Author Topic: Most weird-assed Elect. problems I'll probably not see again ??  (Read 8160 times)

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Offline sibeen

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #50 on: July 17, 2018, 06:21:27 am »
The phase wiring on that largish switchboard has triggered a distant memory. About 30 years ago was called to a site which had a large (>500 kVA) UPS installed. The upstream breaker was tripping regularly, transferring the UPS to battery operation and it would eventually shut down and transfer to the bypass line after the batteries were drained. I had began happening on a daily basis and the client was rightly pissed.

The problem was a combination of factors. Firstly the electrical contractor had installed the cabling to the UPS in phase groups, as per the photos earlier, rather than the required trefoil arrangement. Secondly the contractor had used steel cable ties to hold down the cables to the earthed cable tray, and thirdly the circuit breaker supplying the UPS had ground fault detection installed and this had been set to the minimum value.

Each cable tie was acting as a mini current transformer and inducing a small amount of current into the earth, as the load on the UPS increased the amount of current induced into the earth also increased. It eventually reached a level that was above the ground fault setting on the circuit breaker and this would then trip.  The cable ties would not have been an issue if the incoming cabling had been in a trefoil arrangement as the balanced phases would have resulted in a cancelled magnetic field around the cables and therefore no leakage currents to earth. Eventually replaced the majority of the cable ties with plastic and the problem went away.

Sounds all quite easy, but it took me about a week to figure this one out.
 
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Offline GlennSpriggTopic starter

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #51 on: July 17, 2018, 01:20:33 pm »
Ok... here's another Factory.... (huge automated processing plant).
I had a Chief Engineer above me, (he was non electrical), who could not understand (or be told)
why the main 1,500 amp factory feed was grossly overheating. (Split into 2 parallel sets of cables).

It came down to SIMPLE Ohms Law... :-)
Two 800-amp cables, (each phase), piggy-backed together Lugs, to one side of the huge BusBars.
Unbolted, I calculated about .6 Ohm on one run, and about .3 Ohm on the other runs.  Ok....
Sounds like nothing, but ONE had TWICE the current flow as the other !!!!
(1000 amps in one, and 500 amps in the other). Due to a difference of just .3 Ohm...
They either 'get it' or they dont...

Which connection was not crimped properly then? Did the lug glow or not.

Sorry about the delay mate..... (No, but they were unusable).  There were multiple issues from memory.
The cable runs took different directions/paths due to availability of various concrete 'holes'. (Lengths!!).
Some Lugs were slightly the wrong size for the cable entries !... but here's the main 'NoNo' reason......
Each 'pair' of Phase Lugs were bolted 'Stacked', to one side of the BusBars !!!! (Can't remember 'washers').

I re-routed/shortened some cables, replaced/re-crimped quality lugs with a proper 100-ton tool.....
And re-bolted using appropriate conductive grease with 1 lug "Either-Side" of the BusBars in direct contact.
The problem went away....  I would have discussed alternatives, due to the high requirement/loading, except
that some departments were being moved off site, so the total plant load was diminishing.
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Offline GlennSpriggTopic starter

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #52 on: July 17, 2018, 01:56:56 pm »
After several visits to a site and workshop investigations on a PC with repeat claims of random characters appearing in a rather comely lady's word processor documents we figured out that moving her copy holder closer to her made the problem disappear as her ample chest wasn't hitting the keyboard when she turned the page.
Sounds just like a common legend. But I'm under the impression that area is very sensitive so it would be hard to miss the accidental contact? Closely related to that was a funny story a friend of mine told me about the time in computer repair class when she accidentally knocked over a box of screws...

I don't know about 'ample breasts', but I was called out to Yatala Labour Prison in Adelaide late one night, to their main control room.
The MainFrame computer had locked up. (Swamped with thousands of calls from a P.C. it seems)...
Turns out someone had a BOOK that was resting on the 'Print-Screen' button on one of the P.C.'s.
The 'MainFrame' had a 'Hissy-Fit' with it's buffers, and locked out the whole system !!!!!! Sigh..

