the difference is that the circuit breaker has protection feature (thermal and magnetic protection) while the switch has no protection.
if you want to install a chillar as an example you need to install a circuit switch near you for maintenance purpose,
then you can be sure that no body could switch on power by mistake .so you should install a circuit switch (isolator ) to cut the power and control it . You don't need to install a circuit breaker.
I think the question is about high voltage circuit breakers versus high voltage circuit switchers.
The primary difference is the interrupting rating. The circuit breaker will generally have a higher short circuit interrupting and withstand capability, and is capable of high speed reclosing.
The circuit switcher generally has a lower interrupting rating and is not applied in reclosing applications. But it is much less expensive. These are typically applied for high-side transformer protection.
The S & C Mk V Circuit Switcher, for example, makes absolutely no mention of being built, tested, or rated in conformance with any ANSI, IEEE, or other standards. As dpc states, the interrupting ratings are low and you have to read the fine print to determine your application to get the correct interrupting rating. And since they don't conform to any known standards, you are basically accepting the manufacturer's word for the ratings.
Circuit switchers are generally used as was mentioned for high-side transformer protection. They work very well in that application. The S&C Series 2000 has fault ratings in excess of 20 kA, which is adequate for most applications. The circuit switcher has the following benefits: Compact, low cost, and some models include a visible break switch in their operation. Drawbacks over a circuit breaker include low-speed reclosing, and not designed for high-operation environments.
Circuit switcher is a concept used in USA. It is basically an economic solution adopted for switching (for example transformer). It is basically a switch. It must be in a position to switch ON and OFF the transformers on load or without load (magnetising current). When you build such a switch, you are likely to get some short circuit breaking current also.
IEEE is working to make a standard for the Switcher. They already have a draft standard (P1367).
The draft gives following definition:
QUOTE:
A mechanical switching device with an integral interrupter, suitable for making, carrying, and interrupting currents under normal circuit conditions. It is also suitable for interrupting specified short-circuit current that may be less than its close and latch, momentary, and short-time current ratings.
NOTE: This device may be suitable for transformer protection where the majority of faults are limited by the transformer and system impedance.
UNQUOTE:
This means it is to be used on the inputside of the transformer in a radial system. Any fault on the output side of the transformer will be limited by the transformer (and system) impedance.
Some countries call them interrupters. They are mainly used in railway application. There is always a breaker behind this interrupter.
The difference is very thin and difficult to appreciate. I can not appreciate. However, it is that way.
Hope this clarifies the subject.
Interesting note. This application would seem to violate NESC 171, and I believe the interpretations committee has ruled that way. Do these committees talk to each other? Circuit switchers are commonly used in transformer differential protection schemes, so they would be called on to operate for faults anywhere along the transformer impedance, whether on the source or load side.
The only times I've seen a circuit switcher used has been for transformer protection, and in all cases they've been rated for at least the fault-duty on that bus. For example: on a 138 kV bus capable of 10 kA of fault duty, a circuit switcher is used to feed a 138/12 kV transformer. The circuit switcher is capable of both closing onto and clearing at least that 10 kA fault. Absolutely no thought is placed on the concept of limiting the fault duty by the transformer impedance. How would you plan on clearing a fault on the first few windings in the transformer or the transformer bushings unless you designed the system that way?
The pragamatist will always claim that a piece of equipment can always interrupt a fault, but there may be pieces of it around the yard.
As for S&C, they have a very good reputation in the industry. I have no problem accepting their ratings at their word. You have the same problem with all manufacturers. Can you guarantee that ABB hasn't fudged on their ratings? G.E.? Siemens? You can't, but you can bet that if you buy your equipment from manufacturers with a proven reputation, they've probably not fudged the numbers.
I never said S & C fudged their numbers. I said they don't conform to any known standards. Instead of saying accepting the manufacturer's word, I should have said accepting the manufacturer's test methods and rating definitions.
I'm going from memory here, but when I applied S & C Mk V circuit switchers at 69 and 138 kV, I recall several different application categories numbered A, B, C, etc. The IC ratings varied between categories. We used the Mk V for transformer protection/switching, and I recall it only had about an 8 kAIC rating for that application.
I guess the difference between S & C and manufacturers of ANSI rated gear is that ANSI is an independent body that publishes standards detailing the minimum construction features and test procedures, and defines the ratings. The manufacturer may try to fudge, but you can ask for certified test results and compare them against the ANSI standards.
S & C (for circuit switchers, anyway) doesn't follow standards set by an independent body. S & C finds a niche for products that don't fit the ANSI world, thus giving them a proprietary product that is difficult to specify for competitive bidding and more often than not leading to sole sourcing. It's a brilliant marketing strategy to eliminate the competition. If the customer doesn't require the assurance of ANSI, then buy S & C. In my experience, the S & C circuit switchers are only marginally cheaper than an ABB ANSI-rated live-tank breaker (HFD or LTB).
Having said all that, I have used S & C products several times in the past (usually fuse gear) and agree with Mark that they have a good reputation.
on page 18. Committee finds phrase "typically limited" to be "disturbing."
Redtrumpet, how did that 8kA compare to your maximum available fault current?
One legitimate use of a low rated CS would be on the source side of a delta wye transformer with restricted earth fault protection on the low side. Internal faults on the low side would be cleared by the switcher, while high side faults would be cleared by remote line protection. No attempt by CS to clear the high side internal fault.
I do not understand the logic to have different ratings for fault interrupting current and making (latching) current. Should not they be the same? Can some one explain?
In the example I gave above, CS would be required to make the full available fault current at its terminals, (darn, forgot those grounds again) but would only be required to interrupt the transformer impedance limited current from the restricted earth fault.
This thread seems to be creating an impression that the use of circuit switchers is unusual or controversial. This is not the case in the U.S. Circuit switchers are extremely common and in widespread use in distribution substations throughout the country. These are made by ABB and others as well as S&C.
Circuit switchers are not as capable as circuit breakers, but that is often not the right comparison. Circuit switchers are typically used on distribution transformer primaries where fuses were typically used in the past. Use of circuit switcher in place of fuses is a major improvement in protection. For most of these applications, there is no way that the cost of a 115 kV or 230 kV circuit breaker could be justified.
Circuit switchers have a long history of successful application and I suspect that they will co-exist with circuit breakers (and fuses) for a long time to come.
stevenal - fault level on our application was 4 kA on the 69 kV bus. I don't recall fault level on the 138 kV bus but it wasn't any higher.
dpc - I didn't mean to create the impression that circuit switchers are unusual. I know they are used extensively by utilities. I work in private industry, however, and the circuit switchers I was involved with were installed by an institutional client (university) that subcontracted with the local utility for its substation maintenance. Non-utility clients are often less sophisticated than a utility and may not know the limitations of a circuit switcher. If you are not a utility, I believe you should know these are not ANSI-rated devices. The Mk V circuit switcher cost us about $80k Canadian. An ABB LTB ANSI-rated breaker would have been about $90k Canadian - not a huge difference for a more capable device.
However, in our application the S & C circuit switcher was adequate, the client understood what they were getting, and we used it.
Not everyone in these forums works for a utility and the needs of the non-utility client have to be understood as well.
It is also quite common to use circuit switchers for capacitor bank switching/protection. These CS's are often equipped with a series reactor to limit the inrush current.
I should correct my last post. The installed cost of the ABB breaker would be higher if you installed a visible break disconnect in front of each breaker (instead of relying on the main disconnect and shutting the whole sub down). The S & C circuit switchers include the disconnect in their price.
So, the circuit switcher is quite a bit cheaper in the end.
