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1590053 634881478003587500


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1590053 634881478003587500

  1. 1. Power Factor Improvement
  2. 2. • Power Factor is the ratio between the kW component and the kVA component of power, drawn by an electrical load• Where kW is the actual load power & kVA is the apparent load power• It is a measure of how effectively the current is utilized for doing useful work• In all industrial electrical distribution systems, the major loads are resistive and inductive• Typical inductive loads are A.C. Motors, induction furnaces, transformers and ballast-type lighting
  3. 3. a) active (or working) power to perform the work -- kWb) reactive power to create and maintain electro-magnetic fields -- kVARc) The vector sum of the active power and reactive power make up the total(or apparent) power used -- kVA
  4. 4. Causes of Low Power Factor1. Most of the motors used in industries are of induction type, which have low lagging pf2. Lamps, discharge lamps operate at low lagging pf3. Transformer system work at low lagging pf4. Load on the system is varying which results in decreasing or low pf
  5. 5. Disadvantages of Low Power Factor1. Lower the pf, higher is the load current required2. Lower the pf, kVA rating of the equipment has to be more which means the equipment has to be larger and expensive3. To transmit or distribute a fixed amount of power at constant voltage, the conductor will have to carry more current at LPF which means the conductor size has to be large4. Large current at LPF, makes I2R losses to increase which results in poor efficiency5. The lagging PF reduces the handling capacity of all elements of the system due to the reactive component of the current6. Large current at LPF causes greater voltage drops in alternators, transformers, transmission lines and distributors – poor voltage regulation
  6. 6. Power Factor Improvement – Some important points• The total current is less than the original circuit current• The active component remains the same before and after pf correction i.e., I cosφ1 = I’ cosφ2• The reactive component is reduced i.e., I’ sinφ2 = I sinφ1 – Ic• Active power remains unchanged due to pf improvement since I cosφ1 = I’ cosφ2 => VI cosφ1 = VI’ cosφ2• KVAR (after pf correction) = lagging KVAR (before pf correction) – leading KVAR (after pf correction)• The capacitance of the capacitor required to improve pf from cosφ1 to cosφ2 is given by: C = IC / [ ω*V]• The leading KVAR supplied by pf correction device is given by: kW[tanφ1 - tanφ2]
  7. 7. Advantages of Power Factor Correction• Reduction in Electricity Bill due to reduced maximum demand• No low power factor penalty charges• Improved Voltage Level in System due to elimination of inductive current• KW capacities of prime movers, alternators, transformers and transmission lines is increased• Reduction in System losses; Efficiency of every plant increases; Overall cost per unit decreases• Voltage regulation of transmission lines increases i.e., Voltage drop in the system improves• Distribution capacity is augmented• Premature failure of motors and other inductive equipment can be
  8. 8. • Capacitive power factor correction is applied to circuits which include induction motors to reduce the inductive component of current
  10. 10. Power Factor Correction• Decide most desirable power factor and capacitor rating• Can be corrected by either using shunt capacitors or by using synchronous motors• Determine the reactive power of the load• Decide on the location of capacitors• Automatic control of power factor - APFC• Maintenance: - Current unbalance - Harmonics in the system - Check on the design - revisit
  11. 11. Power Factor Correction• Static Power Factor Correction– By connecting correction capacitors to the motor starters-- Static power factor correction should provide capacitive current equal to 80% of magnetizing current• Bulk Power Factor Correction– Total current supplied to the distribution board is monitored and accordingly switches the banks
  12. 12. Static Power Factor Correction
  13. 13. SPF Correction with a Soft Starter• SPF Correction should not neutralize more than 80% of magnetizing current of the motor• SPF Correction should never be applied when the motor is controlled by a VFD or Inverter• SPF correction should never be applied at the output of a solid state Soft starter
  14. 14. Bulk Correction
  15. 15. Selection of Capacitors
  16. 16. • A chemical industry had installed a 1500 kVA transformer. The initial demand of the plant was 1160 kVA with power factor of 0.70. The % loading of transformer was about 78%. To improve the power factor and to avoid the penalty, the unit had added about 410 kVAr in motor load end. This improved the power factor to 0.89, and reduced the required kVA to 913, which is the vector sum of kW and kVAr.
  17. 17. Considerations of supply harmonics in selection of Capacitors• Supply side harmonics are caused by non linear loads• Variable speed controllers & switch mode power supplies• Result of supply harmonics is heating of capacitors and reduced lifeMitigation of supply harmonics:• Active Filters which are essentially harmonic compensators by means of an inverter• Passive filters are resistors, inductors & capacitors• Detuned filters are reactors which make the circuit very inductive for resonant frequency and very capacitive on fundamental frequency
  18. 18. Performance Assessment of Power Factor Capacitors• Voltage effects: Ideally capacitor voltage rating is to match the supply voltage• Material of capacitors: Power factor capacitors are available in various types by dielectric material used• Connections: Shunt capacitor connections are adopted for almost all industry/ end user applications, while series capacitors are adopted for voltage boosting in distribution networks• Operational performance of capacitors: This can be made by monitoring capacitor charging current vis- a- vis the rated charging current
  19. 19. Various types of automatic power factorcontrols are available with relay /microprocessor logicTwo of the most common controls are:Voltage Control and kVAr Control