transmissionsystem-130209015254-phpapp01

8/12/2019 transmissionsystem-130209015254-phpapp01

1/23


2/23

IntroductionOverhead linesConductor materials

Types of line supportsConductor configurations , span and spacingInsulator materialsTypes of Insulators


3/23

Electrical energy is generated in large hydro-

electric, thermal and nuclear power stations whichare located far away from the load centres.

This necessitates an extensive power supplynetwork between generating stations and theconsumers loads.

This network is divided into two parts:Transmission system

Distribution system


4/23

The three-phase transmission anddistribution system consists of overhead linesand underground cables. Because of cost consideration , the

transmission system in India is generallyoverhead.The overhead line conductor material shouldhave:

High tensile strengthLow resistivity


5/23

The two most common conductor materials areHard drawn copper and aluminium.

Hard drawn copper has very high conductivitygood tensile strength and weather resistingproperties.


6/23

Aluminium has the following advantages

over copper:

a. Lower costb. Lesser weight

c. Larger diameter

However ,the tensile strength ofaluminium is lower than copper. Therefore an All Aluminium Conductor(AAC)is rarely used except for low voltagedistribution lines of short spans.

C


7/23

ACSR (Aluminium Conductor Steel Reinforced)conductor comprises hard drawn aluminiumwires stranded around a core of single ormultiple strand galvanized steel wire.

Aluminium provides conductivity while steelprovides necessary mechanical strength.

All the transmission lines useACSR conductor.

CSR


8/23

Wooden polesRCC polesSteel tubular polesSteel towers

The supports for an overhead line must be capableof carrying the load due to:

ConductorsInsulatorsWind load on the support itself.


9/23

Made of chemically treated wood.Used for distribution lines especially in areaswhere good quality wood are available.

Very economical but susceptible to decay.To protect from decay,poles have zinc oraluminium cap at the top and Bitumencoating at the bottom.


10/23

Made of reinforced concrete cementStronger than wood poles but more costlyVery long life and need little maintenance

Bulky and heavyWidely used for distribution lines upto 33kVCan be manufactured at site.


11/23

Stepped pole manufactured from a singletube , the diameter being reduced in parallelsteps.More costly than RCC and wood polesHave light weight , high strength to weightratio and long lifeWidely used for lines upto 33kV.


12/23

Used for lines of 66kV and aboveVery long life and high degree of reliabilityCan withstand very severe weather conditions

Overhead HV , EHV , and UHV lines mostlyuse self supporting steel towers.


13/23

A longer span means smaller number oftowers but the towers are taller and morecostly.Higher the operating voltage , greater shouldbe the span.From mechanical consideration , there is amaximum value of span for each conductor

size.Modern high voltage lines have spansbetween 200m and 400m.


14/23

There are different conductor configurationsused in practice.

In most cases flat horizontal or verticalconfigurations are used.

Flat horizontal means lesser tower height but awider right of way.

Vertical configuration means taller tower andincreased lightning hazards.


15/23

There must be adequate spacing betweenconductors so that they do not come withinsparking distance of each other , even whileswinging due to wind.


16/23

To provide necessary clearance betweenconductors and metal works , the conductorsare attached to insulators.Also provides mechanical support for the

conductor.The most suitable materials for insulatorsare:Toughened glass

Porcelain


17/23

It is achieved by rapidly cooling the glassinsulator after shaping and then allowing theinterior to cool slowly.Can withstand great tension.Glass is cheaper than porcelain in simplershapes.Used very rarely

For lines below 25kV with short spans.


18/23

Mechanically stronger than glass

Less affected by changes in temperature

Most commonly used material formanufacturing of insulators.


19/23

Pin type insulatorsSuspension typePost type

Strain insulators


20/23

Small , simple in construction and cheap.

Used on lines upto and including 33kV.

For higher voltages they tend to be moreheavy and costly.


21/23

Used for lines above 33kV.

Also known as disc or string insulators.

Consists of porcelain discs mounted oneabove the other.

The conductor is suspended below the pointof support by an insulator string.

Mechanical stresses are reduced.


22/23

Used for supporting bus bars anddisconnecting switches in sub-stations.In extra high voltage sub-stations , polyconpost insulators are used.Similar to pin insulator but has a metal baseand metal cap so that more than one unit canbe mounted in series.


23/23

Special mechanically strong suspensioninsulatorsSimilar to suspension type insulatorsUsed to take the tension of the conductors atthe line terminations and at portions wherethere is a change in direction of line.

transmissionsystem-130209015254-phpapp01

Documents

Transcript of transmissionsystem-130209015254-phpapp01