Power factor improvement of an induction motor

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Power factor improvement of an induction motor

  1. 1. Power Factor Improvement Of An Induction Motor Harshit agarwal 22Under guidance of: Atul kumar sahu 16Mr. Mohamed Samir Ashish kumar singh 14 Ashish pani vimal 15
  2. 2. Introduction Of Induction Motor•Singly Excited A.C machine.•Its stator winding is directly connected to A.C source. Whereas its rotor winding receives its energy by Induction(Transformer Action).• No load Current in Induction Motor varies from 30 to 50 % offull load current.•In Induction motor magnetizing current (lagging nearly 90degree behind the applied voltage) forms a considerableportion of No load current that’s why Induction motor have lowpower factor at no load.•The effect of low value of a No load Power Factor is todecrease the Full Load Operating Power Factor of Inductionmotor.
  3. 3. Introduction Of Power Factor• Working /Active Power: Normally measured in kilowatts(kW). It does the "work" for the system--providing themotion, torque, heat, or whatever else is required.• Reactive Power: Normally measured in kilovolt-amperes-reactive (kVAR), doesnt do useful "work." Itsimply sustains the electromagnetic field.• Apparent Power: Normally measured in kilovolt-amperes (kVA). Working Power and Reactive Powertogether make up apparent power.
  4. 4. To understand power factor, visualize a horse pulling a railroad cardown a railroad track. Because the railroad ties are uneven, thehorse must pull the car from the side of the track. The horse ispulling the railroad car at an angle to the direction of the car’stravel. The power required to move the car down the track is theworking (real) power. The effort of the horse is the total(apparent) power. Because of the angle of the horse’s pull, not allof the horse’s effort is used to move the car down the track. Thecar will not move sideways; therefore, the sideways pull of thehorse is wasted effort or nonworking (reactive) power.
  5. 5. Power Factor FundamentalPower Factor : A measure of efficiency. The ratio of ActivePower (output) to Total Power (input) Power Factor = Active (Real) Power Active Power (kW) Total Power Reactive Power = kW Total Power (kVA) (KVAR) kVA = Cosine (θ) = DISPLACEMENT POWER FACTORA power factor reading close to 1.0 means that electrical poweris being utilized effectively, while a low power factor indicatespoor utilization of electrical power.
  6. 6. Why do we care about Power Factor?• Low power factor results in: – Poor electrical efficiency! – Higher utility bills ** – Lower system capacity – On the Supply Side, Generation Capacity & Line Losses• Good Power Factor results in: Environmental benefit. Reduction of power consumption due to improvedenergy efficiency. Reduced power consumption means less greenhouse gasemissions and fossil fuel depletion by power stations. Reduction of electricity bills. Reduction of I2R losses in transformers and distribution equipment Reduction of voltage drop in long cables. Extended equipment life – Reduced electrical burden on cables andelectrical components.• Power Factor Correction Capacitors (PFCC) provide an economical means for improving Energy utilization
  7. 7. Why do we install Capacitors?Before After  In this example, demand was reduced to 8250 kVA from 10000 kVA.  1750KVA Transformer Capacity Release.  The power factor was improved from 80% to 97%
  8. 8. Power factor correction Of induction motor•Power factor correction is the term given to a technology that hasbeen used since the turn of the 20th century to restore the powerfactor to as close to unity as is economically viable.•This is normally achieved by the addition of capacitors to theelectrical network which compensate for the reactive powerdemand of the inductive load and thus reduce the burden on thesupply. There should be no effect on the operation of theequipment.•To reduce losses in the distribution system, and to reduce theelectricity bill, power factor correction, usually in the form ofcapacitors, is added to neutralize as much of the magnetizingcurrent as possible.•Capacitors contained in most power factor correction equipmentdraw current that leads the voltage, thus producing a leadingpower factor
  9. 9. MOTOR LOAD CHARACTERISTICS
  10. 10. No-load test1. The motor is allowed to spin freely2. The only load on the motor is the friction and windage losses, so all Pconv is consumed by mechanical losses3. The slip is very small Poc = Voc * Ioc * Cos(@oc) Roc = Voc / Ioc Cos(@oc) Xm = Voc / Ioc Sin(@oc)
  11. 11. Blocked-rotor testIn this test, the rotor is locked or blocked so that it cannot move, avoltage is applied to the motor, and the resulting voltage, currentand power are measured. Rsc = Psc / (Isc * Isc) Zsc = Vsc / Isc Xsc = Under root( sqr(Zsc) – sqr(Rsc))
