Generator / supply problem

[Lighthouse Phil]

Hi lads, in most of the installations I would be involved with, we have diesel generators suppling all our equipment. In one particular station it was reported that the lights were constantly flickering. This flicking has being going on for a number of years with no known damage and only when the gensets were suppling high loads. Now that more and more electronic equipment is being added to the station, it was decided to look into this flickering more. So, recently I re-wired the 3 generators and replaced the AVR's. (Automatic Voltage Regulators). The mains output cables were checked and secure. When this work was complete a Voltage Monitor / Logger was installed for a number of days. This was to record every 10mS the condition of the AC from the gensets and each genset was run for equal amounts of time and loadings.
The flickering contined to happen when the gensets were suppling high loads ( + 50Amps ) and we then checked the Voltage logger. The frequency was a constant line (48.5Hz to 52Hz), which we are happy with as our controls allow between 46Hz and 54Hz before shut down. Voltage was also ok with the expected volt drop and raises during high or low load periods (210Vac to 245Vac is exceptable to our control cabinets before shut down). AVR's are set to supply voltage at 230V at 51Hz, we go slightly over the frequency because it will drop down a little during high loads.
I then checked all the wiring / contactors / relays , you name it, it was checked in all control cabinets. The flickering continues to happen.
The gensets are all Neutral / Earth linked, single phase, also recently serviced ( Stripped down and re-built )
No motors would be running or any other equipment on except your normal domestic loads (TV, fridge etc)
Any one with any ideas where this flicking effect is coming from. ?
The effect is seen on fluorescent and incandesent lights and the Electronics guys are worried about damage to thier equipment.

 

[spark 68]

When this work was complete a Voltage Monitor / Logger was installed for a number of days. This was to record every 10mS the condition of the AC from the gensets and each genset was run for equal amounts of time and loadings.

Where was the logging equipment installed ?, I mean was it at the generator end ?, or at the point of utilisaition ? ie. the DB for the final circuits end ?

I wonder if it would make sense to fit logging equipment at both ends to try to determine whats happening, assuming that the generators are remote from the installation end.

 

[Lighthouse Phil]

Good point.
They were plugged in at the point of use, at a socket outlet, as the readings were we geting at the output of the gensets was good. But you have raised a very good point and at the next visit to this station, I will be installing them direct to the output of the alternator.

 

[spark 68]

Hi Phil,

I was thinking more on the lines of power quality logging meters,
one at the generator end, and one at the point of use or at least at the local DB.

Then by comparing both sets of logs you will be able to either rule in/out generator problems or installation problems, or at least have an idea of where the problem/s lie.

 

[Lighthouse Phil]

We have a number of different monitors, the easier one to use is the Vlog, which is just a plug in device but records everything from frequency, voltage, harmonics to true RMS values of the sine wave and all is downloaded to a laptop.
Think I'll be installing a device at both the alternator and DB at next visit.
Thanks for your input S68

 

[Knobhead]

I know this is a shortsighted view, but my gut reaction is fit a UPS unit for the sensitive gear. Most things will just plod on regardless.

I recall this sort of thing cropping up on an international site I’m a member of, but for the life of me I can’t remember the outcome.

Will sent you a PM in a moment.

 

[Lighthouse Phil]

Hi Tony, thanks for the input and reply.

 

[Engineer54]

In my experience, there Are Good Regulators and there are Bad ones, the bad one's will generally give you the sort of problems your experiencing. My advise is to get your company to buy a good well spec'd regulator and hook this unit up to the worst case site and see if this improves the varying load stability.

What size are these generators by the way??

 

[Lighthouse Phil]

Hi E54, thanks for your input. The AVR's are the recommended type by the manufacturer (of the alternator) and we use them in all our other stations with out any problems.

The gen sets Lister Petter TS3's coupled with GEC 12KW alternators. There are 3 installed at this station.
Each genset has its' own control cabinet for auto starting and safety monitoring. The output of the genset is first monitored in its' own control cabinet before it is allowed to go to the distribution cabinet, where again there are Voltage and frequency monitors.

We would have about 30 stations with the same set up, this is the only one giving this kind of problem.
It will be about 6 weeks before I will be visiting this station again. Apart from installing the Vlog's ( Voltage monitors and loggers), I'll be testing the mains supply cables to see if any of our SWA's are breaking down. Terminations and glands look excellent but no one has seen the buried cables for years. Theres no chance of rats as this is an isolated rock out in the sea, but salty water and mild steel armouring dont mix.

 

[Engineer54]

Hi E54, thanks for your input. The AVR's are the recommended type by the manufacturer (of the alternator) and we use them in all our other stations with out any problems.

