3000V spikes, bad earth and burnt out A/C

[johno12345]

Hi,

I work in a large industrial factory in the IT department. We have been having problems with earth in the server room, tingling sensation when touching bare metal on servers and UPSs. I tested the voltage from our earth to an earth supplied from BT and got 130V. After a lot of fuss I got a 35mm earth fitted to the metalwork on the wiring cabinets to the main earth bar in the substation. This helped but we get the UPSs reporting high voltage (264V) and 3000V spikes. REC say that the high voltage is caused by harmonic distortion caused by our machines and also that we are only 150M from the 11kv transformer. Maintenance seem to think that the spikes are caused by a faulty CRT but I am not convinced.
Recently I have discovered from maintenance that the TN-S earth supply was not very good and that the REC have now told us that we have a TT supply. So in fact for years we have not had a proper earth. That has now been rectified with 6 earth rods and my earth has been connected. We no longer get a voltage on the metalwork in the server room and the tingling has gone.
Does anyone have any suggestions on the spike issues? the UPSs have a TVSS ground connection on them, should we make an additional earth connection on this and take it to the main 35mm earth so we have 2 earth paths?
The high voltage causes problems with burning out PSUs and more recently £20k woth of air conditioning. We are looking at getting a voltage stabiliser to fix that.

Could we be getting problems from the way that the server room is wired up? it currently has a 24 way 3 ph n +e board on a 160A supply fed from a set of buzz bars which feeds various plant machinery, this is fed from a 500A supply in the substation. The circuits off my board are connected up in 2.5mm cable on radial circuits with only one socket on each radial, each radial is connected to a 16A RCBO. The board has an active surge protector on it.

Sorry to waffle on a bit and i hope it makes sense

Thanks!

 

[mapj1]

What is the duration of the 3KV spikes ? it may be a simple matter of fitting filters, either made up modules from the likes of Shaffner, or a discrete one made of inductors and capacitors mounted securely in a large metal box (earthed of course!).
Extra transient suppression may require transorbs/VDRs or similar -Rhopoint make a good range.
As regards the over voltage, if the suppliers wont turnn it down, then if for example you want to lose 24V from the supply, then wiring a transformer with a mains primary, and the secondary in series with the mains such that it subtracts (if you get the phase wrong it adds!) is a relatively economical way of lowering your supply voltage. Of course the secondary of the transformer needs to be rated for the final load current, so a surprisingly small transformer can handle significant load wattages.

If the 'plant machinery' includes motors with direct-on-line (think coil and switch) starters, then the spikes are probably locally generated.

Whatever the chosen solution you would be wise to treat each final circuit separately, as this reduces the interactions between the different branches, and keeps the components to a manageable size.

http://www.schaffner.com/components/en/product/productL23.asp?language_id=12 and pages nearby..
regards,
M.

 

[johno12345]

Hi,

The voltage stabiliser we are thinging about is a EMS 21 EOH 3 phase one preset output to 400v regardles of input.

we have a filter installed, the spikes are defined as momentary i will try and post pictures if i can figure out how. The machines are mainly 75 years old! and some have up to a 300A supply. I will look into the TVSS and transorbs to see if i can make sense of that

Thanks for the info

 

[Beanzy]

Sounds like you need to look for a more robust UPS supply to cover the Racks & Machine Rooms. The harmonics issue can be measured direclty for each rack supply if you get somone in with the kit. Do you use small UPS units? or when you say UPS do you mean you have a dedicated UPS room fed from the main riser?

Have you measured the load across all the phases to ensure it's properly balanced?

Does the factory equipment share the same supply?, If so you're riding all the transients and harmonics introduced by that kit (think of the start-up and shut-down surges of things like lighting and inductive machinery), and probably any offices etc.. By the sound of things the place needs a good power audit done. Do you have the original installation design spec and drawings? the original contractor should have supplied some decent manuals for the installation, normally a series of A4 ring binders with some dedicated to drawings and the rest usage and maint info. Once you've locked down the useage and load influences then you can start looking at how practical various options are.
(oops I was typing when you posted so a bit crossed this one).

