Conductors of overhead transmission and Distribution Power Line typically consist of aluminum, which is lightweight and relatively inexpensive, and are often reinforced with steel for strength.Stranded cable is often used, which, as the name suggests, is twisted from many individual strands. At the same diameter or gauge, stranded cable is much easier to bend and manipulate.For underground lines, cables with insulation are use. Here heat dissipation is more of an issue, whereas weight is not.
Basics of Distribution Power Line Characteristics
Copper is the material of choice for underground cables because, while it is more expensive, it has a lower resistance than aluminum.Low resistance is generally desirable for power lines to minimize energy losses, but also because heating limits the conductor’s ability to carry current.
Resistance is given by R = rl/A, Where
- A is the cross-sectional area,
- l is the length of the conductor,
- r (rho) is the resistivity (inverse of conductivity).
The electrical resistance of a Distribution Power Line thus increases linearly with distance and decreases with the conductor cross-section. For the purpose of minimizing resistance, then, conductors should be chosen large. However, resistance must be weighed against other factors, including the cost of the conductor cable itself and its weight that needs to be supported by the towers.
Because even aluminum conducts so well, this trade-off comes out in favor of surprisingly slender lines considering the amount of current and power transferred.
Selection of Route of Distribution Power Line
There are no lay-down conditions the routing of MV Overhead Distribution Lines.However due consideration shall be given for the following factors when selecting route for the MV Line.
1. Straightness of the route.
2. location along the road
3. amount of way leave to be cleared to be
4. inconvenience caused to the other services to be
5. swampy ground and areas liable to flooded to be avoided
6. geological condition of the located pole pit
7. cost of construction shall be kept to minimum
8. use of taller poles at uplifts, and construction of tension points at uplifts to be avoided
Types of Low Voltage Distribution Power Line Supply
Single Phase Supply
Supply to the domestic consumer is given by 415v distribution power lines .By using three phase overhead lines or underground lines take live wire and neutral wire and connected it to the consumer meter as figure shown in bellow then Live wire is connected to the live wire of the house through the breaker. Neutral wire came from meter is connected to neutral wire of house.
Three phase supply
Supply to the domestic consumer is given by 415v distribution power lines by using three phase overhead lines or underground lines then directly supply to factories or consumer through the three-phase meter. Usually this is done when the power consumption or the consumer is very high.
Distribution Power Line Tower Types
Terminal Pole Here the line is terminated with MV Tension Insulators on one side of the pole. This is also called dead end poles
Shackle Pole Here the line is terminated with MV Tension Insulators on both sides of the same pole.
Intermediate Pole Here the line is continuous and is supported on MV Pin Insulators or Post Insulators as necessary.
Installation of Stays, Struts & Flying Stays
When a line changes direction, an additional force is introduced at the angle pole. This force is the resultant of line tensions acting at the pole.
The resultant force tries to move the top of the pole in the direction that bisects the angle between the wires. These forces, due to angles, can be considerable.
The Stays, Struts and Flying Stays shall be fixed to neutralize the resultant force on the poles. Number of stays to be used at any particular pole location is designed on the overturning force acting on the pole.
The force acting on the pole depends on the following factors.
• Number of conductors and size of the conductor, along with conductor tension.
• Length of adjacent spans
• Angle of deviation of the line
• Equipment mounted on the pole
• Geographical position of the pole Following shall be noted in fixing slays & struts
Installation of stay in low voltage electrical lines
- The angle between pole and the stay wire or strut pole shall not be less than 30°.
- Stays, Struts and flying Stays should be erected so as to avoid disturbances to pedestrians or vehicular traffic.
- It shall be ensured that the correct side of the ratchet nut faces the ratchet face of the cross head of the buckle before tightening the stay buckle.
- Stay and Flying Stay Wire over a street must not be less than
- In flat terrain poles used for struts and flying stays shall be of the same size as line poles.
- Stay Insulator shall be positioned below the level of the lowest current carrying conductor and not-less than 3.7m above the ground.
Hope that you have got some basic idaea about Distribution Power Line characterstis and we are plan to discuss more on power distribution system on our future articles.