Question

A 66 kv system has string insulator having five discs and the earth to disc capacitance ratio of 0.10. the string efficiency will be

Answer 1

Answer:

67 %

Step-by-step explanation:

A 66 kv system has string insulator having five discs and the earth to disc capacitance ratio of 0.10. the string efficiency will be

Voltage of disc nearest to conductor V₂ = V₁(1+K)

K = 0.1

V₂ = V₁(1+0.1)  = 1.1V₁

V₃ = V₂ + (V₁ + V₂) K = 1.1V₁ + 2.1V₁(0.1) = 1.31V₁

V₄ = V₃ + (V₁ + V₂ + V₃)K = 1.31V₁ + 3.41V₁ * 0.1 = 1.651V₁

V₅ = V₄ +  (V₁ + V₂ + V₃ + V₄)K = 1.651V₁ + (5.061V₁)*0.1 = 2.1571V₁

String Efficiency = (V₁ + V₂ + V₃ + V₄ + V₅)/(n V₅)  * 100

n = number of disc = 5

=> String Efficiency =  (V₁ + 1.1V₁ + 1.31V₁ + 1.651V₁ + 2.1571V₁)/(5 * 2.1571V₁

) * 100

= 7.2181V₁ / 10.7855  * 100

= 66.93 %

≈ 67 %

Answer 2

Answer:

String Efficiency = 67% Answered above Already.

individual Voltage Across each String = 5.28KV

Step-by-step explanation:

For individual Voltage Across Each Disc:

Vtotal = v1 + v2 + v3 + v4 + v5

     (1 +1.1+1.31+1.651+2.1571)V

 Vtotal = 7.218V

As we know, Voltage Across string = Phase Voltage

line voltage(66KV)  is Given in Question, So,

Phase Voltage = 66KV/$\sqrt{3}$ = 38.105KV

Individual Voltage Across each String = Vphase/Vtotal => 38.105/7.218 = 5.28KV