Transcript Distribution System

Distribution System
Introduction: Distribution system discuss how the power that is generated by the
power stations are supplied to the consumers. i.e. industrial purpose or home use etc.
Distribution system includes the main distribution substation(132/66KV) and sub
distribution substations (large66/33KV small (33/11kV) and distribution system directly to
consumers (11/0.4KV)
The figure below gives an idea of the distribution system
Types of Distribution system according to voltage
range
According to voltage levels distribution system are classified
into two. They are:-
1) Primary Distribution system
Primary distribution the voltages range 2.4KV to 69KV. Actually primary
distribution includes the distribution from high voltage substation
(132/66KV) to (66/33KV) to (33/11KV) distribution substation
2) Secondary Distribution system
Secondary distribution is low voltage distribution that is three phase
440V and single phase two wire 240V or may be 220V. In secondary
distribution voltage is stepped down from 11KV to 440V(three phase)
and 220(single phase)
Primary Distribution system
Primary distribution includes the following topic:1) Substation Arrangement
2) Types of Systems
3) Primary Distribution Feeders Arrangement
4) Primary Network
So to built a primary distribution network we have to fulfill those criteria
Substations Arrangement:-
A simple substation arrangement
consists of one incoming line and one transformer. More complicated
substation arrangements result when there are two or more incoming
lines, two or more power transformers, or a complex bus network. Some
substation arrangement are shown by the figure.
Layout of substation arrangement
Above the substations we select (G) type arrangement because of the following
advantages:-It has two incoming line capacity with breakers placed in line
-It has a re-closer
-Transformer protection capability is high because of an extra breakers in front of it
- Also power by pass capability in case of transformer failure.
Substation Bus Arrangements
A bus is a junction of two or more incoming and outgoing
circuits. The most common bus arrangement consists of one
source or supply circuit and one or more feeder circuits. It is
the most important part of the distribution as well as the total
power system. So we have carefully take the decision which
bus bar is suitable for our system.
The bus bar arrangements are classified into the following
categories –
(a) Single bus bar scheme
(b) Single sectionalized bus bar scheme
(c) Double bus bar single breaker scheme
(d) Double bus bar double breaker scheme
(e) Main and transfer bus scheme etc.
Single bus bar scheme
Advantages:
1)Simple construction and low cost
2)Less maintenance and simple
operation
Disadvantages:
If a fault occurs on the bus bar there is
complete shutdown in the system
resulting a large fault currents
Single sectionalized bus bar
scheme
Advantages:
1)Fault on bus bar will not cause
complete Shutdown.
2)Repair and maintenance can be done
without shutdown the system.
Disadvantages:
Cost is high than that of single bus bar
system
Double bus bar single breaker
scheme
Advantages:
1)Flexibility of operations is increased
2)Non-synchronized systems can be
used, to supply outgoing circuits
3)Fault on bus bar will not cause
complete Shutdown
4)Repair and maintenance can be done
without shutdown the system
Disadvantages:
1) Cost of equipment is more
2) Operation is more complex
Double bus bar double breaker
scheme
Advantages:
1)More Flexibility and more protection is
used
2)Because of Two breakers no
hampering in system continuity in
case of repair or maintenance
3)Fault on bus bar will not cause
complete Shutdown
Disadvantages:
1) Cost of equipment is more
2) Operation is more complex
Decision
According to advantages and disadvantages of above bus bar
we have to select one bus bar arrangement for our desire
system.
So we chose double bus bar single breaker system because
of the following Reasons:
It is more reliable than single bus bar and operation is less
complicated than double bus bar double breaker system.

