Safety Clearance to Exposed Live Conductors
Working Safety Clearance and Phase Gap between Exposed Live Conductor
Herein this article we will focus on “safety clearance to live bare live conductors during working in electrical power distribution substations or switching stations” and “phase gap or safety clearance to electrical energy transmitting energized conductors between others power conductors, communication conductors or transportation navigation system” to ensure safety for human and property, as well as operate a proficient electrical energy network system.
Safety Clearance during Works in Substations
Line crews often work in a substations or switching stations where all the equipment and conductors are not possible to be dead; but possible to ensure minimum safe distance for the working section from the exposed live section following as below:
1. Dead or working section should be identified clearly and barricaded appropriate barrier-rope;
2. Electrical live or non-working portion must be defined with appropriate signs;
3. Recommended notices, flags must be used with recognizable languages and universal signs;
4. Approved types of ladder must be used, not allowed over heighted ladder and others objects;
5. Must follow the minimum horizontal and vertical safety clearances from exposed live conductor or equipment following the degree of voltages as per international standard under a senior authorized persons;
Accordance to BS 7354:1990, the minimum safety working clearances in horizontal and vertical is as below:
Rated Voltage
|
Safety Working Clearance
| |
Horizontal
|
Vertical
| |
Not exceeding 11 kV
|
1.6 m
|
2.6 m
|
Exceeding 11 kV but not exceeding 33 kV
|
1.8 m
|
2.8 m
|
Exceeding 33 kV but not exceeding 66 kV
|
2.1 m
|
3.1 m
|
Exceeding 66 kV but not exceeding 132 kV
|
2.7 m
|
3.7 m
|
Exceeding 132 kV but not exceeding 275 kV
|
4.2 m
|
5.2 m
|
Exceeding 275 kV but not exceeding 500 kV
|
5.4 m
|
6.4 m
|
If the above clearance is not sufficient to ensure safety, additional arrangement should confirm.
Phase Gap or Safety Clearance between Exposed Overhead Live Line and Ground
An overhead line route which crosses or is in proximity to a high risk locality shall be given special consideration. As National and International references on the risk assessment of overhead lines for guidance in the correct identification and recommended minimum mitigating measures.
Where practical all new overhead lines will be routed to avoid the need to pass in close proximity to high risk localities. However where lines are specifically identified as being in close proximity to fishing or high amenity areas.
Right of Way Clearance (As per GETCO Standard)
Must maintain the required clearance space around the transmission line, trees below the transmission line to mitigate and avoid as far as practicable, a tree entering the required clearance space around that line if the tree falls.
KV
|
Min ROW
|
66 KV
|
18 Meter
|
132 KV
|
27 Meter
|
220 KV
|
35 Meter
|
400KV
|
52 Meter (Single Circuit)
|
400 KV
|
48 Meter (Double Circuit)
|
Allowance for Creep
Allowance must be made for the effects of creep in conductors and setting out errors as the specified clearance must be maintained for the life of the conductor. This allowance shall be as follows:
Conductor Type
|
Additional Clearance Required
|
Copper
|
450mm
|
Aluminium Alloy
|
600mm
|
ACSR
|
600mm
|
Minimum Height above Railway as Per IE-1957
Voltage
|
Broad Meter & Narrow Gauges
|
Up to 66 KV
|
14.00 Meter
|
Above 66KV up to 132KV
|
14.60 Meter
|
Above 132KV up to 220KV
|
15.40 Meter
|
Above 220KV up to 400KV
|
17.90 Meter
|
Above 400KV up to 500KV
|
19.30 Meter
|
Above 500KV up to 800KV
|
23.40 Meter
|
Clearance between conductors and Trolley / Tram wires (IE Rule 78)
KV
|
Clearance (Min)
|
66 KV
|
2.4 Meter
|
132 KV
|
2.7 Meter
|
220 KV
|
3.0 Meter
|
Clearance for Telephone line Crossings Power Line
Low and Medium Voltage
|
1.2 Meter
|
High Voltage Line Up to 11KV
|
1.8 Meter
|
High Voltage Line Above to 11KV
|
2.5 Meter
|
Extra High Voltage Line
|
3.0 Meter
|
Permissible Min ground Clearance of Electrical Line
KV
|
Ground Clearance
|
Over National Highway
|
66 KV
|
6.1 Meter
|
8.0 Meter
|
132 KV
|
6.1 Meter
|
8.6 Meter
|
220 KV
|
7.0 Meter
|
9.8 Meter
|
400KV
|
8.8 Meter
|
10.8 Meter
|
Clearance to Waterways
Item
|
Description
|
Clearance (m)
| ||
Lowest conductor (line or earth) to Towpath level or adjacent bank
|
0.433 kV
|
66kV
|
132kV
| |
1
|
River Trent
|
18.3
|
19.2
|
19.8
|
2
|
River Ouse
|
23.2
|
23.2
|
23.8
|
3
|
Aire & Calder Canal
|
14.3
|
15.2
|
15.9
|
4
|
Sheffield & South Yorkshire canal
|
14.3
|
15.2
|
15.9
|
5
|
Calder & Hebble Canal
|
14.3
|
15.2
|
15.9
|
6
|
Other Canals
|
11.3
|
15.2
|
12.8
|
7
|
Reservoirs
|
12.3
|
15.2
|
15.6
|
Clearance from Buildings to low, medium and high voltage lines
Voltage
|
Description
|
Distance
|
Low & Medium Voltage
|
Flat roof, open balcony, verandah roof ,When the line passes above the building a vertical clearance from the highest point
