ELECTRICAL
POWER
DISTRIBUTION
Week 1-2
Course Contents
These are the “main and big headlines” for
the topics we will study
■
■
■
■
■
■
■
■
Introduction to electrical distribution system
Distribution system elements & configurations
Electrical load characteristics
Voltage regulation in distribution systems
Protection and branching circuit design
Distribution transformers
Power factor correction in distribution systems
Operation and control of distribution systems
How will you be graded and assessed?
■ RULE 1: WORK AND READ A LOT!
EVERY WEEK YOU HAVE AN
ASSIGNMENT!
■ RULE 2: BE ON TIME IN
ASSIGNMENTS, NO EXCUSES FOR
LATE OR UN-HANDED ONES. IF YOU
MISS IT, YOU CANT MAKE IT UP!
■ RULE 3: BE ON TIME! LATE ENTRIES
ARE NOT TOLERATED
■ RULE 4: LEAVE THE REST FOR ME
System voltage classes according to
IEEE Std 141-1993
■ Low voltage:
A class of nominal system voltages less than 1000 V.
■ Medium voltage:
A class of nominal system voltages equal to or greater than 1000 V and
less than 100, 000 V.
■
High voltage:
A class of nominal system voltages equal from 100 000 V to 230,000V.
4
System voltage classes according to
IEC Standard no. 38 (International Electro technical
Committee)
■ Low voltage (LV)
For a phase-to-phase voltage between 100 V and 1000 V. The
standard ratings are: 400 V - 690 V - 1000 V (at 50 Hz)
■ Medium voltage (MV)
For a phase-to-phase voltage between 1000 V and 35 kV. The
standard ratings are: 3.3 kV - 6.6 kV - 11 kV - 22 kV - 33 kV
■ High voltage (HV)
For a phase-to-phase voltage between 35 kV and 230 kV. The
standard ratings are: 45 kV - 66 kV - 110 kV - 132 kV - 150 kV - 220
kV.
66 kV= High voltage in Egypt
11-22 kV= Medium voltage in Egypt
‫الكود المصري مستوحي من‬
IEC
Substation and Distribution system
Station switch yard
13.8 kV
Power Plant
Step up
transformer
220 kV rural feeder
Step down
transformer
66 kV su transmission line
11 kV rural feeder
Step down
transformer
Large
industrial
customer
Secondary distribution
substation
11 kV feeder
Step down
transformer
11 kV feeder
66/11 kV
Commercial /
industrial
customer
66 kV sub
transmission line
220/66 kV
13.8/220 kV
Primary distribution
substation
Other 66 kV sub
transmission lines
Sub transmission
sub station
11 kV/ 400 V
11 kV feeder
66 kV
400 v
Radial distributor
Step down
transformer
11 kV/ 400 V
Ring distributor
Sub-transmission lines carry large amounts of
power from the bulk power substations to the
main
distribution
substations
within
the
immediate area of use at intermediate voltages.
The medium voltage network carries electrical
power from the main distribution substations
either directly to large industrial and commercial
consumers or to distributor centers within
residential areas at medium voltages. The
primary feeders carry the electrical power from
distributer centers to step down distribution
transformers. The three-phase 380 V four-wire
secondary cable carries the electrical power
from the distribution transformer to building
main switchboard.
Generating Station:
The place where electric power produced by parallel connected three phase alternators/generators
is called Generating Station. The Ordinary generating voltage may be 11kV, 11.5 kV 12kV or 13kV.
But economically, it is good to step up the produced voltage to 132kV, 220kV or 500kV or greater by
Step up transformer (power Transformer).
Primary Transmission:
The electric supply (in 132kV, 220 kV, 500kV or greater) is transmit to load center by overhead
transmission system.
Secondary transmission:
Area far from city which have connected with receiving station by line is called Secondary
transmission. At receiving station, the level of voltage reduced by step-down transformers up to
132kV, 66 or 33 kV, and Electric power is transmit by three phase three wire overhead system to
different sub stations.
