STRESS CONES???
STRESS CONES???
(OP)
I am new to a group of engineers working on 13.8kV systems and do not want to appear stupid. 
What are stress cones???? I assume that it is some sort of device that connects conductors to terminals on switchgear and transformers. I also assume that they relief stress from the weight of a conductor and that they would supress corona.
What is BIL??? I assume that this stands for Basic Impulse Level. Is this the level of voltage that a device can withstand without failing???
Thanks for the help and I enjoy this forum.
What are stress cones???? I assume that it is some sort of device that connects conductors to terminals on switchgear and transformers. I also assume that they relief stress from the weight of a conductor and that they would supress corona.
What is BIL??? I assume that this stands for Basic Impulse Level. Is this the level of voltage that a device can withstand without failing???
Thanks for the help and I enjoy this forum.
Wirenut






RE: STRESS CONES???
I am not sure about BIL. I will see if I can come up something as I have seen that term before, just not sure where the reference is.
RE: STRESS CONES???
I think BIL is Basic Insulation Level refers to the ultimate voltage at which some device will flashover. For example, an overhead primary distribution pole built for 12 kv will flashover at say, 60 kv. Not sure what the proper voltage is, but that's the concept.
RE: STRESS CONES???
http://www.southwire.com/tech/library/pc/pwrcab08.htm
RE: STRESS CONES???
RE: STRESS CONES???
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The usual test waveform for determining BIL of equipment is a 1.2 x 50 microsecond impulse, meaning the voltage pulse increases from zero to peak value in 1.2 microseconds and declines to one-half peak value in 50 microseconds.
RE: STRESS CONES???
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This place helps alot!!!
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Wirenut
RE: STRESS CONES???
1. A Basic impulse Insulation Level that has been adopted as a preferred American National Standard voltage value is the preferred Basic impulse Insulation Level (insulation strength). Reference ANSI Std C92.1-1971 "Voltage Values for Preferred Transient Insulation Levels"
Essentially, the insulation level is a combination of voltage values (both power frequency and impulse) that characterize the insulation of equipment with regard to its capacity of withstanding dielectric stresses
2. Type cones in advanced search of this Forum. It will return excellent postings on cable stress cones in addition to the starworthy postings above. Why not to use this Forum resources?
RE: STRESS CONES???
Blacksmith
RE: STRESS CONES???
If you find it difficult to achieve the BIL you need using only the stress cones, you also have the option of applying surge arresters to add to the protection provided by the BIL of the stress cones.
As many of you have noted in this post, the voltage spike from some switching transients can be quite formidable. Add the superposition of traveling waves at cable termination points, and you have some significant overvoltages.
IEEE C62.22.1-1996 is a good guide for applying surge arresters.
RE: STRESS CONES???
The resonances and subharmonics that develop during a switchgear opening on its output side (if upstream is transformer winding) are usually suppressed by resitors to protect PTs for burning. The resonance or subharmonic resonance is caused by the transformer nonlinear inductive characteristics in conjunction with capacitive charge currents (or capacitive charges) of the downstream power distribution.
RE: STRESS CONES???
For high voltage application the stress cone is typically called in the USA Pothead. The material used are porcelain or polymer housing.
For specific info on stress cone visit the following sites:
http://www.gwelec.com/images/ca3-00pdf/page2-3.pdf
http://www.hubbellpowersystems.com/powertest/hubbell_cable_acces/pdfs/terminations.pdf
Cable termination are cover in the IEEE Std 48-1990 "Test Procedures and Requirements for Alternating-Current Cable Terminations 2.5 kV Through 765 kV".
The dielectric strength of cable termination are characterized by the typical standard test waves, power frequency voltage tests and Impulse tests (BIL and BSL). BSL is the Basic Switching Insulation level and consist of the standard 250/2500 microseconds.
BIL is applicable to all voltage ranges while BSL are significant above 230 kV per ANSI standard.