Lightning arrestor short circuit rating

[alehman]

I'm trying to select a lightning arrestor for use in medium voltage metal enclosed interrupter switchgear (ANSI C37.20.3). A manufacturer has recommended an MOV type with EPDM package, and a short circuit rating of 15kA. The available fault current is 21kA. Is it required that the arrestor short circuit rating match or exceed the available fault current?

 

[7anoter4]

Hi alehman
In the ABB Switchgear Manual is underlined about MO [metal-oxide surge arrester] the followings [extract]:
"Under extreme fault conditions it is possible for lighting arresters to be overloaded.
In such case e.g. a voltage rise from one level to the next, a single-phase earth fault occurs in the resistor assembly of the arrester. The pressure relief system prevents the porcelain housing from exploding. The system earth-fault current at the arrester's location must be smaller than the guaranteed current of the arrester's pressure relief device."
I think even EPDM is more elastic than porcelain the same rule it must be kept.
Best Regards

 

[stevenal]

Arresters are shunt devices, and do not experience short circuit currents except for those that originate in the device. Perhaps the 15kA is what the unit will conduct during an overvoltage.

Your arrester should be able to handle the amount and duration of any overvoltage that results from a fault. This is the temporary overvoltage or TOV rating, usually shown charted as per unit of MCOV versus time.

 

[7anoter4]

Hi alehman
I have to agree with stevenal as the Hubbell Power Systems company sustains:
"The pressure relief rating of porcelain arresters is valid for only the first fault event. System reclose on a failed porcelain arrester can cause fracture of the weathered porcelain housing being subjected to a second discharge of system fault current.
Polymer arresters have the advantage of being able to withstand multiple system
reclose events without exploding. Therefore, polymer arresters offer a distinct advantage over porcelain."
See:

http://www.hubbellpowersystems.com/POWERTEST/tips_news/pdfs_best/EU1489WB.pdf

My experience is only with porcelain arresters which exploded often [BBC and ASEA] as the pressure relief current was lower with respect to shortcircuit current. But I have experience with Hubbel co. on other field and was satisfactory.
Best Regards

 

[stevenal]

If it's the pressure relief current limit you are speaking of, IEEE 62.22 does say to keep it above the available fault current. They then go on to say to consider the importance of the equipment to be protected. It does not seem to be an absolute requirement, or else station class arresters would be used much more frequently.

 

[alehman]

Thanks for the replies. Yes, my concern is the short circuit pressure relief.