Question

Q1. i). A 3 phase transmission line is supported by 3 suspension insulators. The capacitance of pin to earth is half of the capacitance of disc. Estimate: i Ratio of voltage across discs ii. String Efficiency [1.5] [0.5] For the same transmission line, if number of discs are increased to 4. Estimate: i. Ratio of voltage across discs ii. String Efficiency [1.5) [0.5] ill). What is the change observed in above cases (i & ii)? iv). What can be done to increase the string efficiency? v). Which type of insulator is less susceptible to corona discharge?

Answer 1

elit ut given kauh Na= (IHK JY U₂ = (1+k ] V₂ +V, k = (1+k) (It leju, tuik = (k²+3K+1JV. N= Vitv₂f = tu, (HK) tu (143k+k?] vavi [3+ 46+62] string efficiency V, [ 34 4K tk²] 3+UC%)+ (%) ² 3xV, [ 173k +r2 ] 3[1 +3 (4₂) +28] 5.25 3+24 0.25 361+1+5 +0-21) more disk = Bozo = 63.63-7. ii) If one is added Nu (14 kJ Uz + kV2 (HK) (x²+3 kt) v tk Cktu u = (x² + 3k +1 + K3 + 3 k² + k + k ²4 kJ W = (R² 45k² 456 410V W = V, AV, ty tu = (x3 + 5 k²45 k41 43+4k+k2 gv,

= (x3 + 6x² 9kth Svi string efficiency un a u, [x3+6K² +9kth] ,4 [ k3 + 56² +Sk41] 0-125+ 6 (0.25j + 4.5th 10-125 19.5 4 [0.125 +5(0.85 +2.5+) R = 519-4 3) when number of discs increased the efficiency is decreasing 4 methods to improve string efficiency is using Grading of insulator discs " By using guard ring To improve r k vale should be low for that by increasing longer cross arms Corona rings (01) guard rings are less Sueceptible to Corona discharge which are are toroidal in shape and fixed with metal Bushings at their conductor edge. metal Conductor