Electrical power transmission system

© 2016 Department of Electrical Engineering Mehran University of Engineering & Technology15EL
DR. SYED ASIF ALI SHAH
HEC Approved PhD Supervisor
PhD, TUWien-Austria
PROFESSOR
Asif.Shah@faculty.muet.edu.pk
Department of Electrical Engineering
Mehran UET, Jamshoro, Sindh-Pakistan

Mehran University of Engineering & Technology© 2016 Department of Electrical Engineering 15EL
Electrical Power System

Transmission & Distribution Systems
1. Power station
2. Set of transformers
3. Transmission lines
4. Substations
5. Distribution lines
6. Supplementary Equipment
1. Choice of System Voltage
2. Voltage Variations
3. Voltage Drop
4. Reliability
5. Loading Capacity
6. Location and Load Growth
1506.1
5.5
KVAL
E +=

One-Line Diagram

Control Room

Components of Transmission Lines

HVAC & HVDC
The break-even distance

Mass-Impregnated, Non-Draining, paper insulated HVDC cable
HVAC & HVDC

Power Line Conductors
1. Hard Drawn Copper
2. Cadmium Copper Conductor
3. Steel Cored Copper Conductor
4. Copper Weld Conductor
5. Alluminium
6. Hard Drawn Alluminium
7. All Alluminium Conductor
8. All Alluminium Alloy Conductor
9. Alluminium Conductor Steel
Reinforced (ACSR), (ACCC)

1. Cost
2. Life
3. Brittle
4. Weight
5. Resistance
6. Power loss
7. Tensile Strength
8. Low specific-gravity
9. Temerature Co-efficient
10. Shorter Sag
1. Hard Drawn Copper
2. Cadmium Copper Conductor
3. Steel Cored Copper Conductor
4. Copper Weld Conductor
5. Alluminium
6. Hard Drawn Alluminium
7. All Alluminium Conductor
8. All Alluminium Alloy Conductor
9. Alluminium Conductor Steel
Reinforced (ACSR), (ACCC)

Economic Voltage for Transmission of Power
E = Transmission voltage (KV) (L-L).
L = Distance of transmission line in KM
KVA=Power to be transferred
1506.1
5.5
KVAL
E +=

Skin Effect
δ = √ (2 ρ / ω μ), For copper ρ = 1.7 ×10−8
Ωm and
μ = 4π ×10−7
N/A2
.
Thus δ = 160/√ω mm = 64/√f mm.
@ 1 GHz, δ = 2.1 μm. @1 kHz, δ = 2 mm. @ 50Hz, δ = 9.05mm.
Frequency Type of Material
Dia of Conductor Shape of Conductor
Permeability

Aluminum Conductor Steel Reinforced (or ACSR)
high-capacity, high-strength stranded cable
Outer strands are made from aluminum:
1.Excellent conductivity
2.Low weight
3.Low cost
Center strand(s) is of steel for the strength required to support the weight
without stretching the aluminum
Total number of strands = 1 + 3n (1+n) → n= number of layers
Total dia. of conductor = (1+2n) d → d= dia of single conductor

Aluminum Conductor Composite
Reinforced (ACCR)
More amps on the same size

Galloping
 Transmission lines are arranged in multi-conductors per phase
 Wind-induced vibrations?
 Low-frequency, high-amplitude oscillation caused by a steady wind
Spacers and Dampers
Vibrations On Conductors

Spacers and Dampers
A device to cut down the cable whistling in moderate winds and stop the conductors from
hitting one another in strong winds. Obviously the conductors it braces must all be
carrying the same supply phase.

