Switch-disconnectors 2

[thatmarkdude]

Is a switch- disconnector just another name for a disconnect switch?

Are these circuit elements operated manually (by hand)?

If regular switching is required in the circuit, will it be necessary to also incorporate contactors in series?

Thanks,

Mark

 

[sibeen]

Yes
Yes
No

 

[thatmarkdude]

I've been trying to research this all day but I can't find any website that states the differences between disconnectors and switch- disconnectors. From what i've gathered, a disconnector is incapable of making/breaking current and is only used for the purpose of isolation, once the current in the circuit has already been reduced to 0.

As I said, I haven't been able to find much information on switch- disconnectors, but I assumed that like a disconnector, a switch- disconnector would also be incapable of making and breaking current, hence I thought that in order to have regular switching, another element which is capable of making and breaking current would be needed in series with it.

Are you basically saying that a switch- disconnector is capable of making/ breaking current on a regula basis?

Also if anyone could point out the main differences between a switch- disconnector and a disconnector, I would greatly appeciate it!

 

[DTR2011]

What voltage rating are you looking at? In MV and lower, you may want to use the term "load break switch" in your search.

 

[rasevskii]

A possible item is a load-break switch, which has arc extinguishing chutes around the contact assemblies. Usually used to disconnect idling transformers and unloaded lines. Can be pole-top or inside a metal enclosure. Usually operated by hand, with a spring-trigger mechanism that opens the contacts quickly, can often also be tripped by a solenoid.

Not allowed to open fault currents. Voltage range up to about 35KV (has anyone seen these on 60+ KV?)

Made by many suppliers in the electrical industry.

rasevskii

 

[thatmarkdude]

It's a low voltage network (a crane infeeder, after the voltage has been stepped down). The vlotage on the secondary of the infeed transformer is 480V.

Also I think that a switch- disconnector has to be used for this project, as one of my contacts has stated this-however I am trying to find out why this component is suitable.

The previous circuit consisted of a circuit breaker in series with contactors. The contactors handled the regular switching and the circuit breaker switched rarely- only fo fault conditions.
The goal is to eliminate the circuit breaker from the system.

Does anyone understand how a switch- disconnector in series with fuses can be utilized in order to perform regular switching?

 

[DTR2011]

What you are looking for is a Fused Disconnect Switch (Load Break).
Some OEM's include:
Siemens, GE, Square D...

You need to know your load in amps and the available fault current to properly select your device / fuse size.

The 480V suggests you are in the US. I would recommend you stay with NEMA rated devices, vs. IEC, as NEMA devices tend to be easier to specify and built to withstand more abuse.

How often do you intend to perform switching? There are many applications (plant lighting comes to mind), where fused disconnect switches are utilized.

I'm sure there are others who routinely specify these devices who can chime in.

I would recommend changing your use of the term "switch- disconnector", as this could be confused with "Disconnect Switch", which is often utilized in MV/HV systems to provide non load break functions (breaker isolation, etc) as mentioned above.

 

[jraef]

This actually isn't as simple as it seems on the surface and is indicative of a somewhat wide ranging problem. Part of the problem is semantics. Your helper person is, I'm guessing, from somewhere other than the US but you are looking for information IN the US (also assuming so because you are using 480V). Let me explain.

In the US, there are different UL classifications of disconnect switches, UL98 and UL508. A UL98 disconnect, what we used to call a "Safety Switch" back in the day, is rated to open any load up to it's rating as the primary Branch Circuit Disconnect Device, something that is required in any power circuit per the NEC. A UL508 rated disconnect is not rated as a Branch Circuit Disconnect Device, it can only be used in a MOTOR circuit that ALREADY has another Branch Circuit Disconnect Device ahead of it somewhere, such as a UL98 Disconnect or a UL489 Circuit Breaker. Unfortunately they are both called simply "Disconnect Switches" by most people, we don't really have another differentiator name in common use. Technically we used to refer to UL98 rated switches as "Safety Switches" as I did above, but unfortunately that has now been cobbled up with safety device switches and it's no longer clear enough to use in my opinion. I can't tell you how many times I have used the term "safety switch" lately and had people go off on a tangent about not needing SIL protection levels etc. I have stopped calling them safety switches now.

In other parts of the world however under IEC rules, a "Switch-Disconnector" is a specific term that is used to describe what we essentially use the UL98 listed switches for, it is a device that can be used to disconnect anything up to it's rated load. But the rules are distinctly different between IEC and UL so a lot of devices that are sold in IEC countries as Switch-Disconnectors are only able to be sold in the US and Canada as motor load disconnects (i.e. UL508) because they do not pass the stringent requirements of UL98. You have to be careful, the IEC people are PURPOSELY being coy about making that clear, because otherwise they have nothing to sell. The result is a LOT of people get burned by inspectors who are now being taught on the differences.

So if you are going to get rid of the circuit breaker because you HAVE to have the fuses anyway, then you can replace it with a UL98 listed disconnect switch. But you CANNOT use a UL508 listed IEC style disconnect switch, i.e. the cheap little rotary thru-the-door ones you see being misused everywhere, because you are feeding a transformer (even though there may be a motor down stream.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[thatmarkdude]

Okay, firstly let me clarify a few things that I should have mentioned at the start. I am working in Germany at the moment, not the US. Also, the standards that I have been using refering to throughout this project are IEC as this is what my boss wanted. The person that I have been in contact with is also in Germany- however he is just incredibly busy with projects of his own.