Primary Distribution:
At a sub station, the level of secondary transmission voltage (132kV, 66 or 33 kV) reduced to 11kV
by step down transforms. Generally, electric supply is given to those
heavy consumer whose
demand is 11 kV, from these lines which caries 11 kV and a separate sub station exists to control
and utilize this power. For heavier consumer (at large scale) their demand is about 132 kV or 33
kV, they take electric supply from secondary transmission or primary distribution (in 132 kV, 66kV or
33kV) and then step down the level of voltage by step-down transformers in their own sub station for
utilization ( i.e. for electric traction etc).
Secondary Distribution:
Electric power is given by (from Primary distribution line i.e.11kV) to
distribution sub station. This sub station is located near by consumers areas
where the level of voltage reduced by step down transformers 440V by Step
down transformers. These transformers called Distribution transformers, three
phase four wire system). So there is 400 Volts (Three Phase Supply System)
between any two phases and 230 Volts (Single Phase Supply) between a
neutral and phase (live) wires. Residential load (i.e. Fans, Lights, and TV etc)
may be connected between any one phase and neutral wires, while three
phase load may be connected directly to the three phase lines.
Egyptian Network
‫ الشبكة الموحدة‬220 kV
Any electrical network usually feeds a certain zone or location. In case any power failure in
the network, all services will be interrupted and leads to disconnection of loads. The unified
grid solves such problems since it connects a number or a group of networks together. In
case of any power failure in one network occurs, the rest of the network feeds the loads
and prevents their cut out. There Egyptian grid consists of the following:
Generation : 24- 30 kV ‫محطات التوليد‬
Transmission : ‫محطات الرفع ألغراض النقل علي أكثر من مستوي‬

220 kV: -‫ حدود مصر‬-‫ وجه بحري‬-‫ القاهرة الكبري‬-‫معظم الجمهوريه (شرق الدلتا – غرب الدلتا‬
)‫سيناء‬

500 kV:‫ كم‬950 ‫خط رابط بين أسوان و القاهرة طوله تقريبا‬

‫ كيلو فولت تم إختيارها بهذه القيمة الن المسافة بعيدة بين الصعيد ووجه بحري و‬500 ‫شبكة ال‬
‫بالتالي المقاومة الكلية للكابالت ممكن تؤدي النخفاض التيار للنصف تقريبا و بالتالي الجهد‬
‫ تقريبا‬500 ‫ أو ال‬440 ‫ إلي‬220 ‫سيزداد للضعف من‬
‫‪Egyptian Grid‬‬
‫‪Interconnection‬‬
‫‪Marine‬‬
‫‪cable‬‬
‫‪line‬‬
‫البيان‬
‫‪OH line‬‬
‫خط الربط المصري‬
‫الليبي‬
‫‪Since 1998‬‬
‫خط الربط المصري‬
‫االردني‬
‫‪Since 1998‬‬
‫جهد الربط (ك‪.‬ف)‬
‫‪220‬‬
‫‪400‬‬
‫دول الربط‬
‫ليبيا‬
‫االردن‬
‫سوريا‬
‫لبنان‬
‫الطاقة المباعة (صادرة)‬
‫(ج‪.‬و‪.‬س)‬
‫‪100‬‬
‫‪1277‬‬
‫‪220‬‬
‫‪82‬‬
‫الطاقة الواردة (ج‪.‬و‪.‬س)‬
‫‪64‬‬
‫‪26‬‬
‫‪2‬‬
‫‪-‬‬
‫‪Egyptian Grid Useful Statistics‬‬
‫البيان‬
‫‪%‬إجمالي الطاقة الكهربية المنتجة‬
‫الطاقة المائية‬
‫‪7.94‬‬
‫طاقة الرياح‬
‫‪0.79‬‬
‫الطاقة الشمسية‬
‫‪0.07‬‬
‫كهرباء مولدة من المحطات الحرارية المربوطة بالشبكة‬
‫‪91.02‬‬
‫كهرباء مولدة من المحطات الغير مربوطة بالشبكة‬
‫‪0.14‬‬
‫كهرباء مشتراة من فائض الشركات الصناعية‬
‫‪0.04‬‬
‫إجمالي (مليون ك‪.‬و‪.‬س)‬
‫‪168069‬‬
‫تقرير وزارة الكهرباء عم ‪2014-2013‬‬
‫)‪Alexandria Network (Distribution‬‬
‫‪66 kV‬‬
‫المنتزة ‪+‬‬
‫المعمورة‬
‫‪ +‬أبو قير‬
‫‪11 kV‬‬
‫‪Incoming feeder‬‬
‫‪66 kV‬‬
‫سيدي‬
‫جابر‬
‫جليم‬
‫‪11 kV‬‬
‫سيدي‬
‫جابر ‪+‬‬
‫سموحة‬
‫‪11 kV‬‬
‫غرب‬
‫(المنشيه‬
‫‪ +‬محطة‬
‫الرمل)‬
‫‪11 kV‬‬
‫غرب‬
‫(العجمي)‬
‫‪20 kV‬‬
66 kV Subtransmission
