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??