This document contains 11 problems related to direct current (DC) and alternating current (AC) distribution systems. The problems involve calculating voltages, currents, power dissipation, and phase angles given information about line resistances and reactances, load locations and values, and supply voltages. Solutions are provided for cross-sectional area, voltages, currents, resistances, power dissipation, and minimum voltage points.

1. DC and AC Distribution
1. A 2 wire dc distributor AB is 300m long. It is fed from point A. the various loads and their
positions are given below:
At point Distance from point A in metres Concentrated load in Amp.
C 40 30
D 100 40
E 150 100
F 250 50
If the maximum permissible voltage drop is not to exceed 10V, find the cross-sectional area of the
distributor. Take ρ = 1.78x10-8Ωm. [ 1.164cm2 ]
2. Two tram cars (A & B) 2 km and 6km away from a sub- station return 40A and 20 A respectively
to the rails. The sub- station voltage is 600V dc. The resistance of trolley wire is 0.25Ω/km and
that of track is 0.03Ω/km. calculate the voltage across each tram car.
[Va = 566.4V, Vb = 544V].
3. The load distribution on a 2 wire dc distributor is shown in the figure below:
The cross-sectional area of each conductor is 0.27cm2. the end A is supplied at 250V. Resistivity
of the wire is 1.78µΩcm. calculate (i) the current in each section of the conductor (ii) the 2 core
resistance of each section (iii) the voltage at each tapping point.
[20A,35A,47A; 0.099, 0.132,0.066Ω; 245.35, 240.73,239.41V]
4. A 2 wire dc distributor AB is fed from both ends. At feeding point A, the voltage is maintained as
at 230V and at B 235V. the total length of the distributor is 200m and loads are tapped of as
under:

2. 25A at 50m from A : 50A at 75m from A : 30A at 100m from A : 40A at 150m from A
The resistance per km of one conductor is 0.3Ω. Calculate :
(i) currents in various section of the distributor
(ii) minimum voltage and the point at which it occurs
[ 33.34A, 8.34A, 41.66A, 71.66A, 111.66A ; 228.875V]
5. A 2 wire dc distributor AB, 600m long is loaded as under:
Distance from 150 300 350 450
A(m)
Loads in Amp 100 200 250 300
The feeding point A is maintained at 440V and that at B at 430V. if each conductor has a
resistance of 0.01 Ω per 100m, calculate:
(1)The currents supplied from A to B, (2) the power dissipated in the distributor
[437.5A, 412.5A,; 14.705KW]
6. An electric train runs between 2 sub-stations 6 km apart maintained at voltages 600V and 590V
respectively and draws a constant current of 300A while in motion. The track resistance of go
and return path is 0.04 Ω/km. calculate :
(i) The point along the track where minimum potential occurs
(ii) The current supplied by the two sub-stations when the train is at the point of minimum
potential [3.425km, 170.45A, 129.55A]
7. A 2 wire dc ring distributor is 300m long and is fed at 240V at point A. At point B, 150m from A,
a load of 120A is taken and at C, 100m in the opposite direction, a load of 80A is taken. If the
resistance per 100m of single conductor is 0.03 Ω, find
(i)current in each section of distributor
(ii)voltage at point B and C [86.67A, 33.33A, 113.33A; 232.2V, 233.2V]
8. A 2 wire dc distributor ABCDEA in the form of a ring main is fed at point A at 220 V and is loaded
as under:
10A at B ; 20A at C; 30A at D and 10A at E
The resistances of various sections (go and return) are: AB = 0.1 Ω; BC = 0.05 Ω; CD = 0.01 Ω ; DE
= 0.025 Ω ; EA = 0.075 Ω. Determine:

3. (i)the point of minimum potential
(ii)current in each section of the distributor
[C is at minimum potential, ; 29.04A, 19.04A, 0.96A, 30.96A, 40.96A]
9. A dc ring main distributor ABCDEA is fed from point A from a 250V supply and the
resistances(including both lead and return) of various sections are as follows: AB = 0.02 Ω; BC =
0.018 Ω ; CD = 0.025 Ω ; DA = 0.02 Ω. The main supplies loads of 150A at B; 300A at C and 250A
at D. determine the voltage at each load point.
If the points A and C are linked through an interconnector of resistance 0.02 Ω, determine the
new voltage at each load point. [243.265V,239.904V, 242.735V; 245.93V, 244.97V, 245.1V]
10. A single phase distributor 2km long supplies a load of 120A at 0.8p.f. lagging at its far end and a
load of 80A at 0.9p.f. lagging at its mid-point. Both power factors arereferred to the voltage at
the far end. The resistance and reactance per km (go and return) are 0.05 Ω and 0.1 Ω
respectively. If the voltage at the far end is maintained at 230V, calculate :
(i) Voltage at the sending end
(ii) Phase angle between voltages at the two ends. [261.67V ; 3.82°]
11. A single phase AC distributor 1 km long has resistance and reactance per conductor of 0.1 Ω and
0.15 Ω respectively. At the far end, the voltage VB = 200V and the current is 100A at a p.f. of 0.8
lagging. At the mid-point M of the distributor, a current of 100A is tapped at a pf of 0.6 lagging
with reference to the voltage VM at the mid-point. Calculate:
(i)Voltage at mid-point
(ii)Sending end voltage VA
(iii)Phase angle between VA and VB [217.1V, 252.32V, 3.07°]