IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Lighting fault
Topic Summary: Dodgy generator?
Created On: 10 December 2013 07:31 PM
Status: Post and Reply
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 10 December 2013 07:31 PM
User is offline View Users Profile Print this message



Davesparx

Posts: 262
Joined: 30 October 2009

Evening all and happy Christmas if I don't see you !! I was called out to a lighting fault yesterday. We fitted some 600 x 600 LED panels about 3 weeks ago and the whole lot were out. After a closer look we found that the driver on every light was knackered. Also the battery packs on the emergencies were toast. The owner of the building told me that they had a power cut and the generator kicked in for about 15 mins. I am wondering if over voltage caused the drivers and packs to fail. I have very little experience with gen sets and was wondering if this is possible? The power cut does not seem to be to blame as all other equipment was ok. The I.T kit is all surge protected and none of the fuses had blown. The panels are designed and made by the same company who are very well known in the industry. As always any replies greatly appreciated. Cheers, Dave
 10 December 2013 08:19 PM
User is offline View Users Profile Print this message



eclipse

Posts: 142
Joined: 03 November 2006

Dave,

A call to the technical people at the manufacturers would be the first thing I'd do.

-------------------------
Thanks

Alan.

Now what was that reg no?
 10 December 2013 08:32 PM
User is offline View Users Profile Print this message


Avatar for OldSparky.
OldSparky

Posts: 592
Joined: 28 June 2011

i would have thought if there was over voltage many other things would be damaged, but possible.

The gen set obviously should be set at a predetermined voltage..

why not run it up and put your volt meter on it.. with out it connected to the building of course.
 11 December 2013 07:22 AM
User is offline View Users Profile Print this message



Jaymack

Posts: 4622
Joined: 07 April 2004

Originally posted by: Davesparx
The owner of the building told me that they had a power cut and the generator kicked in for about 15 mins. I am wondering if over voltage caused the drivers and packs to fail.

I'd be looking for a missing neutral.

Regards
 11 December 2013 07:26 AM
User is offline View Users Profile Print this message


Avatar for OldSparky.
OldSparky

Posts: 592
Joined: 28 June 2011

Originally posted by: Jaymack

Originally posted by: Davesparx

The owner of the building told me that they had a power cut and the generator kicked in for about 15 mins. I am wondering if over voltage caused the drivers and packs to fail.


I'd be looking for a missing neutral.

good call ...



Regards
 11 December 2013 08:57 AM
User is offline View Users Profile Print this message



Zs

Posts: 2847
Joined: 20 July 2006

Dave,

I feel for you, this must be like the proverbial hole in the head for you. Now commences the witch hunt?

I'm going to have to look into this for you today but recently got involved with helping someone connect a generator on here. Whilst looking onto it I came across mention of a poorly connected generator motor and the resulting effect being a steady increase in the output voltage. In truth I think you'd know if that had happened because the resultant on that example was a very large bang. However, if for only 15 minutes I'm wondering and I think you should know about it so as to be able to check it for yourself.

Sorry a bit scant but I want to check this properly before I type what's in my head.

I will e-prod OMS later and see if he still has the information at his fingertips. He's very poorly at the moment with a serious attack of Man-Flu so don't breathe as you read his posts today.

Zs
 11 December 2013 11:45 AM
User is offline View Users Profile Print this message



Zs

Posts: 2847
Joined: 20 July 2006

Ok, I'll have a bash at this myself and await a more elegant description. Absolutely agreeing with Jaymack on this about a lost neutral but I'm looking for a bit more of the why for you.

I really want the solving of this to involve money that isn't yours Dave so from my notes some questions for you;

When the supply and the generator are switched from one to the other, is the transition between the two absolutely clean?

Is it possible that the neutral could be open at any point during the transition between the two? A particular place to look for this is at the generator switch. Is it a three pole or a four pole?

If the switch is a four pole it is possible that the neutral to earth bond inside the generator (which makes it a TN system) might have been removed, even if momentarily while that switch was in the off position. If that happened then you could end up with the entire phase voltage of about 400Volts across your LED Drivers and the inverters in the emergency fittings. Bang. It says here in my notes that would fry everything.

By the way is the supply a PME?

At this point I retire and hope that one of the clever blokes will see this and will convert my plain english into proper engineering language.

But I really hope you can identify a reason for this having happened which is well outside of your remit. Good luck.

Zs
 11 December 2013 12:10 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 988
Joined: 04 November 2004

That makes sense Zs but wouldn't all the connected single phase loads be subjected to the over voltage if it was the loss of neutral at the genie.

I saw something similar on a job a few years ago where a temporary supply to a TP&N cremator panel which had outgoing TP & SP&N loads connected was replaced with the permanent supply. The subbie never admitted it but I believe the permanent submain neutral wasn't connected when the supply was switched back on. The neutral was securely connected on Monday morning when the crem staff couldn't operate the kit though.

