This document discusses the mechanical design of overhead transmission lines. It describes the key components of overhead transmission lines including conductors, supports, insulators, and cross-arms. For conductors, it discusses various material types including copper, aluminum, steel-cored aluminum. For supports it discusses wooden poles, RCC poles, and steel poles. It also outlines different types of insulators used in transmission lines like pin, suspension, strain, and shackle insulators. Finally, it briefly covers the two main types of cross-arms used - line arms and side arms.

1. PRESENTATION OF POWER
ELECTRONICS
In Respect of
Resp: Prof: Dr: Ghulam Mustafa Bhutto Sb
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2. Presentation Topic:
Mechanical Design of Overhead
Transmission Lines
By : Ranjeet Kumar ( 13-EL-42 )
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3. 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 . 13-EL-42

4. 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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5. 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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6. (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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7. 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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8. 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 . 13-EL-42

9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. 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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18. 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 .13-EL-42

19. 13-EL-42