what causes a lightning arrester to explode

[IIEE2]

we have a diesel engine with a capacity of 8400 kw , it is use to delivered power to a grid, one time we encountered a problem in one of our switchgear , one of our surge/lightning arrester has been busted,,,....
this is the sequence of events :
our generator is running with a load of 7500 kw, and suddenly it drops to 7000 kw.. after a few seconds our protection instrument trips (micom p627 - negative sequence relay) then our gen. c.b. ... after inspection we found out that one of our arrester is busted...


what is the possible cause that caused our arrester to explode??/pls advice..

regards

iiee2

 

[MikeHalloran]

Uh, lightning?



Mike Halloran
Pembroke Pines, FL, USA

 

[dpc]

Sustained high voltage in excess of the arrester operating voltage will certainly do it.

Moisture is another possibility.

I would check the arrester voltage ratings against the generator operating voltage.

 

[itsmoked]

I believe your sudden drop in P is due to a huge shift in power factor during the arrestor conduction event.

Someone please confirm or correct this.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[msquared48]

I didn't know that there were lightening cops.

Man... They're everywhere now!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[cranky108]

Most of the above are concerns. But simply when the gas buildup inside the container, exceeds the ability of the case to handle.
Mosture is a big concern because it lowers the arresting voltage of the arrester (typical of bad seals on the arrestor case).
Over voltage is a concern as the arrester will conduct and become hot.
And lighting in excess of the arrestor capacity.

Some newer arrestors don't explode, as the skin is more of a rubber compound. Others have a venting cap at the bottom which disconnects the ground lead.

 

[ozmosis]

or a loose connection. However, you would see where the explosion marks are to determine if this was the case.

 

[jraef]

Uh, lightning?

Specifically, terrorist suicide lightning...

Sorry, couldn't resist.



"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[PQ101]

Surge arrester are designed to bleed-off excess energy to earthing-grounding system. Degree of damage may depends on magnitude and duration of the event i.e. transient impulse, system fault, high frequency disturbance, etc. For arrester to blow indicates severe transient event, not necessarily due to lightning event. I was wondering if you have recording power anlayzer installed on your system to go back and look at data leading to the event.

 

[IIEE2]

thanks for those who gave their thougts about this matter!!!...i realy appreciatte it..


moisture/dirt occumolation on the unit ... may probably caused it... but since we conduct PMS recently on the unit and there is a moisture absorber in place, we try to look on other matters..
rating of the unit... i think it is properly rated.. our phase voltage is 19.9 kv. our arrester rates 27 kv/ 22 Kv MCOV..

PQ101---- can you give me more detailes regarding this transient impulse , system faults , high frequency disturbance???.. if some other can advice pls advise....


thaks..iiee2

 

[PQ101]

Back in 1995-1998 I used to eat-smoke-drink diesel all day and design all type of generator systems, sycnhronizing, peak-shaving and load demand switchgears. I recall during testing phase (before customer witness testing) we encountered all type of problems requiring cleanup prior to customer final shipment-crating. Let me go back review some of my files, and get back to you with useful information that you rely on.

For past 8 years I conduct power quality investigations on utility grid and all type of plants-facilities, come across damaged lightning arresters, basically due to direct or indirect lightning strike, but I dont get the feeling this is your case. You folks probably experienced some sort of fault, that went beyond the normal, causing phase-to-ground fault during the arrester failure (momentary short to ground). I would say most likley the situation had existed in low pprofile and most likely lead to busted arrester. Best thing is to set a Dranets-BMI Powervisa, PX5 or Dranetz 658 to determine voltage quality at generator switchgear(s) and establish a baseline. This will also provide you with all information you need to maintain system integrity intact.

For better protection against line-related events i.e. line transient impulses, lightning strikes 50miles away, I suggest you install surge arrester on your outgoing 19.9KV lines (in addition to gen swgr end).

 

[alehman]

22kV MCOV seems a little tight for 19.9kV system.

Alan
----
"It’s always fun to do the impossible." - Walt Disney