Transmission & Distribution updated question bank (III year EEE students)

QUESTION BANK

Subject : EE2303 -Transmission & Distribution

 

UNIT-I INTRODUCTION

 

PART-A

1. What is meant by power supply system?

2. What is meant by Transmission and Distribution system?

3. What are the different types of Power supply system?

4. What are the various components of power supply system?

5. What are the different types of power plants?

6. What are the different operating voltages used for generation, primary

    and secondary transmission in AC power supply systems in India?

7. Define feeder, distributor and service mains.

8. List the advantages of high voltageAC transmission.

9. Define – Break-even distance.

10. List the disadvantages of DC transmission.

11. List the different types of DC links.

12. What is meant by STATCOM

13. What are the advantages &  limitations of high voltage transmission?

14. List the various types of distribution systems.

15.List the different types of distribution systems based on connection

16. What are the different components of a distribution system?

17. What is meant by stringing chart

18. What are the limitations of HVDC system?

19. List the two merits of HVDC system

20. List the HVDC systems present and which are in operation in India.

21. List the applications of HVDC system.

22. List the advantages of EHVAC transmission system.

23. What is the need of load dispatch centres? Where are the LDC's available inTamil Nadu?

24. List out objectives of FACTS.

25.What factors affect sag in transmission line.

26. Name any two FACTS controller devices.

27.What is the highest AC transmission voltage we have in India?

 

PART-B

1.    (i) Discuss various types of HVDC links. Mention any one HVDC   

      link available in India with rating.                     

   (ii) List out the main components of a HVDC system.      

 

2. (i) Draw and explain the structure of modern power systems with              

         typical voltage levels.                                                  

    (ii) What is the highest voltage level available in India?   

 

3. (i). Explain the effect of high voltage on volume of copper and on

          efficiency.                                                                  

    (ii) Explain why the transmission lines are 3 phase 3-wire circuits while

         distribution lines are 3 phase 4-wire circuits.

 

4. (i) Draw the model power system with single line representation. Show

         its essential constituent sections.         

    (ii) What are the AC transmission and distribution level voltages we

           have in India?                                                     

    (iii) What are the different kinds of DC links? Draw relevant diagrams.      

                                            

5. (i)  Explain why EHV transmission is preferred? What are the problems 

           involved in EHV AC transmission?                      

     (ii) With neat schematic, explain the principle of HVDC system  

           operation.                

                                                  

6. Explain about FACTS and its controllers with neat diagram

 

7. (i) Compare EHVAC and HVDC transmission.

    (ii) Explain the applications of HVDC transmission

          System.

8. Explain TCSC and SVC systems .

9. Explain with neat diagram about STATCOM and UPFC.

10. A transmission line conductor at a river crossing is supported from two towers at a height of 50 and 80 meters above water level. The horizontal distance between towers is 300m. If tension in conductor is 200kg, find clearance between conductor and water at a point midway between towers. Weight of conductor/meter = 0.844kg. Derive formula used.

11. An overhead line has a span of 336m. The line is supported at a water crossing from two towers whose heights are 33.6m and 29m above water level. The weight of conductor is 8.33N/m and tension in the conductor is not to exceed 3.34*10⁴N.Find 1)Clearance between lowest point on conductor and water 2) Horizontal distance of this point from lower support.

12. Explain the principle of operation of compensators used for voltage control. (6)

13. What are the advantages of high transmission voltage for the transmission of electric power ? Explain. (8)

14. A 50km long transmission line supplies a load of 5MVA at 0.8pf lagging at 33kV.The efficiency of transmission line is 90%. Calculate the volume of Al conductor required for the line when 3 phase 3 wire system  is used. The specific resistance of Al is 2.85*10^-8 m.

15.Derive an expression for sag calculation in a transmission line

                (i) When the supports are at equal heights                      (8)

                (ii) When the supports are at unequal heights                                (8)

Assume shape of overhead line is a parabola.

