Downlaod is NOW Allowed (08/06/2016) for more help: email me at zunaib_91@yahoo.com Purpose of Electrical Transmission System Main Parts of Power System One-Line Diagram of Generating Station Main Parts of Generating Station Components of a Transmission Line

1. Concept of Energy Transmission
1

2. Group Members
Madiha
Naeem
Muqadsa
Iftikhar
Zunaib Ali
COMSATS INSTITUTE OF INFORMATION &
TECHNOLOGY, ABBOTTABAD
2

3. Purpose of Electrical Transmission System
The purpose of the electric transmission
system is the efficient interconnection of
the electric energy producing power
plants or generating stations with the
loads.
3

4. Main Parts of Power System
Four Main Parts:
Generation System
Transmission System
Distribution System
Consumer (LOAD)
4

5. Simplified Diagram of Power System
5

6. Generating Station
The commonly used power plants are:
Thermal Power Plant
Nuclear Power Plant
Hydro Power Plant
Gas Turbine Power Plant
Combined Cycle Power Plant
6

7. One-Line Diagram of Generating Station
Fig.1: Simplified Connection Diagram
7

8. Main Parts of Generating Station
Circuit Breaker (CB)
A circuit breaker is an automatically
operated electrical switch, designed to
protect an electrical circuit from damage
caused by faultcurrent or short circuit
Types based on Insulators
Oil Circuit Breaker
Air Circuit Breaker
SF6 Circuit Breaker
Vacuum Circuit Breaker
Fig.2: CB Diagram
8

9. Table.1: Circuit Breaker Description
Type
Medium
Air break Circuit Breaker
Air at atmospheric pressure
Miniature CB.
Air at atmospheric pressure (430-600 ) V
Tank Type oil CB.
Dielectric oil
(3.6 – 12) KV
Minimum Oil CB.
Dielectric oil
(3.6 - 145 )KV
Compressed Air
245 KV, 35000 MVA
(20 – 40 ) bar
up to 1100 KV, 50000 MVA
Air Blast CB.
Voltage, Breaking Capacity
(430 – 600) V– (5-15)MVA
(3.6-12) KV - 500 MVA
12 KV, 1000 MVA
SF6 CB.
SF6 Gas
36 KV , 2000 MVA
145 KV, 7500 MVA
245 KV , 10000 MVA
Vacuum CB.
Vacuum
36 KV, 750 MVA
H.V.DC CB.
Vacuum , SF6 Gas
500 KV DC
9

10. Main Parts of Generation Station…
Disconnect Switch
Provides visible circuit separation and
permits CB maintenance. It can be
operated only when the CB is open i.e. in
no-load condition.
Surge Arrester
Used for protection against lightning and
switching over-voltages. They are voltage
dependent, nonlinear resistors (Varistors).
The arrester provides a low-impedance path
to ground for the current from a lightning
strike or transient voltage and then restores
to a normal operating condition.
10

11. Main Parts of Generation Station…
Current Transformers (CT) and Potential Transformers (PT)
Used to lower the magnitude of the current and voltage to be
measured.
In case of normal meters, to measure current and voltage in a high
voltage circuit at 220kV, properly insulated meters are needed to
withstand that voltage. The meters will be very big for that purpose.
The CT and PT is used to solve this problem. The CT and PT works on
the principle of transformer and lowers the current and/or voltage
at a lower value which can be safely and easily measured.
11

12. 12

13. Components of a Transmission Line
Conductor
Earth wire
Insulator
Transmission
Tower
Wave trap and other hardware(Clamp,
Spacer, Vibration dampers, connectors
etc.
13

14. Design Methodology
• Gather preliminary line design data and available climatic data
• Select reliability level in terms of return period of design
• Calculate climatic loading on components
• Calculate loads related to safety during construction and maintenance
• Select appropriate correction factors, if applicable, to the design components
such as use factor, strength factors related to numbers of components, quality
control, and the characteristic strength.
• Design the components for the above loads and strength.
14

15. Selection of Transmission Voltage
Standard Voltage: 66,110,132, 220, 400 KV
Tolerances - ±10% up to 220 KV & ±5% for 400 KV
Selection
Criterion
of
Economic
Voltage
• Quantum of power to be
evacuated
• Length of line
• Voltage regulation
• Power loss in Transmission
• Initial and operating cost
15

16. Economic Voltage of Transmission of Power
E = Transmission voltage (KV) (L-L).
5 .5
KVA
1 .6
*E
L
150
L = Distance of transmission line in KM
KVA=Power to be transferred
*
16

17. Typical Transmission Voltage Levels
Voltages Level
Range
(KV)
Maximum Length (Miles)
High Voltage
100 to 230
200
Extra High Voltage
230 to 800
400 to 500
Ultra High Voltage
Above 800
1300

18. Types of Towers
Type A Tower (Tangent Tower
with suspension string)
Type B Tower (Small Angle
Tower with tension string)
• Used on straight runs and up to 2° line diversion
• Used for line deviation from 2° to 15°
Type C Tower (Medium Angle
Tower with tension string ).
• Used for line deviation from 15° to 30°.
Type D Tower (Large angle
tower with tension string)
• Used for line deviation from 30° to 60°
Type E Tower (Dead End
Tower with tension string)
• Used for line termination & starting
Suspension Tower (Span
≈ 1000 m)
Transposition Tower
• Used for River crossing, Mountain crossing etc.
• Used for transposition of tower
18

