Catastrophic GIS failure 4

[Mbrooke]

What would happen if a flash-over occurred within a section of GIS? Assuming worst case clearing time (1 cycle trip decision + breaker fail + backup breakers operating) how disastrous would it be? Or not much at all?

 

[cuky2000]

SF6 is inert during normal use and It has been identified as one of the greenhouse gases and in small quantities causes the voice to become significantly deeper, due to its density being so much higher than air.
Breathing SF6 is not recommended ==>>

https://www.youtube.com/watch?v=u19QfJWI1oQ

HUMAN EXPOSURE AND TOXICITY: SF6 is a simple asphyxiant. it is chemical inertness and it is very low accumulation potential support the low concern for the toxicity of this substance.][/i]

However, when electrical discharges occur within SF6-filled equipment, toxic byproducts can be produced that pose a threat to the health of workers who come into contact with them. (see below).
For indoor GIS, it is recommended to properly design the HVAC system to remove the concentration of SF6 close to the floor or the building basement. Below is an illustration of the effect of the toxicity of the SF6 courtesy of
Dilo.

 

[Mbrooke]

@crshears: its ok, neither do I lol.

@cuky2000- wow! Leaned some chemistry today.


Is the risk the same (of any toxins) of pure air or CO2 gear?

https://www.siemens.com/content/dam...tchgear/emhp-b10016-01-7600-8vn1-blue-gis.pdf

 

[ScottyUK]

The HF is one of the big problems, because the moisture to produce it is present in normal air: it forms one of the nastier acids. GIS facilities usually have showers provided to enable thorough rinsing after any accidental contamination.

 

[Mbrooke]

Makes me wonder if its worth considering alternatives to SF6, which sadly seem limited.

 

[crshears]

Like this ?

https://www.3m.com/3M/en_US/novec-us/applications/insulating-gas/

I learned of it here @ eng-tips . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Mbrooke]

Yup- like that. As long as it won't produce toxins when subjected to breakdown arcing.

 

[cuky2000]

Hi Mbrooke,

None of the dielectric gases produce toxins. However, all of them are toxic under arcing. The toxicity of the SF6 is larger than the alternative gases mentioned above.

Vacuum is not poison and is widely used in MV but with limited applications up to 69 kV (possible to 138 kV).

 

[Mbrooke]

I know SF6 is safe, but doesn't it produce toxic byproducts when subjected to arcing?

 

[cuky2000]

Yes, SF6 and other alternate gases as well produce toxic byproducts when subjected to arcing

 

[Mbrooke]

Thank you, you and others have given me plenty to think about. I will research the toxins and breakdown properties of SF6.


Are there any resources of published or documented GIS failures?

 

[cuky2000]

One good source is the CIGRE Report on the latest international survey on high voltage gas insulated substations (GIS) ser

vice experience. Below is a glance of the main failure causes in GIS collected from various publications.

 

[Mbrooke]

When a GIS fails, is everything typically contained or does it burst the rupture disk with lots of smoke/discharge?