Project report soofi
- 1. Project Report On “POWER FACTOR IMPROVEMENT” Submitted by A.L Mohamed Soofi TRO3998 Advanced Diploma (Level-V) ELECTRICAL ENGINEERING Year 2012 june Under the Guidance of Prof.Dr.K Chandrabose Department of Electrical Engineering APSS Engineering City and guilds Approved centre 1
- 2. This is to certify that the project report titled “Power Factor Correction ”submitted by A.L.M Soofi (TRO3998), is a record of bonafide work carried out by them, in fulfillment of the requirement for the award. Date Examiner 1: ____________ Examiner 2: ____________ GUIDE (Prof.K.chandrabose) 2
- 3. Personnel Details Title: Power factor correction Full name: Atham Lebbe Mohamed Soofi Address:07 fiscal Road Akkraipattue 02 Institute: APSS Supervisor: Prof. Dr. K Chandrabose ( M.I.E.T) ENR:TRO 39998 Contact: 0755544696 E-mail.Soofi.atham@gmail.com 3
- 4. ACKNOWLEDGMENT I would like to express my deep sense of gratitude to our guide Prof.Dr.K Chandrabose (Chairman and managing director APSS,MIET) for his valuable guidance and motivation and for his extreme cooperation to complete the project work successfully. I would like to express my sincere respect and profound gratitude to Hmark Pvt Ltd, Head of Electrical Engineering Department for supporting us and providing the facilities for the project work. I appreciate all my colleagues whose direct and indirect contribution helped a lot to accomplish this project work. I would also like to thank all the teaching and non teaching staff for cooperating with me and providing valuable advice which helped us in the completion of this project. A.L.Mohamed Soofi) 4
- 5. Abstract Today’s commonly used power converters have a poor input power factor and rich harmonic current, which deteriorates the power line quality and may interfere with other power electronic equipment. This project report is targeted on the prevailing method of power factor control in industries. The present trend is to use facts CAPACITORS OR CAPACITOR BANKS To improve the input power factor, stringent input power factor regulations such as IEC 1000 have recently been enacted. Therefore, power factor correction techniques have been very popular topics in recent years’. Because the addition power factor converter will increase the cost of the overall system, the integrated single-stage power factor correction techniques become attractive especially in low-power cost-effective applications. 5
- 6. Contents Chapters 1. Introduction……………………………………………….…………..7 2. Power Factor 2.1. Power Factor……………………………………………………….8 2.2. Disadvantages of Low Power Factor……………………………...9 2.3. Benefits of Power Factor Correction…………………………… 10 2.4. Need for Power Factor Correction………………………………10 3. Power Factor Correction 3.1. Various Methods of Power Factor Improvement………………11 3.2. Capacitor Banks…………………………………………………12 3.3. Synchronous Condensers………………………………………..13 3.4. Thyristor Controlled Reactors………………………………….14 3.4.1. Principle of Operation…………………………..……….14 3.5. Static VAR Compensator 3.5.1. Principle of Operation………………… …………………..14 3.5.2. Connection……….…………………………………… 15 distortion…………………………………………………………16 Individual PFC 17 Evaluation of results…………………………………………………18 Maintenance and visual check……………………………………….20 Practical recommendation…………………………………………21 Conclusion…………………………………………………………………..22 References……………………………………………………………………23 Appendix …………………………………………………………………….24 6
- 7. Chapter 1: Introduction Power Factor Improvement is the growing issue of concern. Within power quality framework, one of the important aspects is reactive power control. Consumer load requires reactive power that varies incessantly and increases transmission losses while affecting voltage in the transmission network. To prevent unacceptably high voltage fluctuations or the power failures that can result, this reactive power must be compensated and kept in balance. This function has always been performed by passive elements such as reactors or capacitor, as well as combination of the two that supply inductive or capacitive reactive power. The more quickly and precisely the reactive power can be compensated, the more efficiently the various characteristics of transmissions can be controlled. Since most loads in modern electrical distribution systems are inductive, there is an ongoing interest in improving power factor. The low power factor of inductive loads robs a system of capacity and can adversely affect voltage level. As such, power factor correction through the application of capacitors, synchronous Alternators, TCR SVC , Power Electronic DC-DC convertors etc. is widely practiced at all system voltages. As utilities increase penalties they charge customers for low power factor, system performance will not be the only consideration. The installation of power factor correction circuits improves system performance and saves money. In order to ensure most favourable condition for a supply system from engineering and economical standpoint it is important to have power factor as close to unity as possible. Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn from the system. In such cases, active or passive power factor correction may be used to counteract the distortion and raise power factor. The devices for correction of power factor may be at a central substation, or spread out over a distribution system, or built into power-consuming equipment. 7
