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Topic Title: Generator - failed to start
Topic Summary:
Created On: 16 September 2017 11:55 PM
Status: Read Only
Linear : Threading : Single : Branch
 Generator - failed to start   - SreejithK - 16 September 2017 11:55 PM  
 Generator - failed to start   - Dave69 - 17 September 2017 01:00 AM  
 Generator - failed to start   - SreejithK - 17 September 2017 07:16 PM  
 Generator - failed to start   - mapj1 - 17 September 2017 10:43 PM  
 Generator - failed to start   - Dave69 - 17 September 2017 10:51 PM  
 Generator - failed to start   - alancapon - 17 September 2017 11:28 PM  
 Generator - failed to start   - OMS - 18 September 2017 09:45 AM  
 Generator - failed to start   - SreejithK - 18 September 2017 02:24 PM  
 Generator - failed to start   - SreejithK - 19 September 2017 04:56 PM  
 Generator - failed to start   - Zs - 20 September 2017 09:29 PM  
 Generator - failed to start   - OMS - 23 September 2017 09:00 AM  
 Generator - failed to start   - AJJewsbury - 21 September 2017 09:45 AM  
 Generator - failed to start   - kellyselectric - 21 September 2017 10:00 PM  
 Generator - failed to start   - OMS - 23 September 2017 09:08 AM  
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 16 September 2017 11:55 PM
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SreejithK

Posts: 50
Joined: 14 November 2012

Hello everyone, we are looking at a hospital site, where the generator failed to start during a mains failure. There a 3 LV generators paralleled onto a single board and support the load.
Now common reasons why the genny wont start , all to do with the generator coolant,battery being flat etc can be assumed.
However I am more interested on the controls side of things.
One possible reason is , the point where the generator is receiving is loss of mains signal?
PLC did not register loss of mains and hence gennies don't start!
Any other common causes?
Regards
Sree
 17 September 2017 01:00 AM
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Dave69

Posts: 628
Joined: 16 July 2011

A little confuzled, you say there are three generators but then you say the generator failed to start.
Are there three generators and if so did they all fail to start or just one of them?
If all three failed to start then obviously it sounds like the didn't get a start signal, if just one didnt start then it could just be a fault on that genies start circuit, either a simple broken wire or a fault within the generators control circuit or even just that one had a flat battery although as you say it is plc controlled the plc should be monitoring the battery voltage and charging circuits so it should of thrown up an alarm. I am guessing you have tried to start them on the HOA switch off load and they all start ok
If all three failed, start off by isolating all the generator supply outputs at their isolators and lock them off, if you know how to dable with the plc force the generator start signal to on and see what happens, you could drop a fuse out of the pfr and simulate a mains failure but that cause the plc to do other things as well as trying to start the generators. If the generators dont attempt to start then you know you probably have a fault in the wiring from the plc to the generators or a fauly o/p on the plc, you could also prove the wiring from the plc o/p by simply shorting it out with a wire link, if they start now but didnt when you forced the o/p on then you know its a faulty o/p card. You would also need to check the philosophy as depending on what the generators are feeding there may be a delay built in either the plc or possibly the generator sets to prevent them from starting on a slight momentary power blip
 17 September 2017 07:16 PM
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SreejithK

Posts: 50
Joined: 14 November 2012

Hi Dave thanks for the reply..
Sorry we have 3 generators working in parallel.
From what the site guys told us , they had a dip and momentary loss of mains(very brief), but the generators did not start. I am yet to go to the site to check the situation,,
As we have three gennies, all batteries or coolant levels or low oil on all f them is a rare possibility. I think as you mentioned its either the gennies did not receive a start signal or the plc is knackered, and did not register the loss of mains to send a signal.
Will definitely, try the above steps.
Regards
Sree
 17 September 2017 10:43 PM
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mapj1

Posts: 9707
Joined: 22 July 2004

Its a hospital, and while I cannot see it I imagine it will not like even short blackouts, so control will not be as simple as it seems ! How fast are the engines supposed to start and how is the spin-up time managed? Depending on KVA / MVA ratings I'd expect the genset starting to take some ten seconds or more, and by the time they are up to 50Hz, and ready to close contacts onto loads a few times that.
Therefore there would normally be something like a large battery UPS arrangement to handle the gap, the other less common alternative is the 'rotary UPS' where armatures are already spinning none-stop, and the starting of a diesel engine to provide motive power instead of the grid is an inertial thing.
The arrangement to create the 'start signal' will be complex, as a simple sensing of missing volts on the line will not do, as the UPS will put volts on within a half cycle..

