GIS high speed earthing switch

[Mbrooke]

What are high speed earthing switches used for in GIS? And when/what relay logic is used to activate them? Also I've heard (though unsure if there is any truth) that they are used so the DC capacitance of an underground cable does not saturate the line CTs after the breaker has opened. If true I can not warp my mind around how you would coordinate BF around that... Or how you would know the breaker has extinguished its arc at that exact moment.


Voltage of gear in question is 115kv to 500kv.

 

[marks1080]

500kV GIS sends a chill up my spine....

Sorry - I don't have anything useful for you. Good question though, I eagerly await some education.

 

[Mbrooke]

500kV GIS sends a chill up my spine....

I take you know something here...

 

[marks1080]

Just a lack of experience. I've been on sites with 500kV GIS equipment. It's just different. You're literally just a couple feet away from the live 500kV bus work. It goes without saying that extra attention must be given to work procedures with this kind of equipment.

 

[Mbrooke]

In a way yes, but its surrounded by grounded and bonded aluminum.

 

[Power0020]

http://ask.abb.com/products/___/gas...st-Acting-Earthing-Switches--FAES--used-/1377

 

[DTR2011]

I once asked the same question to a Swiss guy installing the GIS. I was informed that it was to
"awake sleepy protection at the other end of the line". I haven't seen a fast acting ground switch
connected to any protection scheme I've ever seen.

 

[Mbrooke]

I think he is saying that the earthing switch can be used to deliberately induce fault current on the line in the event of breaker failure- but thats where DTT comes in.

@Power0020: That would shed some light on it- though I am curious where to hook up the fast switch in field.

 

[mgtrp]

At my previous utility, there were several high-speed ground switches used to trigger the remote protection. This was in cases where there were no communications between the substations, so the local protection would close the ground switch for certain fault types. I suspect that if these substations were built today things would have been done quite differently!

Cheers,
mgtrp

 

[marks1080]

So it's like a 'Poor man's transfer trip'? This is a pretty common technique in for transmission and distribution lines when you only have DUTT. When local protections operate, the assumption is that the remote end may not see the fault. Bond the line directly to ground via a ground switch and the other end definitely see's the fault.

I don't recall seeing this deployed on the 500kV GIS system I was alluding to above... but I can't say for sure they aren't doing this.

 

[Mbrooke]

Shorting (suicide tripping) was very common in distribution substations without primary breakers. If the transformer needed to be disconnected relaying would close an earth switch and clear the T line. Crude, but effective and tolerated in that a transformer failure or fault between the bushings and MV breaker were unlikely overall. Today you have circuit switchers and DTT if that fails.

 

[ScottyUK]

Over here they are called 'fault throwers'. As far as I know they aren't being installed today, or if they are then it is in very small numbers, but there are a lot of legacy devices out there on the system. Haven't heard of any installed on systems operating above 132kV so they're confined to the distribution / sub-transmission system in the UK. They're much more common at the lower voltages such as 11kV through to 66kV.

 

[itsmoked]

We use them in electronics occasionally. We call them 'crowbars".

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crshears]

What are high speed earthing switches used for in GIS?

In "my" utility these are not ever employed for auto-grounding purposes at 500 kV, as anywhere there's 500 kV there's OPGW [ "optical ground wire" ], meaning "sky wire" with a fibre optic bundle in the centre, meaning digital teleprotections can be employed.

Aside: for a while there was a site at a remote tapped location that used vacuum auto-grounds @ 230 kV, but that was only an interim solution until OPGW was installed on the circuit through that site.

We do have one location @ 115 kV where an SF6 fast-acting ground is used as an auto-ground, but other than for that site, any of the auto-grounds we still have in service are all air switches.

All that being said, within my utility SF6 FAGs are almost exclusively employed for the purposes for grounding off-potential circuits for work protection, most commonly in situations where relatively high residual or induced voltages may still be present on that equipment despite its having been switched out of service. The FAGs are typically high speed both when being applied and removed; however there are some legacy ones that are quick on, but slow off, and specific instructions / operating restrictions are in place to ensure proper sequences are followed to preclude these being damaged, these being based on studied of the capabilities of the grounding switches at the various sites connected to that circuit, spelling out in great detail the sequence in which grounds are to be applied and removed, including, when needed and only as a last resort, the grounding or un-grounding of a circuit via circuit breaker, a most time-consuming but necessary procedure.

CR

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

 

[Mbrooke]

SO in other words the breaker just trips on the GIS- not grounding down thereafter- unless of course its maintenance/line repair.

 

[crshears]

Correct.

At this moment I have open before me the display for the station with the GIS auto-ground; it's between the transformer primary switch and the bank itself, so it clearly works the same way as conventional air AGs, viz., operation of transformer protection initiates closure of AG, applying single-phase solid fault which trips the line out of service; opening of transformer primary switch is also auto-initiated. Since ground is fast-acting and bank primary operates somewhat more slowly, automatic re-energization of the circuit from the UV + T breaker is delayed to allow for this.

[edit]

Doh! I've been wrong before, and I was wrong again...I'll be okay once my coffee kicks in...

I gapped on the fact that this is a 230 kV station, not 115, so I guess that at least one location we DO in fact use a GIS FAG this way.

 

[qman5]

It's possible to discharge loaded cables or overhead lines via a fast acting ground switch (the acronym has always made me laugh) or high speed earthing switch (HSES). Protection-wise, this is something that I cannot comment on. At this point, I understand that is a merger is what the switch is capable of versus what the load/line is capable of supplying. If someone can explain how this works on a protection level, it would be appreciated.

 

[cuky2000]

Question 1: What are high speed earthing switches used for in GIS?
Answer 1: Is a high speed switch using motor and/or spring operated mechanism that operate faster than the regular maintenance switch and have limited breaking current capability some of them for 0.5 A. The fast grounding switch is used with dual function:
. a) Provides extra safety to the maintenance personnel
. b) Ground capacitance (cables, transmission lines, etc.). 

Question 2: And when/what relay logic is used to activate them?
Answer 2: The circuit breaker need to be tripped first and interlocked as the regular air insulated substation (AIS). The enclosure of the GIS shall be design to withstand the thermal effects of an arc at the full rated short circuit current until the nearest protective relay has acted and tripped the upstream breaker.

Question 3: Also I've heard (though unsure if there is any truth) that they are used so the DC capacitance of an underground cable does not saturate the line CTs after the breaker has opened. [sub]If true I can not warp my mind around how you would coordinate BF around that... Or how you would know the breaker has extinguished its arc at that exact moment. [/sub]

Answer 3: Rather than CT’s the fast earth switch protect the VT from core saturation during switching the charging current of the line

For illustration of the maintenance and fast grounding (earthing) switch, see the enclosed sketch with a typical 500 kV GIS module.

 

[Mbrooke]

My mistake, VTs. Although technically the caps in the VT (CCVT) would theoretically block it.