Electrical Power Systems (1)

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Electrical Power Systems (1)

• Part II

2nd Grade EE Students
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Fundamentals of Electrical loads

• Chapter 7

pp. 251-264
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Fig 1. Electrical Power System
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• Introduction pp. 251
• The function of a power station is to deliver
  power to a large number of consumers.
• The load on a power station is never constant. It
  varies from time to time.
• Electrical power cannot be stored and, therefore,
  the power station must produce power as and when
  demanded to meet the requirements of the
  consumers.
• The power station should run at their rated
  capacity for maximum efficiency and on the other
  hand the demands of the consumers have wide
  variations. This makes the design of a power
  station highly complex.

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• 7.1 Variable Load on Power Station pp. 251
• In this chapter, we shall focus our attention on
  the problems of variable load on power stations.
  The load varies due to uncertain demands of the
  consumers.
• Effects of variable load.
• Need of additional equipment.
• Increase in production cost.

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7.2 Load Curves pp. 253

• A curve showing the variation of load on the
  power station with w.r.t time.
• These load variations during the whole day (i.e.
  24 hours) are recorded half-hourly or hourly and
  are plotted against time on the graph.
• The curve thus obtained is known as daily load
  curve as it shows the variations of load w.r.t
  time during the day
• There is also monthly and yearly Load Curves

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Typical Daily Load curve
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Yearly Load Curve
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Information attained from Load curves

• Variation of load during different hours of day
• The area under the load curve gives the number of
  units generated in the day (kWh).
• Max. and Min. value s of daily load
• Average annual load on the station
• Average load Area (in kWh) under daily load
  curve
• 24
  hours

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Information attained from Load curves

• Load factor Average Load / Max. load
• The load curve helps in selecting the size number
  of generating units.
• The load curve helps in preparing the operation
  schedule of the station.

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7.3 Important Terms and Factors pp 256

• Connected load It is the sum of continuous
  ratings of all the equipment connected to supply
  system.
• Maximum demand It is the greatest demand of
  load on the power station during a given period.
• Maximum demand is generally less than the
  connected load because all the consumers do not
  switch on their connected load to the system at a
  time.

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7.3 Important Terms and Factors pp 256

• Demand factor It is the ratio of maximum demand
  on the power station to its connected load lt 1
• Average load (Average demand) The average of
  loads occurring on the power station in a given
  period (day or month or year).
• Load factor The ratio of average load to the
  maximum demand during a given period

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• Load Factor
• Daily L.F. Average load / Max. demand
• Monthly L.F.
• kWh supplied in a month
  
• Maximum demand 24 30
• Annual L.F.
• kWh supplied in a year
• Maximum demand 8760

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• Diversity of Load
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• Diversity Factor
• The ratio of the sum of individual maximum
  demands to the maximum demand on power station

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Practical Example on Diversity Factor
Solution 1 Transformer Size (Assuming
Diversity Factor of 1.0) 2,000 1,500 1,000
4,500 kVA Solution 2 Transformer Size
(Assume Diversity Factor of 1.2) Choose 3,750
kVA (4,500 kVA divided by 1.2
3,750 kVA)
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• Capacity Factor
• The ratio of actual energy produced to the
  maximum possible energy that could have been
  produced during a given period.
• Average demand on the
  Station
• Maximum Energy that could
  be produced
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• Average demand
• Plant Capacity
  
• The capacity factor is an indication of the
  reserve capacity of the plant.

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• What is the difference between
• load factor
• and
• capacity factor
• Can they have the same value?

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• Plant use Factor
• It is the ratio of kWh generated to the
  product of plant capacity and the number of hours
  for which the plant was in operation
• Station output in
  kWh
• kW1h1 kW2h2 kW3h3
  .
• It Indicates how best the plant capacity has
  been utilized
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• What is the difference between
• Plant use Factor
• and
• Capacity factor
• Can they have the same value?

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7.4 Units Generated per Annum pp.261

• Plant use Factor
• Load factor Average load
• Max. demand
• Average load Max. demand x L. F.
• Units generated/annum
• Average load (in kW) x Hours
  in a year
• Max. demand (in kW) x L.F. x 8760

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Load Duration Curve pp. 261
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Load Duration Curve pp. 261
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Load Duration Curve
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Load Curve and Load Duration Curve
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Points about load duration curve pp 262

• The load duration curve gives the data in a more
  presentable form.
• Area under daily load duration curve (in kWh)
  will give the units generated on that day. (same
  as load curve)
• The duration curve can be extended to include any
  period of time
• Daily load duration curve
• Monthly load duration curve
• Annual load duration curve

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• Thank You Very Much
• And
• Any Question?

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• Capacity Factor
• is a value used to express the average
  percentage of full capacity used over a given
  period of time.
• Average demand on the
  Station
• Maximum Installed Capacity
  of the Station

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Difference between load curves of summer and
winter
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Load Duration Curve pp. 60
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• Demand Factor the ratio between average load to
  the maximum connected load
• Power Station Maximum Demand is the greatest
  average load on the station during a given period
  (15 min, 30 min or 1 hour as decided)

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• Average Demand the ratio of kWh delivered by the
  station in a particular period divided by the
  hours in that period
• Load Factor
• Monthly L.F.
• kWh supplied in a month
  
• Maximum demand 24 30
• Annual L.F.
• kWh supplied in a year
• Maximum demand 8760

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• Which is better and why
• High or Low load factor value
• High or Low diversity factor value

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• Plant Factor
• Indicates how best the plant capacity has been
  utilized
• Station output in
  kWh
• kW1h1 kW2h2 kW3h3
  .
• Capacity Factor
• is a value used to express the average
  percentage of full capacity used over a given
  period of time.
• Average demand on the
  Station
• Maximum Installed Capacity
  of the Station

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• Connected Load Factor
• Average kWh
• Connected load 8760

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Load Duration Curve pp. 60
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Integrated Load Duration Curve pp. 60
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Integrated Load Duration Curve pp. 60
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• Mass Curve pp. 62
• represent the total kWh used by the load up
  to that hour of the day
• Selection of units pp.61