Transmission Line Supports
Functional Requirements
1.Voltage
2.Number of circuits
3.Type of conductor
4.Type of insulators
5.Future addition of new circuits
6.Tracing of transmission line
7.Selection of tower sites
8.Selection of rigid points
9.Selection of height for each tower
Loading Cases
1.Dead load of tower
2.Dead load of conductors etc
3.Snow on conductors etc
4.Ice load on the tower itself
5.Erection & maintenance load
6.Wind load on tower
7.Wind load on conductors etc
8.Conductor tensile forces
9.Earthquake forces

Voltage Level Clearance to Ground
less than 66kV 20 feet (6.1m)
66kV to 132kV 21feet (6.4m)
132kV to 220kV 22feet (6.7m)
greater than 220kV 23feet (7.0m)
Ground Clearance
Main Requirements
1.Low Cost
2.Longer Life
3.Economical to Maintain
4.Ground Clearance
5.Lighter in weight
6.High Mechanical Strength
7.Accessible

Timber:
1.Best when the tower to be erected
2.Durability is largely affected by many natural factors
3.Usage of timber as construction material is out dated
Concrete:
1.Height is restricted
2.Concrete cannot withstand tensile stress developed by pulling of cables
3.Can not be transported conveniently
Steel:
1.Can be erected as high as up to 200 meters
2.Can be assembled at site
3.Has less dead weight which facilitate the erection

1. Wooden Poles (A, H, T)
2. Reinforced concrete Poles (11 kV, 22kV , 33
kV )
3. Tubular poles (33 kV)
4. Latticed poles (33 kV)
5. Girders (33 kV)
6. Rails (66 kV, H Frame)
7. Towers (Narrow or Broad Base Type)
Types

4321 hhhhH +++=
Height of Tower
h1 = Minimum permissible ground clearance
h2 = Maximum sag
h3 = Vertical spacing between conductors
h4 = Vertical clearance between earth wire
and top conductor

Dr. Syed Asif Ali Shah
PhD, TUWien-Austria
PROFESSOR
Asif.Shah@faculty.muet.edu.pk
HEC Approved PhD Supervisor
Department of Electrical Engineering
Mehran UET, Jamshoro, Pakistan
Thank You
Questions are welcome

• Tower height
• Base width
• Top damper width
• Cross arms length
Typical 500 KV Tower Structure

Spacing and Clearances
Ground Clearances
KCL *305.0182.5 +=





 −
=
33
33V
KWhere-
S.No. Voltage level G. clearance(m)
1. ≤33 KV 5.20
2. 66 KV 5.49
3. 132KV 6.10
4. 220 KV 7.01
5. 500 KV 8.84

Clearance for Power Line Crossings
 Crossing over rivers:
• 3.05m above maximum flood level.
 Crossing over telecommunication lines
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

 Spacing Between Conductor(Phases)
1) Mecomb's formula
1) VDE formula
S
W
D
VcmSpacing 010.43048.0)( * +=
Where-
V= Voltage of system in KV
D= Diameter of Conductor in cm
S= Sag in cm
W= weight of conductor in Kg/m
2000
5.7)(
2
VScmSpacing +=
Where-
S= Sag in cm

 Still's formula



++=
8.27
2
*814.108.5)(
l
VcmSpacing Where-
l = Average span length(m)
 NESC formula
2
681.3*762.0)(
L
SVcmSpacing ++=
Where-
S= Sag in cm
L= Length of insulator string in cm

 Swedish formula
EScmSpacing *7.05.6)( +=
Where-
E= Line Voltage in KV
S= Sag in cm
 French formula
5.1
0.8)(
E
LScmSpacing ++=
Where-
E= Line Voltage in KV
S= Sag in cm
L= length of insulating string(cm)

SYSTEM
VOLTAGE
TYPE OF TOWER Vertical spacing of
conductors(mm)
Horizontal spacing of
conductors(mm)
66 kV
SINGLE
CIRCUIT
A(0-2°) 1080 4040
B(2-30°) 1080 4270
C(30-60°) 1220 4880
DOUBLE
CIRCUIT
A(0-2°) 2170 4270
B(2-30°) 2060 4880
C(30-60°) 2440 6000
132 KV
SINGLE
CIRCUIT
A(0-2°) 4200 7140
B(2-30°) 4200 6290
C(30-60°) 4200 7150
D(30-60°) 4200 8820
DOUBLE
CIRCUIT
A(0-2°) 3965 7020
B(2-15°) 3965 7320
C(15-30°) 3965 7320
D(30-60°) 4270 8540

