Sealing Cables In High Voltage Substations Using Roxtec Cable Transits

By Chris Dodds on 8th January, 2015

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Sealing Cables In High Voltage Substations Using Roxtec Cable Transits




Roxtec commissioned EA Technology to produce a report on the causes and effects of high relative humidity within indoor substation environments and methods of mitigation.

T&D have been selected by Roxtec to circulate this White Paper to the Electrical Industry - we welcome feedback and questions.

Roxtec Cable Seals

The following Comments were generated over the LinkedIn Discussion period of July 2013.

Roxtec approached EA due to their expertise in this area when we wanted to develop our understanding of reasons to specify a more robust method of sealing cables in high voltage substations.

Of key interest to me was the clear benefit of a high degree of high voltage cable retention when selecting a cable sealing product.

Also the need for robust protection against vermin ingress was something we have promoted as a key benefit of the Roxtec sealing system. Gavin Cornall - Roxtec.

Gavin - clearly reading the report there is an urgent industry requirement to adopt an approach to cable sealing based upon a technical specification which defeats water ingress into LV HV substations.

How does Roxtec cable seals handle 3 single core cables ducted in trefoil formation? Ben Riley - Thorne & Derrick.

Hi Ben... we have developed a new cable sealing product for trefoil formation cables, its a simple 3 part composition, it still has our signature Multidimater flexibility but allows for simple installation on heavy duty and high voltage cables.

If you would like to see the H3 Roxtec Cable Seal seal there is a clip here

This cable seal not only retains the cables in normal operation, but also in fault situations. 

Roxtec cable seals and cable transits are very robust. Roxtec experience is that traditional inflatable bags and mastics find it hard to seal effectively these types of cables, certainly on a long term basis due to the continual expansion and contraction in operation.

Its useful to see Roxtec products as not only a seal but as a cable retention aid that goes hand in hand with the cable cleating.
Gavin Cornall - Roxtec

Sealing HV cables is given current press exposure via the Electrical Review Magazine, the leading and longest established electrical trade magazine in the UK if not world : Chris Dodds - Thorne & Derrick.

Roxtec cable seals protect London Array, the worlds largest offshore windfarm - Flickr photo set of project : Gary Amos - Thorne & Derrick.

We have discovered the same failure mechanism on line insulators, both porcelain and polymer, when contamination becomes PD active during high humidity and "cooks" onto the surface.

These Dry Bands do not rinse off during weather events. The buildup of Dry Bands deteriorate the insulating properties and end in a flashover event. 

Sometimes the flashover cleans away the Dry Bands, but also reduces surface hydrophobic quality. This results in more contamination induced Dry Bands and the cycle repeats.

View our lab study on this effect at: "Exploring Insulator Flashover and Scintillation"
John Lauletta - Chairman, CEO, CTO at Exacter, Inc

I cant find a "white paper" to read but Im always interested in this kind of investigation. I find that if you employ a paint company to investigate the state of your walls then they will tell you to paint your house and perhaps not to clean the walls.

Partial Discharge is a very interesting phenomena and detection of discharge events (in HV more so than MV equipment) can be a useful diagnostic indicator.

However when looking for water ingress Im not sure that PD detection is the most useful approach. If there is no electrical activity associated with the damage mechanism then it cannot be detected with PD equipment.

You can hammer a screw into some wood but you are probably better off using a screwdriver to do the job.

Using PD as a maintenance tool for MV equipment is also problematic because there is no independent guide or standard that can relate the various PD characteristics such as inception, magnitude repetition rate, position, type etc to the probability of failure or even to a recommended course of action.

The rate of false positives (PD detected but does not lead to failure) for PD is very high whilst the occurrence of false negatives (no PD detected but equipment fails in service) is also high. (ref CDFI from Neetrac).

Part of the reason for this is undoubtedly the complexities in detecting and measuring PD in the field but also the confusion by the tester with noise and other discharge events such as corona.

Whilst this might sound like "PD bashing" I am certainly not doing this. I repeat that PD detection is a useful diagnostic tool but it must not be promoted or used as a "silver bullet" wonder-diagnostic for all insulation problems. Gary Catlin - General Manager at HV Diagnostics Sarl.

Utility Substation News - T&D & Roxtec press release highlights the importance of new white paper for the electrical utility industry. Cable sealing is the hot-topic, we welcome comments from within the Group.

Why not challenge T&D & Roxtec with your water, gas or firetight cable sealing application today? Chris Dodds - Thorne & Derrick.

Excellent report" Patrick O Halloran, Chief Engineer Condition Monitoring at City Power Johannesburg.

The breakthrough Whitepaper highlighting the connection between relative humidity, PD and power outages is being praised in many places. Chris Dodds - Thorne & Derrick.

The H3 Trefoil cable seal has clear relevance for water-tight sealing of 11kV BS7870 triplex single core cables and 33kV BS6622 single core XLPE cables where inflatable/mastic type duct seals struggle to handle heavy, high voltage power cables. Jeff Jhanke - Thorne & Derrick.

T&D marketing department have produced a Flickr photo set demonstrating Roxtec cable sealing applications in the Wind & Renewable Energy sector - wherever cables enter substations in whatever industry there is critical need for effective cable seals whether low or high voltage  Richard Derrick - Thorne & Derrick.

Thanks Richard - Roxtec cable seals are installed on worlds largest offshore wind farm, The London Array. Flickr project photo album viewed here : Chris Dodds - Thorne & Derrick.

This Cable Sealing report was a real "eye opener " for me. Previously I didn't see the link between flooded cable trenches and excessive humidity in sub-stations. Graham O' Hare - Roxtec UK MD.

Thanks Graham - there is a challenging effort level required to educate the electrical industry and circulate these Whitepaper conclusions. Various factors outside the substation can affect the humidity inside :
  • Plants : avoid excessive plant growth around the substation.
  • Substation Waterproofing : the substation roof must not leak. Avoid flat roofs for which waterproofing is difficult to implement and maintain.
  • Cable Trench Humidity : Make sure cable trenches are dry under all conditions.

A partial solution is to add sand to the bottom of the cable trench but a complete solution is to specify effective Watertight & Ingress Protective Cable Seals where cables enter substations via cable ducts.

Roxtec cable transit frames provide rectangular and round sealing frames for cables and pipes ensuring safety, efficiency and long-term operational reliability - Roxtec cable seals and pipe transit seals and protects against fire, gas, water, dusts, pests, blast load and electromagnetic interference. Chris Dodds Thorne & Derrick.

I think its important to realise that with Partial Discharge there are no absolutes, its not quite an exact science in terms of what causes it to occur.

We know that humidity, dirt, dust and other pollution are some of the factors that cause big issues with respect to cable sealing in electricity substations.

I am very much aware that an active approach in terms of minimising these kind of factors is best practice in terms of ongoing operation.  Gavin Cornall - Roxtec.

VIDEO Tutorial : PD Partial Discharge, Causes & Effects - EA Video Tutorials, 13 Part YouTube Playlist. Click below link. Watch, Listen & Learn about Partial Discharge :

Roxtec cable sealing also ensure maximum uptime in Telecom networks as well as Power applications.

Typical telecom applications include outdoor cabinets, antenna cables, radio links, 3G base station shelters and comms centres.

Telecoms : Roxtec Flickr Photo Album :

Chris Dodds - Thorne & Derrick


Video Playlist - Roxtec Cable & Pipe Sealing Transits

  • Further Reading


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Category:  Cable Transits & Duct Sealing

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