So does this simplify the problem? We are both within Europe- therefore we are effectively on the same wavelength? He has recommended a combination of fuse(s) in series with a "disconnecting- switch".

From what I can see, this is effectively the same thing that you are recommending to me, which is good news. And this disconnect- switch (which is not the same as a switch- disconnector/switch-fuse-disconnector as shown in the attatchment), is also known as a load- break switch. So this load break switch is used in low voltage networks, and from doing a little bit of research, this switch is manually operated, 2 position device, which can open/close during normal operating conditions. So when used in combination with fuses, the load break switch will be able to handle the regular switch on/off of the crane, and the fuses will trip during fault conditions. Am I right so far?

I have calculated that the operating current is 2405A and the maximum possible fault current is 40kA. In the case of a fault current this high, is it possible that the load break switch could be damaged, even if a fuse is being used- is welding an issue with load break switches when dealing with a high level of current?

As for the frequency of switching that is required, I'm not actually sure- I will have to check this- I am only really trying to identify what is needed in the circuit at the moment, designing will come later. One concern that I would have is that if the load break switch is not shown in the picture attatched, then I will need to find the relevent standard as I have not been reading the right one and will not be able to design the switch yet... but that is another story.

Am I on the right track so far?

 

[DTR2011]

Well, now comes the bad news...

~2000A @ 480V and you are looking at a different kind of beast. I've seen (and worked on) switches of this rating, also known as "bolted pressure" switches, "bolt lock" switches, or "pringle" switches. I would not recommend these and shake my head whenever I see them. Operational and maintenance nightmares, which generally have unique traits such as not opening, not closing, falling apart during operation, etc. I've only seen these applied in lieu of a main breaker, and as such don't get a whole lot of use, other than when one of it's fuses blows and the shunt trip coil burns out (failing to open switch), single phasing all motors in a building, etc...


There may be other options available, but this is what I have seen in the ratings you are looking at. I have seen these switches up to 4000A, with 100kA fuses.

If you have to utilize something like this, I would strongly suggest a regular maintenance program on the switch that includes regular and proper operation, lubrication and exercise of the switch. It is the lack of exercise and proper lubrication that generally causes the problems with these devices.

At these ratings, I would personally want a breaker. If you have the ability to isolate the 480V source upstream of the switch, this makes maintenance and repairs of the switch much easier and SAFER. My experience with these has been when they are the secondary main from a utility owned transformer, generally in light industrial or commercial applications, with one side of the switch being energized...

Pringle switch

Bolt-Loc Switch

Bolt Switch

 

[ScottyUK]

Definitely agree with smallgreek: buy an ACB without a tripping unit. I believe ABB actually designate their E-Max ACBs supplied in this state as 'switch-disconnectors': I've just checked and that is certainly marked on ours. In our application the ACB is paired with an external protection relay, which is why there is no tripping unit.

As far as standards are concerned, look at EN 60947-1 and EN-60947-3. Part 1 is a general standard for switching components, part 3 is specific to switches and disconnectors and their sub-types.

There is a requirement that the device should be fit to return to service following a fault, and welding is not permitted.

 

[jraef]

I have calculated that the operating current is 2405A and the maximum possible fault current is 40kA.

Something is not right there. If you have a transformer capable of 2405A on the 480V side, that means a transformer that is something in excess of 1MVA. So the likelihood that the maximum possible fault current at 480V is only 40kA is low in my opinion. I'm not calculating anything here, I'm going by gut feel. Are you sure this isn't a typo?

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[davidbeach]

2MVA transformer with standard impedance would under 42kA on an infinite bus, so 40kA probably isn't a bad number.

 

[jraef]

OK, I was shooting from the hip, just seemed too low to me.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[thatmarkdude]

Brilliant guys, thanks a lot- i'm learning more here than I have over the last 3 weeks researching this thing!

However, I have just been told that it is necessary for the new switch to be capable of carrying out regular switching automatically- i.e. not via a handle. Hence, as far as I can tell, this eliminates all of the options above.

For this reason, it is desired that the contactors are kept in the circuit as they already carry out this function. The main problem at the moment however is that of the 40kA fault current. If the circuit breaker is removed and a fault occurs, this level of current will cause the contacts to weld.

So really what I am looking for is a component/components which can be inserted into the circuit, in series with the contactors and which can offer short- circuit protection, and can eliminate the possibility of contact welding occuring, so that the contactors will be able to handle the regular switching unconditionally, and fuses/short- circuit protective devices will be able to break the large fault current. Is this task even possible without the contacts welding?

 

[ScottyUK]

A contactor meeting the Type 2 coordination requirements of IEC 60947 should not suffer contact welding, so if you are experiencing welding then your protective device is not well-matched to the contactor. If you insist on trying to use a contactor then with a fuse for protection then ABB's R-Line bar & shaft type would be worth a look, but I don't personally think a contactor is the right choice of component for this application.

I don't understand your reluctance to us an ACB because and ACB is completely capable of being electrically controlled from a remote location. Most require a pulse 'close' command and a pulse 'open' command, i.e. it is a latching device unlike a contactor.

Some of these questions are slightly alarming considering you're designing this installation...

 

[thatmarkdude]

Well no need to be too alarmed, I'm just finished my third year of college and have been working for just over a month- so I have very little experience with this stuff! Also I'm pretty sure that my boss is aware of this too...

 

[ScottyUK]

I hope so!

btw, 'Welcome to Eng-Tips!'