3 Phase power keeps on tripping

[pc1966]

Think I'm a little wiser than to work with out turning the MCCB off but hey.

Its a public forum, we can't assume anything!

I would rather risk hurting someone's pride but underestimating them than have to live with overestimating somone by not saying something that ultimately led to an injury.

There are 66 apartments spread over the 12 floors. Rising main with tap off box ever other floor feeding fuse cabinets for the apartments. Which are in turn fed via split concentric to individual boards. Bear in mind these were fitted around 9 years ago so no surge protection. Interestingly though I was informed today that the apartment block next door it one had power outage yesterday as well might be coincidental but who knows

It would take a very high level of lightning hit to trigger an arc, and this is not a country that sees that every day!

I'm guessing the flats are all on 60A fuses and if so they have total selectivity with 100A or more, so anything downstream of those fuses cannot be responsible for blowing the incoming 315A fuses.

So from my armchair view it comes down to a fault the rising main or in one of those boxes on the supply side of the flat's fuses.

Or there is some secret unknown big 3-phase load somewhere!

 

[pc1966]

Incidentally have you been able to speak to folks in various apartments? Has anyone heard a loud noise at the time things tripped out?

Might just help get to which floor(s) are close to a fault.

 

[Spaldingsparks]

someone hasnt got a funny kind of farm in the flats have they?

 

[marconi]

pc1966: I don't feel so ready to dismiss something on the DNO side of the fuses because the timing and regularity of the outages hints at something happening during the quieter hours or lower load periods - so something being done for technical reasons and necessary during these periods and regularly. My money now is on a DNO overvoltage mechanism triggering a busbar arc fault perhaps at an insulator defect. (I discovered by the way high current arcs between busbars tend to move away from their point of initiation due to the usual electrodynamic forces at play.) As ever I could be wrong...

I got myself immersed in this problem to avoid the miserable news about what is happening in Ukraine. This is what I read this afternoon:

https://www.studiecd.dk/cahiers_techniques/Fault_arcs_on_busbar_sets_and_switchboards.pdf

 

[pc1966]

pc1966: I don't feel so ready to dismiss something on the DNO side of the fuses because the timing and regularity of the outages hints at something happening during the quieter hours or lower load periods - so something being done for technical reasons and necessary during these periods and regularly. My money now is on a DNO overvoltage mechanism triggering a busbar arc fault perhaps at an insulator defect. (I discovered by the way high current arcs between busbars tend to move away from their point of initiation due to the usual electrodynamic forces at play.) As ever I could be wrong...

Very true the regular timing of the fault suggests something is a trigger for it.

I can't see high over-voltage (i.e. 8-10kV as mentioned in the article) being the cause as otherwise we would have lots of flat residents complaining of damaged electronics. Still, it would be a good idea to consider having some decent-sized SPD fitted to the incoming supply (e.g. a "type 1+2" and some 100A fuses/MCCB or similar for fault protection).

But the idea that DNO changes are causing electrodynamic forces in a busbar somewhere is very intriguing to me. I was pondering on how you could have a system working perfeclty for a period and then BANG! go the incomer fuses. I was wondering if the rises or one of the fuse cabinets was adjacent to a lift or something that was occasionally hitting it? But maybe there is a loose bar and DNO tap-changing is making it flap?

I got myself immersed in this problem to avoid the miserable news about what is happening in Ukraine. This is what I read this afternoon:

https://www.studiecd.dk/cahiers_techniques/Fault_arcs_on_busbar_sets_and_switchboards.pdf

Yes, a very depressing event all round

 

[Lucien Nunes]

At this point I would be camping in the riser listening carefully around fault time.

 

[pc1966]

At this point I would be camping in the riser listening carefully around fault time.

I wonder if you could get a few long-lasting audio recorders set up in strategic locations?

Easier than camping out for a day or so!

 

[marconi]

At this point I would be camping in the riser listening carefully around fault time.

I would arm myself with a spanner or screwdriver, as required, and some electrician's gloves and goggles and then open up the riser and switchgear and simply have a look with my eyes during daytime!

 

[Daveh36]

someone hasnt got a funny kind of farm in the flats have they?

My first thought lol as come across lots of farming but wouldn't account for it

 

[marconi]

Very true the regular timing of the fault suggests something is a trigger for it.

I can't see high over-voltage (i.e. 8-10kV as mentioned in the article) being the cause as otherwise we would have lots of flat residents complaining of damaged electronics. Still, it would be a good idea to consider having some decent-sized SPD fitted to the incoming supply (e.g. a "type 1+2" and some 100A fuses/MCCB or similar for fault protection).

But the idea that DNO changes are causing electrodynamic forces in a busbar somewhere is very intriguing to me. I was pondering on how you could have a system working perfeclty for a period and then BANG! go the incomer fuses. I was wondering if the rises or one of the fuse cabinets was adjacent to a lift or something that was occasionally hitting it? But maybe there is a loose bar and DNO tap-changing is making it flap?


Yes, a very depressing event all round

I was not clear enough. I meant the electrodynamic forces act on the arc - Fleming's left hand rule. This is illustrated by some time-lapse photos in the reference in one of my earlier posts.

 

[marconi]

Daveh36: Good evening Sir. Had you thought (hoped or wished?) I'd gone away

Just wondered if you had any further developments if only to inform more on the problem? I need things to think about 'cos my wife is back in hospital.

 

[Daveh36]

Oh dear that's not good hope all is ok. On the tripping front though since I replaced the mccb again and got DNO to monitor incoming supply things seem to have settled down (famous last words). I'm thinking they had an issue with the supply but are not for telling me. Fingers crossed for now as it's not gone off in week given my hair chance to grow back haha

 

[timbobelfast]

Oh dear that's not good hope all is ok. On the tripping front though since I replaced the mccb again and got DNO to monitor incoming supply things seem to have settled down (famous last words). I'm thinking they had an issue with the supply but are not for telling me. Fingers crossed for now as it's not gone off in week given my hair chance to grow back haha

It sounds like a head scratcher indeed.

If it continues to trip, check if there is a Telecom Cabin on the rooftop somewhere. As these are normally full of AC-DC rectifiers and PSUs.

Failing that, get the LL to have an Electrical Installation Condition Report on the subs and LL services.

 

[marconi]

Daveh36: Has this problem been resolved or 'simply gone away'? Be interested to know.