Distribution Systems Elements:
General Overview
First: 66 kV Subtransmission line
Load-break Switch
Second: Main
Distribution
Substation
11-kV High-rupture
Capacity Fuse
11-kV bus
Distribution
Transformer
380-V Cable
HV-Circuit Breaker
380-V
Third:
To the
substation
loads
themselves
LV Distribution
Room
N.C
380-V
HRCF
11 kV Primary
feeder
380-V Circuit
Breaker (optional)
N.C
MV Tap Point
Primary
Feeder
Sectionalizing
Switches
Fourth:
to step down
distribution
transformers
11kV/380V
Distribution Systems Configurations:
‫أنماط شبكات التوزيع‬
Primary Distribution System Arrangements
The structure of distribution system and components used
depends on two factors:
•
•
•
•
•
•
The initial cost.
Reliability.
Service continuity.
Voltage regulation.
Efficiency.
Operating and maintenance costs.
More reliable systems mean higher installation costs which will be
translated into higher price for kWh consumption
The choice between reliability and cost depends on the infra structure
example:
Milling factories
Furnaces and steel
residential area
commercial and industrial areas
MV Voltage Network: Primary Feeders
1. Radial configuration
Supply disconnects,
66 kV
down stream loads
‫يتم التحكم في منطقة‬
disconnects
‫كبيره‬
‫التغذية من ناحيه واحده و الحمل من الناحيه‬
‫التانيه‬
Time is required for
BULK POWER LINE
66 kV
Sub TL
fixing faulted cable
and thus power is
interrupted
Main CB
20 kV
LV feeders
3 380/
1 220V
LV
Distribution
Substation
HRCF
DT
HV
HRCF
20 kV
Isolating
Switches
Simplest system with minimum
components , cables and cost
To Major
Consumers
20 kV
MV Primary
Feeders
Distribution
Transformer
20 kV
Disconnection is
done to the faulted
part ONLY, however,
sometimes the main
switch (at
transformer) is
disconnected to
disconnect multi
consumers
Radial System: Rural areas ‫هذا النوع من الشبكات يتواجد في األرياف والقري‬
The system offers the following advantages:
• System investment is the lowest of all circuit
arrangements.
• Distribution is done at secondary voltage level
• Operation and expansion are simple.
• Simpler power flow calculations.
• Current magnitude is high upsteam and lessen
as we go downstream, thus the size of the
conductor feeders are smaller downstream.
BUT sometimes this puts more limitations to
voltage drop allowance
• One transformer is responsible for a group of
loads having only one primary feeder. The
system takes advantage of the total diversity
among the loads and requires less space.
• Each feeder is connected to the switchgear or
switchboard bus through a circuit breaker or
other overcurrent protective device. A
relatively small number of circuits are used to
distribute power to the loads from the
switchgear or switchboard assemblies and
panelboards.
Usually is very convenient up to
1000 kVA (1 MW) capacity
The reliability of simple radial systems has the
following characteristics:
• Loss of a cable, primary supply, or transformer
will cut off service.
• Equipment must be shut down to perform
routine maintenance and servicing.
• When high quality components and appropriate
ratings are used reliability is high.
• The system is satisfactory for small industrial
installations
Radial Systems: A “new look”
The modern simple-radial distribution system :
 It distributes power at the primary voltage level so that
the length of the low-voltage feeders is kept to a
minimum, reducing cable cost and energy losses and
improving voltage regulation.
