بسم الله الرحمن الرحيم رب اشرح لى صدرى ويسر لى أمر ...
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الرحيم الرحمن الله بسم
رب اشرح لى صدرى ويسر لى أمر
واحلل عقدة من لسانىيفقهوا قولى
العظيم الله صدق104/21/23 Prof. Dr. Magdi El-Saadawi
Electrical Power Systems
(1)Part II
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2nd Grade EE Students
Fundamentals of Electrical loads
Chapter 7
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pp. 251-264
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Fig 1. Electrical Power System
500 kV TransmissionPower Plant
Generation
TransmissionSystem
DistributionSystem(12kV)
UndergroundDistribution Transfomer
ResidentialCustomer
Commercial/IndustrialCustomer
ResidentialCustomer
OverheadDistributionTransformer
UrbanCustomers
69 kV Sub-transmission
230 kVTransmission
Distribution Substation(69/12 kV)
High-Voltage Substation(230/69 kV)
Extra-High-Voltage Substation(500/230 kV)
Distribution Line
Underground Cable
To OtherHigh-VoltageSubstations
Prof. Dr. Magdi El-Saadawi
04/21/23 5
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.
Prof. Dr. Magdi El-Saadawi
04/21/23 6
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.
Prof. Dr. Magdi El-Saadawi
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 Curve04/21/23 Prof. Dr. Magdi El-Saadawi 11
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 04/21/23 Prof. Dr. Magdi El-Saadawi 12
• 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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Information attained from Load curves
• 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 < 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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7.3 Important Terms and Factors pp 256
• Load Factor
• Daily L.F.= Average load / Max. demand
Monthly L.F. =
kWh supplied in a month
Maximum demand * 24 * 30Annual L.F. =
kWh supplied in a year
Maximum demand * 8760
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• Diversity of Load
فترة فى تعمل ال المختلفة األحمال أن يعنىواحدة زمنية
إلى تدفع سياسات تتبع الكهرباء شركات أن أو ذلك
• 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
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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)
• 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
• إلى المحطة أنتجتها التى الطاقة بين النسبةالمحطة تنتجه أن مايمكن
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
kW1*h1 + kW2*h2 + kW3*h3 + …….
It Indicates how best the plant capacity has been utilized
المعامل : هذا أن السابق المعامل وبين بينه الفرقوالسابق للمحطة الحقيقى االستخدام عن يتحدث
المحطة تشغيل امكانيات عن يتحدث
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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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• 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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7.4 Units Generated per Annum pp.261
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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• 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 curveAnnual load duration curve
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Points about load duration curve pp 262
Thank You Very MuchAnd
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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34
حكومى لحمل توضيحى شكل
الحمل يمثل الرأسى المحوروات بالكيلو
الزمن يمثل األفقى المحوربالساعات
04/21/23 Prof. Dr. Magdi El-Saadawi
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 FactorMonthly L.F. =
kWh supplied in a month
Maximum demand * 24 * 30Annual 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
kW1*h1 + kW2*h2 + kW3*h3 + …….
• 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
• Mass Curve: pp. 62
represent the total kWh used by the load up to that hour of the day
• Selection of units pp.61
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