circuit switcher, circuit breaker

[Mbrooke]

Are circuit switchers employed on the basis which assume bolted faults on the primary are rare? What is the advantage of a circuit switcher over a breaker?

 

[davidbeach]

Circuit switchers rather than breakers are used where an interrupter is needed but CTs aren't. We use them on transformers where we use the CTs on the transformer bushings. We also use them for switching where CTs don't even enter the picture. The decision is economic, both in terms of purchase price and in terms of the space required to install a breaker instead of a circuit switcher. Interrupting ratings are similar.

 

[scottf]

We supply a lot of free-standing CTs to circuit switcher manufacturers, so they must be used commonly when CTs are in the equation too. Normally in the 36kV - 115kV range and typically for capacitor bank switching/protection and sometimes reactor protection...both are cases where CTs aren't likely to be available from other equipment.

 

[Mbrooke]

Im confused, how are the interpreting ratings similar? My understanding is that a circuit switcher opens to draw an arc, and then a vaccum bottle opens in the horizontal bushing and breaks it? Are all circuit switchers like this? Or am I thinking of something else?

 

[davidbeach]

That sounds more like a transrupter, an early version of the circuit switcher. What we're using now all use SF6 interrupters just like breakers. Typically the interrupter can be mounted vertically which is a space saver.

 

[Mbrooke]

Does the air portion of the switch open before of after the SF6 interrupts? It just puzzles me why such a design would be chosen over a breaker.

 

[davidbeach]

No air portion, but we install a separate disconnect to provide the visible open. Look at

http://www.energy.siemens.com/us/en...age-circuit-switchers.htm#content=Description

for an example.

 

[DTR2011]

We just installed an S&C unit and the SF6 chamber definitely opens prior to the disconnect switch.

 

[Mbrooke]

@davidbeach, I must ask, what is the different then between a circuit switcher and circuit breaker? The ones you link seems to be no different then a circuit breaker.


@DTR2011, Thank for the info

 

[jghrist]

On a recent project, we solicited bids for a 138 kV circuit switcher (without integral disconnect switch) with 20 kA primary fault interrupting capability. The lowest bid turned out to be an Alstom live-tank circuit breaker with 40 kA interrupting.

 

[bacon4life]

In the early days of circuit switchers, the air portion closed after the SF6 portion. This prevented arcing during closing from damaging the interrupter contacts inside the SF6 chamber. I don't think this is still the case with any modern designs. Some manufactures have simply quit making circuit switchers and just submit live tank breakers for all bids.

 

[Mbrooke]

By the sound of it, why would anyone bother with a circuit switcher? Are they a hybrid transition from motorized air breaks?

 

[rterickson]

As you noted, what we call a circuit switcher in North American looks a lot like what is called a live tank circuit breaker in other parts of the world. Both are capable of interrupting load and fault currents.

The simplest form of a switcher is the “candlestick” model with vertically aligned interrupters. This is good for when you want to add say transformer protection to a substation that didn’t have it before. There are also combination models with interrupter and motorized disconnect switches (but of course the interrupter opens first, not the switch). Typically fewer foundations are required vs. stand-alone circuit breakers and switches. Also less physical space is required.

 

[Mbrooke]

Basically the circuit switcher interrupters are none reclosing? Do they have a limited number of fault interruptions? I read an S&C PDF which mentioned the interrupter in a C/S is only good for two interruptions at rated fault current.

 

[Overvoltage]

Another reason they are used is the obvious visual open indication without having to open (or install) additional breaker disconnect switches.

 

[dpc]

Circuit switchers are available with or without the air break disconnect switch. Historically, circuit switchers were much less expensive than circuit breakers and did not always meet the more stringent standards required of circuit breakers for interrupting rating, close & latch ratings, and reclosing. They also are more compact. When I last went through a bidding process for 115 kV circuit switchers a couple of years ago, the Areva live tank breaker (with CTs) was virtually the same price as the S&C circuit switcher. Circuit switchers from Southern States and others tend to be less expensive than S&C. Circuit switchers were originally intended to be an upgrade to primary fuses on distribution substations.

 

[cranky108]

Mbrooke, If you look at breaker ratings, they also are only expected to operate for a few operations at rated before being maintained.
In either case it is better to buy a breaker or circuit switcher with a rating higher than you expect to see, so that you can reduce the maintenance cost.

The issue is the contact errosion of interrupting the fault. For some applications the lower rating will work, but for most over head line protection needs a higher interrupting device for a longer life.

 

[Mbrooke]

Circuit switchers are available with or without the air break disconnect switch. Historically, circuit switchers were much less expensive than circuit breakers and did not always meet the more stringent standards required of circuit breakers for interrupting rating, close & latch ratings, and reclosing. They also are more compact. When I last went through a bidding process for 115 kV circuit switchers a couple of years ago, the Areva live tank breaker (with CTs) was virtually the same price as the S&C circuit switcher. Circuit switchers from Southern States and others tend to be less expensive than S&C. Circuit switchers were originally intended to be an upgrade to primary fuses on distribution substations.

Do today's circuit switchers meet such standards of interrupting as breakers? My understanding (correct me if I am wrong) is that much of the advertised claims regarding circuit switchers are never verified?


As for replacing fused, Ive heard of C/S also replacing motorized disconnects where transformer protection trips the nearest breakers, the motorized air break opens and the breakers re-close. With a C/S implemented this does not have to be done, a bonus because normally it takes out a line position.

Mbrooke, If you look at breaker ratings, they also are only expected to operate for a few operations at rated before being maintained.
In either case it is better to buy a breaker or circuit switcher with a rating higher than you expect to see, so that you can reduce the maintenance cost.

The issue is the contact errosion of interrupting the fault. For some applications the lower rating will work, but for most over head line protection needs a higher interrupting device for a longer life.

I saw that which is a concern to me. While I do not expect a transformer protective device interrupting a dozen bolted faults, it gives me piece of mind knowing I have more interrupting attempts.

My feelings lean toward a live tank circuit breaker over a circuit switcher.

 

[jghrist]

Circuit switchers used for transformer protection have a higher rating for primary faults than for secondary faults. For instance, an S&C Series 2000 230 kV circuit switcher is rated for 20kA primary fault interrupting and 4kA for secondary faults (reflected to primary side). See

http://www.sandc.com/edocs_pdfs/EDOC_001825.pdf

I assume that this is because of the higher transient recovery voltage (TRV) for secondary faults. Is there an easy way to determine what the rating of a circuit breaker would be for a secondary fault?

 

[Mbrooke]

I am wondering the same about transient recovery. Currently the primary breakers protecting the transformers also provide secondary protection from buss faults.