 The voltage is stepped down to utilization level in the
several load areas within the building typically
through secondary unit substation transformers. The
transformers are usually connected to their associated
load bus through a circuit breaker
 Each transformer must have sufficient capacity to
carry the peak load of the area it serves. The main
disadvantage of this system is that service to all
transformers will be interrupted in case of a fault in
the primary circuit or maintenance work on the main
circuit breaker.
 Like the simple radial system continuity and
flexibility are poor.
Modern simple-radial distribution
system
Used with systems more than 1000
kVA (1 MW) capacity
Radial Systems: A “new look”
•
•
•
•
The modified modern simple-radial distribution system:
Reducing the number of transformers per primary
feeder by adding more primary feeder circuits will
improve the flexibility and service continuity of this
system provides all the advantages of the modern
simple-radial type, but includes important
improvements in reliability.
Each distribution transformer is fed from an
individual primary feeder so that under fault
conditions only the loads supplied by the faulted
feeder are disconnected.
Initial cost is higher mainly due to having a circuit
breaker in each primary feeder. The cost can be
reduced by replacing the circuit breakers with loadbreak switches.
In this case a fault on a primary feeder will cause
power disconnection to all loads due to the
operation of the main circuit breaker. The faulted
feeder is identified by opening all load-break
switches and then reclosing them one by one. The
faulty feeder is isolated and service can be restored
to all the others.
Modified modern simple-radial
distribution system
2.
Open-Loop
Configuration
‫مشهور جدا في المدن مثل‬
‫القاهره واإلسكندريه‬
BULK POWER LINE
‫ عادة بتكون‬66 ‫شبكة ال‬
)‫ (حلقه‬Ring Main Unit
(RMU)
Loop-connected 66-kV
Sub-TL
Means that NORMALLY the loop is
open and in EMERGENCY the loop
closes
Each is fed from TWO WAY
power supplies
Two-way HV subtransmission
66 kV power supply
Very large
industrial
substation
Primary
Distribution
Substation
MV Primary
Feeders
Radial
system
Disconnecting
Switches (NO)
Tie Lines
‫خط ربط‬
Radial
system
Open loop Configuration
•
‫ لو لم تكن في شكل «حلقة» ده معناه إن عند‬66 ‫شبكة ال‬
‫إنقطاع الكهرباء جزء كبير جدا سيتأثر بهذا األنقطاع‬
This is a “normally open system”, this means that normally the
downstream acts as a radial system.
In case of any fault in the downstream circuit,
1- First the main section CB trips so that all the downstream cct is
isolated from the power source then determines which section is
faulted (through SCADA and monitoring station)
2- the disconnecting switches isolates the faulted section and closes
the tie line
3- then gets service back again through connecting the main CB
again
During fault the system becomes a “loop system” through the
connection of the tie line while the faulted part is isolated from the
system.
High reliability system
3. Loop Configuration
Two loops exist so any
load has two supplies
The higher the
reliability, the more
complex the control
and decision making
Sub-transmission Line
Sub-transmission
Line
‫مشهور جدا في المناطق الحيويه‬
‫ووسط المدن‬
BULK POWER LINE
Major
Load
Distribution
substation
MV Primary
feeders
MV Primary
feeders
4. Combination of Loop Subtransmission & Radial Primary
Feeders
BULK POWER LINE
Main
distribution
substation
Sub-transmission
Line
‫كوكتيل و موجود في القاهرة‬
‫مثال‬
Loop
configuration
for MV
Primary
feeders
MV primary feeders
Distribution
substation
Loop configuration for sub
transmission system
Distribution
substation
MV primary
feeders
Disconnecting
Switches (NO)
Radial
configuration for
MV primary
feeders
Tie line between two
adjacent primary feeders
(open loop_ MV primary
feeders configuration
Sub transmission and MV
network Layout
Radial


Open loop



Loop layout


Combination (loop and
radial)


Advantages
Disadvantages
Applications
Simple layout
Low reliability
Not used in sub
