How to identify powerline voltage level and safe clearance level

Powerline

Overhead Powerline

Powerline (Overhead Poweline): In my previous article on electrical safety and portable electrical safety inspection checklist, i highlighted the hazards that accompanies electrical equipment; e.i (Portable electrical equipment), and the safety precaution which are necessary for safe use of these equipment, with the need for portable electrical equipmentchecklist.

This article intends to consider another part of the electrical safety, which is the overhead powerline.

Powerline

According to wikipedia: “An overhead powerline is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors (commonly multiples of three) suspended by towers or poles.”

Types of overhead powerline

There are different types of overhead powerline:

Overhead power transmission lines are classified in the electrical power industry by the range of voltages:

  • Low voltage (LV) – less than 1000 volts, used for connection between a residential or small commercial customer and the utility.
  • Medium voltage (MV; distribution) – between 1000 volts (1 kV) and 69 kV, used for distribution in urban and rural areas.
  • High voltage (HV; subtransmission less than 100 kV; subtransmission or transmission at voltages such as 115 kV and 138 kV), used for sub-transmission and transmission of bulk quantities of electric power and connection to very large consumers.
  • Extra high voltage (EHV; transmission) – over 230 kV, up to about 800 kV, used for long distance, very high power transmission.
  • Ultra high voltage (UHV) – higher than 800 kV.

 

How to identify voltage level of a powerline

The voltage level can be recognized by the length of the insulator string and the number of insulator elements.

Voltage level of a transmission line
Length of insulator string
​Number of insulator discs

110 kV

approx. 1 metre​

6–8

220 kV​

​approx. 2 metres

10–12

400 kV

approx. 4 metres

18–21

 

Safe use of machinery close by powerline

When working close to electrical powerlines we have to exercise caution not to work too close to the live phase conductors. No machinery must be brought into the tower area. Never drive machinery between the tower legs, under a guy wire, or closer than 3 metres from the tower structures.

The minimum clearance distances o powerline are as specified:

Voltage (kV)  Minimum Clearance Distance (ft)
 Up to 50  10
 >50 to 200  15
 >200 to 350  20
 >350 to 500  25*
 >500 to 750  35*
 >750 to 1,000  45*
 >1,000  determined by the utility/owner

HSE Executive has also given a guideline on electrical safety at work and working safely under electrical power lines.

Also see Guidance on Overhead power line Pdf

To work safely around powerlines, you have to be conversant with the voltage levels of the different powerlines and the safe clearance level stipulated for each.

Never be careless around overhead power-lines since the risk involve are so severe, ranging from severe shock, burns, electrocution, fire, etc.

 

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