Flickering Lights & Stuff

[SLIPSHOD & SLAPDASH]

I have a problem thats causing some head scratching.  Large old factory divided up into smaller units and sub let. Mixture of light industrial, storage, offices & a gym.  I have been told of problems a short while ago when tenants complained of flickers in the supply, the DNO came & said they would have to dig up the road but they did not, although after their visit apparently the supply improved drastically. I have to assume they simply tightened up all their connections.

This week a few tenants have complained again about fluctuations in the supply. One office has said there computers are now crashing a few times a day due to this. Their servers are ok as they are  on a UPS which is showing it has been activated every time they look.

The supply is TP & N 100A PME. Main switchfuse feeds a busbar chamber, then into various switchfuses and landlords check meters then onto the units own distribution boards.   Although most units have a  3 phase supply, only  1 has any 3 phase equipment, this is an engineering company with large presses, bench drills  etc.

The DNO came again yesterday who said there is nothing wrong on their side, but as the supply was not turned off  i dont know how they can claim this.

I thought it must be a loose connection, possibly the neutral so today we did a total shutdown and went through every single connection at the distribution ( this took 2 hours).  No loose connections or signs of arcing, overheating was found. We also checked the boards in the offices and found nothing. We checked the voltages & did a Ze (cant remember the figures) but all was acceptable. The seal fairy really had been so we checked even all those connections.

After we had finished, the offices IT guy,  who also rents a unit upstairs  said he has not had a problem but described a buzzing sound for fractions of a second coming from the office DB when the power flickers. This appears to be random, the DB is an old TP &N with rewirable fuses. No breakers or electronics.

I have not been into the engineering unit yet, but am trying to work out if they have say a loose connection somewhere could this be causing harmonics on the supply ? grabbing at straws here.

Any ideas ???

 

[NozSpark]

Have they had a data logger fitted?

 

[ProDave]

What are the loop tests L-E from each phase, and L-N from each phase?

I'm inclined to think high impedance on N causing N to wander up and down a bit depending on ballance of loads.

Get the DNO to fit a voltage monitor, preferably three single phase monitors on each phase.

It's probably something outside your control, you just need to find what, and prove it to the DNO to get them to fix it. 

 

[SLIPSHOD & SLAPDASH]

I knew data loggers were going to  be mentioned. We dont have any and i dont know if i would know how to read them, beside the costs in hiring equipment. I will have to get the loop reading from my mate.

 

[NozSpark]

The costs are irrespective if there's a fault it needs fixing,, I'm sure the DNO would fit one eventually if they were called for each occurance of a fault once you've proived that there aren't any internal faults

 

[batty]

Some of these engineering units use a lot of juice. I have done work at one that had problems in the past DNO had to upgrade there supply in the end. No problems since though I think.

 

[steptoe]

does the engineering unit have any plasma cutters?

they can be really funny if they dont have a low earth path, and Im talking in the 0.0x  range,

the few I have wired required <0.05 hms , dunno what happens if its over this, but I do know DNO came out and made sure we had the required path when they were informed of the requirements.

 

[SLIPSHOD & SLAPDASH]

Not been emailed the details of the engineering unit yet.  Once i have been in there i will report back.

Its the buzz from the DB thats concerning me, harmonics ? 

 

[Marvo]

Harmonics can cause MCB's to buzz depending which harmonics are present but I've never heard of buzzing fuses, sounds like a long shot to me. I'd shut the DB down for a while and get in there to check busbar mounts etc and maybe use a thermal imaging/FLIR camera to check any crimped ferrules and other mechanical connections.  

 

[SLIPSHOD & SLAPDASH]

Job is in Ware, Hertfordshire

 

[SLIPSHOD & SLAPDASH]

Thank you for the offer. A weeks gone by and no one has contacted us. Even the engineering firm haven't sent us their contact details so i wonder if  we have fixed the problem without realising it.

What does a power analyser actually record & how do you access the results ?

 

[SLIPSHOD & SLAPDASH]

Well, i have not been back to site but done work for the landlord elsewhere so asked whats happening. It turned out the engineering firm had already been complaing to the DNO about this problem so when the landlord started they came back again . The landlord told me they had fitted a 'voice recorder' on the cable (i assume  some sort of power analyser/date logger) & would leave it a week or so. They came back and within an hour shut the whole supply down, dug the road up and ran new cables. I asked the landlord to call but he could get no further info . I guess from the speed they acted it was a neutral breaking down. 

And it turned out the buzzing from the board was a loose connection in the fluorescent light above the board that arced each time the power dipped.

 

[ProDave]

I'll bet the "voice recorder" was a voltage recorder.