Fault Lightning Arrestor 1

[khara]

What is the probability of a faulty lightning arrestor at a substation in the HV section to cause an entire power plant to crash / shutdown. Please shed some light.

 

[rasevskii]

for khara:

Yes if the LA failed (shorted out for whatever reason) and you have a busbar differential protection (if the LA is on the busbar itself), that protection would clear the bus (trip all connected breakers simeltaneuosly) within something like 50 to 100ms.

And there is your station shutdown or blackout.

Do you have a busbar diff. protection in place?

However I think it would be unusual to have LAs on the bus itself, rather on the feeders, and the failed LA would cause an earth fault which should be cleared by the E/F protection for that circuit only which would be set at a lower trip setting than any phase protections. And it depends on the method of earthing used on the system.

I can think of a certain 132kV station in the Middle East where the bus diff (RADSS) kept tripping the entire station. So they disconnected it. On the next re-energization of the bus, a 132kV voltage transformer exploded: That was the fault in fact, the bus diff was correctly tripping all along.

rasevskii

 

[odlanor]

I guess you never go to protect LA by protection.
If a LA exploded means that incoming travelling wave voltage was very high and/or LA had some problem ,and it will not dischage completelly travelling wave voltage. That wave will impinge a stress in some equipment(in nanosecond time ) while that explosion (in milisecond time) will cause a fault and protection will trip.
Any how, some equipment with winding ( CT, PT, transformer , reactor) will be damage.

 

[EngAust]

It's very unlikely for a surge arrester to cause a fault of this magnitude, arresters do sometimes fail short circuit though. If you want the arrester where it is and want to reduce the likelihood of the arrester failing short circuit you could insulate the base and use a quality disconnector.

 

[khara]

Thanks all for your valuable information.

 

[stevenal]

MOV or SiC?

http://www.nemaarresters.com/

 

[odlanor]

LA protect equipments (CT,PT,..) against surge voltage originated from lightning discharge.
To protect equipments against lightning discharge, include LA, you must provide subestation with shielding protection.

 

[bacon4life]

Everything in the same zone of protection as the failed arrestor would need to clear. In our substations they are usually attached to the transformer, so we would loose the entire plant in some cases.

We have had three cases in recent years of substation class MOV surge arrestors failing shorted without any precipitating overvoltage event in the last few years. No lightning in the area and no voltage transients captured by nearby fault recorders.

 

[odlanor]

I have seen this case in 69 system grounded by zig-zag transformer, sized to 3 < X0/X1 < 10.
With the evolution X0/X1 exceed 10.
A ground fault at Van increase Vbn and Vcn above arrestor duty.