Lecture:33 Comparison of various Distribution Systems, AC four-wire Distribution System, Comparison of Conductor Material in Overhead System In comparing the relative amounts of conductor material necessary for different systems of transmission, similar conditions will be assumed in each case viz (i)same power (P watts) transmitted by each system. (ii)the distance (l metres) over which power is transmitted remains the same. (iii)the line losses (W watts) are the same in each case. (iv)the maximum voltage between any conductor and earth (Vm) is the same in each case. 1. Two-wire d.c. system with one conductor earthed In the 2-wire d.c. system, one is the outgoing or positive wire and the other is the return or negative wire as shown in Fig. The load is connected between the two wires.Max. voltage between conductors = Vm Power to be transmitted =P current, I1= P/Vm If R1 is the resistance of each line conductor, then, ∴Load R1=ρl/a1 where a1 is the area of X-section of the conductor. Line losses, W=2I21R1= 2(P/Vm)2 ρl/a1 of X-section, a1=2P2ρl/WV2m ∴Area Volume of conductor material required l= =2 a1l = 2( 4P2ρl2/WV2m It is a practice to make this system as the basis for comparison with other systems. There- fore, volume of conductor material required in this system be taken as the basic quantity i.e. =K 4P2ρl2/WV2m (2) . Two-wire d.c. system with earthed. Fig. shows The two-wire d.c. system with mid-point earthed. The maximum voltage between any conductor and earth is Vm so that maximum voltage between conductors is 2Vm .
Lecture:33 Comparison of various Distribution Systems, AC four-wire Distribution System, Comparison of Conductor Material in Overhead System In comparing the relative amounts of conductor material necessary for different systems of transmission, similar conditions will be assumed in each case viz (i)same power (P watts) transmitted by each system. (ii)the distance (l metres) over which power is transmitted remains the same. (iii)the line losses (W watts) are the same in each case. (iv)the maximum voltage between any conductor and earth (Vm) is the same in each case. 1. Two-wire d.c. system with one conductor earthed In the 2-wire d.c. system, one is the outgoing or positive wire and the other is the return or negative wire as shown in Fig. The load is connected between the two wires.Max. voltage between conductors = Vm Power to be transmitted =P ∴Load current, I1= P/Vm If R1 is the resistance of each line conductor, then, R1=ρl/a1 where a1 is the area of X-section of the conductor. Line losses, W=2I21R1= 2(P/Vm)2 ρl/a1 ∴Area of X-section, a1=2P2ρl/WV2m Volume of conductor material required =2 a1l = 2( l= 4P2ρl2/WV2m It is a practice to make this system as the basis for comparison with other systems. There- fore, volume of conductor material required in this system be taken as the basic quantity i.e. 4P2ρl2/WV2m =K (2) . Two-wire d.c. system with earthed. Fig. shows The two-wire d.c. system with mid-point earthed. The maximum voltage between any conductor and earth is Vm so that maximum voltage between conductors is 2Vm .
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