- 8. Chapter 2: Power Factor 2. 1.Power Factor Power Factor is the ratio between the real power (kW) and apparent power (kVA) drawn by an electrical load. It is a measure of how effectively the current is being converted into useful work output and a good indicator of the effect of the load current on the efficiency of the supply system. Poor power factor results in increase load current draw that causes additional losses in the supply and distribution systems. Power factor can also be measured as the cosine of the phase difference between the voltage and the current, however, where the current is distorted such as with electronic equipment loads, this may not be a true indication of the power factor. Power factor can be can be determined as follows: Power Factor = Active Power (kW)/Apparent Power(kVA)……………..Eqn 1.1 Fig2.1. Power Factor Triangle kVA COS = --------=--PF kVAR kVA kW Active power COS θ = Apparent power 8
- 9. Power factors range from zero (0) to unity (1) with a typical power factor being between 0.8 and 0.95. The power factor can also be leading or lagging depending on whether the load is predominantly capacitive or inductive in nature. Poor power factors are typically due to the effect of inductive or capacitive loads such as with a motor or with long cables providing capacitive coupling. Poor power factor due to distorted current waveforms such as with high harmonic content caused by electronic equipment cannot normally be corrected with PFC alone and will typically require complex or costly filtering. • !!!!!!Should I be concerned about low power factor? Low power factor means you’re not fully utilizing the e le ctrical power you’re paying for . As the triangle relationships in As the triangle relationships in as power factor increases . At 70% power factor, it requires 142 KVA to produce 100 kW . At 95% power factor, it requires only 105 KkVA to produce 100 kW . Another way to look at it is that at 70% power factor, it takes 35% more current to do the same work . 2.2 Disadvantages of Low Power Factor 1. KVA rating of the electrical equipments increases due to low power factor as power factor is inversely proportional to the KVA rating of the equipment. This increases the size and cost of the equipment. 2. Conductor size increases. To transmit the same amount of power at low power factor at constant voltage needs to carry high current. So to keep the current density constant conductor area increases. 3. Copper loss of the equipment increases. 4. Voltage regulation becomes poor. Current at low lagging power factor causes greater voltage drop in alternators, transformers and transmission lines causing to have low power supply at the receiving end. 9
- 10. 5. Handling capacity of the equipment decreases because the reactive component of current prevents the full utilization of the installed capacity. 2.3 Benefits of Power Factor Correction (PFC) 1. Electricity tariff savings. 2. Avoidance of Network Service Provider (NSP) penalties for low power factor, including restricted access to more suitable tariffs (minimum of 0.9 for large and high voltage supply establishments in most states). 3. Reduced losses. 4. Reduce power drawn from distribution systems, optimum sizing of electrical infrastructure. 5. Stabilized site voltage levels by reducing the inductive effect of the connected load. The payback for PFC installations can be very reasonable and should not be over looked when considering PFC for existing installations 2.4 Need for Power Factor Correction New Works, Upgrades And Refurbishments. Power factor correction shall be provided under the following circumstances for new, upgraded or refurbished buildings: 1. To meet the IEC and B.S requirements for minimum power factor. 2. At defense establishments with a high voltage tariff, any new building refurbished or upgraded building with a power factor less than 0.9. 3. Where the feasibility assessment determines a worthwhile cost benefit or greenhouse reduction measure. Where assessment of the natural power factor confirms it will remain within the prescribed range (e.g. above 0.9) and it is unlikely that the facility will require PFC at a later stage, PFC or provision suitable space is not required. Where assessment of the natural power factor cannot confirm suitability, however, there is some uncertainty as to the need for PFC, the PFC equipment may be omitted provided adequate space is allowed in the design of the building to incorporate PFC equipment as a future requirement. This would also apply to buildings where it would be reasonable to assume that PFC may be required at a later stage. When allowing for future PFC installations the designer shall make all practical provisions for the installation and connection of the future PFC equipment. 10
