بسم الله الرحمن الرحيم رب اشرح لى صدرى ويسر لى أمر واحلل عقدة من لسانى يفقهوا قولى

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

04/21/23 Prof. Dr. Magdi El-Saadawi 2

2nd Grade EE Students

Fundamentals of Electrical loads

Chapter 7


pp. 251-264

04/21/23 4

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.


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.


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



Typical Daily Load curve



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.


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.


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


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


• 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


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)

• 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.


?What is the difference between

load factor

and

capacity factor

Can they have the same value?


• 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


?What is the difference between

Plant use Factor

and

Capacity factor

Can they have the same value?


• 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


7.4 Units Generated per Annum pp.261

Load Duration Curve pp. 261




Load Duration Curve


Load Curve and Load Duration Curve


• 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


Points about load duration curve pp 262

Thank You Very MuchAnd

Any Question?


• 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




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




• 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)


• 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


?Which is better and why

High or Low load factor value

High or Low diversity factor value


• 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


• Connected Load Factor

Average kWh

Connected load * 8760




Integrated Load Duration Curve pp. 60



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


بسم الله الرحمن الرحيم رب اشرح لى صدرى ويسر لى أمر واحلل عقدة من لسانى يفقهوا قولى

Documents

load curves variation

load variations

stationaverage load

saadawiconnected load

loadthe load curve

saadawiyearly load curve

greatest demand of load

yearly load curves