Regards
 11 December 2013 12:36 PM
User is online View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19550
Joined: 23 March 2004

When the supply and the generator are switched from one to the other, is the transition between the two absolutely clean?

Is it possible that the neutral could be open at any point during the transition between the two? A particular place to look for this is at the generator switch. Is it a three pole or a four pole?



That seems elegant enough to me - for what it's worth, I'd also suggest you get some details on the AMF changeover panel as Zs suggests - this is almost certainly a los of neutral on the loss of mains transition.

In terms of overvoltage, whilst a lot of kit is sensitive to overvoltage, LED drivers are particularly sensitive to it, so I can see damage to just the LED lighting being quite credible - it depends on the prevailing loads when the neutral went OC as to what voltage was presented across the drivers.

I'd get the LED panels back to manufacturer for analysis and a statement about the damage - coupled with a look at the AMF, that may well prove that this was an underlying building problem, rather than any problem with your selection and installation of the lighting.

Regards

OMS

-------------------------
Failure is always an option
 11 December 2013 01:07 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11349
Joined: 13 August 2003

That makes sense Zs but wouldn't all the connected single phase loads be subjected to the over voltage if it was the loss of neutral at the genie.

No - usually only the loads on the less loaded phase(s). (If the loads across all three phases were perfectly balanced then N would naturally stay at 0V and the break wouldn't matter - if one of the phases is more heavily loaded N is dragged towards that line's voltage (& in phase with it), so loads on other phases see a higher voltage (as N goes -ve from the point of view of the phase they're on).

- Andy.
 11 December 2013 01:07 PM
User is offline View Users Profile Print this message


Avatar for rocknroll.
rocknroll

Posts: 8835
Joined: 03 October 2005

He's very poorly at the moment with a serious attack of Man-Flu so don't breathe as you read his posts today.


What a shame. shoulda had the flu jab.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 11 December 2013 01:30 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 988
Joined: 04 November 2004

Thanks for the explanation Andy.

Anyone fancy doing an example with three different SP&N loads?

Regards
 11 December 2013 01:42 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11349
Joined: 13 August 2003

I find thinking about a split phase (2-phase) version easier to start with. 230-0-230V supply (i.e. 460V across the outer lines)

say you had a 6 Ohm load on one line and a 40 Ohms load on the other and N broken. You've effectively got 46 Ohms across 460V so 10A will flow through both loads. Ohms Law again gives us 400V across the 10 Ohm load and 60V across the 6 Ohm load.

I think you'll have to start drawing vectors to 'see' the 3-phase equivalent.
- Andy.
 12 December 2013 07:27 PM
User is offline View Users Profile Print this message



Davesparx

Posts: 262
Joined: 30 October 2009

Many thanks for taking the time to respond. The gen had been serviced by a well known company shortly before we installed the LED's. The building manager got them back in just in case and the engineer was not best pleased with his work mate. The engineer had fixed the fault and yes, Zs well done. The manager called me and told me that according to the service engineer "A neutral fault was always going to happen". I would like to have been there and taken a look but to be honest I am just pleased that its not us who will be getting slapped !! Have a good evening, from the most relaxed man this side of the Thames!!
 12 December 2013 10:09 PM
User is offline View Users Profile Print this message



Zs

Posts: 2847
Joined: 20 July 2006

Thank you Dave,

I'm so glad you posted the outcome because few do that. Also that any fingers are not pointing at you now. Happy Days.

I was afraid to post that info because I am not endowed with natural ability to explain. I see our science in images in my head and without my hands to wave in illustration whilst speaking it I stumble like mad. Not least, if I get it wrong on here I don't half get told about it! Jaymack was already there. Very validating and I smiled broadly reading yours, enjoy the relax, thank you.


Zs
 12 December 2013 11:57 PM
User is offline View Users Profile Print this message


Avatar for AncientMariner.
AncientMariner

Posts: 511
Joined: 14 December 2004

A changeover switch suitable for a 3-phase generator back-up supply needs to be 4-pole with the Neutral pole breaking last and making first; this for both sides (mains & generator) of the switch. Otherwise there will be a momentary loss of Neutral whenever the switch operates either to make to a live supply, or to break from a live supply. Also there needs to be an OFF position between the two running states, if not the generator will momentarily be connected (in full or in part) with the mains supply.

Incidentally, if a large back-up supply with two or more generators which have to be synchronised and paralleled with each other, then the individual generator contactors need to be rated at TWICE the system voltage to allow for the voltage between phases of the two machines prior to achieving synchronism.

At sea was always amazed at the speed an automatic synchroniser could bring a 6.6 kV 2.5 MW diesel alternator into synchronism and put it on-line with whatever else was running, another diesel alternator or the shaft alternator - which was a 6.6 kV 2.5 MW inverter, powered from a low frequency 3-phase alternator 12 - 16 Hz at around 900 volts - if I remember correctly. This alternator was directly mounted on the propeller shaft.

Cheers!

Clive

-------------------------
Clive S Carver GCGI IEng MIET
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.