IEEE Std 2778-2020 pdf download

IEEE Std 2778-2020 pdf download.IEEE Guide for Solar Power Plant Grounding for Personal Protection.
4.3 Auxiliary systems (equipment frames) for grounding
As noted above, SPP grounding design often makes use of auxiliary systems (such as cable trays, PV frames, support posts, etc.) as part of the grounding system. These auxiliary Systems are primarily above-grade, and in most cases they provide electrically-continuous paths for current to distribute through the SPP. However, there are caveats to he aware of when the grounding system is dependent on these auxiliary systems.
For instance, the path needs to be truly electrically continuous across any joints and connections; full compliance with UL 2703 [86] and 3703 [B7] is one way to provide confidence in this continuity. If the support posts are covered with a corrosion-prevention coating. embedded in high resistivity (gravel) backfill, or otherwise not in solid electrical contact with native soil, their benefit may be reduced or eliminated. These effects can be properly accounted for if modeled and analyzed properly.
Similarly, the electric resistivity of steel is higher than that of copper, potentially resulting in greater voltage drop along the line of panels. There may also be concerns regarding galvanic corrosion between dissimilar metals when connecting grounding conductor to the equipment frames. Where the NESC is applicable, there are a variety of requirements for these auxiliary grounding electrodes including materials, size, etc. [13 1].
4.4 Fence grounding
Where the National Electrical Safety Codek’ (NESC®) (Accredited Standards Committee C2) is applicable, metal fences surrounding a SPP may require grounding as of the publication of this document [B 1]. From a technical standpoint, additional fence grounding may not be necessary if the fence posts are metallic and bonded to any fence mesh material. However, analysis of touch voltages on the fence is required to confirm compliance with the practices of IEEE Sid 80.
It is not uncommon to have fence-plant separation of 6 m (20 ft) or more if there is a perimeter road, which significantly decreases the conductive coupling between the fence and faulted equipment. Bonding the fence causes the fault voltages to be transferred onto the fence, which in many cases would require a significant amount of additional grounding andlor surfacing along the site fence.
A more practical option is to analyze the site’s metal fence(s) with faults at various locations near the perimeter of the SPP grounding system. If the analysis indicates that touch or step voltage limits are exceeded along portions of the site fence, additional localized fence grounding andior crushed rock surfacing may be placed in those specific areas.
When fences are parallel to or crossing under transmission lines, magnetic and capacitive induction can also pose a concern, although this effect may be substantially smaller than the conductive component from a fault scenario. These aspects can he considered on a case-by-case basis.
4.5 Personnel protection in SPP
An SPP grounding system serves the same function as a traditional grounding system. This includes limiting touch and step voltages to the limits determined in IEEE Std SO. Under fault conditions, personnel protection is examined for the following:
— Touch voltages on all equipment within the SPP fence electrically connected to the SPP grounding system
– Touch voltages on the SPP and any connected fence, possibly due to transfer voltage
Touch voltages on other grounded objects in the vicinity of the SPP that may be alkcted by transfer voltage from the SPP grounding system, as required
Step voltages throughout and just beyond the entire area within the SPP and SPP grounding system
5. Design and analysis approach
The following subclauses discuss a useful design approach, with signifIcant references to IEEE Std O. The goal of this section is to identify differences in design and analysis compared to a substation environment, allowing a user familiar with substation grounding design to understand additional considerations for large SPPs.
5.1 Soil
Because of the size of SPPs. the soil generally cannot be considered consistent across larger sites, and merits more extensive testing and modeling than substation or traditional power plants. Testing is typically performed at a variety of locations with soil models developed for specific areas to capture local differences in the soil characteristics throughout the SPP.