- 11. Comprehensive Maintenance Contract (CMC) or Comprehensive Maintenance Services (CMS) contractor or design consultant shall monitor buildings not provided with PFC during the defects liability period to confirm suitable power factor performance. Where the performance is found to be unsuitable during the defects liability period, PFC shall be installed and commissioned prior to completion of the project. Existing Installations PFC shall be considered for existing buildings to comply with the NSP requirements for minimum power factor to avoid disconnection of supply, costly penalties, tariff restrictions or where the feasibility assessment determines a worthwhile cost benefit or greenhouse reduction measure. The funding of power factor correction works for existing buildings shall be in accordance with regional funding and prioritising arrangements. New Equipment Equipment performance, both individual performance and the cumulative effect of non PFC equipment needs to be considered as part of the design and also for equipment specifications. Ensure that all equipment meets appropriate standards for harmonic content and that the equipment power factor performance is considered to avoid the need for PFC or expensive filtering in the first instance. Chapter 3: Power Factor Correction 3.1. Various Methods of Power Factor Improvement Industrial loads, which normally operate at poor power factor, are induction motor, arc and induction furnaces. Fluorescent tubes, fans etc also operate at low value of power factor. All these loads working at low power factors need large amount of reactive power which results in reduced voltage level at the load terminals. A low voltage at consumer terminals is undesirable as it leads to the impaired performance of their utility devices. The various methods of power factor improvement are as under: 1. Use of capacitor banks. 2. Use of synchronous condensers. 3. Use of thyristor controlled devices. 11
- 12. 3.2. Capacitor Banks bank of capacitors is connected across the load. Since the capacitor takes leading reactive power, overall reactive power taken from the source decreases, consequently system power factor improves. Fig3.1. PFC Using Capacitor Bank Advantages of using capacitor banks 1. They have low losses. 2. They require little or no maintenance as there is no rotating parts. 3. They can be easily installed as they are light and do not require foundation. 4. They can work under ordinary atmospheric condition. Disadvantages of using capacitor banks 1. They have short life span of 8-10 years. 2. They get easily damaged if exceed the rated value. 3. Once damaged, they have to be removed as their repairing is uneconomical. 12
- 13. 3.3. Synchronous Condensers In electrical engineering, a synchronous condenser (sometimes synchronous compensator) is a specialized synchronous motor whose shaft is not attached to anything, but spins freely. Its purpose is not to produce mechanical power, as other motors do, but to adjust electrical conditions on the local electric power distribution grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to support the grid's voltage or to maintain the grid's power factor at a specified level. The condenser’s installation and operation are identical to large electric motors. Increasing the device's field excitation results in its furnishing magnetizing power (kVAR) to the system. Its principal advantage is the ease with which the amount of correction can be adjusted. The energy stored in the rotor of the machine can also help stabilize a power system during short circuits or rapidly fluctuating loads such as electric arc furnaces. Large installations of synchronous condensers are sometimes used in association with high-voltage direct current converter stations to supply reactive power. Advantages and Disadvantages Unlike a capacitor bank, the value of reactive power can be continuously adjusted. However, the synchronous condenser does have higher losses than a static capacitor bank. The motor windings are thermally stable to short circuit current and faults can be easily removed. They produce noise and have high maintenance cost. Most synchronous condensers connected to electrical grids are rated between 20 MVAR and 200 MVAR and are hydrogen cooled. 3.4. Thyristor Controlled Reactors 13
