What is ground clearance in transmission and distribution line?

Introduction

Hey, I’m sure you guys understand how power is transferred from one location to another. In this method, we use an overhead transmission line by means of a supporting pole and tower. But one question remains: what should the pole’s height be? Is there a set standard? So, in this post, we will discuss the ground clearance of the line.

What is ground clearance?

A proper height between the earth and the conductor in an overhead line is called ground clearance. It means that in India, there is a proper rule about this.

What is ground clearance

According to the rule, at every type and level of voltage, ground clearance will be different. Sometimes we have to bypass these rules due to the circumstances. This can be called an exception. Now I’ll go over some ground clearance rules based on Indian electrical codes.

Ground clearance for service mains and overhead lines

If you have to connect the house with service mains wire, then you have to bring a service mains wire through overhead, and in this context, we keep a proper distance between earth and service mains and other overhead lines. Firstly, we should know that these lines can be run by two types.

  • In street
  • Other than street

On the street, we can use two types of methods. And it is dependent on your requirements.

  • Along the street
  • Across the street

Along the street denotes that your line runs along the side of a road or street. And across the street denotes that your line crosses the road or street.

A table is now provided below. in which every aspect is covered regarding service mains and overhead lines.

LINE VOLTAGEALONG THE STREETACROSS THE STREET
LOW & MEDIUM VOLATGE18 FEET19 FEET
HIGH VOLTAGE UP TO 11 KV19 FEET20 FEET

Other than streets, ground clearance

Previously, we talked about streets. But what is the ground clearance if we run service mains wire or another overhead line somewhere other than a street, like in a field?

So, if the voltage is low, medium, or high (up to 11 kV), the ground clearance should be 13 feet. But these 13 feet are valid when the conductor is a cable-type conductor. It denotes the use of insulated wire in a line.

However, if we use bare conductors in this condition, our ground clearance will be 15 feet.

Ground clearance for more than 11 kV and up to 33 kV

For voltages greater than 11 kV and up to 33 kV, ground clearance should be 17 feet.

Ground clearance for 33 kV and up to 765 kV

As we notice, the ground clearance for 33 kV is 17 feet. So, if we add more 33 kV, then every 33 kV increases 1 foot of ground clearance. It means that if 33 kV + 33 kV = 17 + 1 = 18 feet.

Thus, 33 kV is the base voltage for 17 feet of ground clearance. and we add one foot for every 33 kV increase.

For extra-high voltage, we can find out the ground clearance by following a given formula. Now we will find out the ground clearance for 132 kV using this formula.

Thus, the ground clearance for a 132 kV line should be 20 feet.

Thus, the ground clearance for a 220 kV line should be 23 feet. If you put the value in the given formula, you get 17 + 5.66. In this situation, we take a round number, like 5.66, and take it as 6, and the whole value becomes 23 feet.

By the above formula, the ground clearance for a 400 kV line should be 29 feet.

Clearance between conductor and trolley wire Indian Electrical Rule No. 78:

If the overhead conductor is an insulated cable for low and medium voltage, the clearance between the conductor and trolley wire should be 2 feet. And for a bare conductor, it should be 4 feet.

And if the line voltage is 11 kV, the clearance should be 6 feet. It should be 8 feet for voltages greater than 11 kV and up to 33 kV. And for extra-high voltage, it should be 10 feet.

Clearance between the conductor and building structure, Rule No. 79:

For low and medium voltage

  • If a line is crossing over the building and its various parts, then the clearance should be 8 feet.
  • If a line crosses along the building or from the side of the building, clearance should be 4 feet.

For high voltage and extra high voltage, see Rule No. 80

  • If the high voltage and extra high voltage are crossing over the building for a 33 kV line, the clearance should be 12 feet.
  • If the line voltage is greater than 33 kV, such as 66 kV, 132 kV, or 220 kV, 1 foot is added for every 33 kV increment
  • If high voltage or extra high voltage is passing along the building, the clearance for 11 kV should be 4 feet. For 11 kV and up to 33 kV, it should be 6 feet. For voltages greater than 33 kV, 1 foot is added every 6 feet.

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Minimum clearance between lines crossing each other, Rule No. 87:

If the lines cross each other, the clearance between them should be a proper distance. For this statement, there is a rule in the Indian electrical rule book. A table is given below. In which every type of voltage line is crossing each other, what should be the clearance? This is given in this table.

LINE VOLTAGE11KV33KV66KV132KV220KV400KV765KV
11KV8 feet8 feet8 feet10 feet15 feet20 feet26 feet
33KV8 feet8 feet8 feet10 feet15 feet20 feet26 feet
66KV8 feet8 feet8 feet10 feet15 feet20 feet26 feet
132KV 10 feet10 feet10 feet10 feet15 feet20 feet26 feet
220KV15 feet15 feet15 feet15 feet15 feet20 feet26 feet
400KV20 feet20 feet20 feet20 feet20 feet20 feet26 feet
765KV26 feet26 feet26 feet26 feet26 feet26 feet26 feet

For example, if an 11 kV line crosses a 220 kV line, then, according to the table, the clearance between these lines should be 15 feet. As a result, we can calculate every type of voltage level crossing distance.

Crossing of a national highway and a major road

  • In this case, we prefer underground wiring to an overhead system for voltages less than 66 kV.
  • For 66 kV and up to 132 kV, ground clearance should be 14.6 meters.
  • For 132 kV and up to 220 kV, clearance should be 15.4 meters.
  • For 400 kV, clearance should be 17.4 meters.
  • For a 765 kV line, clearance should be 23.4 meters.
  • If the line is crossing a national highway or major road, the minimum span should be 250 meters.

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