Sunday, 8 July 2012

POWER FACTOR IMPROVEMENT


Tariff Powerfactor Supplysystem MechProperties ElecProperties Transmission UGCable DCDistribution ACDistribution



POWER FACTOR IMPROVEMENT

Q.  Define  power factor . 
A. The cosine of the angle between the voltage and current of an ac circuit is known as power factor for that circuit . 
Q.  Write different formula for the power factor . 
A.  Cosø = active power ( KW )/ apparent power(KVA) 
                = r/z
Q.  What you meant by 0.6 lagging ? 
A.  This means that the power factor of a load is 0.6 where current lags the voltage by an angle equal to Cos -1 (0.6) . 
Q.  Write down the relation between different powers . 
A.  (apparent power)2  = (active power)2   + (reactive power)2  . 
Q.  What is the equation of reactive and apparent power and their unit ? 
A.  Reactive power = V*I*sinø = kw*tanø
      Unit kvar
      Apparent power = V*I = kw/cosø
      Unit kva
Q.  What is the power equation for 3-phase and 1-phase system ? 
A.  P = 3*V*I*cosø (for 3-phase ) 
      P = V*I*cosø ( for 1-phase ) 
Q.  Why electrical machines are rated in KVA ?
A.  Because at the time of manufacturing of electrical equipment the power factor of the load is unknown . 
Q.  What is the effect of power factor on the voltage regulation ? 
A.  At low power factor for lagging load the load current is large which causes more voltage drops in electrical equipments , transmission and distribution lines . So the receiving end voltage decreases and causes voltage fluctuation . 
Q.  Write the name of different equipments used for power factor improvement ? 
A.  Static capacitor
Synchronous condenser
Phase advancers
Q.  What is the value of pf on a large generating station ? 
A.  0.8 to 0.9
Q.  What is synchronous condenser ? 
 A.  A synchronous motor when running at no load and over excited condition , it takes leading current from the supply. At this condition that synchronous motor is called synchronous condenser . 
Q.  How you meet the increased kw demand ? 
A.  There are two process
      By increasing the kva capacity  at the same power factor . 
      By improving the power factor  at same kva . 
Q.  Power factor improvement means _________ . 
A.  Increasing the value of power factor or decreasing the power factor angle . 
Q.  ________the power factor of the generating station _____________is the kwh it delivers to the system . 
A. Greater , higher
Q.  I*cos ø always is in _________with v . 
A.  Phase
Q.  The angle between the I*sin ø and V is __________.
A.  900
Q.  Lower the value of power factor _________the kva rating of equipment . 
A.  Greater
Q.  The electrical equipments are rated in ________ . 
A.  KVA
Q.  If power factor increases the load current _________ . 
A.  Decreases
Q.  For carrying the current at constant voltage and power the conductor size is __________for low power factor . 
A.  Large
Q.  Arc lamps operate at _________ power factor . 
A.  Low lagging
Q.  The maximum value of power factor is_________ . 
A.  (unity) 1
Q.  Pf correction equipments are connected in__________with electrical equipment . 
A.  Parallel
Q.  The reactive power taken by a synchronous motor depends on ___________ and__________.
A.  Dc field excitation , mechanical load 
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TARIFF

TARIFF  POWERFACTOR

TARIFF

Q. What is tariff ? 
A. The rate at which the electrical energy is supplied to the consumers is known as tariff. 
Q. What are the objectives of tariff ? 
A.  => recovery of cost for producing electrical energy. 
      => recovery of cost on the capital investment. 
      => earn suitable profit on capital investment. 
      => recovery of cost due to operation and maintenance. 
Q. What consideration should be taken during applying a tariff system ? 
A. => proper  return
     =>  fairness
     => simplicity
     => reasonable profit
     => attractive
Q. Classify the tariff system . 
A. => simple tariff
     => flat rate tariff
     => block rate tariff
     => two part tariff
     => maximum demand tariff
     => power factor tariff
     => three part tariff
Q. Classify the power factor tariff .
A. => KVA maximum demand tariff
    => sliding scale tariff
    => KW and KVAR tariff
Q. Which tariff is also known as uniform rate tariff ? 
A. Simple rate tariff.
Q. Which tariff system is based on classes of consumers ? 
A. Flat rate tariff. 
Q. In which tariff system charged per unit is constant ? 
A. Simple or uniform rate tariff. 
Q. On which running charges depends ? 
A. It depends on kwh i.e. Number of units consumed by the consumers. 
Q. Which is most suitable tariff system for any type of consumers ? 
A. Three part tariff. 
Q. Which tariff system is normally employed for residential and small commercial consumers ? 
A. Block rate tariff. 
Q. Where two part tariff is used ? 
A. For industrial consumers. 
Q. Which tariffs can be used for big industrial consumers ? 
A.  => maximum demand tariff
     => power factor tariff
     => three part tariff
Q. What is the relation between power factor and apparent power ? 
A. Apparent power is inversely proportional to power factor i.e. KVA ∞ 1/cosø . 
Q. Why price per unit for first and second blocks of energy is high ?
A. Because the fixed cost , charged on each consumer is merged into the running charges for these two blocks . 
Q. On which fixed charges depends ? 
A. Maximum demand of the consumers . 
Q. Why consumers having low power factor have to pay more charges ? 
A. Low factor of the load means that the load draws more reactive power from the supply line, so the respective consumers  have to pay more charges . 
Q. For low power factor a consumer have to pay _______charges. 
A. More
Q. Uniform tariff system is ________tariff system . 
A. Simplest . 
Q. The flat rate per kwh for ________is less than________load . 
A. Power , lighting load
Q. Different  classes of consumers are divided  based on__________and_________factor. 
A. Diversity , load
Q. Cost of generation is reduced as load factor is ___________ . 
A. Increased
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