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Transmission and Distribution Lines Key Facts and Tutorials

Key Facts and Tutorials On Electrical and Distribution Lines

1. The economical section of a feeder can be obtain by applying Kelvin's law.
2. There should be be no break in the neutral, which is usually earthed at the supply end, of a two wire Alternating Current distribution system because excess current protection would be affected.
3. In actual practice the potential at the two feeding points is unequal. To calculate the voltage drop, the difference in potential is converted into ampere metres and the moments of the lower feeding point start from this initial value.
4. Uniformly loaded distribution fed at equal potential from both ends is treated like the distributor because the voltage drop is exactly halved.
5. Voltage drop in a uniformly loaded distributor fed at once end is calculated by assuming the whole of the load concentrated at middle point.
6. For Alternating current distribution the power factor of the load has to be taken into consideration and the calculations become cumbersome. The approximate method which gives results with in plus or minus five percent of the actual voltage drop involves calculating the centre of gravity of the load, resistance and reactance per double run and average power factor.
7. To determine the distribution of load at the point of minimum potential, the moments in ampere metres about of the feeding points must be equal to the moment in ampere metres about the other feeding point.
8.At the point of minimal potential in a distributor fed from both ends, the load at the point is supplied from right and left hand feeding points.
9. With point loads in a distributor fed at both ends, in order to determine the maximum voltages drop it is necessary to know the point of minimum voltage.
10. For a three wire Direct Current distributor fed at one end, if the total voltage drop in the neutral is positive it is added to the positive drop and deducted from the negative drop.

Limitation of high transmission voltage
a. Increased cost of line support
For high transmission voltage, the insulation required between the conductors and the earthed tower is more. This increases the cost of line supports.
b. High towers:
For high transmission voltage, the clearance between conductors and groundo should be more. Therefore, higher lower is required.
c. Longer cross arms:
FOr higher transmission voltage, distance between the conductors should be more. Therefore, longer arms are required.

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