|
2.5 Meter
|
Low & Medium Voltage
|
Line passes adjacent to the building a horizontal clearance from the nearest point
|
1.2 Meter
|
Low & Medium Voltage
|
Line passes above the building a vertical clearance
|
2.5 Meter
|
Low & Medium Voltage
|
Vertical distance or line passes adjacent the building a Horizontal clearance
|
1.2 Meter
|
11 KV to 33 KV
|
Vertical distance or line passes above or adjacent to any building or part of a building
|
3.7 Meter
|
Above 33 KV
|
Line passes above or adjacent to any building or part of a building
|
3.7+(0.3 for every additional 33 KV )
|
Up to 11 KV
|
The horizontal clearance between the nearer conductor and any part of such building
|
1.2 Meter
|
11 KV to 33 KV
|
The horizontal clearance between the nearer conductor and any part of such building
|
2.0 Meter
|
Above 33 KV
|
The horizontal clearance between the nearer conductor and any part of such building
|
2.0 + (0.3 for every additional 33 KV )
|
Minimum Clearance between Lines Crossing Each Other (IE-1957)
System Voltage
|
132KV
|
220KV
|
400KV
|
800KV
|
Low & Medium
|
3.05
|
4.58
|
5.49
|
7.94
|
11-66KV
|
3.05
|
4.58
|
5.49
|
7.94
|
132KV
|
3.05
|
4.58
|
5.49
|
7.94
|
220KV
|
4.58
|
4.58
|
5.49
|
7.94
|
400KV
|
5.49
|
5.49
|
5.49
|
7.94
|
800KV
|
7.94
|
7.94
|
7.94
|
7.94
|
Clearance above ground of the lowest conductor As per IE Rule 77
Overhead Line Across Street
| |
Low and Medium Voltage
|
5.8 Meter
|
High Voltage
|
6.1 Meter
|
Overhead Line Along Street (Parallel To Street)
| |
Low and Medium Voltage
|
5.5 Meter
|
High Voltage
|
5.8 Meter
|
Overhead Line Without Across or Along Street
| |
Low/Medium /HT line up to 11KV If Bare Conductor
|
4.6 Meter
|
Low/Medium /HT line up to 11KV If Insulated Conductor
|
4.0 Meter
|
Above 11 KV Line
|
5.2 Meter
|
Above 33KV Line
|
5.8 Meter + Add 0.3 meter for every additional 33KV
|
Clearances from Buildings of low & medium voltage lines (IE Rule 79)
For Flat roof, Open Balcony, Verandah Roof and lean to Roof
| |
Line Passes Over Building Vertical Clearance
|
2.5 Meter
|
Line Passes Adjustment of Building Horizontal Clearance
|
1.2 Meter
|
For pitched Roof
| |
Line Passes Over Building Vertical Clearance
|
2.5 Meter
|
Line Passes Adjustment of Building Horizontal Clearance
|
1.2 Meter
|
Minimum Clearance Spaces Surrounding a Transmission Line
Nominal voltage
|
Dimension
vertical below
|
Dimension
horizontal
|
66 kV
|
3000 mm
|
3000 mm
|
Over 66 kV,
less than 220 kV
|
3700 mm
|
4600 mm
|
220 kV
|
3700 mm
|
4600 mm
|
275 kV
|
4200 mm
|
5000 mm
|
330 kV
|
4700 mm
|
5500 mm
|
500 kV
|
6400 mm
|
6400 mm
|
Clearance to Obstacles for Nominal system Voltage 230kV (as per PGCB)
The minimum clearances defined below shall not be infringed at the specified maximum conductor temperature with the phase conductors and suspension insulators hanging vertically or deflected to any angle up to 70° from the vertical.
This is describe as Minimum Clearance for where maximum conductor temperature is 80°C.
Ground (see note d) (m) 8.0
Roads (m) 14.0
Buildings, structures, walls or other objects on which a person can stand or against which he can lean a-
Ladder (m) 7.0
Trees (m) 5.5
Shrubs (m) 5.5
Railways (measured from railway track) (m) 18.0
River Crossing (m) 25.0
Where:
Clearances are measured to the nearest projection of an object.
For ladder clearances also apply to earthed metal clad buildings.
For trees clearances applicable to trees under the transmission line and to trees adjacent to the line. Clearances also applicable to trees falling, towards the line with conductors hanging in a vertical plane.
For ground clearance shall be measured from the highest flood level.
Clearances Where Transmission Lines Cross for 230kV (as per PGCB)
Where a transmission line crosses above or below another transmission line, the following clearances shall be obtained.
In still air, and with the phase conductor temperature of the lower transmission line at 5°C or 80°C for 400 kV line whilst the assumed phase conductor temperature of the higher transmission line is at its maximum operating temperature, the following minimum clearances between the lowest conductor (phase or earth) of the higher transmission line are applicable:
The highest conductor (phase or earth) of the lower transmission line 5.5 m
The voltage specified is that for which transmission lines are ultimately designed to operate.
Clearances are determined by the ultimate voltage of either the upper or lower transmission line, whichever is the greater.
Clearances are determined by the ultimate voltage of the upper/lower transmission line.
In addition to the above at the point of crossing, the clearance in (a) shall be obtained assuming the conductors of the lower transmission may swing up to 45° from the vertical. The sags of the upper and lower transmission lines shall be those at the maximum operating temperature.
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