EE3401 Transmission and Distribution Important Questions

EE3401 Transmission and Distribution Important Questions

Unit 1

1. Derive the expression for capacitance of a three-phase transmission line for symmetrical and asymmetrical spacing.
2. Derive the expression for inductance of a three phase transmission line for symmetrical and asymmetrical spacing.
3. Derive an expression for loop inductance of a single phase transmission system.
4. Derive the expression for inductance of three phase line with unsymmetrical spacing.
5. 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 1.81 cm. Find the capacitance per phase per km. Capacitive reactance per phase, Charging current and Charging Mega volt-amperes.

Unit 2

1. Derive the expression for voltage regulation and transmission efficiency of a short transmission line.
2. Describe the importance of power circle diagram and explain the procedure to draw the power circle diagram at the receiving end.
3. A three phase 5km long transmission line, having resistance of 0.52/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
   (i) Line current
   (ii) Regulation
   (iii) Efficiency of the transmission line.
4. Using rigorous method, derive expression for sending end voltage and current for a long transmission line.
5.  Assume a three-phase line has the impedance of 5+j20 ohm per phase delivers a load of 30MW at a power factor of 0.8 lag and voltage of 33kV. Determine the capacity of the phase modifier to be installed at the receiving end if the voltage at sending end is to be maintained at 33kV. Assume the shunt admittance is neglected.
6. Explain various steps involved in receiving end power circle diagram with neat sketches.

Unit 3

1. A transmission line has a span of 214 meters between level supports. The conductors have a cross-sectional area of 3.225 cm². Calculate the factor of safety under the following conditions: Vertical sag 2.35 m; Wind pressure 1.5 kg/m run Breaking Stress = 2540 kg/cm² Wt. of conductor 1.125 kg/m
2. The towers of height 30 m and 90 m respectively support a transmission line conductor at water crossing. The horizontal distance between the towers is 500 m. If the tension in the conductor is 1600 kg, find the minimum clearance of the conductor and water, and clearance mid-way between the supports. Weight of conductor is 1.5 kg/m. Bases of the towers can be considered to be at water level.
3. A transmission line conductor is supported on the towers of equal height. The height of each tower is 30 m. The distance between the towers is 160 m, tension in the conductor is 2500 kg and cross sectional area of conductor is 2.5 cm². Compute the sag.
4. In a 33 kV overhead line, there are three units in the string of insulators. If the capacitance between each insulator pin and earth is 11% of self capacitance of each insulator, find the distribution of voltage over 3 insulators and string efficiency. Draw the equivalent circuit.
5. Derive an expression for sag of a line supported between two supports of the same height. Also Explain the effect of ice and wind loading.
6. Define string efficiency of suspension insulator string. List the methods to improve it.
7. Each line of 3 phase system is suspended by the string of 3 identical insulators of self-capacitance ‘C’ F. The shunt capacitance of connecting metal work of each insulator is 0.2 C to earth and 0.1 C to line. Calculate the string efficiency of the system if a guard ring increases the capacitance to the line of metal work of the lowest insulator to 0.3C.

Unit 4

1. What is grading? Explain the methods of grading of cables, with neat diagrams and equations.
   The following are the two main methods of grading of cables:
   (i) Capacitance grading
   (ii) Intersheath grading
2. With neat diagrams, explain the constructional features of following types of cables.
   (i) Belted cables.
   (ii) Screened cables
   (iii) Pressure cables
3.  Explain, the methods of grading of cables with neat diagrams and equations.
4. Derive the expression for insulation resistance, capacitance, electric stress and dielectric loss of a single core cable.
5. With neat diagram, explain the various methods of grading of underground cables.
6. Derive an expression for the insulation resistance, capacitance and the electrostatic stress of a single core cable.

Unit 5

1. What are the different types of bus bar arrangements used in substations? Illustrate your answer with suitable diagrams.
2. ) Discuss the advantages of HVDC transmission over HVAC transmission in detail.
3. Explain, with a neat layout the modern EHV system. What is the highest voltage level available in India for EHV transmission?
4. Find the ratio of volume of copper required to transmit the power over a given distance, by overhead system using,
   (i) DC 2 wire and 3 wire system,
   (ii) 3 phase, 3 wire AC system.
5. Explain the following types of FACTS controllers with necessary diagrams.
   (i) Shunt controller
   (ii) Combined series series controllers
   (iii) Combined series shunt controller
6. Describe the following methods of voltage control with necessary diagrams.
   (i) Tap changing transformers.
   (ii) Auto-transformer tap changing.
   (iii) Booster transformer.