Load Break Switch 1 vs Load Break Switch 2

[Juffy]

Hi everyone! My first post here. I hope I can take some of your opinion regarding my concern.

A newly constructed industrial factory will be supplied by a 1.5 MVA transformer and is metered in the primary. The utility will erect a new 34.5kV overhead electrical facility to supply this factory. In other words, that primary line will solely serve the said factory.

My task is to source out a Load Break Switch that fits the system requirements. As of now, I'm looking between LBS 1 and LBS 2. Here are their specifications:

LBS 1

LBS 2


Assuming full load, the primary current would only be 1.5MVA/(sqrt3*34.5kV) = 25.1 Amperes.

Am I right if I say that [1] since the load interrupting rating of both LBS is greater than 25.1 A (630 A and 600 A at 34.5 kV, respectively), either of these LBS can safely break a fully loaded 1.5 MVA transformer (of course under normal conditions)? I know that there are other ratings needed to be considered as well before I can finally select one LBS over the other. But if we solely focus on the interrupting rating, and assuming that LBS 1 is little cheaper than LBS 2,do you agree that [2] the LBS 1 is better than the LBS 2?

Here in our area, LBS 2 is commonly installed by contractors for 34.5 kV primary metered projects. If LBS 1 is indeed better than LBS 2, I will have an impression that lot of contractors in our area might not know LBS 2 exists. So, I'm afraid I'm going against the grain in this situation. Your opinions are highly appreciated and will give me encouragement.

Thank you!

 

[waross]

solely focus on the interrupting rating,

I don't see an interrupting rating for LBS2. Could it be an isolating switch rather than a load break switch?
LBS1 give symmetrical Amps.
LBS2 gives asymmetrical Amps.
When comparing ratings remember;
Asymmetrical may approach 2.8 times the symmetrical Amps.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Kiribanda]

From the given spec it seems that,
LBS 1: Since its interrupting amps is equal to continuous amps, it cannot be called as a LBS switch. A LBS switch should have
a separate load break capability typically 1.5xcontinous amps. This should be a normal 35kV/630A/ 25kA/ 1sec disconnect switch suitable for your utility connection
provided that the X/R ratio at the location is not higher than 17. To honor its 25kA withstand capability, the upstream protection should isolate
this switch within one second for a downstream fault.
LBS 2: This is also not a real LBS instead it is also a normal 35kV/600A disconnect switch suitable for your suitable for your utility connection.

I believe that LBS1 is little pricier than LBS2. In my opinion both are acceptable. But their data sheets will give us a better picture.

 

[jghrist]

What is the available fault current? What is the interrupting rating of LBS2? Could the load be interrupted at the secondary side instead of on the primary? Can the utility use their line circuit breaker to interrupt load if necessary?

 

[bacon4life]

There are many of factors to determine the "best" switch other than cost. If your pool of maintenance contractors is already familiar with LBS2 but not with LBS1, it is possible that the unfamiliarity with LBS1 could have a significant hidden training cost every time someone goes to use it.

As others noted, the image you posted about the LBS2 does not explicitly state that LBS2 is suitable for load breaking. Depending on the utility, sometimes primary metered customers have switches capable of isolation rather than load breaking.