What Is Electrical Stress?
Published 24 Nov 2020
This article was originally posted in February 2016 to our mothballed website, www.cablejoints.co.uk
Today, we received a surprising email from Douglas Page.
Doug would not admit it but he is an acknowledged expert in the jointing and termination of EHV cables. Yes, you are Doug.
Doug has been in the industry since 1984 and is currently Work Methods and Training Instructor, EHV and HV Cable Splicer, Environmental Health Technician at Hydro One.
Expert and competent at jointing and terminating Extra High Voltage Cables (HPOF, XLPE and LPOF) and using leading Medium & High Voltage Cable Accessories from manufacturers including 3M, Raychem and Pfisterer.
This surprising email read, “a whole bunch of questions in response to recent posts by Thorne & Derrick, have asked me to explain some industry misconceptions. I am in no way trying to instruct, these are just my opinions, but hopefully they will answer some of the strange questions I have been receiving. Let me know what you think, or even if I should go down this road. The problem is, the same misconceptions have been causing cable failures for years”.
We say, steam on down that road Doug – we’ll rocket propel your content via our LinkedIn Discussion Group and social networks. You are a thought-leader with vast experience and are attracting a definite fan-base. We see that through the Google traffic rushing into www.powerandcables.com from your Posts.
Be as flattered by the attention as we are honoured to have the opportunity to be your online voice.
R.E.S.P.E.C.T to you.
Lets pass you all over to Doug to explain some of those Electrical Stress misconceptions.
Electrical Stress Explained
Without an insulation shield, you can see how the voltage leaves the conductor travelling through the insulation, very erratically and effectively seeking ground/earth, creating hot spots and eventually cable failures – basically this is electrical stress.
The creation of an “insulation shield” allows the stress/flux to travel very efficiently and evenly, along the cable, dissipating the “stress” evenly.The problem arises when we remove the insulation shield for cable splicing and terminating.
The abrupt end to the shield allows the different percentages of voltage to escape the insulation at a concentrated point, creating an area of extreme stress, as the voltage seeks ground/earth. This electrical stress again creates intense heat and eventually failure. In a cable splice, we are not trying to eliminate the stress, but rather control it.
In some cable splice kits gradient mastic, and “heat shrink stress control tubes” are used to contain and control the deflection of the flux lines. In other cable joint kits it could be push-on single mass control tubes. In hand tape kits, it is all built with different types of tape, put on in specific order, to very specific measurements.
With cable terminations it is different. We are not trying to control and contain, we are trying to control and dissipate as much electrical stress as possible.
Again this can be achieved in various ways. Mastic and heat shrink stress control tubing, a solid push-on mass, or again hand taping.
The type of cable termination doesn’t matter, they are all trying to achieve the same result. Control and dissipate electrical stress through deflection.
“Hopefully this clarifies some of the cable jointers questions. It doesn’t matter the type of cable or manufacturer, the importance around the quality of work, cannot be stressed enough, if you have a cable splicer telling you that the semi-con removal isn’t important, or the cable doesn’t need to be sanded…look elsewhere for a cable splicer,” concludes Doug.
LV, MV & HV Jointing, Earthing, Substation & Electrical Eqpt
Thorne & Derrick International are specialist distributors of LV, MV & HV Cable Installation, Jointing, Duct Sealing, Substation & Electrical Equipment – servicing UK and global businesses involved in cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.
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