220 kV
SINGLE CIRCUIT A(0-2°) 5200 8500
B(2-15°) 5250 10500
C(15-30°) 6700 12600
D(30-60°) 7800 14000
DOUBLE CIRCUIT A(0-2°) 5200 9900
B(2-15°) 5200 10100
C(15-30°) 5200 10500
D(30-60°) 6750 12600
500 KV
SINGLE CIRCUIT A(0-2°) 7800 12760
B(2-15°) 7800 12760
C(15-30°) 7800 14000
D(30-60°) 8100 16200

System Voltage Level Broad Gauge
Inside station limits(m) Out side station
limits(m)
≤ 66 KV 10.3 7.9
132 KV 10.9 8.5
220 KV 11.2 8.8
400 KV 13.6 11.2
Tracks electrified on 25 kV A.C. system
Tracks electrified on 1,500 volts D.C. system
System Voltage Level Broad Gauge Meter & Narrow Gauge
Inside station
limits(m)
Out side
station
limits(m)
Inside
station
limits(m)
Out side
station
limits(m)
≤66 KV 10.3 7.9 9.1 6.7
132 KV 10.9 8.5 9.8 7.3
220 KV 11.2 8.8 10.0 7.6
400 KV 13.6 11.2 12.4 10.0

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
Crossing over rivers:
3.05m above maximum flood level.
Crossing over telecommunication lines
Voltage Level Minimum Clearance(mm)
≤33 KV 2440
66KV 2440
132 KV 2740
220 KV 3050
400 KV 4880

 Single circuit Tower/ double circuit Tower
 Length of the insulator assembly
 Minimum clearances to be maintained between ground conductors, and
between conductors and tower
 Location of ground 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
KCL *305.0182.5 +=





 −
=
33
33V
K

Vertical distance between the point where the line is joined to the tower and the
lowest point on the line
T is a tension of the conductor in Kg
W is a weight of the conductor
L is a span length
Unequal supports:
Sag D1 & D2 will be worked out by formula
D1 = ( W X1
2
/27),
D2=(W X2
2
/27)
where,
X1 = (1/2)+(Th/WL)
X2 = (1/2) (Th/WL)
where h= difference in height of supports.
Sag and Span
Span, Tension, Weight, Wind and Climate

Sag and Tension Calculation
 Parabolic formula:  Catenary formula:
Span >300 mSag & TensionSpan ≤300 m

Wind and Ice Loading
Wind pressure in lbs/ft^2 is calculated using
Pw = 0.00256*(Vw)^2
Vw = Wind speed in miles per hour
Wind load per unit length is equal to the wind pressure multiplied by the
conductor diameter.
Using the same units, Fw comes out in lbs/ft
LI = Pw * (Dc + 2t)/12
Dc = conductor diameter (inches)
t = ice thickness (inches)
Suggestion: Reference:
1. Wadhwa C. L., "Electrical Power Systems," Second Edition, John Wiley & Sons, 1991
Reference 1 Chapter 7 Mechanical Design of Transmission Lines includes a good treatment of sag,
including wind, ice, conductor bundles.

Transmission Line Insulators
Disc-Type Insulators
Can be connected together in strings to accommodate the requirements of any transmission
voltage. They are usually bell shaped, and have mechanisms on the top and bottom for
connecting.
Pin-Type Insulators
Are generally designed for use on lower range of transmission voltages. They are
mounted on poles or cross arms using an insulator pin, made up of metal or wood.
Pin insulators are always designed to support a conductor upright or vertical on top.
1.To support conductors and attach them to structures
2.To electrically isolate conductors from other components on a transmission line
The second purpose is very important to operation since without some form of insulating
material, electrical circuit cannot operate.
To be able to isolate conductors, insulators must be made of materials that offer a great
deal of resistance to the flow of electricity. Porcelain is one of the most highly used
insulator type along with glass and other synthetic materials.