  12. 12. Installation Of Static Capacitor•This method involves the connection of static capacitor acrossstator terminals Of Induction motor.•In smaller size motors Controlling the Power factor by staticcapacitor is a Simplest & most economical method.
  13. 13. Phasor Diagram•The stator current is I1 & motor operating PFis Cos(@1).•When Capacitor are connected across statorterminals, The current Ic through thecapacitors lead the voltage V1 by 90 degree.•The Phasor sum of I1 & Ic is I1’ drawn bysupply.•The PF of the combination is improved fromCos(@1) to Cos (@1’) and stator currentdecreases from I1 to I1’.
  14. 14. Pertaining to IM PF control By Static Capacitor•The stator current locus to the IM is shifted to the left, this shiftbeing equal to the length of the current phasor Ic.•This means that the centre of current locus shift from C to C’.Such that the length CC’ = Ic.•By the fig. it is clear that if full load PF is near to unity the PF atNo load & Half load are leading.
  15. 15. Self Excitation Of IM•Self-excitation occurs when the capacitive reactive current fromthe capacitor is greater than the magnetizing current of theinduction motor. When this occurs, excessive voltages can resulton the terminals of the motor. This excessive voltage can causeinsulation degradation and ultimately result in motor insulationfailure.Simplified Circuit Diagram forMotor Controller and PowerFactor Correction Capacitors(Diagram Shown For MotorController in Open Position)
  16. 16. •The rotating magnetic field can be thought of as stored energy.•When the motor is switched off, the stored energy still present inthe air-gap of the motor begins to collapse and produce a currentin the rotor winding.•This rotor current induces a voltage on the stator winding andterminals of the motor which are disconnected (the motorbecomes a generator).•Because the motor has just been disconnected, it is still spinningdue to its rotating inertial speed which will decrease in time.•The decaying speed produces a subsequent voltage (and currentflow through the capacitor) at a decaying frequency (starting at avalue near 60 hertz).•When the frequency of the motor terminal voltage equals theresonant frequency of the motor and capacitor reactancecombination, high voltage may be produced. This high voltage canlead to insulation failure on the motor.
  17. 17. •To create self-excitation, the capacitive reactance of the capacitormust be less than that of the motor reactance (this occurs when tolarge of a capacitor is chosen).•If the capacitive reactance is greater than the motor magnetizingreactance (this occurs for a properly sized capacitor), the resonantfrequency is greater than the motor speed (greater than 60 hertz).Under this condition, when the motor is disconnected, thefrequency of the decaying terminal voltage will never correspondwith the resonant frequency of the motor and capacitor reactancecombination. Therefore, a high voltage condition will not occur.
  18. 18. •The figure shows a plot of thecapacitor and motor magnetizingvoltage verses current waveforms.•The motor magnetizing curve issloped over, which is acharacteristic of iron.•The capacitor characteristic is astraight line.•The curve labeled "A" is sized properly because its capacitivecurrent is less than that of the magnetizing current at nominalvoltage.•The curve labeled "B" is sized improperly because its capacitivecurrent is greater than the magnetizing current at 1 per-unitvoltage.•When disconnected, the "B" curve in figure 3 shows a validoperating point at 140% voltage.•This voltage may occur as the motor slows in speed and passesthrough its resonant frequency.
  19. 19. The following techniques be used when applying capacitors orharmonic filers directly on the terminals of an induction motor.•Request a recommended kvar rating from the motormanufacturer.•Size the capacitor at 80% of the no-load current rating(magnetizing current) of the motor. In no case should the rating begreater than 90%.•Utilize recommended capacitor sizing tables induction motors.•Measure the no-load motor current and size the capacitor at 80%of the no-load current rating of the motor.
  20. 20. Practical Aspects•Small Induction motor have low Pf than large motor at Low load.•Small induction motor also have low PF at Full load.•Our objective Of project is to improve the Power factor Of smallInduction motor at Low as well as Full Load.
  21. 21. Procedure & Feasibility Of Project•Perform No Load test & Blocked Rotor test to find out Internalimpedance of the Motor.•Determining The power factor & Efficiency of the Motor.•Making calculations For the size of Capacitor Bank should beinstall to Improve the Power factor.•Determining The New improved Power Factor & Efficiency.•Compare the New Power Factor With Previous Power Factor.•Calculation for the Net saving In operating cost Of the Motor. By the best of our research and Knowledge this project is feasible & worth while to perform.

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