undergraduate Gabidullin I.R., Associate Professor Dyakov I.A.

Tambov State Technical University, Russia

 

METHOD OF CALCULATING THE LIGHTNING ROD FOR THE MAIN STEP-DOWN SUBSTATION

 

On the substations of 6 to 500 kV transformers, outdoor (ORU) switchgear including bus bridges and flexible connection, closed (ZRU) switchgear, oil facilities and other explosive and flammable structures must be protected against direct lightning strikes. To protect the used rope lightning. Lightning rods installed on structures ORU, searchlight towers or substations separate lightning rods with separate grounding resistance of 80 ohms [1, p. 426].

Consider the methodology for calculating lightning rod for the main step-down substation. Let the protection zone must apply open substation 4 lightning rods, of equal height.

Step 1. Defining the parameters of the protected area:

Let us check the height of the lightning rods    and protection. Maximum height of the protected object .  Then the active height of the lightning rod (excess height of lightning rod above the object to be protected) is given by:   .

The radius of the base of the cone at ground level: .

The top of the cone of protection: .

The radius of the horizontal section at the height of the protection zone hõ from ground level:

         When ,

where          L – is the distance between the lightning rod, m; – height of protection zone midway between the lightning rod, m;  – the width of the joint zone on the ground level of protection, m; – width of the horizontal section of the joint zone of protection hX height from ground level, m. Then  è

Fig.1. Protection zone of multiple lightning rod

         Step 2. Defining Reliability lightning.

Let the number of breakthroughs lightning strikes per year on the protected object:

where  N – the total number of lightning strikes to the lightning rod for one year; Y = 10-3 – the likelihood of a breakthrough in the area of lightning protection. Then    The probability of lightning into the protected object   .

         1. Barybin, YU.G.  Reference design power /YU.G. Barybin - M .: Nedra, 1990. - 576 p.