 

 

UNIT- II

TRANSMISSION LINE PARAMETERS

PART-A

1. Define Skin effect. On what factors does the skin effect depend.
2. What is meant by proximity effect?
3. Differentiate the stranded conductor and bundled conductor.
4. List out the advantages of double circuit lines.
5. Define - Self and mutual – G.M.D.
6. What is meant by inductive interference?
7. What is transposition of conductors?
8. What is ACSR conductor?
9. What is fictitious conductor radius?
10. Define unsymmetrical and symmetrical spacing.
11. State why transposition of line conductors are needed?
12.  List the advantages of bundled conductors.
13. What are the factors that affect the skin effect?
14. Why the effective resistance is more than the static resistance of a

transmission line?

15. Why does a transmission lines have resistance, inductance, and

capacitance?

16. List the factors that governing the capacitance of a transmission line.
17. State the advantages of double circuit line over single circuit line.
18. What do you understand by inductive interference?
19. What is corona? State its advantages & disadvantages.
20. Define critical disruptive voltage.
21. What are the factors which affect corona?
22. Define transmission efficiency.

 

 

PART-B

1. From the fundamentals derive an expression for inductance of a single

    phase transmission system.

 

2. Derive an expression for capacitances of a single phase transmission

    system and discuss the effect of earth on capacitance with suitable  

    equation. 

 

3. Derive an expression for inductance

          i) Of a single-phase overhead line.

          ii) A conductor is composed of seven identical copper strands each

               having a radius r. Find the self-GMD of the conductor.

 

4. i) Derive an expression for the capacitance between conductors of a

        single phase overhead line.

    ii) Find the capacitance between the conductors of a single-phase 10 km

         long line. The diameter of each conductor is 1.213 cm. The spacing     

         between conductors is 1.25 m. Also find the capacitance of each

         conductor  neutral.

5. i) Derive the expression for inductance of a two wire 1Φ transmission

        line.

   ii) Derive the expression for capacitance of a 1Φ transmission line.

 

6. (i) What are the advantages of bundled conductors?  

   (ii) Derive the expression for capacitance of a double circuit line for

         hexagonal spacing.

   (iii) Why is the concept of self  GMD is not applicable for capacitance?

 

7. (i) Explain clearly the skin effect and the proximity effects when referred

         to overhead lines.

   ii) Write a short note on the inductive interference between power and

        communication lines.

 

8. i) Derive the expression for the capacitance per phase of the 3 phase

       double circuit line flat vertical spacing with transposition.

    ii) A 3 Φ overhead transmission line has its conductors arranged at the

        corners of an equilateral triangle of 2 m side. Calculate the capacitance

        of each line conductor per km. Given the diameter of each conductor is

        1.25 cm.

 

9. Find the capacitance per km per phase of a 3 Φ line arrangement in a

    horizontal plane spaced 8 metres apart. The height of all conductors

    above the earth is 13 metres. The diameter of each conductor is 2.6 cm.

    the line is completely transposed and takes the effect of ground into

    account.

 

10. Discuss the concept of GMR and GMD in the calculation of

       transmission line inductance.

11.i) Derive the expression for the voltage induced  in communication lines 

        due to current in power lines.     (8)

     ii) Explain the various factors affecting corona loss and methods of 

          minimizing them        (8)

12.Derive the expression for inductance of a 3 phase line with 

      Unsymmetrical & symmetrical  spacing. 

13. A 220KV, 50Hz, 200Km long three phase line has its conductors on the  

       corners of a triangle with sides 6m,6m and 12m. The conductor radius  

       is 1.81cm. Find the capacitance per phase per km, capacitive reactance

       per phase, charging current and total charging Mega volt amperes.

14. Derive the equation of capacitance of a 3 phase unsymmetrically spaced   

      & symmetrically spaced overhead lines.

15. Calculate the loop inductance per km of a single phase line comprising 

       of 2 parallel conductors 1m apart and 1 cm in diameter, when the 

       material of the conductor is

       i) Copper        ii) Steel of relative permittivity 50

16. Calculate the capacitance of a 100km long 3 phase,50 Hz overhead 

       transmission line consisting of 3 conductors each of diameter 2 cm and  

       spaced 2.5m at the corners of an equilateral triangle.

