Distribution systems engineering

Course Code: EE2326

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Prof. Dr. Magdi M. El-Saadawi

www.saadawi1.net

E-mail : saadawi1@gmail.com

www.facebook.com/magdi.saadawi

Assessment Schedule

Assessment 1: test in Lecture week 4

Assessment 2: Midterm exam week 8

Assessment 3: test in Lecture week 11

Weighting of Class Grading

Lecture Exams 5 marks

Midterm Exam 10 marks

Reports and Sheet 5 marks

Team work project 10 marks

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Students’ Assessment كیفیة تقییم الطلاب

ContentsChapter 1

Fundamentals of Distribution Systems Chapter 2

Distribution SubstationsChapter 3

Primary SystemsChapter 4

Secondary SystemsChapter 5

Capacitor Applications and Power Factor Correction

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Distribution Substations

Chapter 2

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Contents2.1 Main types of distribution substations

2.2 Transformer Substations

2.3 Equipment in a transformer substation

2.4 Substation costs

2.5 Substation bus schemes

2.6 Key diagram of 66/11 kV substation

2.7 Key diagram of 11 kV/400 V indoor substation

2.8 The rating of a distribution substation

2.9 Comparison of the four- and six-feeder patterns

2.10 Mathematical formulation of the K constant

2.11 Interpretation of percent voltage drop formula 5

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Important points for laying out a substation:(1) It should be located at a proper site. (at the center of

gravity of load or close to the load center).

(2) It should provide proper voltage regulation.

(3) It should provide proper access for incomingsubtransmission lines and outgoing primary feeders andalso allows for future growth.

(4) It should be easily operated and maintained.

(5) It should involve minimum capital cost.

(6) It should provide enough space for the futuresubstation expansion and not be opposed by land useregulations, local ordinances, and neighbors.

Introduction pp. 19

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• Two ways of classifying distribution substations:

(1)According to service requirement(i) Transformer sub-stations.

(ii) Switching sub-stations.

(iii) Frequency changer sub-stations.

(iv) Converting sub-stations.

(v) Industrial sub-stations.

(2)According to constructional features.(i) Indoor sub-stations,

(ii) Outdoor sub-stations.

(iii) Underground sub-stations.

(iv) Pole-mounted sub-stations.

2.1 Main types of distribution substations

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(i) Transformer sub-stations.

• They are used to change the voltage level of electric supply.

• They substations receive power at some voltage and deliver it at some other voltage.

• Most of the substations in the power system are of this type.

According to service requirement

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(ii) Switching sub-stations.

• These substations do not change the voltage level

• They simply perform the switching operations of power lines.

(iii) Frequency changer sub-stations.

• They change the supply frequency.

• Such a frequency change may be required for industrial utilization.

According to service requirement

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(iv) Converting sub-stations.

• They change a.c. power into d.c. power.

• These substations receive a.c. power and convert it into d.c. power with suitable apparatus (e.g. ignitron) to supply for such purposes as traction, electroplating, electric welding etc.

(v) Industrial sub-stations.

• They supply power to individual industrial concerns.

According to service requirement

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(i) Indoor sub-stations.

• For voltages up to 11 kV, the equipment of the sub-station is installed indoor because of economic considerations.

• When the atmosphere is contaminated with impurities, they czn be erected for voltages up to 66 kV

(ii) Outdoor sub-stations.

• For voltages beyond 66 kV, equipment is invariably installed outdoor.

• For such voltages, the clearances between conductors and the space required for switches, circuit breakers and other equipment becomes so great that it is not economical to install the equipment indoor.

According to constructional features

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Indoor substations.

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Indoor substations.

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(iii) Underground sub-stations.

• In thickly populated areas, the space available for equipment and building is limited and the cost of land is high. Under such situations, the sub-station is created underground.

(iv) Pole-mounted sub-stations.

• This is an outdoor sub-station with equipment installed overhead on H-pole or 4-pole structure.

• It is the cheapest form of sub-station for voltages not exceeding 11kV (or 33 kV in some cases).

• Electric power is almost distributed in localities through such substations.

According to constructional features

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• The majority of the substations in the power system are concerned with the changing of voltage level of electric supply.

• These are known as transformer substations because transformer is the main component employed to change the voltage level.

• Depending upon the purpose served, transformer substations may be classified into:

(i) Step-up substation

(ii) Primary grid substation

(iii) Secondary substation

(iv) Distribution substation

2.2 Transformer Substations

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•

• The generation voltage (11 kV in this case) is stepped up to high voltage (220 kV) to affect economy in transmission of electric power.

• The substations which accomplish this job are called step-up substations.

• These are generally located in the power houses and are of outdoor type.

(i) Step-up sub-station

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• From the step-up substation, electric power at 220 kV is trans mitted by 3-phase, 3-wire overhead system to the outskirts of the city.

• Here, electric power is received by the primary grid sub-station which reduces the voltage level to 66 kV for secondary transmission.

• The primary grid substation is generally of outdoor type.

(ii) Primary grid substation (Transmission substation)

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• At a secondary sub-station, the voltage is further stepped down to 11 kV.

• The 11 kV lines run along the important road sides of the city. It may be noted that big consumers (having demand more than 50 kW) are generally supplied power at 11 kV for further handling with their own sub stations.

• The secondary substations are also generally of outdoor type.

(iii) Secondary substation (Distribution substations)

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• The electric power from 11 kV lines is delivered to distribution sub-stations.

• These substations are located near the consumers localities and step down the voltage to 400 V, 3-phase, 4-wire for supplying to the consumers.

• The voltage between any two phases is 400V and between any phase and neutral it is 230 V.

• It may be worthwhile to mention here that majority of the distribution sub stations are of pole-mounted type

(iv) Distribution substation (Distribution Transformer)

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• The equipment required for a transformer substation depends upon

– the type of substation,

– the service requirement and

– the degree of protection desired.

• However, in general, a transformer substation has the following main equipment:1. Bus-bars 2. Insulators.

3. Isolating switches. 4. Circuit breaker

5. Power Transformers. 6. Instrument transformers

7. Metering and Indicating Instruments.

8. Miscellaneous equipment.

(iii) Secondary substation (Distribution substations)

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