Data Centre Earthing Design Case Study

Objectives

Supplied from multiple HV Transmission lines.  GreyMatters given the task, to examine the existing earthing system design. For an established large scale Data Center. To study how the existing Data Center earthing would perform under electrical fault conditions. Also, to provide the necessary electrical earthing design improvements. Also, to EN50522 and IEC standards to cope with the increased capacity of the Data Halls.

Due to the ever-increasing demand for cloud-based and remote hosting resources. There has been a significant increase in calls for more capacity on Data Center providers worldwide.

Data Center Earthing – Project Features

Soil resistivity (ρ):	high-low-high
Geology:	clay on mudstone
Primary Voltage (V1):	<200 kV
The number of line towers:	~100

Data Center Earthing – Results

For this site. Multiple soil resistivity tests using the Wenner method. Because of its high signal energy soil resistivity testing instrument (400 V). Also, carried out in 6 locations across the large site.  Wenner traverses varied in spacings from short surface samples to long lead traverses (soundings) of up to 300m.   Why so long? Every Earthing Electrode System has a sphere of influence in the ground. Not just across the surface. But in all 3 dimensions.  So, it’s just as important to understand what is going on. At the deeper layer(s) of the influence of the electrode. As it is at the surface layers.  Because this is, the deeper layers have a role to play. During the discharge of electrons into the ground from a fault.

The results from the soil resistivity tests, processed using CDEGS – RESAP engineering module. Also, which indicated a multi-layer soil structure.   Thus, the data modelled in CDEGS RESAP contrasted with the previous data assumptions held. Therefore, which allowed an improvement in soil model accuracy of 30%.

The Soil Model

From the soil resistivity model for this data centre site. It became clear a higher than average amount of earth-return-current would pass through the soil. On its path back to the source.  As in all cases, it’s imperative to reach a clear understanding of the soil structure. Also, the electrical properties of the ground itself. 

The key point is an accurate Soil Model. Therefore, is the foundational cornerstone that ALL subsequent parts of a valid Electrical Earthing System Design, build upon.  Therefore, this means, eliminating error from Soil Resistivity Testing. Hence, at this stage is of absolute capital importance.

HV Source Power

So, once an appropriately accurate soil model had been derived. From the soundings data. Attention turns to characterising the HV source power from the overhead transmission lines. And, which supports a significant quantity of tower structures. Tower chain impedance. And also, remote earthing arrangements feeding a local substation. Including the build of the step-down transformers and associated earthing transformers in CDEGS HIFREQ virtual model space.

CDEGS Software HIFREQ

As a result, using Finite Element Analysis software CDEGS HIFREQ. The model representing all the existing (and proposed) above and below earthing arrangements. For the entire data centre and its data halls. Subsequently analysed. Also, including impedance contributions and parallel return paths. From reinforcement, overhead earth wires, OHL towers, cable sheaths, pits, lightning protection and plant bonding arrangements.

Key Points:

• Performance & Safety: A comprehensive Earth Fault Study using CDEGS Hifreq of the Electrical Earthing Design, from source to the site’s local substation and data halls to establish a SAFE electrical earth system to EN 50522 capable of protecting life (touch and step voltages) against the risk of an imported fault.
• Performance & Safety:  Electrical properties of the ground were comprehensively studied and an accurate model was delivered forming the basis of all present and future electrical earthing system designs.
• Economy:  Utilising an accurate multiple-layer soil model of the ground allows present and future electrical earthing designs to be optimised with a sense of certainty, which allows Electrical Earthing Designs to be right-sized, saving money by avoiding the risk of over-engineering on installed arrangements.

If you are responsible for your Data Centre Earthing and believe your current Electrical Earthing System Design needs a rethink from some new GreyMatter then get in touch and we can discuss your challenge.

Earthing Course – Free Trial

Do you want to understand more about Electrical Earthing System Design – Greymatters Academy is our Earthing Training site take a look or access your free trial here.