What Is Electrical Stress?

By Chris Dodds on 16th February, 2016

Follow us on LinkedIn

What Is Electrical Stress?

We received a surprising email today from Douglas Page.

Doug would not admit it but he is an acknowledged expert in the installation, jointing and terminating of EHV cables.

Yes, you are Doug.  

The email read "a bunch of questions from recent posts working with Thorne & Derrick, have asked me to explain some misconceptions. I am in no way trying to instruct, these are just my opinions, and hopefully 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 Juggernaut 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 coming into www.cablejoints.co.uk 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 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.

HV 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.

HV Cable Joints

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.

HV Cable Terminations

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.

Cable Joints

HV Cable Jointing

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.

Cable Terminations 11kV 33kV

Again this can be achieved in various ways. Mastic and heat shrink stress control tubing, a solid push-on mass, or again hand taping.

Jointing Cables

The type of cable termination doesn’t matter, they are all trying to achieve the same result. Control and dissipate electrical stress through deflection.

Cable Terminations

33kV

11kV 33kV

HV 11kV

Cable Joint

Cable Jointing

Pfisterer Joint

Conclusion

"Hopefully this clarifies some of the cable jointers questions. Sometimes some types of cable splices can be a “back to back” cable termination, like the stop joint pictures I showed in a previous post. 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.

Cable Jointing

Pictured : Cable Fault - this medium voltage cable fault was detected on the 13.8kV stress cone of a heatshrink cable termination.

Note the blue / green "electrical fault dust" inside the yellow circle where the concentric neutral is in contact with the stress cone. 

See : 11kV Heat Shrink Terminations - Stress Control Tubing Installation Guidelines

Cable Termination Stress Control

 

 

  • Further reading from Douglas Page

115kV Straight & Stop Joint On LPLF, PILC Cables In Cable Vault 

EHV Cable Splicing - 115kV Stop Joint (Taped) Flickr Album

Jointing 44kV High Voltage Submarine Cables Using 3M Cold Shrink Splices

Masterclass : 230kV Pipe Type Pothead Replacement /Cable Freeze

Photoblog - Water Treeing in High Voltage Cables : A 230kV HPPT Termination Repair

 

Invitation

Thorne & Derrick are inviting you to join LinkedIn’s fastest growing Discussion Group : Low & High Voltage Power, Cabling, Jointing, & Hazardous Area Electricals (LV-HV).

Discussion subjects include cable installations, cable jointing, electrical substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.

Network, engage and promote your profile, company or products with over 10,000 influencers.

linkedin-logo Click Here To Join




Category:  HV Cable Jointing & Terminating

Go back to blog index