 

 

   

 

 

UNIT-III

MODELLING AND PERFORMANCE OF TRANSMISSION LINES

PART-A

1. Classify overhead transmission lines.
2. Define transmission efficiency.
3. List out the methods of representation of medium transmission lines.
4. What is Ferranti effect?
5. Define regulation of power transmission line.
6. What is the use of power circle diagram?
7. What is meant by the receiving end power circle diagram?
8. What is the cause of Ferranti effect?
9. What is the use of power circle diagram?
10. What are the causes of voltage drop and line loss in a transmission line?
11. What are the advantages of using series compensation?
12. What are the factors which govern the performance of a transmission line?
13. What is shunt compensation?
14. Distinguish attenuation and phase constant.
15. Define surge impedance
16. Draw the phasor  representation of short transmission line.
17. For controlling reactive power what adjustment should be done in transformer present in the system.

 

 

PART-B

1. Determine the efficiency and regulation of a 3phase, 100 Km, 50 Hz

     transmission line delivering 20 MW at a power factor of 0.8 lagging and

     66  kV to a balanced load. The conductors are of copper, each having

     resistance 0.1 Ω / Km, 1.5 cm outside dia, spaced equilaterally 2 meters

     between centres.Use nominal T method.

 

2. A three phase 5 km long transmission line, having resistance

    of 0.5 Ω / km and inductance of 1.76 mH / km is delivering power at 0.8  

    pf  lagging. The receiving end voltage is 32kV. If the supply end voltage

    is 33 kV, 50 Hz, find line current,   regulation and efficiency of the

    transmission line.

 

 

3. Derive the expressions for sending end voltage in nominal T method and

    end Condenser method.

 

4. i) What is an equivalent  circuit of long line? Derive expression for

        parameters of this circuit in terms of line parameters.

    ii) A 50Hz transmission line 300 km long total series impedance of

         40  +  j25 Ω and total shunt admittance of 10-3 mho. The 220 KV with

         0.8 lagging powerfactor. Find the sending end voltage, current,

         power and power factor using    nominal  method.

 

5. i) Define regulation of a transmission line and derive the approximate

       expression for the regulation of a short transmission line.

    ii) What is corona loss? How do you determine this loss?

6. A 220  kV, 3 Φ transmission line has an impedance per phase of

    (40  +  j200)  Ω and an admittance of (0  +  j0.0015) mho. Determine the

    sending end voltage and sending end current when the receiving end

    current is 200 A at 0.95 pf lagging.   Use nominal T method.

 

7. Determine the efficiency and regulation of a three phase 200 km, 50 Hz

    transmission line delivering 100 MW at a pf of 0.8 lagging and 33 kV to   

    a balanced load. The conductors are of copper, each having resistance

    0.1 Ω / km, and 1.5 cm outside diameter, spaced equilaterally 2 m

    between Centers. Neglect leakage reactance and use nominal T and π  

    methods.

 

8. i) Explain the Ferranti effect with a phasor diagram and its causes.

   ii) Explain the classification of lines based on their length of transmission.

   iii) What are ABCD constants.

9. A 3 phase line having an impedance of (5+j20)Ω per phase delivers a 

    load of 30MW at a power factor of 0.8 lag and voltage of 33 kV. 

    Determine the capacity of the phase modifier to be installed at the

    receiving end if the voltage at the sending end is to be maintained at        

    33kV. Assume the shunt admittance is neglected.

10. Write short notes on

                i) Shunt compensation  ii) Series compensation

11. A 3 phase, 50Hz, 150 km line has a resistance, inductive reactance and  

      capacitive shunt admittance of 0.1Ω, 0.5Ω and 3*10^-6 mho per km per   

       phase. If the line delivers 50MW at 110kV and 0.8pf lagging.  

       Determine the sending end voltage and current. Assume nominal π

       circuit for the line.

