Surge arrester grounding

[KillBill7]

I’d like to get your thoughts on the best grounding practices for overhead line structures equipped with surge arresters. My understanding is that surge arresters should have the shortest possible path to ground via a dedicated ground wire. Additionally, other pole-mounted equipment (power cables, reclosers, transformer etc) shouldn’t be bonded to the arrester’s ground wire to avoid surge currents flowing through and potentially damaging these equipment. However, I’ve noticed that, in most cases, distribution poles have all equipment— including the arrester—bonded to the same ground wire leading to the ground rod. What are your thoughts on the optimal approach for grounding in this scenario?

 

[jghrist]

The ground connection from the arrester ground to the equipment ground should be as short as possible. This would normally be at the pole neutral/ground where the equipment is grounded at the pole.

 

[cuky2000]

The optimal approach in the ideal world is to have a dedicated unigrounded system. Most distribution systems in the USA are arranged as a multi-grounded system similar to the picture below where not only the equipment (transformers, surge arrester, etc) are grounded but also the neutral is bonded to the grounding conductor at the poles. The shortest distance to the ground point on the earth and any other bonding to the equipment should be as close as possible to reduce the conductor impedance to the ground knowing that a large impedance makes the surge arrester ineffective and not only could compromise the good operation of protective devices but also the safety of the system.

 

[LionelHutz]

You want the arrestor connected across devices so the voltage across the device (line to ground and/or line to neutral) doesn't rise too high. The ground rising at the top of the pole compared to ground potential at the bottom is of less concern than stressing the insulation of devices on the pole.

 

[bacon4life]

The surge arrestor on a transformer is intended to limit the voltage magnitude between components inside the transformer. As long as the voltages inside the transformer stay within the rating, the relative voltage been the top of the pole versus the bottom of the pole is irrelevant.

So rather than trying to make the shortest path down to the dirt, proper surge arrestor protection is all about minimizing the length of the surge arrestor path that is in parallel to the component you are trying to protect.