The gen sets Lister Petter TS3's coupled with GEC 12KW alternators. There are 3 installed at this station.
Each genset has its' own control cabinet for auto starting and safety monitoring. The output of the genset is first monitored in its' own control cabinet before it is allowed to go to the distribution cabinet, where again there are Voltage and frequency monitors.

We would have about 30 stations with the same set up, this is the only one giving this kind of problem.
It will be about 6 weeks before I will be visiting this station again. Apart from installing the Vlog's ( Voltage monitors and loggers), I'll be testing the mains supply cables to see if any of our SWA's are breaking down. Terminations and glands look excellent but no one has seen the buried cables for years. Theres no chance of rats as this is an isolated rock out in the sea, but salty water and mild steel armouring dont mix.

OK, ...fair enough!! I'll think a little more.. lol!! The only other thing that springs to mind, is has anyone checked the engine governor at times of high load ?? Seems strange this occurrence is only at the one location site. A weak governor, will give a slight change of engine note as it drops and increases speed, and would be noticeable to the ear...lol!! And that would only be present on one gen-set. ..Scrub that thought then...lol!!!

How are these 3 Genny's operated?? Do they come on line as the load increases?? Sequence alternate between the 3 Genny's?? Supply separate areas of the installation?? Or use some other operational method??

 

[Knobhead]

It would be interesting to know Phil.

 

[Lighthouse Phil]

The speed governors were checked on all 3 engines at a very recent over haul. The mech fitters stripped the engines down to thier underpants and rebuilt them. The engines are now as good as they were when first bought. (so they tell us).
The fitters knew we were having what we first thought of as frequency problems so they (the governors) were set for a electricial load of 30A, the frequency matched to suit. (50hz at 230V, 30A load). The engines are normally set for 51Hz as this falls away at load, as does the Volts.
To answer your Question E54, the engines are controlled normally from a photocell, via a PLC, so that when the Main Light is called for, 1 of the engines start. This would supply the light and other navagational aids. (Its a lighthouse by the way).If this engine were to fail for any reason the control cabinets would detect a loss of power and start engine 2. Likewise, if this engine were to fail, engine 3 would start. When people are staying at the lighthouse for maintenance works, 2 engines can be run, 1 to supply the Light (called the A load), the other to supply the dwellings (called the B load). Loads can be split form a distribution control cabinet.
Under normal operating conditions when no one is at the station the load would be around 25A. 5A for the light, (1000W) 20A for a storage heater and battery chargers. The engines dont like working without a load so we install ballast loads (storage heaters etc), the maintain a decent loading on them.
During the maintenance visits we would keep an eye on the running time of each engine and decide which engine should be the main one (No.1) until the next visit. It would not be uncommon for a genset to run for 3 or 4 months constantly. ( we have long running oil sumps on each one)

 

[Engineer54]

Thank's for the heads up on the operation set-up...lol!! Though i would of thought a flip over control circuit would be a better system of selecting the prime generator. The overall wear of each gen-set would then be far more near equal, to each other... eg, Prime generator sequenced at every start....

Getting back to your problem, it's got to be something that is common, that all 3 Genny's will see then!! Which will include the load control panel, main lighthouse supply cable(s) and the distribution loads within the lighthouse. You can virtually rule out the individual gen-set control/protection panels, as it's unlikely that all 3 will have the same fault (not completely unheard of though...lol!!)

By the way, how do you achieve the extra +25A to the +50A load, where you say this problem starts showing itself??

You are so right about gen-sets not liking to run on low loads. These are generally spec'd by inexperienced Electrical Engineers or Mech Engineers, who really should know different, as it's the driving engine that is effected/damaged, rather than the alternator!! lol!!!

 

[Knobhead]

Got to admit I’m surprised there’s no auto cycling of the sets, especially as there is a PLC present.
The way the weather is at the moment, a job on a remote island sounds ideal. OK I know there’s always a downside, foul weather is never far away.

 

[Lighthouse Phil]

Will be going back out to this Lighthouse in a few weeks and I plan to do lots of different tests on the wiring side of everything. Personly I'm 100% happy with the gensets, as all 3 have new AVR's and are newly rebuilt.
The extra loading comes from us guys living at the station, we would have the usual domestic loads on, ie, TV, lights, fridges/ freezers etc. (I was thinking about the motors in the fridges/freezers -- maybe something will show up when they are PAT tested)
I'll keep you posted as to my findings and will include some photo's. If I can, I'll post the Vlog graphs on here too.

Thanks to ALL for for inputs / advice.

Phil