Basic Electrical

OVERHEAD LINE CLEARANCE

OVERHEAD LINE CLEARANCE

We must take care of the following points before erecting poles:

  1. Keep equal distance in between the poles.
  2. Use low height poles in a high/up place in hilly area to get proper ground clearance.
  3. Never erect poles near the river bank, stream side and erosion-possible places. In the unavoidable circumstances, proper masonry works, adequate protection must be provided to the poles to prevent erosion of earth near the pole.
  4. Double Pole’ must be provided at ‘Cut Point’ in every one k.m. to strengthen the line. It would also facilitate proper/easy stringing of conductor.

 

SIDE CLEARANCE:

While we erect our electric lines, it is very important to maintain proper “side clearance”. We must obey some rules to maintain proper side clearance in electric lines.

Let us discuss it:

(1) What is the side “Clearance” in a forest path?

The ‘side clearance’ should be maintained according to the “voltage level” of the lines as follows:

The distance of the side tree/tree branches from the live conductor in different voltage levels are as furnished below:

11KV =2.6 metres

33KV =2.8 metres

66KV =3.4 metres

110KV = 3.7 metres

132KV =4.0 metres

 

(2) What would be the “width” of forest clearance to construct electric line In a forest area?

It should be as per voltage levels as mentioned below:

11KV = 7 metres width

33KV= 15 metres width

66KV= 18 metres width

110KV =22 metres width

132KV=27 metres width

(3) If we have to draw a LT 250 volts or 440 volts line, what should be the minimum clearance between the roofs of a house with the LT live line?

 As per I.E. Rules 1956, Sec 79, it should be minimum 2.5 metres.

(4) What should be the ‘side clearance’ of LT line from a house?

As per I.E Rules 1956, Sec. 79, it would be minimum 1.2 metres.

(5) What should be the “vertical clearance’ of the lowest conductor of HT & EHT line over a building?

As per I.E. Rules 1956, Sec. 80, the vertical clearance should be

For 11KV = 3.7 metres (min.)

For 33KV = 3.7 metres (min.)

For 132KV=3.7metres+ (0.3×132/33)=4.9 metres (min)

For 220KV =3.7metres + (0.3×220/33)= 5.7 metres (min)

7.2 metres (min.)

(6) What should be the “horizontal clearance’ of the nearest conductor of HT & EHT line over a building?

As per I.E. Rules 1956, Sec. 80(2), the horizontal l clearance should be

For 11KV = 1.2 metres (min.)

For 33KV = 2.0 metres (min.)

For 132KV= 2 metres+ (0.3×132/33)=3.2 metres (min)

For 220KV =2 metres + (0.3×220/33)= 4 metres (min)

(7) What should be the minimum ground clearance at the lowest part of the sag of the line conductor?

As per I.E. Rules 1956, Sec 77: The minimum ground clearance should be

(a) If the line is crossing a road

(i) For 230 volts, 400volts service connection=5.8 metres (min)

(ii) For 11KV & 33KV line = 6.1 metres (min.)

(b) If the line is passing along the road side:

(i) For 230 volt, 440 volt, Service connection = 5.5 metres (min.)

(ii) For 11KV & 33KV line = 5.8 metres (min.)

(c) If the line is passing in any other place:

(i) For 230 volts, 440 volts, 11 KV, and

Service connection lines = 4.6 metres (min.) (for bare) = 4.0 metres(min) (for insulated)

(ii) for 33KV lines = 5.2 metres (min.)

(iii) for 132KV lines = 5.2 metres + (0.3 x 132/33) = 6.4 metres (min.)

(iv) for 220KV line = 5.2 metres +(0.3 x 220/33) =