Distribution Systems
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Calculate the volume of the conductor material required for 1-ϕ, 2 wire a.c. system with one conductor earthed for overhead transmission system. 2. Prove that the volume cf copper material required by three phase three wire system is 0.5 / cos2ϕ times the volume of copper required by two wire d.c. system, irrespective of whether system is star or delta connected, in overhead type of transmission. 3. Compare the various overhead a.c. and d.c. systems based on the volume of copper required. State the assumptions used. 4. Find the ratio of volume of copper required to transmit a given power over a given distance by overhead system using : i) D.C. 2 wire and 3 wire system, ii) 3ϕ, 3 wire AC system.
Volume of Copper – Line Efficiency - Line Drop - Advantages – Disadvantages
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Explain the effect of high voltage on volume of copper and efficiency. 2. What are the advantages of high transmission voltage for the transmission of electric power ? 3. For the same power transmitted over the same distance, show that the increase in transmission voltage of a transmission line results in : i) Increased efficiency ii) Decreased line loss iii) Reduced weight of conductor material
Distribution Systems
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. Explain stepped or tapered distributor.
Calculations - Methods of Solving - Power Factors Referred to Respective Load Voltages
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Draw and explain the phasor diagram for an a.c. distributor with power factors referred to the receiving end voltage. 2. Draw and explain the phasor diagram for an a.c. distributor with power factors referred to the respective load voltages. 3. A single phase a.c. distributor AB has length cf 300 m and is fed from end A and is loaded as under : i) 100 A at 0.707 pf. lagging 200 m from point A ii) 200 A at 0.8 p.f. lagging 300 m from point A The total resistance and reactance of the distributor is 0.2 Ω and 0.1 Ω per kilometer. Calculate the voltage drop in the distributor. The load power factors refer to the voltage at the far end.
Load Fed at Both Ends - Load Fed at One End
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Prove that the shape of voltage drop diagram for a distributor, with uniform loading of 1 A/m fed at one end, is a parabola. Derive suitable expressions, draw current loading diagram and voltage drop diagram for uniformly loaded distributor of length f fed at one end. How is power loss in the whole distributor computed ? 3. Prove that the maximum drop for the distributor with distributed loading fed at both ends with equal voltages is IR/8 where I is total current and R is total resistance of both go and return. 4. Derive the expressions for the power loss in the distributor which is uniformly loaded with a) Ped at one end b) Fed at both ends with equal voltages. 5. Consider a distributor loaded with uniform loading of i ampere per meter run and are fed from two feeding points at different voltages. Find the point of minimum potential occurrence in the distributor. 6. A 2 wire d.c. distributor 200 m long is uniformly loaded with 2 A/m. Resistance of single wire is 0.3 Ω/km. If the distributor is fed at one end, calculate : 1. The voltage drop upto a distance of 150 m from the feeding point. 2. The maximum voltage drop. 7. Calculate the voltage drop at a distance of 200 m of a 300 m long distributor uniformly loaded at a rate cf 0.75 A/m. a. When it is fed from one end at 250 V b. When it is fed from both ends at 250 V The resistance of each conductor for both go and return per metre is 0.00018 Ω. Determine the power loss in each case.8. A 800 m, 2 wire d.c. distributor AB is fed from both ends is uniformly loaded at the rate of 1.25 A/m run. Calculate the voltages at the feeding points A and B if the minimum potential of 220 V occurs at point C at a distance of 450 m from the end A. The resistance cf each conductor is 0.05 Ω/km.
Concentrated Loads Fed at One End - Concentrated Loads Fed at Both Ends
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Explain the d.c. distributor fed at one end. 2. Explain the d.c. distributor fed at both ends. 3. Draw and explain the current loading and voltage drop diagrams for : a. Concentrated loading on distributor fed at one end b. Concentrated loading on distributor fed at both the ends with equal and unequal voltages. 4. A 2 wire distributor 500 m long is loaded as shown in the Fig. 7.11.16. If the maximum voltage drop allowed is 5 % of the supply voltage, calculate the cross-sectional area of the conductor to be used. Take ρ = 1.73× 10-8 Ω 5. A two conductor distributor has a length of 700 m and is loaded as shown in the Fig. 7.11.17. The ends A and B are maintained at 250 and 255 V respectively. If the minimum potential allowable at consumer's terminal is 245 V, calculate the diameter of the conductor used. p = 1.7 μ-cm. 6. A 2 wire d.c. distributor AB is fed from both ends. At feeding point A the voltage is 230 V while at B it is 235 V. The total length of distributor is 200 m and loads connected are, 25 A at 50 m from A, 50 A at 75 m from A 30 A at 100 m from A, 40 A at 150 m from A The resistance cf one conductor is 0.3 Ω/km, calculate a. Currents in various sections b. Point of minimum potential c. Value of minimum potential 7. An electric train moves between the substations 8 km apart and draws a constant current of 600 A. The two substations are maintained at a potential of 580 and 575 V respectively. The resistance for both go and return path is 0.05 Ω per km, calculate the minimum potential point and currents supplied by each substation at that instant of minimum potential.
Distribution Systems
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
It has been mentioned that the d.c. distributors are fed at one end or at both the ends. The voltages used to feed the distributors at both the ends may be equal or unequal.
Limitations - Modified
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. State the Kelvin's law and obtain the expression for the economic current density. 2. State and explain the limitations cf Kelvin's Law. 3. State and explain modified kelvin’s Law.
Current Distribution of
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Explain different methods to obtain 3-wire DC system. 2. In the 3 wire d.c. distributor shown in the Fig. 7.8.8 the resistances of various sections shown are in ohms. Calculate the voltages at various load points.3. A load supplied on a 3 wire d.c. system takes a current of 50 A on the positive side and 40 A on the negative side. The resistance of each outer wire is 0.1 Ω and the cross-section of the middle wire is one half that of the outer. If the system is supplied at 500 / 250 V, find the voltage at the load end between each outer and middle wire.
Distribution Systems
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. Discuss the design of primary distribution system with respect to i) Selection of voltage ii) Choice cf scheme iii) Size cf feeders.
Radial - Ring Main - Interconnected
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Questions : 1. Explain radial distribution system in detail. 2. Explain about ring main distribution system. State its advantages. 3. Explain ring main distribution with interconnector. 4. Explain the interconnected system of distribution. State its advantages. 5. Discuss and compare radial and ring main distribution systems. What is the role of interconnectors ?
Subject and UNIT: Transmission and Distribution: Unit V: (a) Distribution Systems
Question : 1. Explain the general d.c. distribution system.