Electrical Power Systems

370 Electrical Power Systems
HG
Deq \ ln
0. 013KJ
=5.44
I
\ D eq = 0.013 e 5.44 = 3 m Ans.
Example 14.6: A three phase equilateral transmission line has a total corona loss of 55 KW at
110 KV and 100 KW at 114 KV. What is the disruptive critical voltage between lines? What is the
corona loss at 120 KV.
Solution:
Power loss due to corona for three phases is given by
P c = 3 ´ 244
d
(f + 25)
Taking d, f, r and D are constants.
\ P c a (V n – V 0) 2
HG
HG
I KJ
2
r
D (V n – V 0) 2 ´ 10 –5 KW/Km
\ 55 a 110
- V 0
...(i)
3
I KJ
2
and 100 a 114
- V 0
3
...(ii)
Dividing eqn.(i) by eqn. (ii), we get
55
100
2 b 0g
2
0
635 . - V
=
65. 8 - V
\ 635 . - V0
65. 8 - V =0.74
0
b g
\ V 0 = 57 KV.
In the 2nd case,
HG
W a 120
- V
3
\ W a (69.28 – V 0) 2
Dividing eqn. (iii) by eqn. (i), we get
W
55 =
2 b69. 28 - V0g
2
635 . - V
b 0g
0
I KJ
2
...(iii)