OHTL

ELECTRIC NETWORKS

COMPARISON BETWEEN DC & AC NETWORKS

TYPES OF CONDUCTOR “CLASSIFICATION”

STANDARDS AND CONSTRUCTION

SPECIFICATION

O.H.T.LOver Head Transmission line

NETWORKSNETWORKS

Electric Networks

Generation

Transmission

Distribution

G

Step up transformer Step down transformer

T.L. D.

Generation “Power station”

The electric power is generated by: Hydraulic power Thermal power Nuclear power Gas Sun Wind …

Source Mechanical

Alternator

Prime mover“Turbine”

Transmission

The generation stations (power plant )are away from consumption centers .

The generated voltage is raised to high voltage ( 750 kV ) by step up transformer .

The generated power should be transmitted through the Transmission Network line :

a. Overhead conductor for Medium voltage , High voltage and Extra high voltage (ACSR-AAAC-AACSR)

b. Under ground Cables for Medium voltage , High voltage and Extra high voltage .

Distribution

To deliver power to the consumers the voltage is reduced to Low voltage 0.4 kV.

Distribution Networks :

a. Overhead conductor in urban areas ( ACSR , AAC )

b. Underground cables inside town .

Example Egypt

20 kV Generation

220 kV or 500 kV (depend on network) transmission

66 kV

22 kV – 11 kV

380 V distribution

AC & DC Transmission

DC Advantages: Two wires No inductance - No capacitance Better voltage regulation Better efficiency No skin effect Less voltage drop Less losses No power factor

DC Transmission

DC Disadvantage:

Can not generated at high voltage DC

No stepping up or stepping down

Protective devices are complicated

AC & DC Transmission

AC Advantages: Generated at high voltage Stepping up and stepping down Protection devices are less complicated

AC Disadvantage: Three wires system Effect of skin Losses R, C, L (Losses).

Conclusion

There are two main applications for Dc transmission Connection between two grids which have two

different frequencies. Point to point transmission “Egypt – Libya”

AC transmission is cheaper than DC transmission.

Type of conductor “Classification”

O.H.T.L. can be made of different types of materials: Copper and Aluminum

Specific weight of Copper 8.9 kg/m3 Specific weight of Aluminum 2.7 kg/m3 So 8.9/2.7 = 3.3 Aluminum is lighter 3 times than Copper

For economic wise we use aluminum conductor because of low price and light weight.

Copper Aluminum

Better tensile strength Cheaper

Better conduction Lighter

Different type for OHTL

O.H.T.L.

Ground wire

AAC AAAC ACSR AACSRHard

DrawnCopper

ABCCable

AAC (All Aluminum Conductor)

In Egypt H14 1. These conductors are formed by stranded

aluminum wires .

2. All the wires have the same nominal diameter .

3. Main applications : Low Voltage lines Low span application (30-50mt)

AluminumH14

span

Standards

IEC International Electro-technical commission

IEC 60889, IEC 61089

BS EN 60889, BS EN 50182

Resistivity at 20 0C 28.264 (61% IACS)IACS: International Annealed Copper Standards

Density 2.703 kg/dm3

Coefficient of linear expansion 23 * 10-6 1/C

Constant mass temperature coefficient of resistance at 20 0C = 0.00403 1/C

AAAC (All Aluminum Alloy Conductor)

we add 0.5% si 0.6% mg

Tensile strength will be approx. double of AAC

Long span application

Medium, high, extra high voltage line

Electric conductivity is approx. 15% lower than AAC

AAAC

span

AAAC Standards

IEC 60104 – IEC 61089 BS EN 50183 – BS EN 50182 ASTM 398

ASTM (American Society for Testing and material)

Classification of AAAC According to IEC 60104 Type A and Type B

Type A: higher tensile strength and lower conductivity than type B

According to BS EN 50183: there are 6 types according to the country.

Density at 20 0C 2.703 kg/dm3

Coefficient of linear expanse 23*10-6 1/CConstant-mass temperature coefficient of resistance at 20 0C 0.00361 1/C

ACSRAluminum conductor steel reinforced1. These conductors are formed by stranded wires the

core are made of galvanized steel and the external layer of aluminum .

2. Due to the greater diameter of the conductors electric losses by the by the corona effect are greatly reduced .

3. The diameter of steel and aluminum wires can be alike or different .

4. For large Span (320-350mt) and economical advantages in the installation of Over Head lines .

5. Layer of grease between Aluminum and steel wires .6. Main Application : Medium , High and extra high

voltage

7. Standard: IEC 60888 , 60889 & 61089 BS EN 50189 , BS EN 50182

We use steel core to increase tensile strength Electrically: approximate no effect due to skin effect

Why we use grease?1- In case of 2 different material to avoid chemical reaction between the two material

2- To Avoid friction effect between 2 material due to different linear expansion3- In case of the material to improve conductivity

- StandardsIEC 60889 IEC 60888 IEC 61089BS EN 60889 -BS EN 50189 - BS EN 50182ASTM 498 ASTM 232

Classification of Steel According to IEC 60888:

Regular, high strength, extra high strength

According to BS EN 50189:6 types of steel

Density of steel 7.78 kg/dm3

Coefficient of linear expansion 11.5*10-6 1/C

AACSRAluminum Alloy Steel Reinforced

We obtain the advantage of steel and AAAC

Hard Drawn Copper

“what is the different between hard drawn and soft drawn?”

Density 0.01777 m

Tensile strength 400:415 N/mm2

Standards DIN 48201 BS 7884

SteelGreaseAAAC

ABC Cable (Arial Bundled cable)

Single - duplex – triplex or Qandruplex

Messenger

Lighting

Power

OPGW – Ground wire

Steel: Lightening current and short circuit

OPGW: Optical Grounding Wire to transfer data

SPECIFICATION

State the type of conductor

Standards

Sizes

Code name “ASTM, BS”

Customer requirement

Prepared byEng. Waleed Abdel Azeem

Approved byEng. Mohamed Farrag