19. Suspension Tower
Transposition Tower
Tension Tower

20. Different Types of Towers
20

21. Selection of Tower Structure
Single circuit Tower/ double circuit Tower
Length of the insulator assembly
Minimum clearances to be maintained between conductors, and between
conductors and tower
Location of earth wire/wires with respect to the outermost conductor
Mid-span clearance required from considerations of the dynamic behavior of
conductors and lightning protection of the line
Minimum clearance of the lowest conductor above ground level
21

22. EHV- Tower
Tower:
• The figure shows a lattice,
steel tower.
Insulator:
• V strings hold four
bundled conductors in
each phase
Conductor:
Foundation and
grounding:
• Each conductor is
stranded, steel reinforced
aluminum cable.
• Steel-reinforced concrete
foundation and grounding
electrodes placed in the
ground
Shield conductors:
• Two grounded shield
conductors protect the
phase conductors from
lightning.
22

23. Tower Design
Tower height
Base width
Top damper width
Cross arms length
Fig. Typical 765 KV Tower Structure
23

24. Height of Tower Structure
Height of tower is determine by-
H
h1
h2
h3
h4
h1=Minimum permissible ground
clearance
h2=Maximum sag
h3=Vertical spacing between conductors
h4=Vertical clearance between earth-wire
and top conductor
24

25. Determination of Base Width
The base width(at the concrete level) is the distance between the centre of
gravity at one corner leg and the centre of gravity of the adjacent corner leg.
A particular base width which gives the minimum total cost of the tower and
foundations
Ryle
Formula
An applied force that causes a structure to turn over
The ratio of base width to total tower height for most towers is generally
about one-fifth to one-tenth.
25
25

26. Spacing and Clearances
Ground Clearances
CL
5.182
Where-
K
0.305 * K
V
33
33
S.No.
Voltage level
Ground clearance(m)
1.
≤33 KV
5.20
2.
66 KV
5.49
3.
132KV
6.10
4.
220 KV
7.01
5.
400 KV
8.84
26

27. Clearance for Power Line Crossings
Crossing over
rivers:
Crossing over
telecommunication lines
• 3.05m above maximum flood level.
• Minimum clearances between the conductors of a
power line and telecommunication wires are
Voltage Level
Minimum Clearance(mm)
≤33 KV
2440
66KV
2440
132 KV
2740
220 KV
3050
400 KV
4880
27

28. Power line Crossing another Power line
System Voltage Level
Clearance(m)
≤ 66 KV
2.40
132 KV
2.75
220KV
4.55
400 KV
6.00
28

29. Spacing Between Conductor(Phases)
Mecomb's formula
WhereSpacing ( cm )
0 . 3048 * V
4 . 010
D
W
S
V= Voltage of system in KV
D= Diameter of Conductor in cm
S= Sag in cm
W= weight of conductor in Kg/m
VDE formula
Spacing ( cm )
7 .5 S
V
2
2000
Where-
V= Voltage of system in KV
S= Sag in cm
29

30. Still's formula
2
Spacing ( cm )
5 . 08
l
1 . 814 * V
Wherel = Average span length(m)
27 . 8
NESC formula
Spacing ( cm )
0 . 762 * V
3 . 681
S
L
2
WhereV= Voltage of system in KV
S= Sag in cm
L= Length of insulator string in cm
30

31. Swedish formula
Where-
Spacing ( cm )
6 .5 S
0 .7 * E
E= Line Voltage in KV
S= Sag in cm
French formula
Where-
Spacing ( cm )
8 .0 S
L
E
1 .5
E= Line Voltage in KV
S= Sag in cm
L= length of insulating string(cm)
31

32. Clearances b/w Conductors
SYSTEM
VOLTAGE
TYPE OF
TOWER
Vertical spacing b/w
conductors(mm)
Horizontal spacing b/w
conductors(mm)
SINGLE
CIRCUIT
132 KV
4500
DOUBLE
CIRCUIT
2060
5550
SINGLE
CIRCUIT
66 kV
1080
4200
7140
DOUBLE
CIRCUIT
3965
7320
32

33. Types of Conductors
•
AAC(All Aluminium Conductor)
•
AAAC(All Alloy Aluminium Conductor)
•
ACSR Conductor(Aluminium Conductor Steel
Reinforced)
Fig. AAC Conductors
Fig. AAAC Conductors
33

