34.5 kV indoor metal clad air insulated switchgear

[psycholuck]

I work for a midwest utility company and we are investigating 34.5 kV indoor metal clad air insulated switchgear with continous current rating of 3000 Amps. The switchgear application would be on the low side of our 138-34.5 kV substations. I was wondering if any other forum members have experience in this area. Also i am asking for likes, dislikes, problems or comments on this issue.

 

[alehman]

I commissioned some outdoor GE gear with Cutler-Hammer SF6 breakers a few years ago for a small private substation in the Los Angeles area. It seemed to work out fairly well in the end. One problem I recall was that the engineer wanted to use AC control power for some reason. GE chose to derive it from downstream of the secondary side breakers. That didn't work too well when the breakers were open.

 

[busbar]

You may want to review applicability of IEEE Std C37.20.2-1999 IEEE Standard for Metal-Clad Switchgear Publication Date: 2000 References Cited: 44 Number of Pages: viii+64

Abstract: Metal-clad (MC) medium-voltage switchgear that contains drawout electrically operated circuit breakers is covered. MC switchgear is compartmentalized to isolate all components such as instrumentation, main bus, and both incoming and outgoing connections with grounded metal barriers. Rated maximum voltage levels for metal-clad switchgear range from 4.76 kV to 38 kV with main bus continuous current ratings of 1200 A, 2000 A, and 3000 A. MC switchgear also contains associated control, instruments, metering, relaying, protective, and regulating devices, as necessary. Service conditions, ratings, temperature limitations and classification of insulating materials, insulation (dielectric) withstand voltage requirements, test procedures, and applications are discussed

Description of contents at standards.ieee.org/reading/ieee/std_public/description/switchgear/C37.20.2-1999_desc.html

 

[busbar]

For many engineers/designers/specifiers in ANSI regions, it is routine to include compliance with C37.20.2 as part of a switchgear purchase order.

 

[dpc]

One potential concern is the potential arc-flash hazard of metal-clad switchgear, especially air breakers. You may want to investigate availability of arc-resistant gear.

I would also suggest providing for remote operation of the breakers and possibly motor-operated racking operator to allow remote racking of breaker.

You will also want to consider investing in an electrically-operated ground/test device.

I'm a little surprised that air-insulated 34.5 kV gear is still available in metal-clad design. These puppies must be big. I believe SF6 is available in 34.5 kV metal-clad as well.

 

[MDom]

Look also

http://217.153.88.147/PDF_ENG/2_MV_PRODUCTS/04_ISF2_CIRCUIT_BREAKERS.pdf

 

[gordonl]

We have a lineup of Siemens metalclad switchgear. It has been in service now for about 5 years with no peoblems. It uses the siemens 3AF circuit breaker. (available up to 3000A I beleive) I'm not sure if it is arc resistant (I didn't spec this job) but I suspect it is from looking at the door fastners.

 

[busbar]

dpc's comment on arc-resistant gear may be based on Canadian standard EEMAC G14-1

http://www.sandc.com/edocs_pdfs/edoc_001678.pdf

http://www.powellelectric.com/powlvac/pv_pvar.htm

http://www.gs.on.ca/acrobat/GSC Medium Voltage Arc-Resistant Switchgear.pdf

http://www.gs.on.ca/arc-resi.htm

 

[dpc]

Gordonl - The Siemens 3AF is a vacuum breaker, correct?

 

[psycholuck]

dpc
yes the 3AF is a vacuum breaker but only has a maximum voltage of 14 kV. Here is the link to the 3AF

http://www.sea.siemens.com/SpecGuide/Sections/Sec03.pdf

Our substation maintenance department has similiar concerns with arc flash. The collateral damage that could occur with a circuit breaker failure is a real problem. We have had Cutler hammer give use a presentation on there partial discharge Insulgard product. This product monitors the partial discharge in the switchgear insulation and is more of a early warning system.

http://www.partialdischarge.com/

But the product seems to be a little pricey at the moment.
Also Siemens makes a product that we are looking into that limits the damage during an arch flash. They use a compartment approach seperating the metal clad enclosure into four compartments (low voltage, breaker, bus and feeder) and vents the arc flash material towards the top of the enclosure.

Question dpc why do you find it is a good idea to have remote contol of the rake out circuit breakers?

With regards to your question about SF6 breakers yes they do make a much smaller 34.5 kV indoor metal-clad switch gear.(Siemens, ABB, and Alstom) But we are debating whether the hassles of SF6 from a maintenance and cost stand point out weights the smaller foot print.

Thanks for the good comments. dpc

 

[psycholuck]

gordon1
What voltage level was this set of switchgear rated? Also when your company initially built the metalclad switchgear enclosure did they make provisions for additional feeder positions?

 

[gordonl]

It is a 34.5kV lineup with 3AF breakers, but according to the brochure I have they are only available upto 2000A at 38KV. (1500MVA SC) I pulled out the manual to reassure myself, and find that it is indeed listed as arc proof. The switchgear is listed as 8BK20 Metalclad arc resistant switchgear.

It has the Siemens 7SJ relays which I'm not fond of. (We've had a few failures, and they aren't very user friendly, but I'm happy with the switchgear)

ABB has a neat solution for arcing fault protection, it uses light detectors which trip the mains instantaneously. I haven't used it myself but it has been out for a while.

Later,
Gord

 

[dpc]

The concern about remote racking is simply safety. There have been fatal accidents related to breaker removal and insertion. It's one of the more dangerous things that happen around metal-clad switchgear.

With remote-racking, using motor operators, you can be safely out of room when the breaker is moving in and out.

Having said that, I have to say that I've never seen one actually used in the real world. GE has offered this option for years, but I don't know of anyone who ever purchased it. But with the increased concern over arc-flash safety, there is more interest in remote-racking and I would certainly try to use it on a 34.5 kV system if it was available on new equipment.

If arc-resistant gear is available at this voltage, I would seriously consider it.