Gas Insulated MV Switchgear Low Gas

[anggapra]

Hi All,

In my plant, there are some MV Gas Insulated Switchgear (SF6) that have low gas indication.

Is it safe to operate it with no load but energized condition?

Thanks,
Angga

 

[RRaghunath]

No.
The gas provides insulation.
Enhanced cooling is insignificant and hence it is nothing (or very little if at all) to do with loading.
So, any switching or lightning surge entering the switchgear could cause flashover.
This is presuming that the low gas is in the enclosure and not in any of the breaker interrupting chamber.

 

[dik]

Insulation big time, I understand... it allows equipment to be real close... GIS gas can leave quite a carbon footprint (worse than freon), I understand and they sometimes leak...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[anggapra]

@RRaghunath thanks for your reply

I'm not really sure wether the low gas indicator is for the gas in the enclosure or in the breaker interupting chamber.
But my guess is the former is correct.
So, what would you suggest I do? Do you think the switchgear needs to be deenergized asap?

 

[GroovyGuy]

Angga,
To be on the conservative side of this issue. I would say that it is not safe to keep this gear energized.
Having said that, are you absolutely convinced that you so have a low-pressure event occuring (and not just say a faulty pressure-switch}?
If I recall correctly MV SF6 switchgear uses SF6 gas to insulate the main-bus, isolation-switches, etc as well as he arc-chambers, include the interrupting chamber which s a more-or-less standard vacuum bottle. This implies that any low-pressure event can result in a significant hazard.
BTW How old is this switchgear?
GG


"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[RRaghunath]

anggapra,
Generally speaking, GIS is always compartmentalised with each compartment having its own gas pressure switch and filling/evacuation arrangement.
Check the Drawings/Manual of your GIS model and find out the details.
Once you identify which compartment is having problem, it will be easy to take shutdown of that panel alone and do rectification.
In case of doubt, it is better to contact the OEM.
GIS is supposed to be maintenance free for life. So, it may be better to talk to the OEM and follow their advice.

 

[anggapra]

@GroovyGuy

Thanks for pointing out the fact that there is possibility of a faulty pressure indicator. Is it possible to detach the indicator and check/calibrate it? We've never done this before in our site.

But I wonder if there's actually a gas leak and the gas pressure is already low, then it'd mean the insulation level would already reduce. But how come there's no arc/fault inside the compartment under operating voltage?

The switchgear is a 24 kV GIS that operated on 13.8 kV system. I'm not really sure about the age, but I think it's between 10-15 years old.

@RRaghunath

I've checked the manual, there is no gas filling facility. They stated that the compartment is sealed for life.

 

[Aradhana Ray]

According to me it is not safe. Do Proper GIS testing power, check all functionality and manual or AC voltage test.

 

[RRaghunath]

Anggapra,
I suggest you contact the manufacturer with all your observations and take their guidance. Since it is sealed you say, there is nothing that can be done at site it appears.
As long as there is no switching or lightning surge or any transient giving rise to over voltage, the low pressure may not lead to flashover in the switchgear.
So, it is important to rectify soonest but not critical as to demand immediate shutdown.
But, do inform your management the situation so that in case something untoward happening later they are aware.

 

[crshears]

How low is the density? Is the low pressure indicator scaled in such a way as to indicate [1] first stage low density, meaning "Take notice and report, but still okay to operate," [2] second stage low density, meaning "Can stay in service but promptly initiate replacement," and [3] critical low density, meaning "no longer safe to remain in service; do not operate, and promptly remove from potential using only adjacent devices" ?

Which brand are the devices?

My utility has begun installing sealed devices that are never and cannot be refilled, only completely replaced; is that what these are?

CR

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

 

[anggapra]

thanks all for your advice.
I've contacted the manufacturer, in line with RRaghunath, they said it's still safe to keep it energized under normal operating voltage and recommend to de-energize and replace it.

crshears,
It's siemens 8DJH, the pressure indicator only indicating two level: low (not safe to operate) and high (safe to operate)

 

[crshears]

Hmmm . . . for a binary alarm like that and based upon the descriptions you provided I'm surprised Siemens would say it's OK to leave it energized . . .

CR

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