Electrical power transmission system

© 2016 Department of Electrical Engineering Mehran University of Engineering & Technology15EL

DR. SYED ASIF ALI SHAHHEC Approved PhD Supervisor

PhD, TUWien-AustriaPROFESSOR

[email protected] of Electrical Engineering

Mehran UET, Jamshoro, Sindh-Pakistan

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

Electrical Power System


Transmission & Distribution Systems

1. Power station2. Set of transformers3. Transmission lines4. Substations5. Distribution lines6. Supplementary Equipment

1. Choice of System Voltage2. Voltage Variations3. Voltage Drop4. Reliability5. Loading Capacity6. Location and Load Growth

1506.15.5 KVALE

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One-Line Diagram

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Control Room


Control Room


Control Room


Control Room


Control Room


Control Room


Control Room


Control Room


Control Room


Control Room


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)







5. Alluminium








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





5. Alluminium







Economic Voltage for Transmission of Power

E = Transmission voltage (KV) (L-L). L = Distance of transmission line in KM KVA=Power to be transferred1506.1

5.5 KVALE


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 MaterialDia of Conductor Shape of ConductorPermeability



Aluminum Conductor Steel Reinforced (or ACSR) high-capacity, high-strength stranded cable

Outer strands are made from aluminum: 1.Excellent conductivity2.Low weight3.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 layersTotal 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 Groundless 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




TOWER MATERIALS :(a) Timber:Temporary purpose when the tower to be erected, timber is the bestmaterial. The durability of timber is largely affected by many natural factors and henceusage of timber as construction material is out dated.(b) Concrete:Comparatively durable cost of construction is less.Disadvantages :(1) Height is restricted.(2) Large height(3) Concrete cannot withstand tensile stress which are developed dueto the pulling of cables.

Timber:1.Best when the tower to be erected2.Durability is largely affected by many natural factors 3.Usage of timber as construction material is out dated

Concrete:1.Height is restricted2.Concrete cannot withstand tensile stress developed by pulling of cables3.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

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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 ShahPhD, TUWien-Austria

[email protected] Approved PhD Supervisor

Department of Electrical EngineeringMehran UET, Jamshoro, Pakistan

Thank YouQuestions 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

33VKWhere-

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 linesMinimum 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

SWDVcmSpacing 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

20005.7)(

2VScmSpacing Where-


S= Sag in cm



Still's formula

8.27

2

*814.108.5)(l

VcmSpacing Where-

l = Average span length(m)

NESC formula

2681.3*762.0)( LSVcmSpacing

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

5.10.8)( ELScmSpacing

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 levelKCL *305.0182.5

33

33VK






Economic Voltage for Transmission of Power

E = Transmission voltage (KV) (L-L). L = Distance of transmission line in KM KVA=Power to be transferred1506.1

5.5 KVALE


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 KgW is a weight of the conductor L is a span length

Unequal supports:Sag D1 & D2 will be worked out by formulaD1 = ( 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)^2Vw = 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/ftLI = Pw * (Dc + 2t)/12Dc = conductor diameter (inches)t = ice thickness (inches)

Suggestion: Reference:1. Wadhwa C. L., "Electrical Power Systems," Second Edition, John Wiley & Sons, 1991Reference 1 Chapter 7 Mechanical Design of Transmission Lines includes a good treatment of sag, including wind, ice, conductor bundles.


Transmission Line Insulators

Disc-Type InsulatorsCan 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 InsulatorsAre 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 structures2.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 InsulatorsThese are mostly applied to support line strain (tension), such as at changes of transmission line direction

Strain-Type InsulatorsA 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 structures2.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



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 problems2)Greater installation cost


UNDERGROUND CABLES


UNDERGROUND CABLES

• Core or ConductorA 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.

• InsulationThe core is provided with suitable thickness of insulation, depending upon the voltage to be withstood by the cable.

• Metallic SheathA metallic sheath of lead or aluminum is provided over the insulation to protect the cable from moisture, gases or other damaging liquids


UNDERGROUND CABLES

BeddingBedding 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.

ArmoringIts 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.

ServingTo 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

• RubberIt 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.cmRelative 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 RubberIt 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


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 cablesa. Self-contained circular typeb. Self-contained flat typec. 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 Layingb. Draw in systemc. 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 methodDisadvantages• 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


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


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 CollectorMain 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 thetransformer 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.


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


UNDERGROUND CABLES


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 theentire 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 interconnectelectrical power production systems and to provide a means of deliveringelectrical 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, interconnectedpower lines, to carry the electrical current from where it is producedto 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


HVDC


HVDC


Inductance of Conductors


Power System Planning

ConduitsHollow 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.

ManholesOpening 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.


Dr. Syed Asif Ali ShahPhD, TUWien-Austria

[email protected] Approved PhD Supervisor

Department of Electrical EngineeringMehran UET, Jamshoro, Pakistan

Thank YouQuestions are welcome