1. In a 3 unit insulator string, the voltage across the lowest unit is 17.5 kV and string efficiency is 84.28%. The total voltage across the string is

1. 58.27 kV
2. 32.48 kV
3. 40.87 kV
4. 44.274 kV

2. Two insulators of identical capacitance C forms a string for a 22 kV, 50 Hz, single-phase overhead line insulation system. If pin to earth capacitance is also C, then string efficiency is

1. 75 %
2. 50 %
3. 25 %
4. 60 %

3. A string insulator has 5 units. The voltage across the bottommost unit is 25 % of the total voltage. The string efficiency is

1. 60 %
2. 80 %
3. 45 %
4. 55 %

4. There are 20 discs in the string insulators of a 3-phase, 400 kV transmission line. The string efficiency is 80%. What is the maximum voltage across any disc?

1. 24 kV
2. 12 kV
3. 17 kV
4. 14.43 kV

5. If the voltage across a string insulation assembly is 38 kV, number of insulator discs are 4 and voltage across lowermost disc is 12 kV the string efficiency is

1. 80 %
2. 79.16 %
3. 75.27 %
4. 85 %

6. Consider a 3-phase, 50 Hz, 11 kV distribution system. Each of conductors is suspended by an insulator string having two identical porcelain insulators. The self-capacitance of the insulator is 5 times the shunt capacitance between link and ground. The voltage across two insulators are

Answer. 2.89 kV and 3.46 kV

7. Two insulators of identical disc form a string. The self-capacitance is 8 times the pin to earth capacitance. The maximum voltage each unit can withstand should not exceed 17.5 kV. The line voltage of the complete string is

1. 33 kV
2. 44 kV
3. 22 kV
4. 34 kV

8. A string of suspension insulators consists of 4 units. The capacitance between each link pin and earth is (1/10)th of self-capacitance of a unit. The voltage between the line conductor and earth is 100 kV. Find string efficiency?

1. 76.4 %
2. 80 %
3. 75 %
4. 78.4 %