35kv Cable Terminations 1

[duki]

We have two sites that have experinced catastrophic failure of the 35kv cable terminator to switchgear breaker. Both sites used termination kits manufactured by a well known manufacturer. Has anyone had failures involving permolded termination kits?

 

[cuky2000]

I saw similar failures in an industrial facility.

One weak point is in the transition of underground to overhead cable where a traveling wave is reflected exposing the component to nearly twice the incoming overvoltage.

If the cable termination rating is below to the BIL or if the surge arrester will not been properly selected or has mal function, the result could overstress the termination causing the failure.

Sustain overvoltage or even ferroresonance could cause overstress in the cable termination and eventually induce the failure. Manufacturer or workmanship defect could also contribute with the fault.

Consider perform an insulation coordination analysis to determine the withstand capability of the termination and the surrounding power components.

 

[busbar]

The termination-kit producer will likely question installer competence, and want to see acceptance-test reports.

 

[jbartos]

Suggestion: Contact the cable termination kit manufacturer for the history of this kit; if there is any specific recommendation for the 35kV cable terminations using the kit.

 

[sdlloyd]

There are a number of reasons why terminations might fail and you really need to have a look at them closely to see why. As you have had two failures you should be able to home-in on the problem.

Some simple things to look for are:
Did both fail in the same way?
Are adjacent terminations showing signs of distress?
Have there been any system events that could have weakened the terminations (lightning strike)?
Have components been fitted correctly?
Are the premoulded components sized correctly for the prepared insulation (cable can be over or undersized for premoulded components)?
Did the same jointer terminate them, was he trained?

The evidence normally lies in an unfailed accessory. If you can, strip down an adjacent termination and inspect it for installation quality, dimensional check, fit and incipient distress.

The highest stress on the termination insulation is invariably at the insulation screen (shield) termination.

http://www.cableconsulting.net

 

[jbartos]

Suggestion: Essentially, the insulation systems must be properly matched in addition to the good workmanship (or workpersonship)