- 14. Static thyristor controlled reactors are connected in parallel with load for the control of reactive power flow. With increase in the size of industrial connected loads, fast reactive power compensation has become necessary. For such loads, thyristor controlled reactors are now becoming increasingly popular. Fig.3.2. Thyristor Controlled Reactor 3.5. Static VAR Compensator A Static VAR Compensator (or SVC) is an electrical device for providing fast-acting reactive power compensation on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage and stabilizing the system. The term "static" refers to the fact that the SVC has no moving parts (other than circuit breakers and disconnects, which do not move under normal SVC operation). Prior to the invention of the SVC, power factor compensation was the preserve of large rotating machines such as synchronous condensers. The SVC is an automated impedance matching device, designed to bring the system closer to unity power factor. If the power system's reactive load is capacitive (leading), the SVC will use reactors to consume VARs from the system, lowering the system voltage. Under inductive (lagging) conditions, the capacitor banks are automatically switched in, thus providing a higher system voltage. They also may be placed near high and rapidly varying loads, such as arc furnaces, where they can smooth flicker voltage. 14
- 15. 3.5.1. Principle of Operation Typically, a SVC comprises a bank of individually switched capacitors in conjunction with a thyristor-controlled air- or iron-core reactor. By means of phase angle modulation switched by the thyristors, the reactor may be variably switched into the circuit, and so provide a continuously variable MVAr injection (or absorption) to the electrical network. In this configuration, coarse voltage control is provided by the capacitors; the thyristor-controlled reactor is to provide smooth control. Smoother control and more flexibility can be provided with thyristor-controlled capacitor switching. The thyristors are electronically controlled. Thyristors, like all semiconductors, generate heat, and deionized water is commonly used to cool them. Chopping reactive load into the circuit in this manner injects undesirable odd-order harmonics, and so banks of high-power filters are usually provided to smooth the waveform. Since the filters themselves are capacitive, they also export MVARs to the power system. 3.5.2. Connection Generally, static VAR compensation is not done at line voltage; a bank of transformers steps the transmission voltage (for example, 230 kV) down to a much lower level (for example, 9.5 kV).This reduces the size and number of components needed in the SVC, although the conductors must be very large to handle the high currents associated with the lower voltage. 3.5.4. Advantages The main advantage of SVCs over simple mechanically-switched compensation schemes is their near-instantaneous response to changes in the system voltage. For this reason they are often operated at close to their zero-point in order to maximize the reactive power correction they can rapidly provide when required. They are in general cheaper, higher-capacity, faster, and more reliable than dynamic compensation schemes such as synchronous condensers. 15
- 16. Total Harmonic Distortion The ratio between apparent power associated with higher order harmonics and apparent power associated with fundamental harmonic is called Total Harmonic Distortion (THD). …….. Eqn 5.1 Where Inrms is RMS value of the n-th harmonic of the current. Any periodic non-sinusoidal current can be presented by Fourier transform. For a periodic current waveform mentioned above: Where Io - DC component of the current. In AC lines Io=0. …………….. Eqn 5.2 We can also derive the relationship between PF and THD, ………………….. Eqn 5.3 ……………. Eqn 5.4 Where, θ1: the phase angle between the voltage Vs (t) and the fundamental component of Is (t). Is1, rms: rms value of the fundamental component in line current. 16
- 17. Is, rms: total rms value of line current. kdist = Is1, rms /Is, rms: distortion factor. kdisp = cosθ1: displacement factor. Fig.5.5. Typical waveforms in a poor PF system Individual correction: Where loads consist of reasonably-sized motors, say 7.5 kW and above, operating with a low- diversity factor, or where there are special drives running continuously, then individual correction of each motor can be considered. The main advantage of individual correction is that both motor and capacitor are switched as one unit and no additional control gear is required for control of the capacitor. Apart from reducing the demand, which is separately charged by the power utilities, it can be seen that the current drawn is reduced by applying capacitors and improving power factor; and consequently, the l2 R losses in the distribution elements, i.e., cables, transformers, busses etc. , Hence, the most appropriate location at which the capacitor bank to be installed is as near as possible to the inductive loads, mainly the motors, Fig. 1. If not possible due to environment or areas classifications, they have to be installed at the nearest distribution board. A case study is enclosed in annexure 3, for highlighting the reduction in losses. 17
