EE2303 Transmission and Distribution -Unit 4 and 5- Oct 2012 Question Paper

[Srini]

Anna University

October 2012 Monthly Test Question Paper

Unit 4 and 5

EE2303 Transmission and Distribution

Semester : V
3rd Year
EEE Department

Part A

1.Mention the insulating materials used for cables.
2.How are cables classified based on operating voltage?
3.What is armouring and serving?
4.Define string efficiency.
5.Why loss angle of cable should be very small?
6.What are the equipments used in a transformer substation?
7.State the role of circuit breaker in power system.
8.Define the term feeders and service mains.
9.Why are transmission lines 3 phase 3 wire circuits while distribution lines are 3 phase 4 wire circuits?
10.What are the objectives of earthing?

Part B

11.(a) Explain any two methods of grading of cables with necessary diagrams. (16)

Or

(b) (i). A cable is graded with three dielectrics of permitivities 4,3 and 2. The maximum permissible potential gradient for all dielectrics is same and equal to 30 kV/cm. The core diameter is 1.5cm and sheath diameter is 5.5cm. Determine the working voltage. (8)
(ii) Prove that the ration of voltage gradient with and without intersheeth will be 2/(1+α), when there is only one layer of intersheath. (8)

12(a)(i) What are different methods to improve string efficiency of an insulator? (8)
(ii) Explain the types of insulators with neat diagram. (8)

(or)

(b)(i) A 3 phase over head transmission line is being supported by three disc insulator. The potential across top unit (i.e near the tower) and the middle unit are 8kV and 11 kV respectively.
Calculate
a)The ration of capacitance between pin and earth to the self capacitance of each unit.
b)Line voltage
c)String Efficiency (8)

(ii) An insulator string consist of three units,insulator nearest to the line having a safe working volage of 20kV. The ratio of self to shunt capacitance is 6.1. Determine the line voltage and string efficiency. (8)

13.(a)(i) Explain the constructional features of various types of cables. (8)
(ii) List out the properties of insulating materials used for cables. (8)

(or)

(b)(i) A single core cable of conductor diameter 2 cm and lead sheath of diameter 5.3 cm is to be used on a 66 kV, 3 phase system. Two intersheaths of diameter 3.1 cm and 4.2 cm are introduced between the core and lead sheath. If the maximum stress in the layers is the same , find the voltages on the intersheath. (10)
(ii) Describe with the neat skecth, the construction of a 3 core belted type cable. (6)

14.(a). Draw the circuit arrangement and expalin the various elements of substation schemes. (16)

(or)

(b) A DC ring main distributor is fed at A and the load is tapped at points B,C,D. The distributor length is 400m long and points B,C,D are 150m,250m,375m from A. Loads are 150A,40A respectively. If resistance /100m of single conductor is 0.04Ω and Va = 220 V.
Calculate i)Current in each distributor
ii)Voltage at points B,C,D (16)

15.(a) i) Explain various methods of neutral grounding. (16)

(or)

(b)(i) Discuss and compare radial and ring main distribution system, What is the role of interconnectors in distribution system. (8)
(ii) Explain about the various types of substations. (8)