Safety Clearance to Exposed Live Conductors

Safe Clearance of Exposed Life LineWorking 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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