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PRESENTATION OF POWER ELECTRONICS

In Respect of Resp: Prof: Dr: Ghulam Mustafa Bhutto Sb

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Presentation Topic: Mechanical Design of Overhead Transmission Lines

By : Ranjeet Kumar ( 13-EL-42 )

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Introduction To OVER HEAD T/M Line

• Universally Adopted .

• Subjected by Stormy weather conditions & external interferences .

• The successful operation of Overhead T/M line depends to great extent on its mechanical design .

• In general overhead line should have great Mechanical Strength .

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An Overhead T/M Line has Following Components :

• Conductors( Carry Power from Sending end station to receiving end station )

• Supports( Provide Suport to Conductors & keep those @ suitable level above the ground )

• Insulators( Provide Electrical Isolation to Poles )

• Cross-Arms( These provide Support to the Insulators )

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CONDUCTORS( Types of Conductors )

(1) COPPER Conductor : ( 97.4 % ) • High conductivity + Greater tensile strength .• Also called Ideal Conductor for T/M .• Reason to it’s high conductivity .• Costly & Non-availability for T/M .

(2) STEEL CORE COPPER CONDUCTOR (SCCC) :• Steel is used in the center surrounded by the copper conductors .• Tensile strength + Flexibility increases . • High cost , Low Availability .

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(3) CADMIUM COPPER CONDUCTOR ( CCC ) : ALLOY OF CD + CU . TENSILE STRENGTH INCREASES 50% THAN CU ALONE . BUT IT’S CONDUCTIVITY REDUCES 15% . BUT COSTLY , THAT’S Y RARELY USED .

4) ALL ALUMINUM CONDUCTOR ( AAC ) : ( 61% ) ONLY ALUMINUM IS USED . HAS LOW CONDUCTIVITY AS COMPARED TO “CU” . LOW TENSILE STRENGTH BECAUSE OF LIGHT IN WEIGHT . CHEAP

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5) Steel core Aluminum Conductor ( SCAC ) OR Aluminum Conductor Steel Reignforced (ACSR ) To increase tensile strength , Steel is reignforced in Aluminum conductors . Diameter increases & Corona loss is reduced as compare to Cu . Weight = 75% of Cu . Suitable for Transmission Lines .

6) All Aluminum Alloy Conductor ( AAAC ) : Mg + Si with Al Conductor . Provides better tensile strength but less conductivity . Suitable for populated urban areas and populated industrial areas or central areas .

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02) Line Supports• Supporting Structure of T/M Lines consists of Poles &

Towers .• Function of Line Supports are : i) Maintaining proper spacing between conductors . ii) To provide min: ground clearance of conductor &

earth .• Line Supports should have these properties . i) High mechanical strength . ii) Cheap in cost iii) Longer Life iv) Easy availability .

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SOME TYPES OF LINE SUPPORTS :1) WOODEN POLES : ( SUITABLE FOR 11KV )

CHEAPEST AMONG ALL LINE SUPPORTS . CAN BE USED FOR SHORT DISTANCE UPTO 50M T/M OR DISTRIBUTION . HIGHLY INSULATED BECAUSE OF WOOD . THAT’S WHY MOSTLY USED FOR DISTRIBUTION . BUT HAVE SHORTER LIFE TIME & REQUIRES PERIODICAL INSPECTION . TWO TYPES OF WOODEN POLES ARE USED , SHOWN BELOW :I) SINGLE POLE SHAPED II) DOUBLE POLES SHAPED

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2) RCC Poles : Recently have become more popular because of High Mechanical Strength . Have longer lives due to little deterioration . Require little maintenance Also have insulating property . But they are suitable for 11KV . High cost of transportation due to heavy weight .

. 3) Steel Poles : Have good mechanical srength . Possess longer life and can be used for longer distance than wooden poles . Suitable usage is for High Voltage & Extra High Voltage . Double Circuited Steel Poles provide Continuity of Supply during breakdown situation .

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03) Overhead Line Insulators• Overhead Insulators are used to isolate electrically

the conductors from towers .• Also prevent leakage current from conductor to

cross arms .• An Insulator should have properties :

i) High Electrical Resistance .ii) Non-porous .

• Electrical Failure of Insulators occurs due to :i) Puncture ii) Flash over

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Types Of Line Insulators : 01) Pin Type Insulators :• Earliest developed overhead insulator .• used in power network up to 33KV system.• In 11 KV system we generally use one part type insulator .• Beyond 33 KV , Pin Type Insulators become bulky & uneconomical .

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02) Suspension type Insulators :• Consists of number of Porcelain discs , connected in series to form a string . • Used for Voltage > 33 KV .• Each disc is designed for low voltage , say 11KV .• The number of discs used depend upon working voltage .

Suppose for 66 KV working voltage , 6 discs in series will be provided on string .

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03) Strain Type Insulators :• Consists of assembly of suspension type insulators . • Used When there is a dead end or there is a sharp corner in

transmission line .• Used for higher transmission . • Used in parallel arrangement .

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04) Shackle Type Insulators :• Similar to strain type insulators , but used for low

voltage .• 1st these type of insulators were used as Strain

type. Later on these were only used for distribution.• These are single Porcelain material , mounted

horizontally or vertically .

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04) Cross-Arms• Cross arms of transmission tower hold the

transmission conductor.

• The dimension of cross arm depends on the level of transmission voltage, configuration and minimum forming angle for stress distribution.

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Types of Cross-Arms: 01) Line Arms :• Straight line form .• Mounted equally weight distributed to poles .• Used for Short Transmission but Mostly used for

Long Transmission ( Double Circuited Transmission System ) .

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02) Side Arms :• Also called Braced Horizontal arms .

• Three single arms are used on poles , fitted alternatively .

• Used for Single Circuit Transmission .

• Mostly used for Short Transmission .

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