12. A 15 km long 3 phase overhead line delivers 5 MW at 11kV at 0.8

       lagging pf line loss is 12% of power delivers. Line inductance is 1.1mH  

       per km per phase. Find the sending end voltage and regulation.

13.i) Explain surge impedance loading with respect to an overhead

         transmission line .

     ii) Explain the end condenser method for medium transmission lines.

14. The A,B,C,D constants of a 3 phase transmission line are 

       A=D=0.936+j0.016, B=33.5+j138Ω, C=(-0.9280+j901.223)*10^-6 mho.

       The load at the receiving end is 40MW at 220kV with power factor of

       0.86 lagging. Find the magnitude of the sending end voltage, current,

        power, line efficiency and voltage regulation. Assume the magnitude

       of the sending end voltage remains constant.

15. Deduce an expression for the sending end and receiving end power of a 

       line in terms of voltage and ABCD constants. Show that the real power

       transferred is dependent on the power angle and reactive power

       transferred is dependent on the voltage drop in the line.

 

 

 

UNIT-IV

INSULATORS AND CABLES

PART-A

1. What is the purpose of insulator?
2. What is the main purpose of armouring?
3. What is meant by efficiency of an insulator string?
4. List out various types of insulators used for overhead transmission lines.
5. Mention the advantages of the pin type insulator
6. What are the main causes for failure of insulators?
7. What are the different tests that are conducted on an insulator?
8. Define string efficiency and what are the methods for improving string efficiency?
9. Write short notes on puncture test.
10. Define impulse ratio.
11. State advantage of polymeric insulators over porcelain insulators.
12. What are the routine tests conducted on insulators?
13.  What are the performance tests conducted on insulators?
14. What are the merits of under ground cables?
15. How are cables classified based on operating voltage.
16. What is the main purpose of bedding?
17. What are the common materials used for insulation?
18. What is the main purpose of armouring?
19.  What is serving?
20. What is dielectric stress?
21. What is grading of cables and give the methods of grading.
22. What are the main advantages of suspension type insulators over pin type ones?
23. Why the potential distribution across the string units of insulator is not uniform.
24. Name the two methods of locating cable faults.
25. State two types of faults in a cable.
26. Show that insulation resistance of cable is inversely proportional to its length.
27. What are the advantages of string insulators?
28. Why loss angle of cable should be very small?

 

PART-B

1.Discuss any two methods to increase the value of string efficiency, with

   suitable sketches.

2.Explain any two methods of grading of cables with necessary diagrams.

3. i) What are different methods to improve string efficiency of an

        insulator?

    ii) In a 3-unit insulator, the joint to tower capacitance is 20 % of the

        capacitance of each unit. By how much should the capacitance of the

        lowest unit be increased to get a string efficiency of 90 %. The

        remaining two units are left      unchanged.

4. i) Derive the expression for insulator resistance, capacitance and electric

       stress in a single core cable. Where is the stress maximum and

       minimum?

   ii) A single core 66 kV cable working on 3-phase system has a conductor

       diameter of 2cm and sheath of inside diameter 5.3 cm. If two inner

       sheaths are introduced in such a way that the stress varies between the

       same maximum and minimum in the three layers find:

a) position of inner sheaths

b) voltage on the linear sheaths

c) maximum and minimum stress                                                                                                                  

5. i) Draw the schematic diagram of a pin type  & suspension type insulator  

        and explain its function.                                                               

    ii) A 3 phase overhead transmission line is being supported by three disc

         insulators. The potential across top unit (i.e. near the tower) and the

         middle unit are 8 kV and 11 kV respectively. Calculate,

a) The ratio of capacitance between pin and earth to the self

     capacitance of each unit

b) Line Voltage

c) String Efficiency

6. i) Describe with the neat sketch, the construction of a 3 core belted type

       cable.

    ii) A conductor of 1cm diameter passes centrally through porcelain

         cylinder of internal diameter 2 cms and external diameter 7 cms. The

         cylinder is surrounded by a tightly fitting metal sheath. The

         permittivity of porcelain is 5 and the peak voltage gradient in air must

         not exceed 34 kV / cm. Determine  the maximum safe working

         voltage.