Shackle-Type Insulators
These are mostly applied to support line strain (tension), such as at changes of transmission
line direction
Strain-Type Insulators
A stain insulator is an insulator generally of elongated shape, with two transverse
holes or slots. It is mainly used on the guy wire structure to balance the tension
strength and also provide the insulating.
1.To support conductors and attach them to structures
2.To electrically isolate conductors from other components on a transmission line
The second purpose is very important to operation since without some form of insulating
material, electrical circuit cannot operate.
To be able to isolate conductors, insulators must be made of materials that offer a great deal
of resistance to the flow of electricity. Porcelain is one of the most highly used insulator
type along with glass and other synthetic materials.

1. Pin Type
2. Suspension/Disc Type
3. Strain Type
4. Sheckle Type

Underground Power Transmission

UNDERGROUND CABLES
• Since the loads having the trends towards growing density. This requires the
better appearance, rugged construction, greater service reliability and
increased safety
• An underground cable essentially consists of one or more conductors
covered with suitable insulation and surrounded by a protecting cover
• The interference from external disturbances like storms, lightening, ice, trees
etc. should be reduced to achieve trouble free service
• The cables may be buried directly in the ground, or may be installed in ducts
buried in the ground

UNDERGROUND CABLES
The underground cables have several advantages such as,
Better general appearance
Less liable to damage through storms or lighting
Low maintenance cost
Less chances of faults
Small voltage drops
Disadvantage:Disadvantage:
1)Insulation problems
2)Greater installation cost

UNDERGROUND CABLES

UNDERGROUND CABLES
• Core or Conductor
A cable may have one or more than one core depending upon the type of
service for which it is intended. The conductor could be of aluminum or copper
and is stranded in order to provide flexibility to the cable.
• Insulation
The core is provided with suitable thickness of insulation, depending upon the
voltage to be withstood by the cable.
• Metallic Sheath
A metallic sheath of lead or aluminum is provided over the insulation to protect
the cable from moisture, gases or other damaging liquids

UNDERGROUND CABLES
Bedding
Bedding is provided to protect the metallic sheath from corrosion and from
mechanical damage due to armoring. It is a fibrous material like jute or hessian
tape.
Armoring
Its purpose is to protect the cable from mechanical injury while laying it or
during the course of handling. It consists of one or two layers of galvanized
steel wire or steel tape.
Serving
To protect armoring from atmospheric conditions, a layer of fibrous material is
provided.

UNDERGROUND CABLES
1) High resistivity
2) High dielectric strength
3) Low thermal co-efficient
4) Low water absorption
5) Low permittivity
6) Non – inflammable
7) Chemical stability
8) High mechanical strength
9) High viscosity at impregnation temperature
10) Capability to with stand high rupturing voltage
11) High tensile strength and plasticity
PROPERTIES OF INSULATING MATERIALS

TYPES OF MATERIALS USED FOR INSULATION
1) Rubber
2) Vulcanized India rubber
3) Impregnated paper
4) Silk and cotton
5) Enamel insulation
6) Polyvinyl chloride
7) Varnished cambric
UNDERGROUND CABLES

INSULATING MATERIALS FOR CABLES
• Rubber
It can be obtained from milky sap of tropical trees or from oil products.
It has the dielectric strength of 30 KV/mm.
Insulation resistivity of 10 exp 17 ohm.cm
Relative permittivity varying between 2 and 3.
They readily absorbs moisture, soft and liable to damage due to rough
handling and ages when exposed to light.
Maximum safe temperature is very low about 38 C
• Vulcanized India Rubber
It can be obtained from mixing pure rubber with mineral compounds i-e zinc
oxide, red lead and sulphur and heated upto 150 C.
It has greater mechanical strength, durability and wear resistant property.
The sulphur reacts quickly with copper so tinned copper conductors are used.
It is suitable for low and moderate voltage cables.