Also, just because all three did not start, do not rule out that it could still be a fault in one (but it would imply a weak design that was not stress tested.)
It is possible, and actually fairly common, in non critical systems to tandem genset controls so that there is a definite master and slave relationship, to avoid frequency hunting where two or more machines chase each other round - it maybe wired/programmed that way and the master failed to spin up.
Ideally you will need advice from the folk that configured it originally, or the suppliers of the control gear at least.
Let us know how you get on.

-------------------------
regards Mike
 17 September 2017 10:51 PM
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Dave69

Posts: 628
Joined: 16 July 2011

If the loss was only momentary it could well be that either the phase failure relay has a built in time delay or that the plc has a timer circuit programmed in, the last thing you want is the generators starting up every time you have a blip. Most generator circuits ive worked on are for the water industries and the generators wont start until the mains power has been off for 20 seconds and then it wont reinstate the mains until it has been stable for 15 minutes, this also means at least the generator gets a half decent run on load when it does start, I am sure in hospitals the start delay time will be a lot less but it could still be that the momentary loss of power wasnt long enough to call for the generators to run.
 17 September 2017 11:28 PM
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alancapon

Posts: 6942
Joined: 27 December 2005

I agree with Dave, that it is usual to have a delay of several seconds before starting generators. This prevents them starting during faults on the supply network that are quickly cleared. In a hospital, it would be rare (in my experience) to rely on the "raw mains" for those aspects that are "critical for life" such as ITU, and I would expect them to have their own UPS arrangements to allow critical functions to continue while the generator(s) start and prepare for load. It would also be usual for each theatre to be individually covered with its own UPS.

Regards,

Alan.
 18 September 2017 09:45 AM
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OMS

Posts: 22435
Joined: 23 March 2004

You probably want to have a read through HTM 06-01

In terms of starting the standby power supply, it mentions:

A short delay of between 0.5 and 6.0 seconds is normally chosen at the voltage detector device to discriminate against a fall in normal voltage due to a voltage transient or auto-reclose switching operation (that is, a time delay to establish that the under-voltage is an outage rather than a disturbance). When the chosen time delay confirms the loss of normal supply voltage, the engine start is initiated. A time delay of up to 15 seconds (following the initial confirmation time) is allowed between loss of normal supply and connection of the standby generator to the essential circuits. The essential circuits are defined as those which cannot accept an interruption of electrical energy greater than 15 seconds plus the detection time (that is, clinical risk Category 4 and above).


Sounds to me that the fail to start was probably based on the fact the supply was not lost - more a switching transient or voltage depression - and as such, the start signal wasn't initiated.

For clinical risk category 5 (and possibly some elements of 4) there will be UPS in place to cover the detection and start time

Typically, we would now not only parallel the sets but also with the mains when returning to minimise return transfer disruption - so obviously if that's the case, you may need to also look at the G59 arrangements

If you have CHP in place, it all gets a bit more complicated

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 18 September 2017 02:24 PM
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SreejithK

Posts: 50
Joined: 14 November 2012

Thanks everyone!!Very helpful!!
They do have UPSs. From the info received the blip was for a period of 3 Seconds. The generators didn't start . By the time they got the APs in , it took them 3 hours to get the building up and running.
Regards
Sree
 19 September 2017 04:56 PM
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SreejithK

Posts: 50
Joined: 14 November 2012

So was on site today..Recap on the events:
All breakers were closed and everything was working fine;
Momentary dip, all breakers closed except 1 breaker which feeds most of the load opened. The breaker has a PFR, where the relay is set to 100ms. So its probably that the duration was very short and hence it tripped..
Cheers
 20 September 2017 09:29 PM
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Zs

Posts: 3830
Joined: 20 July 2006

Oms, We need a cloning cabinet for you and about 1000 of you around the UK. One of those in my handbag of course as a condition of the cloning cabinet.

