MV Vacuum Interupter AIC rating 1

[Live2learn]

I have attached a Vacuum Interrupter Name plate
specs. Type: PM, Style: VSA, BIL: 95kV, Phase: 3, Max Design Volt:15.5, Continuous Current 600A, Interrupt Rating: 12,000A, MOMENTARY (10 CYC.): 40,000A, Make and Latch: 20,000A, Mfr Dat: 1994, Interrupting time: 3 cycles, Weight: 2100 lbs
Insultating Medium: Air, MVA: 300

Questions - here are my assumptions...

Interrupt Rating: Design limitation for interrupting fault current associated with the device, but for how many cycles? 30?


Momentary (10 CYC): This is the maximum instantaneous current for which the interrupter can handle for 10 cycles. So does this mean the interrupt rating is for 30 cycles?

MVA: 300, does that correspond to the interrupt rating. 300MVA/(15.5kV*1.73)? - 11187A?

Make and Latch: The interrupter can open and close with 20,000A running through it? Is there a time constant associated with this like 15 seconds?

 

[davidbeach]

Probably rated at 14.4kV (at which point 300MVA=12kA). Momentary is what it can carry starting with closed contacts and not attempting to open, maximum of 10 cycles. Interrupting is is the maximum current, at a specified X/R, that the parting contacts can interrupt. Make & Latch has nothing to do with opening. That is the maximum value of current that result if the breaker closes into a fault. Both momentary and make & latch assume a fair amount of DC offset that will decay to below 12kA prior to an attempt to interrupt.

Hiding the Instruction Bulletin number probably wasn't necessary, and it probably has all your answers.

 

[rbulsara]

MVA rating is a rounded number, more important is the amps rating. So 300MVA and 12000A at 15.5 kV is close enough.

12kA is the symmetrical ampere SCC rating.
20kA is the Asymmetric Peak, typically the first half cycle or the worst moment of closing and latching. Note that it is not interrupting or opening rating.

40kA momentary is the just withstand rating without opening or closing.

Interrupting rating does not have a time rating, as as and when the breaker is commanded to interrupt(open) by a relay, the process is immediately started and it takes 3-5 cycles.


Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

breaker=interrupter in this case. A modern true breakers would have much higher ratings.

Rafiq Bulsara

http://www.srengineersct.com

 

[Live2learn]

So it is rated for 12kA symetrical
with the DC offset and utilizing the x/r ratio we come to 20kA (make and latch). I know LVPCB can have a multiplication factor of up to 1.26 with and 20 x/r ratio and a 5% pf, so does that mean in medium voltage systems it can have a multiplication factor of 1.67? What standard is that?

Still a little confused on the momentary rating vs SCC rating. Please correct me if I am wrong but that would mean while the interrupter is closed in, the device can handle 40kA for 10 cycles - without doing anything. While it is open it could close into 12kA or vice versa?

 

[rbulsara]

Yes, 1.6 is a common multiplier at this voltage level per ANSI standards. There are methods to adjust this rating based on the actual X/R ratio. Do a search on some mfr's websites.

As to your other questions:

while the interrupter is closed in, the device can handle 40kA for 10 cycles - without doing anything

Yes. Hopefully the upstream device will open in time to save it.

While it is open it could close into 12kA or vice versa?

Yes, up to 20 kA peak. I am not sure what is vice versa condition?

The ratings are this way because the idea is that the device is too slow to open during the first half cycle or to see the asymmetric peak during opening. By the time (3-5 cycles)the contacts interrupt the current, it would have decayed within its interrupting rating.

While if you close it on a faulted condition, it will see the peak current.

Rafiq Bulsara

http://www.srengineersct.com

 

[rockman7892]

Great information rbulsara. I've often wondered about these ratings myself.

So the close and latch rating is assuming that the breaker is closed into the peak of the fault which would be the peak asymmetrical value of the symmetrical momentary rating? Does this reference value of 1.6 come from the red book or is this just the typical multiplier used for determining aysmmetrical current in an RL transient such as motor inrush etc...

Is the aysmmetrical or close and latch rating typically considered in an equipment duty evaluation? I have typically only seen the 1/2 cycle momentary and interrupting ratings used for comparison with associated fault vaule in equipment duty evaluations?

 

[rbulsara]

rockman:
That is how they are tested to meet ANSI standard, probably based on historical knowledge. I have to look up the exact standard number, but you can find them on many mfr's websites.

I must add that this 1.6 multiplier (20 kA in this case) would generally mean Asymmetric "rms" value. The corresponding peak will be 34 kA. Some manufactures are more clearer about stating those units than others. When in doubt ask their technical support.

Yes, those ratings are considered in an equipment evaluation duty. Take a close look at reports generated by a good software.

Bear in mind that LV and MV breakers are evaluated differently. LV breakers, especially MCCBs are designed to open during the first half-cycle. MV breakers are not. LV ICCB and PCBs with short time ratings only can wait longer.



Rafiq Bulsara

http://www.srengineersct.com

 

[dpc]

Close & latch rating = 1/2 cycle momentary rating for ANSI C37-based breakers.



David Castor

http://www.cvoes.com