I remember a similar problem from the early 90s from dad's workplace (where the young me was moonlighting as an unpaid computer tech/support here and there). They had an SCO Unix server there, with an UPS for an orderly shutdown in case of a power failure. Both the UPS and the server were in tower cases, sitting on the floor under the desk in the office.

At some point the machine started to turn instantly off, losing power (and some data in the process). That was weird, the UPS was there meant to prevent exactly that and it didn't work? After a lot of testing of both the computer and the UPS everything seemed to be OK. Real headscratcher ...

This went on for a while, with several crashes a week. Until one day someone saw one of the office workers sit down at that desk to do some paperwork - and hit the big button on the front panel of the UPS with their knee in the process. POOF, server down. The protruding button on the UPS was the main shut-off switch for the load (really oddball design, IMO, don't recall the brand of the UPS anymore though). So the UPS remained up, beeping furiously about an apparent loss of power and the server was turned off instantly ... The result was lots of red faces and  a makeshift safety cover out of a piece of acrylic taped over that button. No problems since.

Ha!!!... yea  UPS's are funny things at times....   Some people might not understand that a proper UPS does not 'Switch-In' or 'Change-Over', but is ALWAYS working, and making a new 'Sinewave' from 'DC'. Either from converted AC supply, or from batteries.

This 'generated' Sinewave waveform is 'Synced' to the mains supply, while the Mains is present.  I used to look after large such systems, and while working on, testing, adjusting the UPS, (for prisons/banks etc), I would throw a huge manual change-over switch.
Here's the catch though !!!....  it HAS to be a 'BREAK before MAKE' change-over, as you now cant guarantee it to be in 'PHASE'.
But being 'break before make', you have to throw it REAL FAST, so that all the electronic equipment/computers has to run on their own Capacitors in their own Power Supplies, for a 1/3 or a 1/6th of a second without crashing !!  (Worked 95% of the time  :) )
Diagonal of 1x1 square = Root-2. Ok.
Diagonal of 1x1x1 cube = Root-3 !!!  Beautiful !!
 

Offline NiHaoMike

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #53 on: July 17, 2018, 02:09:32 pm »
The last idiot who served my house LOCKED the outdoor fuse panel (in my house, the indoor fuse panel handles appliances and sockets, the outdoor unit handles AC/heat pump and emergency heater).

That is of course, illegal. Last time AC technicians came to my house install the new AC, they had to pick the lock.
Locking out means to disconnect power does make it more difficult for thieves to steal the A/C condenser.
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Offline sibeen

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #54 on: July 17, 2018, 02:46:58 pm »


Ha!!!... yea  UPS's are funny things at times....   Some people might not understand that a proper UPS does not 'Switch-In' or 'Change-Over', but is ALWAYS working, and making a new 'Sinewave' from 'DC'. Either from converted AC supply, or from batteries.

This 'generated' Sinewave waveform is 'Synced' to the mains supply, while the Mains is present.  I used to look after large such systems, and while working on, testing, adjusting the UPS, (for prisons/banks etc), I would throw a huge manual change-over switch.
Here's the catch though !!!....  it HAS to be a 'BREAK before MAKE' change-over, as you now cant guarantee it to be in 'PHASE'.
But being 'break before make', you have to throw it REAL FAST, so that all the electronic equipment/computers has to run on their own Capacitors in their own Power Supplies, for a 1/3 or a 1/6th of a second without crashing !!  (Worked 95% of the time  :) )


Say what? It just doesn't work like that. Maintenance bypass switches are 'make before break' and are interlocked with the UPS so that the UPS must be in bypass before the switch can be activated.  What you have described is just madness, and I have never seen an installation done that way in Australia, and I've been involved with UPS systems for around thirty years.
 

Offline rsjsouza

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #55 on: July 17, 2018, 04:29:42 pm »
This stops nuisance attacks by people flipping switches on you while still allowing access to those who require it.

