ohtl
TRANSCRIPT
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