138kV GIS Switchgear 2

It appears that this gear is arranged with 5 breakers in a ring bus configuration with feeder cables and two SF6 busses (trafficators). The sketch below is a 6 breakers ring bus with fed with cables only.
I hope this help to clarify how a ring bus is arranged in a GIS.

Thanks that's excellent!

Coupe of other questions - when you say "trafficator" are you talking about the (2) buses which leave the gear? Those are actually feeder busways to transformers. Also, as I understand this particular project intercepted existing HPFF cables and routed them in and out of the substation (basically extend the existing circuit in and out of the GIS gear). Can HPFF cables terminate directly to GIS gear, or do they need to transition splice to XLPE before they connect to the gear?

I think G&W makes an oil-stop GIS termination but not sure if it is applicable to this style of switchgear. Even though a lot of people are jumping on the XLPE bandwagon, I still like HPFF cables because they have very good proven service life, great impulse resistance, and are more tolerant of small manufacturing imperfections in the insulation which XLPE cables cannot have. The downside is obviously having to deal with the oil. They also typically have lower current carrying capabilities since they are 85C rise maximum and are triplexed in a single pipe versus XLPE which is 1 conductor per conduit (or direct burial).

Thanks

Also, something else I noticed, the design I'm referencing has the cable positions all in the center, whereas the typical you show shows the cables alternating between the lower and middle bus. Basically your example would look like this:


Position #1



Position #2



Instead of the way the bays are arranged, in the typical view, the cable exits are all in-line and don't alternate upper to lower.



So not entirely sure how the buswork would need to be to make it like that. Perhaps this was an early mock-up drawing that isn't quite correct in terms of the actual manufactured layout of the gear and how it would be done.

A said:

....when did you say "trafficator" are you talking about the (2) buses which leave the gear? Those are actually feeder busways to transformers.]

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OK. I understood better now.
[sub]Just for curiosity: Is the 3-phase SF6 bus connected directly to the transformer or with and overhead jumper from SF6 bus/Air bushings to the transformer bushings?[/sub]

B said:

... this particular project intercepted existing HPFF cables and routed them in and out of the substation.]

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It is suggested to install a transition splice HPFF-to-XLPE at the interception of the existing pipe type cable outside the GIS particularly if this is an indoor substation. The reason for that is that 3-cable module is more cost effective and efficient than the individual cable GIS cable module termination. The other major challenger is to deal with oil fire/explosion hazard in the basement (cable vault) and the GIS deck.

C said:

...in the typical view, the cable exits are all in-line and don't alternate upper to lower]

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To meet the client complicate clearance requirement, the cable termination was alternated to achieve the required cable termination distances without changing the pre-defined GIS cable module. [sub]I do no know good technical reasons to justify the additional complications.[/sub]




SUGGESTIONS: Ask the GIS manufacturer to furnish a cable holding hardware bolted to the bottom of the cable module to limit the cable SC forces. Also, the cable should be adequately routed to avoid safety exit constraints in the cable vault below the GIS with enough height for appropriate bending ratio and holding cable clips.

Thanks! Great info!

Would this help by chance? Similar setup.

With 345kV the layout changes a lot because you don't typically see combined 3-phase bars in the same GIS pipe, they are separated into individual pipes per phase. Most likely I'm thinking its because of the insulation requirements at the extra high voltage.

But yes what you show is indeed a ring-bus arrangement.

FWIW I've seen phase segregated 138kv GIS drawings- it seems to be either or at that voltage. Why you would choose one over the other I'll leave that to other members.

For the 138 kV application, there are two types of GIS design available into two main categories:
a) Type 1: a non-segregated bus with the breaker in a single tank. The majority design rated up to 170 kV, with some exception rated up to 230 kV. Up to know, this is the most cost-effective option available in the market.

b) Type 2: Segregated /Isolated phase design, which 3 breakers tanks. This is a compact design rated for 145 kV show in the market around the year 2000 as an option with reducing weight and SF6 gas volume up to 40%.

[highlight #FCE94F]It should be mentioned that there is becoming recently available option for SF6 free gas for both types of GIS.[/highlight]

Trafficator? I've never heard of these...

Did you by any chance mean trifurcator? Those I know aught about...

CR

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

A better description for a three-phase overhead line connection is "SF6-air bushings Module"