) 4983 8014 2404200 056043 4 Total 114350 144601 43380300 8521468 5 67 FAISALABAD REGION Study Peformed By WAPDA AEB Faisalabad (Year 1990-91) — KVA savings : 1,14,350 — KVAR required : 1,44,601 — Investment : Rs. 4,33,80,300.00 — Penalty charged : Rs. 85,21,468.00 — Pay back period : 5 months (only based on penalty) 68 ENERCON STUDY ENERCON (National Energy Conservation Center) piloted the idea of energy conservation and system capacity release through power factor improvement of industry in Pakistan. The estimate made by ENERCON, projected that power factor improvement at 2400 industrial units had the potential of relieving around 76 MW of system capacity. 69 PENALTY FOR LOW POWER FACTOR Average Power Factor of a consumer at the point of supply shall not be less than 90 percent. In the event of the said power factor falling below 90 percent, the consumer shall pay a penalty of two percent increase in the fixed charges corresponding to one percent decrease in the power factor below 90 percent. The fixed charges for the purpose of calculating the penalty for low power factor shall, however, be determined with reference to maximum demand during the month. “ Power Factor “ means the ratio expressed as a percentage of the kilowatt -hours to the kilovolt ampere- hours consumed during the month. In case of those connections where KVAh meters do not exist and KVARh meters are installed, Power Factor shall be the ratio of KWh to square root of sum of square of KWh and KVARh, i.e. -1 P.F.= KWh = KWh = Cos (Tan KVARh ) KVAh (KWh)2+ (KVARh)2 KWh 70 71 72 73 74 75 76 77 78 SCHWABE Inductance: 0.756 Without Capacitor W/Capacitor 3.5 uF + - 5% Voltage : 225 VAC Voltage : 225 VAC Ampere: 365 mA Ampere : 217 mA Wattage: 46 W Wattage : 46 W Power Factor : 0.57 Power Factor 0.95 79 HELVAR Inductance: 0.91 H Without Capacitor W/Capacitor 3.5 uF + - 5% Voltage : 225 VAC Voltage : 225 VAC Ampere: 352 mA Ampere : 208 mA Wattage: 44 W Wattage : 44 W Power Factor : 0.56 Power Factor 0.95 80