Dc and AC Distribution


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Problems on AC and DC distribution

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Dc and AC Distribution

  1. 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 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: 25A at 50m from A : 50A at 75m from A : 30A at 100m from A : 40A at 150m from A
  2. 2. 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: (i)the point of minimum potential
  3. 3. (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°]