Mehran University of Engineering & Technology© 2016 Department of Electrical Engineering 15EL© ng
• Impregnated Paper
 This material has superseded the rubber, consists of chemically pulped
paper impregnated with napthenic and paraffinic materials.
 It has low cost, low capacitance, high dielectric strength and high
insulation resistance.
 The only disadvantage is the paper is hygroscopic, for this reason paper
insulation is always provided protective covering.
• Varnished Cambric
 This is simply the cotton cloth impregnated and coated with varnish.
 As the varnish cambric is also hygroscopic so need some protection.
 Its dielectric strength is about 4KV / mm and permittivity is 2.5 to 3.8.
• Polyvinyl chloride (PVC)
 This material has good dielectric strength, high insulation resistance and
high melting temperatures.
 These have not so good mechanical properties as those of rubber.
 It is inert to oxygen and almost inert to many alkalis and acids.

XLPE Cables (Cross Linked Poly-Ethene)
 This material has temperature range beyond 250 – 300 C
 This material gives good insulating properties
 It is light in weight, small overall dimensions, low dielectric constant
and high mechanical strength, low water absorption.
 These cables permit conductor temperature of 90 C and 250 C under
normal and short circuit conditions.
 These cables are suitable up to voltages of 33 KV.
A cable may have one or more than one core depending upon the type of service
Single Core, Two Core, Three Core or Four Core

1. Low Tension or Voltage (L.T.) Cable (operating Voltage up to 1 kV)
2. High Tension or Voltage (H.T) Cable (operating voltage up to 11 kV)
3. Super Tension or Voltage (S.T) Cable (operating voltage Up to 33 kV)
4. Extra High Tension or Voltage (E.H.T.) Cable (operating Voltage up to 66kV)
5. Extra Super Tension or Voltage Cable (operating voltage up to 132 kV)
UNDERGROUND CABLES

TYPES OF CABLES
Oil filled cables
(a) Single core oil filled cables used up to 132 kV
(b) Three core oil filled cables used up to 66 kV
Gas pressure cables
(a)External pressure cables
(b) Internal pressure cable
(i) High pressure gas filled cable
(ii) Gas cushion cable
(iii) Impregnated pressure cable
UNDERGROUND CABLES

2. Screened Cables
• These can be used up to 33kv but in certain
cases can be extended up to 66kv
• These are mainly of two types
 H-type and
 S.L type cables
a. H-TYPE Cables:
• Designed by H. Hochstadter.
• Each core is insulated by layer of impregnated paper.
• The insulation on each core is covered with a metallic screen which is
usually of perforated aluminum foil.
• The cores are laid in such a way that metallic screen make contact with one
another.
• Basic advantage of H-TYPE is that the perforation in the metallic screen
assists in the complete impregnation of the cable with the compound and
thus the possibility of air pockets or voids in the dielectric is eliminated.
• The metallic screen increase the heat dissipation power of the cable.
UNDERGROUND CABLES

b. S.L - Type: (Separate Lead)
• Each core insulation is covered by its own lead sheath.
• It has two main advantages, firstly the separate sheath minimize the
possibility of core-to-core breakdown. Secondly the, bending of cables
become easy due to the elimination of over all sheath.
• The disadvantage is that the lead sheaths of S.L is much thinner as
compared to H-Type cables, therefore for greater care is required in
manufacturing.
UNDERGROUND CABLES

• In these cables pressure is maintained above atmosphere either by oil or by gas
• Gas pressure cables are used up to 275KV
• Oil filled cables are used up to 500KV
• Oil Filled Cables
• Low viscosity oil is kept under pressure and fills the voids in oil impregnated
paper under all conditions of varying load
• There are three main types of oil filled cables
a. Self-contained circular type
b. Self-contained flat type
c. Pipe Type cables
UNDERGROUND CABLES

UNDERGROUND CABLES

Pipe Type Cable
Sheath Channel Oil Filled 3-Core Oil filler Cable
UNDERGROUND CABLES

LAYING OF UNDERGROUND CABLES
a. Direct Laying
b. Draw in system
c. Solid system
Direct Laying
• This method is cheap and simple and is most likely to be used in practice.
• A trench of about 1.5 meters deep and 45 cm wide is dug.
• A cable is been laid inside the trench and is covered with concrete material or
bricks in order to protect it from mechanical injury.
• This gives the best heat dissipating conditions beneath the earth.
• It is clean and safe method
Disadvantages
• Localization of fault is difficult
• It can be costlier in congested areas where
excavation is expensive and inconvenient.
• The maintenance cost is high.