We also take cost into considerations
Types of Primary Feeder System
1)Tie Feeder:
The main function of a tie feeder is to
connect supply source to load. It
may connect two substation buses
in parallel to provide service
continuity for the load supplied
from each bus.
2) Loop Feeder:
A loop feeder has its ends connected to
a source (usually a single source),
but its main function is to supply
two or more load points in
between. Each load point can be
supplied from either direction; so it
is possible to remove any section
of the loop from service without
causing an outage at other load
points.
3) Radial Feeder :
A radial feeder connects between a
source and a load point, and it may
supply one or more additional load
points between the two. Each load
point can be supplied from one
direction only.
4)Parallel Feeder:
Parallel feeders connect the source
and a load or load center and
provide the capability of supplying
power to the load through one or
any number of the parallel feeders.
Parallel
feeders
provide
for
maintenance of feeders without
interrupting service to load.
Decision
From above four types of feeders we chose the parallel
feeder. Because of the following reasons:


More reliable and flexible
It provide for maintenance of feeders without interrupting service
High protection capability
One line diagram of a typical primary
distribution feeder
A feeder includes a main or main feeder which usually is a three phase
four wire circuit and branches, which usually are single or three
phase circuits tapped off the main. A given feeder is sectionalized
by re-closing devices at various locations in such a manner as to
remove as little as possible of the faulted circuit so as to hinder
services to as few consumers as possible. This can be achieved
through the co-ordination of the operation of all the fuses and reclosers.
There are various and yet interrelated factors affecting the selection of
a primary feeder rating.
Examples are:
1)The nature of the load connected
2)The load density of the area served
3)The growth rate of the load
4)Providing spare capacity for emergency operations
5)The type of regulating equipment used
6)The quality of service required
7)The continuity of service required.
Types of Primary Feeder Distribution
Now we discuss about the types that are used in primary distribution
feeder. There are the five types of primary distribution feeder
arrangement which is given below:1) Radial type primary feeder
2) Radial Type primary feeder with tie and sectionalizing switches
3) Radial type primary feeder with express feeder and back feed
4) Loop Primary-Radial Distribution System
5) Primary Selective Distribution System
Decision
Although the cost is a little high because of primary cables and
switchgear but because of the following advantages we chose the
primary selective distribution feeder arrangement.
1) Protection against losses
2) Each section can be operated separately
3) Provides normal and alternate sources operation
4) No discontinuity in case of maintenance
Primary Network
(Interconnection Between Substations)
Selection of Primary Feeder Voltage Level
When we are about to select the voltage level we have to
consider the following things:1. Primary feeder length
2. Primary feeder loading
3. Rating of distribution substations
4. Number of transmission lines
5. Number of customers
6. System maintenance practices etc
Secondary Distribution System
The voltage levels for a particular secondary system are determined by
the loads to be served. The utilization voltages are generally in the
range of 120 to 600 V.
Secondary Distribution Design Considerations
1)Choice of voltage: For secondary distribution system the voltage chosen is
the standard voltage used in the country at the consumer’s level, i.e.
440/415V three phase for motor loads and 240V/220V single phase for
lighting loads etc
2) Conductor size: The conductor size is chosen mainly on the basis of the
permissible voltage drop in the distribution section under consideration. The
secondary distributors are designed for 6% voltage drop from the transformer
to the last consumer in the system.
Types of Systems
1) Conventional SimpleRadial Distribution
System
Advantages:
Operation and expansion is simple
and Reliability is high
Disadvantages:
In case of maintenance service
interrupted
2) Expanded Radial
Distribution System
Advantages:
a) Operation and expansion is
simple and Reliability is high
b) Capability to work with lager
loads
Disadvantages:
a) In case of maintenance service
interrupted
3) Secondary Selective-Radial
Distribution System
Advantages:
a) Operation and expansion is simple
and Reliability is high
b) Capability to work with lager loads
c) In case of maintenance no service
interrupt
Disadvantages:
a) Cost is high
4) Secondary Network
Distribution System
Advantages:
a) Operation and expansion is simple
and
Reliability is high
b) Capability to work with lager loads
c) In case of maintenance no service
interrupt
d) Network Protection is used
Disadvantages:
a) Cost is high
Final Decision
For Primary Distribution
Substation Arrangement
( Double breaker with automatic re-closer)
Substation Bus arrangement
(Double bus bar with double breaker)
Types of Primary feeder Systems
( Parallel feeders)
 Primary Distribution Feeders
Arrangement
For Secondary Distribution
System
 Types of Systems
(Expanded Radial Distribution
System)
The End