Economical to install
transmission systems
compared to other
layouts
Simple layout
Failure of one of the two Residential type consumers
Economical to install
primary feeders leaves a
in urban areas and less
compared to other
number of consumers out density population areas
layouts
of service until the tie line
Provision for switching
switches are manually
the load to the good line
closed
in the event of supply
outage
Reliable with two way
Expensive and requires Residential type consumers
supply
more equipment
in urban areas and less
Malfunction section can
density population areas
be repaired without
removing much of the
sections from service
Reliable and suitable for
The radial part is
Combination of residential,
critical loads (such as
arranged so that only
industrial and commercial
business and industrial residential customers are customers with a degree of
loads)
out of service in case of
reliability which is load
Reasonably econimical
supply failure
dependent
Low-voltage Distribution Network
Mesh system STANDARDIZED
LV
meshed
feeder
MV
primary
feeder
BULK POWER
Cable
distribution
cabinet
Distribution
transformer
‫التخطيط للمدن‬
‫العمرانيه الجديدة‬
Each
transformer
receives a two
way supply
from two
primary
feeders
One feeder
Disconnecting or
isolating switch
Multi-line
Fed meshed
Single-line
Fed meshed
In single-fed meshed system, all
In multi-line fed meshed systems, the
substations of several medium-voltage lines can substations connected via the lowvoltage network are supplied from a
be connected in parallel through the lowsingle medium-voltage primary feeder
voltage system.
Under ground low-voltage
radial distribution system 3 to
6 MVA/km2 load density
Residential area
(3 to 6 MVA/km2
load density)
Distribution
Box
D
Typical residential area (Street
width 7 meters), 5 floors
C
B
Distribution
transformer
A
Main cable
Out of distribution box
cable
240 mm2 4/C Aluminium conductor 1 kV
185 mm2 4/C Aluminium conductor 1 kV
50 mm2 4/C Aluminium conductor 1 kV
To inside SMALL (5 FLOOR)building cable
Or copper equivalent
cable
Another “dry type” transformer for voltage drop
(expensive a bit, 11kv rating)
Low voltage system of
high rise buildings
Lifts
‫مباني مرتفعه‬
)‫ طابق مثال‬14 ‫(فوق‬
Automatic sourcechangeover systems
with mechanical
interlocking
Sub-panel boards for
distributed loads in the floor
‫ شقق‬8
‫أكثر من‬
‫محول‬
‫توزيع‬
‫غرفة‬
‫الكهرباء‬
‫و‬
‫الدخول‬
Bus-way type shaft
riser for main supply
Sub-panel board
for Floor Emergency
Bus-way type shaft riser
for emergency supply
‫الدورالثاني‬
‫بدال من‬
‫الكابالت‬
ATS
LV emergency
bus
11 or 20 kV
MV Feeder
Entrance Cables
Dotted line means
emergency, solid
means main
G
LV Main supply bus
‫مولد‬
‫إحتياطي‬
Types of Installation of LV Distribution Systems in Buildings
1.
Distribution by insulated conductors and cables:
‫يستعمل في البنايات ذات‬
‫عدد طوابق محدود‬
Local general
distribution board
Sub-distribution
board
‫لوحة التوزيع الفرعية‬
There could be 1 riser
or more than one
depending on the
building size
Main general
distribution board
Heating,
etc.
‫لوحة التوزيع الرئيسية‬
General utilities
distribution board
Types of Installation of LV Distribution Systems in Buildings
2.
Distribution by prefabricated bus-trunking & cables channels
Bus-duct
transformer to
Main dist. board
Main dist.
board
Main bus-bar
trunking
Transformer
Local dist.
board
Prefabricated power and
light current column
Prefabricated prewired cable channels
Also known as
“bus way”
Prefabricated bustrunking
CHALLENGE QUESTION OF THE WEEK! TO BE HANDED
IN BY NEXT WEEK IN THE SECTION.
“Can you find other primary / secondary distribution
systems layouts?”
YOUR REPORT MUST:
1- hand written in clear (or computer typed), neat handwriting
2- includes references
3- Clear diagrams, labels .. Look first in your text book then you can look in the internet
4- cover page with your name and registration number
5- Be Subjective… don’t talk too much
6- DO NOT COPY AND PASTE
7- Marks will be rewarded according to subjectivity, organization, clarity and creativity