7.i) What are the various properties of insulators? Also briefly explain about

       suspension type insulators.  

    ii) Calculate the most economical diameter of a single core cable to be

         used on 132 kV, 3 phase system. Find also the overall diameter of the

         insulation, if the peak permissible stress does not exceed 60 kV / cm.

         also derive the formula used here.

8. i) Briefly explain about various types of cables used in underground

        system.

    ii) A string of 4 insulator units has a self capacitance equal to 4 times the

        pin to earth capacitance. Calculate,

            a) Voltage distribution as a % of total voltage

            b) String efficiency

9. i)  Give any six properties of a good insulator.

    ii) With a neat diagram, explain the strain and stay insulators.

    iii) A cable is graded with three dielectrics of permittivities 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 5.5 cm. Determine the working voltage.

10. Explain the constructional features of various types of cables

11. i) Compare and contrast overhead lines and underground cables.

      ii)List out the properties of insulating materials used for cables

12. An insulator string consist of three units, insulator nearest to the line having a safe working voltage of 20kV. The ratio of self to shunt capacitance is 6:1. Determine the line voltage and string efficiency.

 

 

 

UNIT-V

SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM

PART-A

1. What is substation?
2. What are the classifications of substation according to service?
3. What are the types of transformer substations?
4. What are the factors to be considered for busbar design?
5. What is neutral grounding or neutral earthing?
6. What are the equipments used in a transformer substation?
7. What are the different types of bus bar arrangements in substations?
8. What is bus bar and what are its components?
9. What are the materials mainly used in busbars?
10. What are the factors to be considered for busbar design?
11. Which tests are necessary on station busbars?
12. What is neutral grounding or neutral earthing?
13. What is equipment grounding?
14. What are the advantages of neutral grounding?
15. What is earth resistance?
16. What are the devices used for DC power at the substation by using

converting machinery?

17. Define distribution substation.
18. Define service mains?
19. What are the types of nature of current in distribution system?
20. What is interconnected system.
21. State the advantage of ring main distributor.
22. Give the disadvantage of single bus scheme.
23. State the role of circuit breaker in power system.
24. Define the term feeders and service mains.
25. What are the various methods of earthing in substations?
26. Why are transmission lines 3 phase 3 wire circuits while distribution lines are 3 phase 4 wire circuits?
27. Give the difference between disconnector switch and isolator.
28. Give the protective device present in substation.
29. State the advantages of outdoor substation over indoor substation.
30. What are the objectives of earthing?

 

 

 

PART-B

1. With a neat sketch explain double bus with double breaker and double

    bus with single breaker. State their advantages and disadvantages.

2. Explain the following:

(i) Neutral grounding

(ii) Resistance grounding.

3. Explain about the various types of substations

4. Write short notes on

i. Sub mains

ii. Stepped and tapered mains

5. Explain the various types of bus bar arrangements in a substation.

6. Write short notes on

i. Busbar arrangement in substation

ii. Grounding grids

7. i) Explain the design principles of substation grounding system.

    ii) Explain the equipments in a transformer substation.

8. Draw the circuit arrangement and explain the various elements of the 

    following bus bar arrangements.

                i)Single bus scheme

                ii)Double bus bar scheme

                iii) Double bus bar with bypass isolators

                iv)Main and transfer bus bar

                v)Mesh scheme

9. Discuss briefly each of the following

                i)Feeders

                ii)Radial distribution

                iii)Ring main distribution

                iv)Interconnected system

10. 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,200A respectively. If

       resistance/100 m of single conductor is 0.04Ω and V_A = 220V.

       Calculate  i) Current in each distributor  ii) Voltage at points B,C,D.

11. Discuss and compare radial and ring main distribution system. What is 

       the role of interconnectors in distribution system.

12. Discuss the design of primary distribution system with respect to

       following   i) Selection of voltage  ii)Choice of scheme

                         iii)Size of feeders