• Minimal visual impact
• Low EMF
• No corona discharge and RI
• No bush fire problems
• Minimal lightning problems
• High level of personnel and public safety
• Good working conditions
• No effect of snow, rain, wind, dust, smoke or fog, ice storms, Tornadoes
• Difficult to be stolen
• Low maintenance costs, land use minimized
• Value of land and buildings unaffected
• High reliability and availability
UNDERGROUND CABLES

• Outage time, locate fault and repair(OH one day, UG 7-10 days)
• Fault location instantaneous, can have longer repair time
• Continuous trench required (sensitive areas, directional boring)
• Soil thermal conditions modified
UNDERGROUND CABLES

New York City: No overhead since 1890’s
Singapore: 100% underground
Netherlands: Distribution 100%
Belgium: Ban on OH Lines since 1992
Denmark: Replaced six 132 kV OH lines with two new 400 kV UG cables
in 1997 and 1999
France: December 1999 storms has caused many blackouts-new policy
25% HV lines are UG
UNDERGROUND CABLES

SUBSTATIONS

SUBSTATIONS
Classifying criterion:
 Primary voltage
 Secondary voltage
 Location
 Transformer type
 Primary breaking device type
 Secondary switching device type
Elements of indoor and outdoor substations:
 Primary breaking devices
 Transformer and its secondary switching device
 Switchgear lineup
 Instrument transformers
 Relays
 Meters & instruments
 Transducers & SCADA
 Cables & bus ducts
 Control & communication wires/cables

SUBSTATIONS
Types of substations:
 Transmission
 Terminal
 Transformer
 Distribution
 Unit
 Collector
Main functions of substations:
Transfer of power in a controlled manner as well as to make it possible to perform
the necessary switching operations in the grid (energizing and de-energizing of
equipment and lines) and provide the necessary monitoring, protection and control
of circuits under its control and supervision.
A substation is a high-voltage electric system facility. It is used to switch
generators, equipment, and circuits or lines in and out of a system. It is also used to
change AC voltages from one level to another, and/or change alternating current to
direct current or direct current to alternating current. Some substations are small
with little more than a transformer and associated switches. Others are very large
with several transformers and dozens of switches and other equipment.

SUBSTATIONS
Transmission substations:
Connects two or more transmission lines. The simplest case is where all
transmission lines have the same voltage. In such cases, the substation contains
high-voltage switches (and or circuit breakers) that allow lines to be connected or
isolated for fault clearance or maintenance. A transmission station may have
transformers to convert between two transmission voltages, voltage control
devices such as capacitors, reactors or Static VARs and equipment such as phase
shifting transformers to control power flow between two adjacent power systems.
Terminal substations:
A facility that forms a strategic node point in an interconnected electricity
transmission system. A terminal substation fulfills either or both roles:
1)Provides a connection point where transmission lines of the same voltage may
be joined to enable an electricity supply to be established to a new demand center.
It is a bulk supply point in the electrical grid, where it may serve a significant area
within metropolitan area and/or some country areas.
1)It is a transformation point where lower voltages are produced to supply the
metropolitan transmission system.

SUBSTATIONS
Transformer substations:
A transformer substation is a point where the transmission voltage level is
stepped down to the sub-transmission voltage level. The latter voltage is then
either used to feed a distribution substation to further reduce the voltage level to
the distribution level or itself used as an input to distribution transformers (e.g.,
33 kV/ 440 V or 230 V) i.e. power is tapped from the sub-transmission line for
use in an industrial facility along the way, otherwise, the power goes to a
distribution substation. Thus the major components in such a station will be: one
or two high voltage disconnect switches, one or two power transformers, one or
two medium voltage switchgear lineups with their breakers, instrument
transformers, relays, communication and control networks.
Distribution Substation:
Distribution substations are located near to the end-users. Distribution substation
transformers change the transmission or sub-transmission voltage to lower levels.
From here the power is distributed to industrial, commercial, and residential
customers through distribution transformers, pad mounted, overhead pole
mounted, vault installed, the secondary of which is 440 V or 230 V.

