Ground Clearance of Different Transmission Lines
As per Indian Electricity Rule,The minimum distance between bottom conductor and ground of a 400KV transmission line is 8.84 meters.
The minimum ground clearance of a 33KV uninsulated electrical conductors is 5.2 meters.
The minimum ground clearance of a 33KV uninsulated electrical conductors is 5.2 meters.
This clearance is increased by 0.3 meters for every 33KV above 33KV.
According to this logic, the minimum ground clearance of 400KV transmission line would be,
400KV – 33KV = 367KV and 367KV/33KV ≈ 11
Now, 11 × 0.3 = 3.33 meter.
So, as per logic, the ground clearance of 400KV bottom conductor would be, 5.2 + 3.33 = 8.53 ≈ 8.84 meter(considering other factors).
For, same logic the minimum ground clearance of 220KV transmission line would be,
220KV – 33KV = 187KV and 187KV/33KV ≈ 5.666
Now, 5.666 X 0.3 = 1.7 meter.
So, as per logic, the ground clearance of 220KV bottom conductor would be, 5.2 + 1.7 = 6.9 ≈ 7 meter.
For, same logic the minimum ground clearance of 132KV transmission line would be,
132KV – 33KV = 99KV and 99KV/33KV = 3
Now, 3 × 0.3 = 0.9 meter.
So, as per logic, the ground clearance of 132KV bottom conductor would be, 5.2 + 0.9 = 6.1 meters.
132KV – 33KV = 99KV and 99KV/33KV = 3
Now, 3 × 0.3 = 0.9 meter.
So, as per logic, the ground clearance of 132KV bottom conductor would be, 5.2 + 0.9 = 6.1 meters.
The minimum clearance of 66KV transmission line is also taken as 6.1 meters.
Actually, in any case, the ground clearance should not be less than 6.1 meters across a street. So, ground clearance of 33KV line should also be maintained 6.1 meters across a street.
Ground clearance of 33KV bottom conductor would be 5.2 meters above cultivated land.
Ground Clearance for all lines
- For 400KV Lines - 8.84 Meters
- For 220KV Lines- 7 Meters
- For 132KV Lines- 6.1 Meters
- For 66KV Lines - 6.1 Meters
- For 33KV Lines- 6.1 Meters
Number of insulator discs n = ( Operating voltage/phase)/ Maximum voltage of each disc
Operating voltage/phase = 220*10³/√3 = 127 kV
Maximum voltage of each disc = 11 kV
Number of insulator discs n = 127/11 =11.547 ≈ 12
For safety operation one extra disc is added to the string.
Therefore, total number of insulator discs = 13
Number of Insulator per String
- For 400KV Line ---- 22 Disc
- For 220KV Line ---- 13 Disc
- For 132KV Line ---- 8 Disc
- For 66KV Line ----- 5-6 Disc
- For 33KV Line ----- 3 Disc
Some Useful MCQS
1. The minimum distance between bottom conductor and ground of a 400KV transmission line is
A. 8.84 m
B. 7.32 m
C. 8.0 m
D. 7.5 m
Answer: A. 8.84 m
2. The minimum distance between bottom conductor and ground of a 220KV transmission line is
A. 7 m
B. 7.5 m
C. 6.5 m
D. 7.1 m
Answer: A. 7 m
3. The minimum distance between bottom conductor and ground of a 132KV transmission line is
A. 6.2 m
B. 6.1 m
C. 6.3 m
D. 6.5 m
Answer: B. 6.1 m
4. The minimum distance between bottom conductor and ground of a 66KV transmission line is
A. 6.3 m
B. 6.4 m
C. 6.6 m
D. 6.1 m
Answer: D. 6.1 m
5. The minimum distance between bottom conductor and ground of a 33KV transmission line is
A. 6.2 m
B. 6.3 m
C. 6.1 m
D. 6.5 m
Answer: C. 6.1 m
6. The number of discs in a string of insulators for 400 kV ac overhead transmission line lies in the range of
A. 22
B. 25
C. 26
D. 29
Answer: A. 22
7. The number of discs in a string of insulators for 220 kV ac overhead transmission line lies in the range of
A. 13
B. 16
C. 22
D. 15
Answer: A. 13
8. The number of discs in a string of insulators for 132 kV ac overhead transmission line lies in the range of
A. 7
B. 8
C. 9
D. 10
Answer: B. 8
9. The number of discs in a string of insulators for 66 kV ac overhead transmission line lies in the range of
A. 5-6
B. 6-7
C. 3-6
D. 2-5
Answer: A. 5-6
10. The number of discs in a string of insulators for 33 kV ac overhead transmission line lies in the range of
A. 1
B. 4
C. 3
D. 5
Answer: C. 3