- 18. Individual power factor correction of motors: As seen, the best location of connecting the capacitor bank is across the terminal of an induction motor, but care should be taken in deciding the kVAr rating of the capacitor in relation to the magnetizing kVA of the machine. If the rating is too high, damage may result to both motor and capacitor, as the motor, while still revolving after disconnection from the supply, may act as a generator by self excitation and produce a voltage higher than the supply voltage. If the motor is switched on again before the speed has fallen to about 80% of the normal running speed, the high voltage will be superimposed on the supply circuits and there may be a risk of damaging other types of equipment. As a general rule the correct size of capacitor for individual correction of a motor should have a kvar rating not exceeding 85% of the normal no load magnetizing k VA of the machine. However, 85% does not constitute an invariable rule, and for slip-ring motors and direct-on-line started squirrel cage motors on drives which never entail running over synchronous speed, the figure may be exceeded, although never beyond 90%. Evaluation on the results. the Kvar rating of the capacitors required for the desired correction in p.f can be obtained by using table in appendix b1 So how we are going to calculate the load in kw is multipilied by the appropriate factor from table b1 in appendix to achieve at the required kvar rating of capacitor. Eg .from table intial power factor-0.6 proposed power factor from using economical equation for eg.0.95 so the load is 0.6 x 100kva= 60KW multiplying factor from the table b1 appendix is 1.005 60x1.005= say 60kvar so we will have to order supplier 60kvar capacitors. General format- Load X multiplying factor to desired p.f But econmical consideration and suitable Power factor, P.F = √1− ( b/ a )2 … (1) where b is yearly cost owning a capacitor or any other improving elements and a is the maximum demand tariff per year. Maximum demand tariff by supply authority - cost of owning a capacitor in capital investment- 18
- 19. In case if we cant find power monitoring digital equipments to hire ,we can use watt meters using basic two watt meter method to determine the power factor , but digital equipments gives more other facility such history,recording,harmonics analyzing, Actual work & calculation carried Max Dand Billing of Ceylon Electric Board first 40kw at Rs 10.00/kw next 160kw at Rs 9.50/kw next 200kw at Rs 9.00/kw Demand tariff billig before Load was a induction motor of 400kw ,motor rated 240 kw P.F without PFC-0.6 P.F required by authorities-0.90 Calculating capacitor KVAR for 400kw load 400 x 0.85=340kvar ,it cannot be achieved by single capacitor 0.85 determined from appendix chart first 40kw at Rs 10.00/kw Rs 40.00 next 160kw at Rs 9.50/kw Rs 1520.00 next 200kw at Rs 9.00/kw Rs 1800.00 total 400kw Rs 3720.00 Penalty for low power factor Rs 1200.00 After power factor correction to 0.90 240kw =267kw 0.90 billing after power factor corrected first 40kw at Rs 10.00/kw Rs.40.00 next 160kw at Rs 9.50/kw Rs.1520.00 next 67kw at Rs 9.00/kw Rs .603.00 total 267kw Rs 2163.00 Billing saving Rs3720-Rs2163+ Rs 1200.00=Rs 2757.00 Per year saving Rs 2757.00 x 12 =33084.00 Rs, per year cost of capacitor bank maintenance,and owning a capacitor bank, 19
- 20. 9000.00 rs SO net saving Rs 24084.00 Maintenance and Tests Visual Check For damaged or dirty bushings, obvious leads, and finish damages needing touch-up. Capacitance Check The measured capacitance of a unit tests between 90% and 100% of nominal capacitance. If not, consult the manufacturer for comparison with original factory test value. Capaciance higher than 120% of nominal generally indicates one or more short circuited groups of internal windings, and the capacitor should be considered defective. Capacitance readings should be made when the capacitor temperature is at 20 to 30 degrees Celsius. Dielectric strength tests Preferably made using a direct current voltage of 75 present of original factory test level equal to 3.2 times the nameplate voltage ratings. The test voltage should be held for ten seconds. On single phase units this voltage is applied bushing - to - bushing or bushing to ground stud for single bushing capacitors. On there phase RYB-connected units apply voltage phase to - neural at a direct-current voltage of 3.2 times the rated one line to neutral voltage between all pairs of bushings. Avoid danger to personnel during this test from possible case repture by maintaining adequate shielding. Discharge Resistance Check: Discharge resistors are included in more high voltage capacitors to reduce the voltage from rated voltage to 50 units in five minutes or less. The actual value of resistance may vary with different designs but a maximum value can be determined from the following formula. R = 300 Sec.