EXPLAIN BASICS WIRING AND OVERHEAD TRANSMISSION & DISTRIBUTION LINE

 

       Basics of Overhead Transmission and Distribution Line

• Introduction :-

                                  Now-a-days electricity has become necessity in our daily life. Electricity generation done in power plants. Generally it is in high voltage. Then this voltages stepped down to a Low voltage by various processes and supplied to the consumers at their places. Electrical wiring is necessary for use of electricity at required place in such a way that safety of human-being is assumed.  There is a one act for wiring, Indian electricity rules for wiring and Electricity supply Act 1956, testing of installation, panel wiring etc.

• Below are the various types of  Wires are explained:-

    Wire are used to conduct electric current in many ways from generating end to receiving ends like, 

1. Overhead Transmission and Distribution Line,
2. Service connection to various consumers,
3. Winding coils of Electrical Machines,
4.  In-house and Industrial Wiring,
5. Underground Cable.

1. Overhead Transmission and Distribution Line :-                 

                       Are power lines for sending large quantities of electricity to far removed places and they are used mainly between power stations and substations, or between substations. The bar wire conductors on the line are generally made of aluminum (either plain or reinforced with steel or sometimes composite materials), though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises.

              Transmission lines are generally classified by Operating Voltage and by its Length of line. 

Overhead Transmission Line by its Operating Voltage are as under,    

•  Low voltage :-  Less than 1000 volts - Used for connection between a residential or  small commercial customer and the utility.  

• Medium Voltage (Distribution) :- between 1000 volts (1 kV) and to about 33 kV - Used for         distribution in urban and rural areas.

• High Voltage (Sub transmission if 33-115kV and transmission if 115kV+) :- between 33 kV and about     230 kV - Used for sub-transmission and transmission of bulk quantities of electric power and connection to very large  consumers.                                                                                                             
• Extra High Voltage (Transmission) :- over 230 kV, up to about 800 kV - Used for long distance,   very  high power transmission.                                                             

• Ultra High Voltage :-  higher than 800 kV

Overhead Transmission Line by its Length as under,

• The transmission lines which have a length less than 50 km are generally referred to as short transmission lines.
• The transmission line having its effective length more than 50 km but less than 150 km is generally referred as medium transmission line.
• A transmission line having a length more than 150 km is considered as a long transmission line.

For more information about Overhead power line you can refer this link, Overhead power line.

• Materials Used for Overhead Transmission Lines:- 

                                       The most common materials are used for Overhead Transmission Lines are Copper, Aluminum, Steel Cored Aluminum, Galvanized Steel and Cadmium Copper. These all are categorized separately by its nature and conductivity. All having unique functions so we will see below how they works and effects.

                                  

                                         Transmission line is an important part of power system. The cost and life of transmission line primarily depend on the material used for making conductors for transmission line. The most important and much  suitable material for conductor of transmission line is copper as it having high conductivity and high tensile strength.

 

                                          Generally for transmission line the material is mostly used is Aluminum. It also having as same as and sufficient conductivity as well. Compare to Copper it is light in weight. Because of low weight of conductor and less in sag. It's only draw back is only its tensile strength. To overcome this drawback of conductor, generally taken in use aluminum conductor such as ACSR ( Aluminum Conductor Steel Reinforced ) conductor.     

• At What Parameters Conductor Should be Selected :-

1. High Conductivity
2. High Tensile Strength
3. Light Weight
4. High Resistance to Corrosion in Weather Conditions
5. High Thermal Stability
6. Low Coefficient of Thermal Expansion
7. Low Cost

• Let's Have a Look of Following Materials Are Used for Transmission Lines:-

1. Copper
2. Aluminum
3. Cadmium - Copper Alloys
4.  Phosphor Bronze
5. Galvanized Steel
6. Steel Core Copper
7. Steel Core Aluminum

                

• Copper ( Cu ) :-  In the most of the electric machines, equipment's for current carrying conductor widely used. Malleability, Weldability and Solder ability are most important properties of Copper.  It having very high resistivity. Temperature coefficient of resistance at 20 degree calciols. Vey high melting point up to 1085 degree calciols. Specific gravity is 8.96 gm/cm^3. It's only limitation is its cost.

• Aluminum :-   The most commonly used material in transmission line is Aluminum. It is the most lightest. Also having sufficient conductivity. The only limitation is it's low tensile strength. To overcome this limitation streel core is used for increase it's tensile strength. ACSR conductor is very popular for high voltage overhead transmission.

• Cadmium - Copper Alloys :-  When cadmium is added to copper, the material becomes more resistant to softening at elevated temperatures. The cadmium copper alloys contains cadmium from 0.6 to 1.2%. The more cadmium that is added, the more heat resistant the material becomes. This small addition of cadmium increase the tensile strength and corrosion resistance. The conductivity of cadmium copper alloys is 90% to 96% of pure copper. It is also used for soldering applications. It is used to joint components in automobiles and truck radiators also in semi-conductor packaging operations.

• Phosphor Bronze :-  Phosphor bronze is an alloy of copper with 3.5 to 10% Tin and Phosphorus. It's a highly-valuable, specialty metal with many positive attributes. This is generally also called as "Phos-Bronze". During melting process, The phosphorus deoxidizing agent is added. It has good strength, toughness, low coefficient of friction and fine grains. Useful to pass through marine atmosphere. Useful in manufacturing of springs and bolts where high resistance fatigue is required. It is used to make electrical contacts. It is corrosion resistance, good in electrical conductivity, it also having excellent elasticity.

• Galvanized Steel :-  Pure Iron and steel gets rusted and corroded in open whether conditions. galvanizing is the process of applying a protective coating to steel or iron. To avoid corrosion, of sheet and wire etc. made of these metals are coated with Zinc. For Zinc coating Hot-dip galvanization is used. In this process the iron or steel in dipped in molten Zinc at a temperature around 449 degree. When exposed to atmosphere, the zinc reacts with oxygen ( O2 )and forms the substance zinc oxide ( Zno ), which further reacts with carbon dioxide and form zinc carbonate (ZnCo3). This is important because of it feature of long-lasting protection for steel and iron products. 

1. The zinc coating prevents corrosive substances like acid
2. Galvanization protects from rusting.
3. The zinc protects the metal by corroding faster than the base metal.

• Benefits of Galvanizing :- 

1. Economical
2. Low-maintenance
3. Long Lasting
4. Unparalleled Protection
5. Fast