 :wtf:? Why? What do they get besides a potentially hefty fine or a few days in police detention?
Well, there are idiots pointing lasers to pilots on duty. And there are idiots went to prison for this.
Blueskull, you underestimate bored teens rummaging around during summer vacation. I had a similar scenario where some passersby simply shut off the water supply to our home - it took a few hours to find out we had no water (in Brazil all houses have a 500 or 1000l water tank) and a few more hours to figure out what exactly happened.

For something that needs $3000 service fee to install that is only worth half of <$2000, I seriously wonder if anyone is willing to steal it, and it would be even harder to sell it. And consider the potential risk of being frostbitten by refrigerant, being shock by electricity and being charged by not only homeowner and PD, but also OSHA and EPA, I don't think it's remotely worth it.
During the foreclosure days of 2008/2009, it was not uncommon to have external HVAC units stolen from foreclosed houses, so there is certainly a market for it (I even had friends have their units stolen as well). In fact, there is a market for everything.

In newer neighbourhoods around where I live, the double-pane windows act as great noise insulators, thus any "hiss" can easily be confused with a running faucet while doing dishes, for example.
« Last Edit: July 17, 2018, 05:05:24 pm by rsjsouza »
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Offline Leiothrix

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #56 on: July 18, 2018, 01:39:14 am »
:wtf:? Why? What do they get besides a potentially hefty fine or a few days in police detention?

It's also so potential thieves can figure out which houses are empty.  Turn off the electricity or water and check it again in a day or two.  If it's still off chances are there is no one home.  Especially good in touristy areas where there are lots of holiday homes.
 

Offline Cyberdragon

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #57 on: July 19, 2018, 02:16:45 pm »
This stops nuisance attacks by people flipping switches on you while still allowing access to those who require it.

 :wtf:? Why? What do they get besides a potentially hefty fine or a few days in police detention?
Well, there are idiots pointing lasers to pilots on duty. And there are idiots went to prison for this.
Blueskull, you underestimate bored teens rummaging around during summer vacation. I had a similar scenario where some passersby simply shut off the water supply to our home - it took a few hours to find out we had no water (in Brazil all houses have a 500 or 1000l water tank) and a few more hours to figure out what exactly happened.

Lol, my dad used to do that shit all the time back in the olden days. Him and his naughty friends would wait untill there was a big party (with drunks usually) then shut off the water. If they didn't notice there went the power. >:D
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Offline rrinker

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Re: Most weird-assed Elect. problems I'll probably not see again ??
« Reply #58 on: July 19, 2018, 02:57:00 pm »


Ha!!!... yea  UPS's are funny things at times....   Some people might not understand that a proper UPS does not 'Switch-In' or 'Change-Over', but is ALWAYS working, and making a new 'Sinewave' from 'DC'. Either from converted AC supply, or from batteries.

This 'generated' Sinewave waveform is 'Synced' to the mains supply, while the Mains is present.  I used to look after large such systems, and while working on, testing, adjusting the UPS, (for prisons/banks etc), I would throw a huge manual change-over switch.
Here's the catch though !!!....  it HAS to be a 'BREAK before MAKE' change-over, as you now cant guarantee it to be in 'PHASE'.
But being 'break before make', you have to throw it REAL FAST, so that all the electronic equipment/computers has to run on their own Capacitors in their own Power Supplies, for a 1/3 or a 1/6th of a second without crashing !!  (Worked 95% of the time  :) )


Say what? It just doesn't work like that. Maintenance bypass switches are 'make before break' and are interlocked with the UPS so that the UPS must be in bypass before the switch can be activated.  What you have described is just madness, and I have never seen an installation done that way in Australia, and I've been involved with UPS systems for around thirty years.

 Of course, you also need to operate the switches correctly - bunch of years ago I was doing work in a client's data center, couple of racks of PC servers plus a pair of HP minis. Electrician was in to do UPS maintenance. Suddenly, the whole room went dark. Someone said "oops". Electrician swore the UPS was in bypass, but pretty obviously it wasn't as when he turned it off it killed power to everything. I ended up spending 24+ hours straight cleaning up the corrupted databases on the Windows servers.

 


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