* 1.1 * 1nV 81.414 C nom 50 R - is in megohms. Cnom - is in micro farads. V - is the rated voltage in volts. A resistance reading in the range of 70 to 100 percent of this value indicates the resistors are probably all right. If value lower that 70 percent are obtained, consult the manufacturer for precise limits. For units rated 600 volts or less, replace 300 seconds in the above formula with a value of 60 seconds. Capacitor Maintenance Before re-fusing make a visual inspection and capacitance test. Also check for terminal-to-terminal shorts; can be performed using a medium voltage supply. A small 90 volt battery and an indicating light will detect more shorted capacitors than lower voltage. Caution !!!!!! capacitors shouldnot be discharged by short circuit ,it should be discharged through suitable resistance or discharging device according B.S 2834 20
- 21. Capacitors must be checked periodically ,for blown fuse and loose connection,and other possibel deposition of dust and dirts, if we using capacitor bank we have to give proper ventilation overheating will reduce the capacitor life time it should never be operated without fuse protection Practical recommendation In practical situation we have to use several charts to obtain the most suitable power factor to the specific need Location of the capacitors this determined by many factor such load layout ,number length of circuit, variation of load, the number and length of circuit, variation of load, sizes of individual appliances ,type of motor s and their control gear etc capacitors located near the service entrance relieve the power system of the magnetizing current and improve voltage but there is no effect on the losses within the plant itself. This arrangement has the merit of centralized control and less cost, but is not suitable for large plants with scattered heavy load ,where local and group p..f correction is more desirable. Capacitors placed ear the loads as possible ,or at the end of the feeders ,posses the following advantage : Reduced losses in the distributing circuit Improved voltage ,Giving better motor performance Automatic reduction of the kvar capacity with reduction of load ,when the capacitors are installed directly on the appliances. Capacitor Protection Main Bus or Feeder Fused Switch or Circuit Breaker 21
- 22. Conclusion The key factor is that power factor correction and most other concepts are not new from the point of view of formal circuit theory. The question is how the problem can be best understood from the basics and then tackled in the best possible way. PFC is rapidly becoming a mandatory feature in AC power sources because IEC 6100-3-2 requires the use of PFC circuits. Active and passive PFC circuits are designed to bring the PF of a system closer to unity (PF = 1.0). While no system is 100% efficient, most PFC technology makes the power factor of a system greater than 0.95. Highly efficient electrical systems have the advantage of supplying less current to drive a load. This is beneficial to customers that have low power factor problems because utilities sometimes charge penalties for low power factor. While cost savings from PFC on small AC sources isn’t nearly as noticeable as money saved from PFC on large systems, in the long run PFC will provide reduced costs for high energy consumers. Power factor correction should be extensively considered in industrial places and other places occupied with large motors, low power factor leads to many losses such lose in investment to machinery, increased utility bill, reduced life span of main feeders, motor insulation failures, could not operate for long ,or cant overload for urgent needs, and unwanted penalty charges. So care should be practiced for power factor correction, It cannot be easily done within hours, carefully it should be calculated, carefully we have to decide the method,(capacitor bank or individual), 22
- 23. Reference……………………… ………………….. • Standard handbook of electrical engineering eleventh edition by (Fink and Beaty Mcgraw Hill) • Handbook of electrical engineering,(S.L Bhatia) • Wikipedia encyclopedia • Electrical technology by Hughs • Electrical technology text book by B.L Theraja 23