Power Systems 2

ELE3015

Lecture 1: Transmission Lines

Transmission Lines: Introduction

• Use to carry electrical power from point of

generation to the point of use.

• Usually over large distances.

• Made with electrical conductors.• Made with electrical conductors.

Transmission Lines: Introduction

• Transmission lines are normally operated at

high voltages to reduce the line current for a

given power level.

• Lower current results in lower I2R losses.• Lower current results in lower I2R losses.

• Lower losses means a more efficient

transmission system that is more economical

for system operators.

Transmission Lines: Introduction• Standard voltage levels (ANSI C84.1)

Transmission Lines: Introduction• Example transmission lines

Transmission Lines: Introduction• Example transmission lines

Transmission Lines: Introduction• Example transmission lines

Transmission Lines: Introduction

• Transmission lines consists

of:

– Three phase conductors

– Insulators to support and

isolate the conductorsisolate the conductors

– Supporting structure which

holds the conductors and

insulators

– Foundation and grounding

– Optional lightning

protection ‘shield’ wires

Transmission Lines: Introduction

• Transmission line basic overview:

Transmission Lines: Conductors

• The conductors carry the actual electric

current.

• They must be of adequate rating to carry the

required power without overheating.required power without overheating.

• For overhead lines they are generally made

primarily of aluminum.

• Underground lines are normally made with

cables and will be considered later.

Transmission Lines: Conductors

• Types of aluminum conductors:

– All Aluminum Conductor (AAC)

• Concentric lay stranded All Aluminum Conductor ( AAC)

is made up of one or more strands of hard drawn 1350 is made up of one or more strands of hard drawn 1350

aluminum alloy.

• AAC has seen extensive use in urban areas where spans

are usually short but high conductivity us required.

• Because of its relatively poor strength to weight ratio,

AAC had limited use in transmission lines and rural

distribution because of long spans utilized

Transmission Lines: Conductors

• Types of aluminum conductors:

– Aluminum Conductor Steel Reinforced(ACSR)

• Aluminum Conductor Steel Reinforced (ACSR) is concentrically stranded conductor with one or more layers of hard drawn 1350-H19 aluminum wire on concentrically stranded conductor with one or more layers of hard drawn 1350-H19 aluminum wire on galvanized steel wire core.

• ACSR conductors combine the light weight and good conductivity of aluminum with the high tensile strength and ruggedness of steel.

• ACSR can therefore provide higher tensions, less sag, and longer span lengths than obtainable with most other types of overhead conductors.

Transmission Lines: Conductors

• Types of aluminum conductors:

– All Aluminum Alloy Conductor (AAAC)

• Concentric lay stranded Aluminum Alloy Conductors

(AAAC) are made out of high strength Aluminum-

Magnesium-Silicon Alloy.Magnesium-Silicon Alloy.

• AAAC has better strength to weight ratio and offer

improved electrical properties, excellent sag-tension

characteristics, and superior corrosion resistance when

compared with ACSR.

• AAAC can be used on the distribution system and for

medium & high voltage transmission lines but is more

expensive than ACSR.

Transmission Lines: Conductors• Examples of available ACSR conductors (Midal Cables)

Transmission Lines: Insulators

• Insulators are used to support and isolate the

conductors from the tower.

• They require both mechanical strength and

excellent electrical insulating properties.excellent electrical insulating properties.

• They are generally made of ceramics or

composite materials.

Transmission Lines: Insulators

• Insulators are used to support and isolate the

conductors from the tower.

• They require both mechanical strength and

excellent electrical insulating properties.excellent electrical insulating properties.

• They are generally made of ceramics or

composite materials.

• They must be rated for the voltage levels they

are required to insulate from.

Transmission Lines: Insulators

• Example ceramic insulator.

Transmission Lines: Insulators

• Ceramic insulators can be chained for higher voltages.

Transmission Lines: Insulators

• Example composite insulator.

Transmission Lines: Insulators

• Example composite insulator.

– Alternating diameter silicone

weather sheds

– Fiberglass insulating rod

– Silicone also serves as rod – Silicone also serves as rod

covering

– Galvanized steel end fitting