Download Class 8 - Generation Technology ~EMD 1305

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
Class 8 and 10
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 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.
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
Generator
Single Line
Representation
10 to 30 KV
of
Step-up T/F
Power System
132 KV, 220 KV, 400 KV.
Transmission EHV
Step down T/F
66 KV, 33 KV OR 11 KV
Distribution HV Receiving
Station
Step Down
T/F
To large Industries at 11 kv or 33 kv or
66 kv
consumer of HV level
440V (Utilization)
Consumers of LV level
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.
The following connection schemes of
distribution system are generally employed:
(1) Radial system
(2) Ring main system
(3) Interconnected system
 1.Radial Distribution system
- only one/single path is connected between each
Distribution and substation is called radial Distribution system.
- Fault occurs either on feeder or a distributor, all the
consumers connected to that distributor will get affected.
- In India, 99% of distribution of power is by radial
distribution system only.

Advantages-
- Its initial cost is minimum
- Simple in planning, design and operation.
- Useful when the generation is at low voltage.
- Station is located at the center of the load
 Disadvantages-
- • Distributor nearer to the feeding end is heavily loaded.
- The consumers at the far end of the feeder would be
subjected to series voltage fluctuations with the variations in load.
 (2 ) Ring main system
- Feeder covers the whole area of supply in the ring fashion
and finally terminates at the substation from where it is started.
- Closed loop form and looks like a ring.
 Advantages-
- Less conductor material is required as each part of the ring
carries less current than in the radial system.
- • Less voltage fluctuations.
 Disadvantage-
- It is difficult to design when compared to the designing of a
radial system.
 Interconnected system-In this system, the feeder is energised by two or more than two
generating station or sub station.
 Advantages-
-There is more flexibility.
-Reliability is more. If fault occur on one section, supply can
be continued by other route.
-Good voltage regulation is achieved.
-Size of substation is less compared to the radial system.
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 coordination of the operation of all the fuses and re-closers.
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.
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
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
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.
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
Single line diagram
13.8 KV
13.8 KV
13,800/120V
50/51
13,800/120V
51N
3-100/5
50/51
51N
2
1
3-100/5
1
2
T
T
500MVA
13.8KV
1200A
500MVA
13.8KV
1200A
1000 KVA
13,800 - 480 Y/277V
3-1500/5
A
WHM
1000 KVA
13,800 - 480 Y/277V
3-1500/5
V
T
A
WHM
V
T
480/120V
480/120V
1600A
1600A
1200A
200A
100A
400A
M
150 KVA
480 - 208Y/120Y
600A
600A
75HP
Feeder 1 Feeder 2
200A
M
Feeder 3
150HP
112.5 KVA
480 - 208Y/120Y
 It requires much lesser space and hence leaves
room for designer for providing other useful
information in the drawing
 It is very versatile and comprehensive because it
can depict very simple DC circuits, or very
complicated three-phase system
 Simple, hence requires much lesser time for reader
to understand the basic system design
One-line diagram
3-line diagram
Provide a basic roadmap to the interconnections of the electrical
system, and serve as a building block from which all types of
system analyses are based.
Prepared as a result of further working on the basis of single line
diagrams as they provide details for electrical wiring connections.
Part of initial plant electrical design. Is usually a part of the initial
tender document.
Part of detailed design document. Is prepared usually after the
tendering stage i.e. before manufacture.
Mainly used for working out panel schedules, load schedules,
fault analysis, protection system deign
Used for control designing circuit diagrams, control circuits,
phase sequencing, differential relay settings, metering
transformer connections etc.
Simplified notation for representing a three-phase power
system. Since the loads on the three phases are identical , any
one phase can be used for representing either of the phases
Here all three conductors of the three phase system are shown
individually.
Details of the power and the control circuits are also shown as
per actual field connections.
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ELECTRICAL POWER MEASUREMENTS
32
Wattmeter
A
AC
Source
I(t)
V(t)
+
W
One - phase
two - wire
Load
V
.
+
Single Wattmeter Method
33
34
Single-Phase Two-Wire System
 The voltage and current detected by the
METER are the voltage and current
applied directly to the Load.
 The indication on the Meter is the POWER
being dissipated by the load.
Wattmeter 1
A
L1
AC
Source
+
W
I(t)
V
V(t)
One - phase
three - wire
Load
.
N
+
V(t)
I(t)
L2
V
W
A
+
Wattmeter 2
Two Wattmeter Method
PT = W1 + W2
35
36
Single-Phase Three-Wire System
(Split Phase)
 The voltage and current detected by the METERS are the
voltage and current applied directly to the Load.
 The indication on EACH METER is the power being
delivered by the LINE to which the meter is connected.
 The total power dissipated by the load is the ALGEBRAIC
SUM of the two indications.
Blondel Theorem
Blondel theory states that total power is measured
with ONE LESS wattmeter than the number of
WIRES.
1-P 2-W
1 Wattmeter
1-P 3-W
3-P 3-W
2 Wattmeters
2 Wattmeters
3-P 4-W
3 Wattmeters
37
vcn
vca
120o
120o
vbc
n
van
120o
vab
vbn
38
a
b
vab
van
c
vbn
vbc
vca
Four - Wire
Three - Phase
System
vcn
n
Vl-n = 120 / 277 Volts
Vl-l =  3
* Vl-n
Vl-l = 208 / 480 Volts
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A
a
AC
Source
b
Wa
+
V
A
Wb
+
V
van
c
vbn
A
Three Wattmeter Method
+
V
vcn
n
Wc
Four - Wire
Three - Phase
Load
+
PT =  W a + W b + W c
40
41
Three-Phase Four-Wire System
 The three meters use the FOURTH wire as the
common voltage REFERENCE.
 Each meter indicates the PHASE power.
 The TOTAL POWER for the three phases is the
ALGEBRAIC SUM of the three meters.
 In essence, each meter measures a SINGLE
PHASE of the three phase system.
a
vab
vca
Three - Wire
Three - Phase
System
b
vcb
c
42
43
Remember
Blondel’s Theory
. . . total power is measured with ONE LESS
wattmeter than the number of WIRES.
44
Three - Phase Three - Wire System With Two Meters
A
a
Wa
+
V
V
AC
Source
vac
vab
b
A
+
Wb
Three - Wire
Three - Phase
Load
+
+
vcb
c
V
A
Two Wattmeter Method
Wc
+
+
PT =  W a + W b
Three-Phase Three-Wire System
The wattmeters used for this connection each
measure the PHASE CURRENTS
The measured voltages are the LINE-TO-LINE
values, NOT Phase Voltage.
Thus the indications on each of the meters IS NOT
the power delivered by the PHASE of the measured
current.
This configuration is a very NON-INTUITIVE
connection!
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