Module-2 Set-1 Short Questions 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?
Long Questions 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 centers. 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 power factor. 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?
Set-2 Short Questions 1. What are the advantages of using series compensation? 2. What are the factors which govern the performance of a transmission line? 3. What is shunt compensation? 4. Distinguish attenuation and phase constant. 5. Define surge impedance 6. Draw the phasor representation of short transmission line. 7. For controlling reactive power what adjustment should be done in transformer present in the system? 8. What is the purpose of insulator? 9. What is the main purpose of armoring? 10. What is meant by efficiency of an insulator string? Long Questions 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 Set-3 Short Questions 1. What are the factors which affect corona? 2. Define transmission efficiency. 3. List out various types of insulators used for overhead transmission lines.
4. Mention the advantages of the pin type insulator 5. What are the main causes for failure of insulators? 6. What are the different tests that are conducted on an insulator? 7. Define string efficiency and what are the methods for improving string efficiency? 8. Write short notes on puncture test. 9. Define impulse ratio. 10. State advantage of polymeric insulators over porcelain insulators. Long Questions 1.
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. 2. 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. 3. i) Explain surge impedance loading with respect to an overhead transmission line . ii) Explain the end condenser method for medium transmission lines. 4.
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. 5. 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.