34. Table: Technical Data of ASCR Conductors Commonly used in EHV Transmission By Wapda.
Code
Words
Stranding
Aluminum Steel
Conductor Core
Weight Per Km
Aluminum Steel
No/mm
kg/km
No/mm
kg/km
Weight
Complete
Conductor
kg/km
Diameter
Complete Steel
Conductor Core
mm
mm
Cross
Area of
Aluminum
Area of
Complete
Conductor
Rated
Ultimate
Strength
D.C
Resistance
at 200
mm2
mm2
kg
ohm/km
Gopher
6/2.36
1/2.36
72
34.1
106
7.08
2.36
26.25
30.62
980
1.093
Rabbit
6/3.35
1/3.35
145.1
68.8
214
10.05
3.35
52.88
61.69
1875
0.543
Dog
6/4.72
7/1.57
288.1
106.2
394
14.15
4.71
104.98
118.53
3225
0.273
Hare
6/4.72
1/4.72
288.1
136.5
425
14.16
4.72
105
122.5
3225
0.273
Osprey
16/4.465
¼.465
777
121.8
898.8
22.23
4.465
281.9
297.56
6220
0.123
Cuckoo
24/4.62
7/3.08
1116
407.6
15424
27.72
9.24
402.33
454.48
12385
0.072
Zebra
54/3.18
7/3.18
1182
439
1621
28.62
3.18
428.9
484.59
13000
0.0686
Moose
54/3.53
7/3.53
1463
535
1998
31.77
3.53
528.5
597.0
16224
0.0559
Panther
30/3
7/3
588
387
976
21
3
212.1
261.5
9150
0.07311
400kv - 'Moose' ACSR
220kv - 'Zebra' ACSR
132kv - 'Panther' ACSR
Fig. ASCR Conductors
34

35. Selection of Conductor Size
• Mechanical Requirement
• Electrical Requirement
• Tensile Strength(For
Tension)
Mechanical
Requirement • Strain Strength(For
Vibration)
Use vibration damper for vibration control.
35

36. Electrical
Requirement
• Continuous current rating.
• Short time current carrying rating.
• Voltage drop
• Power loss
• Minimum dia to avoid corona
• Length of line
• Charging current
36

37. Continuous Current Rating.
The designated RMS alternating current in amperes which a
conductor will carry continuously in free air without tripping or
exceeding temperature limits.
The normal continuous current rating of line traps is per
manufacturer’s nameplate and based at 40°C ambient temperature.
This current rating can be adjusted for specific ambient
temperature without exceeding the normal allowable
maximum temperature a line trap can withstand.
37

38. Short Time Rating
According to short time rating conductor size is given by-
A
7 . 58 * I F * t
Where A=area of conductor(mm2)
IF= fault current(KA)
t= fault duration(1 sec.)
38

39. Corona
A corona discharge is an electrical discharge brought on by
the ionization of a fluid surrounding a conductor that is
electrically energized.
Visual corona voltage in fair weather condition is given
by-
V
0
21 . 1 m
r (1
0 .3)
r
•
•
•
•
log
n
D
r
V0= corona starting voltage, KV(rms)
r= radius of conductor in cm
D= GMD equivalent spacing b/w conductors in cm
m= roughness factor
= 1.0 for clean smooth conductor
=0.85 for stranded conductor
39

40. INSULATOR
Insulator are required to support the line conductor
and provide clearance from ground and structure.
Insulator material• High grade Electrical Porcelain
• Toughened Glass
• Fiber Glass
Choice of insulator material is govern by availability,
price and ease of maintenance.
Porcelain insulator are largely used in Pakistan.

41. Earth Wire
Earth wire provided above the phase conductor across the
line and grounded at every tower.
• It shield the line conductor from direct strokes
• Reduces voltage stress across the insulating strings during lightning
strokes
Design criterion:
• Shield angle
• 25°-30° up to 220 KV
• 20° for 400 KV and above
•
Earth wire should be adequate to carry very short
duration lightning surge current of 100 KA without
excessive over heating
• Duration should be consider as 200 µ-sec
A
5 I
t
A= Area(in mm2) of cu conductor
I =current in KA
t = Time insecond
• Safe temp rise limited to 300°C
41

42. Mid span clearance:
• Direct distance b/w earth wire and top power conductor.
Following value of mid span clearance should be considered
System voltage
Mid span clearance(m)
≤ 66 KV
3.0
110 KV
4.5
132 KV
6.1
220 KV
8.5
400 KV
9.0
42

43. Tower Grounding
Used to reduce earth wire potential and stress on
insulators at the time of stroke and also for safety
• Tower footing resistance will be 10Ω and
should not be more than 20 Ω under any
condition throughout the year
• Earth resistance depend upon soil
resistivity(general 100 Ω-m)
43

44. Method of Tower Grounding
Buried
Conductor
• One or more conductor are connected to tower
lags and buried in back filled of tower foundation.
• Used where soil resistivity is low
Counterpoise
Wire
• A length of wire/ Strip of 50 m is buried horizontally at depth
of 0.5 m bellow ground. This wire is connected to tower lags.
• Used when earth resistance is very high and soil
conductivity is mostly confined to upper layer)
Rod Pipe
• Pipe/Rod of 3 to 4 m is driven into ground near the
tower and top of rod is connected to tower by suitable
wire/strip
• Used where ground conductivity increase with depth
Treated Earth
Pits
• Pipe/Rod of 3 to 4 m are buried in treated earth pits and
top of rod is connected to tower by suitable wire/strip.
• Used in very high resistivity near tower
44

45. 45