SUBSTATIONS
Unit substations:
A unit substation would typically consist of a load break switch with a set of
power or current limiting fuses, in series with it ,connected to the high voltage
winding of a distribution (or a power transformer), the low voltage winding of the
transformer would be connected to the main circuit breaker plus the feeder circuit
breakers, motor contactors plus disconnect switch and fuses, or load break
switches in the switchgear lineup. Within the lineup, there would be the utility
metering compartment with the current and voltage transformers approved for
utility meter application as well as the user instrument transformers, meters,
protection and control.
Collector substation:
In distributed generation projects such as a wind farm, a collector substation may
be required. It somewhat resembles a distribution substation although power flow
is in the opposite direction, from many wind turbines up into the transmission
grid. Usually for economy of construction the collector system operates around
and the collector substation steps up voltage to a transmission voltage for the grid.

Parallel Connected Power Systems

Parallel connection of two three-phase alternators

Distance
Joining two power plants in parallel
as part of a regional power system

The process of putting the output of a power plant back on-line, when the system
is down during power outages, can be a long and difficult procedure.
The major problem of parallel-connected distribution systems occurs when
excessive load demands are encountered by several power systems in a single
region. If all are operating near their peak power-output capacity, there is no back-
up capability.
The equipment-protection system for each power plant, and also for each
alternator in the power plant, is designed to disconnect it from the system when its
maximum power limits are reached.
When the power demand on one part of the distribution system becomes
excessive, the protective equipment will disconnect that part of the system. This
places an even greater load on the remaining parts of the system. The excessive
load now could cause other parts of the system to disconnect. This cycle continues
until the
entire system is inoperative. No electrical power can be supplied to any part of the
system until most of the power plants are put back in operation.

HVDC
Power transmission and distribution systems are used to interconnect
electrical power production systems and to provide a means of delivering
electrical power from the generating station to its point of utilization.
These interconnections of power production systems are monitored and
controlled, in most cases, by a computerized control center. Such control
centers provide a means of data collection and recording, system
monitoring, frequency control, and signaling. Computers have become an
important means of assuring the efficient operation of electrical power
systems.The transmission of electrical power requires many long, interconnected
power lines, to carry the electrical current from where it is produced
to where it is used.

HVDC
An alternative to transmitting AC voltages for long distances is high-voltage direct
current (HVDC) power transmission. HVDC is suitable for long-distance overhead
power lines, or for underground power lines.
Because of its fewer power losses, DC power lines are capable of delivering more
power per conductor than equivalent AC power lines
HVDC is even more desirable for underground distribution. The primary
disadvantage of HVDC is the cost of the necessary AC-to-DC conversion
equipment.
HVDC systems have been designed for transmitting voltages in the range of 600
kV. The key to the future development of HVDC systems may be the production of
solid state power conversion systems with higher voltage and current rating.
With a continued developmental effort, HVDC play a more significant role in
future electrical power transmission systems.

HVDC

HVDC
Mass-Impregnated, Non-Draining, paper insulated HVDC cable

HVDC
Germany
Sweden

Inductance of Conductors

Power System Planning
Conduits
Hollow tubes running from manhole to manhole in an underground transmission or
distribution system. They can contain one or more ducts. They can be made of plastic
(PVC), fiberglass, fiber, tile, concrete, or steel. PVC and fiberglass are most
commonly used.
Manholes
Opening in the underground duct system which houses cables splices and which
cable men enter to pull in cable and to make splices and tests. Also called a splicing
chamber or cable vault.

Electrical power transmission system

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