A hospital goes without power and it buggers things up for too long a period of time. Someone who has to sort it out has to find a forum to ask for advice and fortunately stumbles across you. Sreejithk, you can trust this man.

No criticism of you by the way Sreejithk and I admire you for asking. But why are you in the position of having to sort this out when a power 'dip' as you call it, in a Hospital, had to happen before anyone knew that the system did not perform?

So now you are losing sleep about it and charged with sorting it. This should never have happened to you. Please make sure that you do not become the stool pigeon for somebody else's shocking design or maintenance. May I suggest that you disclaim yourself legally from responsibility for the former before proceeding?

I'm open mouthed at this.

Zs
 23 September 2017 09:00 AM
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OMS

Posts: 22435
Joined: 23 March 2004

Originally posted by: SreejithK

So was on site today..Recap on the events:

All breakers were closed and everything was working fine;

Momentary dip, all breakers closed except 1 breaker which feeds most of the load opened. The breaker has a PFR, where the relay is set to 100ms. So its probably that the duration was very short and hence it tripped..

Cheers


Can't you clarify that (and PFR)

Under loss of mains it's quite usual to open all the output circuit breakers plus the incoming mains circuit breaker to allow the generator to close into a presumed fault free busbar

You then sequentially close the output breakers to manage the generator load steps - it's not usual to close the set(s) into a full load condition

You would almost certainly not close power factor correction capacitors back into the busbar when operating on generator

OMS

-------------------------
Let the wind blow you, across a big floor.
 21 September 2017 09:45 AM
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AJJewsbury

Posts: 16113
Joined: 13 August 2003

I'm open mouthed at this.

I'm afraid this kind of thing is all too common - a few years ago a company I worked for transferred some of its IT kit from an informal "machine room" in the corner of the office to a "proper" data centre - the kind of place where everything is electrical is at least duplicated, you need two forms of ID plus an authorized appointment to get onto the site and the 'turn styles' to get into the machine areas weigh you on the way in and out so you can't add or remove anything without pre-arranged permission. One day one bit of equipment developed a fault and took out one of the supplies - which should have been no problem since everything was dual PSU'd and the other supply was quite independent. Except that someone had overlooked the fact that under such circumstances the load on the remaining supply was almost doubled - they hadn't allowed for that, so sure enough a few minutes later the 2nd supply tripped out on overload.

- Andy.
 21 September 2017 10:00 PM
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kellyselectric

Posts: 191
Joined: 22 July 2016

I remember a good few years ago exactly the same thing happened at a big hospital in the next town we had some really rough weather and the mains dipped several times then eventually supply was lost for about a half second there was a major row about why hadn't the genset started I imagine the conventions in the office went along similar lines to whats been discussed here. The dips in mains were seen in my town and the one where the hospital was and I did here that a HV line had actually come down when an ancient oak tree fell on it!!
 23 September 2017 09:08 AM
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OMS

Posts: 22435
Joined: 23 March 2004

Originally posted by: kellyselectric

I remember a good few years ago exactly the same thing happened at a big hospital in the next town we had some really rough weather and the mains dipped several times then eventually supply was lost for about a half second there was a major row about why hadn't the genset started I imagine the conventions in the office went along similar lines to whats been discussed here. The dips in mains were seen in my town and the one where the hospital was and I did here that a HV line had actually come down when an ancient oak tree fell on it!!


Bad drills on the part of the hospital engineer and the SAP - if you know your mains are likely to be unstable then it would be wise to transfer to the generators (or secondary intake) beforehand

It's why some facilities get detailed weather alerts so plans can be put in place

That said - loss of power in healthcare isn't the worst problem to deal with - experienced nurses can keep critically ill people going for quite a long time with pretty basic kit

What will kill people is moving them - fire evacuation is the real drama

In LOOP or fire conditions there should be emergency plans in place for other local facilities to gear up to assist

OMS

-------------------------
Let the wind blow you, across a big floor.
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