 

[Big_Spark]

A good quality UPS would iron out such high voltages and the output should be regulated to 230V +/- 5% normally. So perhaps your UPS has a problem or is inferior in quality to that which your IT room requires.

Regarding the 3K Spikes, no way will it be a CRT, you would see some serious problems in the way the CRT did it's job and you would know pretty soon it was faulty.

3K sounds about right for harmonic distortions introduced by multiple neutral paths from the sub-station. It is not uncommon to record such high level spikes within a reasonable distancs of the Tx. Your bad earth would mean that the spike was not grounding, so that is why you managed to measure them. With a proper Earth installation you will not record these as they will dissipate at the frequency they are generated at, there will be no dopler or di-polar reduction of the frequency caused by the installation. It is possible though that you may still be able to measure them on the Hertz range of a quality multimeter.

Some of the distortion that you would have had on the system would be intoduced by your own kit not being grounded correctly. As you know, PC hardware, as do all electronics, creates "noise" on any Earth to which they are connected, this noise will be spread across a wide range of frequencies and can become amplified by the characteristics of the installation, so it is equally possible that the 3kV spike could be partially caused by your own kit.

 

[johno12345]

Hi,

Thanks for all the replies.

Each server has its own UPS, they are all APC Smart UPSs so they arent cheap ones. The A/C didnt have a UPS so that is why it broke. We dont need a room UPS, that is why we want a voltage stabiliser. nor do we have room for a large UPS. there is is about 80A per phase in use in the server room.

It is the UPSs that are logging the spikes so hopefully it shouldnt reach the servers. dont know what would happen if a large current appeared on the earth, the UPS may pass it through.

There are no maps for the mains installation, it was originally installed in 1968 and it shows, wooden fuse boxes, ceramic fuse links etc. the feeder from the substation does indeed feed factory machinery. In fact today they have installed a new machine and every time they try to start it, all the lights go out and come back on, the sodium lamps have to go through a 20 min cooling cycle!

We were looking at getting an audit done of the wiring but it was going to cost over 20K all i know is that it is a mess but i can trace my dis board cable back to the substation.

The voltage is different on each phase, one is lower than the rest by about 10-15V. I know that there is more load on one phase as the main cable from the substation to the buzzbars is warm on one side and cooler on the other.

Does anyone think that a supplimentary earth on each UPS back to the main earth would improve safety and or help with any problems?

Thanks

 

[Big_Spark]

Jono, a supplemeantary Earth will not make that much of a difference if the kit is already earthed. In fact you could be introducing a danger due to parallel earth paths, something that should always be avoided due to the inherent risks created when testing and at other times.

You have wooden fuse boards!!!! How the hell does that building hold a fire Certificate? I'll bet it has't been inspected in years.

Jono, where is the factory? 20K for a survey seems damned steep, perhaps you want a second opinion and quote?

 

[Beanzy]

The problem with the Smart-UPS units is they're not really that good at stabilising the incoming transients. I had big problems a year or so ago with a VideoWall supply which had PCs fed via individual UPS. If I recall they were Leibert 'powersur'. The in-rush currents of associated lighting boards and studio supplies were killing the PCs regularly!. We took them all & associated kit(46 in total) off the existing supply and supplied them via a dedicated board, with the VideoWall projectors remaining on the old supply. Not one problem since.

An initial recommendation I'd make is to check out the possibility of a dedicated incomer for your Technical supplies. This could be as simple as a small 3 phase DB branched off a fused 3 phase isolator following the Distributors metering. This could then be used to supply the racks. The incoming supply could be filtered using various mechanisms. Have a rummage on http://www.reo.co.uk/ to get a feel for what's possible (nowt to do with me by the way I just found it useful).

Initially a comparative test between the surges in the existing machine room and those at the main incoming board would show you if the problem was actually caused internally or mainly external. This would show whether the 'bypass' solution above would do anything to alleviate the problem, or just be a waste of time. If it's your own factory machinery causing the problem then it may help.

