For the past few years. GreyMatters has been fortunate enough to support the rail electrification and upgrade programmes across the UK for Earthing Design. And maintaining a consistent approach across a building programme of this scale can be a massive engineering headache for all design teams concerned. Especially, when Earthing Design Standards touches on so many disciplines along the way - from civils, OLE (Overhead line equipment), signals, EMC, 3rd parties, ecologies, geophysical as well as the more obvious general E&B (earthing and bonding).
The one thing that provides a form of "glue" to help keep the various disciplines and schemes on track (excuse the pun) are the codes of practice or earthing design standards and their correct interpretation. I say 'interpretation' because the codes cannot account for all the scenarios encountered. Invariably, there are the not-so-common, or dam right awkward scenarios that no-one has foreseen which get everyone scratching their heads to resolve.
In addition, an electrification scheme has to consider the interface between two sectors, i.e. rail and the energy sectors. Both are regulated environments in the UK / EU and both have subtly different requirements and focus.
Top tier Earthing Design standards
In the UK, the fundamental standards for Railways are named below;
- BS EN 50122: Railway applications — Fixed installations — Electrical safety, earthing and the return circuit. In 3 parts.
- BS EN 50522: Earthing of power installations exceeding 1 kV a.c.
Network Rail has a very talented technical engineering team who have studied/developed and codified specific practices to supplement and to help bridge the two sectors. These Rail specific supplemental standards support the above top tier standards and can be extensive in number as well as detailed in content to provide the necessary design guidance required to meet expectation and achieve compliance during construction. n.b. You'll excuse me if I don't include them here as that would make life too easy for competitors.
Problem sites that don't play ball
One of the most common challenges for the current / planned electrification schemes is ...
The size and shape of footprint available for track sectioning cabins and substations
You can imagine, the land owned by the rail company is usually restricted to a corridor to accommodate the rail network and associated infrastructure. So, the typical rail substation tends to be located in a long and elongated patch of land within or near, this corridor.
This means if the geology is mildly non-conductive. Trying to contain and control a fault current can be like trying to "squeeze a Quart into a Pint Pot", as the image above, i.e. leading to a spillage of energy into areas where you do not want it to go.
So, the Earthing Design lead really will have to start earning their fee as there are many safety concerns to factor in that are unique to Rail and can make construction a real challenge.
Some common Earthing Design challenges for Rail are:
- Size and shape of footprint
- Relatively high fault level to control (encroachment, hot site)
- Elongated conductive structures (rails, etc) that do a great job of transferring hazardous voltages (including those from lightning), if not careful
- Public accessibility
- Track formation doesn't overly help earth leakage
- Stray current and enhanced corrosion
- Interface between AC and DC traction systems
Why not drop us a line or chat with our team?
This post is written by Ian Griffiths, Principal Engineer at GreyMatters, an Earthing & Lightning Consultant of 27 years, one of the top 1% accredited CDEGS consultants and professional advisor to international utility companies, data centre and infrastructure developers.
Tagged: Rail Electrification