If you want to look for something you could hire to run on each point for a week or so try someone like www.cuthbertsonlaird.co.uk, I have used them for test kit and calibration before, they'll tell you if the kit is available or not & will give you solid advice on which kit is best suited.

 

[johno12345]

Hi,

The factory is in Sheffield, it is quite large, 3/4 mile long, we got 3 quotes, all about the same. We do have a fire certificate but i dont think he is too interested in the electrics, more in the oil and furnaces.

It would seem logical to have the server room fed from its own breaker in the substation, i will look into that, see if there is any space in the ductwork. Maintenance have a company who will put tracers on the power lines to track the spikes.

We have a supressor, i have found the link to it: http://www.memonline.com/f09.html it is the one on the right. we were advised that this would iron the spikes out. perhaps that suggests that the spikes are generated internally, perhaps when one of the 10kva UPSs changes over (they change over due to high voltage(264)) i will have to keep an eye on that.

Thanks

 

[dw3101]

I work in an IT Department for a large call cente solutions provider in Leeds (Also in Dearne Valley too)

We spend a lot of money on our infastructure.. APC Ups are ok for a small company.. but for the loading your talking about forget them. Its just not cost effective to have a ups per server, and the apc ones are quite tempremental.. Booting NT4 with a powerchute cable connected used to crash the ups and make it start shutting down..

Speak to someone like GE Digital Energy and get yourself a nice 40kva or similar UPS.

We have a fair few of these, Our business uses a lot of computers and we have to have equiptment on our LV distribution to remove the harmonics etc induced by switched mode PSU's

We have two 11kv - 415 transformers on site and deal with all our side ourselves.. however we dont have any probs with air con.

Our comms room has N+1 on air handling, each of these has 100A supply from a non essential DB.

The UPS is supplied via a changeover switch (And maintence bypass sack of poo switch) which then supplies a Computer distribution board, with displays that show Pf, amps, volts, etc.. (Merlin Gerin)

Our phases are all balanced within 5a of each other.. Around 50a per phase at mo (in one room) and voltages are steady.

Aircon breaks reguarly, but looking at ups logs, there are no major surges. Also Aircon shouldnt be supplied via a UPS.

I would recommend someone like McMullen Electrical they do our work for us and are good. They dealt with all our switchgear in the LV room too.

David

 

[Big_Spark]

Why not consider a Rotary UPS straight from the 11kV supply..ok a bit more expensive to run in, but so much better than standard UPS's, and they do deal with the spikes and over volts better than the electronic type.

 

[ban-all-sheds]

APC Ups are ok for a small company.. but for the loading your talking about forget them.

? http://www.apcc.com/resource/include/techspec_index.cfm?base_sku=SY1000K1000G ?

 

[plugwash]

mmm a 1MW ups

 

[johno12345]

Hi,

We have individual UPSs so that there are fewer points of falure, with one main UPS, should an individual circuit trip then one server will immediately fail, at the moment if a RCBO trips we get a couple of hours to fix it, on the really important servers, there are 4 PSUs and 4 UPSs. I dont think we can afford a really big UPS as the current UPS setup works fine. We have n+1 A/C and they arent fed via a UPS, they just need a clean supply. my trician said that it was pointless connecting the TVSS up so it looks like it is all down to fixing the feed with a stabiliser and a direct feed from the substation.

Thanks!

 

[Beanzy]

johno a main UPS would be the other side of the breakers supplying the DB they're on, so breakers tripping will only knock out a single circuit, and the breakers are very unlikely to ever trip on a properly installed system. I can't recall any Machine Room breakers tripping in the one I maintain, although we did loose the Blue phase 1kA incomer to the whole building once, and wen't 2 hrs on the UPS for the duration. (I can e-mail you some piccies of one I maintain if you want to get an idea of the space involved, as it will require space)

It would be a more long-term solution to have a UPS room, but you'll need to consider the maintainance and expected life of the installation. The current situation of multiple Smart-UPS would begin to get unweildly after a very short time of expansion, and you'll be generating an awful lot of heat in the machine room, putting extra demand on the air con too.

Keep us in touch with the progress (because I'm a nosey bu99er )