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Re: Flickering Lights
krruss   8/22/2013 10:34:07 AM
We had a similar situation with a LIM launched roller coaster - we were experiencing all kinds of problems with our distribution system, so went to put in an AVC unit.  During our meetings with our power company on the installation, one of their engineers looked at scope traces we had taken and said "hey - I'll bet this is why we burnt out the tap changer on the sub!".  Since we were already spending big bucks to resolve the issue, they didn't charge us for the repair.  

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Re: Flickering Lights
dbues   8/19/2013 7:25:24 AM
Wow!!!  You guys REALLY dug into my story.  Since this was 30 years ago, some of the details are fuzzy, but I remember hearing about OLD neighborhoods having problems with voltage levels due to the steel plant.  The problem changed when they "fixed" it by moving NEWER developments (this was where I lived) to the same feeder to add "load".


I believe that the FINAL fix was to change the time-constant of the control loop on the tap-changing transformer, so that it would not be a susceptible to oscillation as it had before.


Of course, this isn't QUITE as interesting as tripping out a power plant while it is operating, but that's ANOTHER story.       : )

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Flickering Lights
wbswenberg   8/18/2013 12:20:53 PM
I purchased a new house in a new subdivision.  In fact the 1st house.  The master bath had a gang of 6 lights.  A little too bright, especially at night, so I put in a dimmer.  Then the lights were flickering. Went on for some time.  When I paid the power bill I included a note about the flickering lights.  I kind of thought that it was emi triggering the dimmer.  The power company came out when I was at work and fixed the problems so I HAD to call and find out what they did. The Tech called me back.  They had put a power analyzer on the meter.  They not only saw the spikes but low voltage.  The spikes were do to a loose ground.  The low voltage was do to all the houses being built adding loads.  They changed the tap on the subdivision transformer.  May be the lights were flicker BEFORE I put in the dimmer.

William K.
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Re: Separation of cause and effect
William K.   8/17/2013 6:29:11 PM
My point was intended to be that the events caused by the call, in that story, were not related to the happenings that resolved the problem.

What I have observed on quite a few occasions has been somebody interpreting the result of a problem as the cause of the problem, and then working to prevent the results without ever considering the cause of the problem. Sort of like opening the windows because the house is too hot, when the cause is a fire downstairs. That is a rather extreme example of what I am referencing. Or extending the time limit on a watchdog timer when it is timing out because the processor is stuck in a short loop due to a program error. The most expensive example that I can recall from recent projects was the crew attempting to limit the return stroke of the die closing cylinder because it was pulling back to far, and breaking teeth on the pinion that linked the two racks that synchronized the two die halves. The cheap fix that I suggested was to gring two more teeth into the rack so that the pinion would not crash into the part beyond the teeth. Grinding out one more tooth was a lot cheaper than replacing a custom ground pinion gear, and it solved the problem permanently. So the limit switch failing allowed the damage to happen, but the solution was not a new limit switch but instead a mechanical change of adding one more tooth cutout in the rack.

Debera Harward
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Re: Separation of cause and effect
Debera Harward   8/17/2013 3:52:27 AM
I totally agree with William, Industrial and residential feeders are not the same they both have usually different feeders , I guess the flickering was because of some other issue and when you called the centre they might have forwarded  the complain and issue was resolved .

William K.
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Separation of cause and effect
William K.   8/16/2013 8:12:57 PM
This is one of those instances where it appeared that your call actually had some effect, but it didn't. I would not have anticipated that the power for any large industrial plant would be on the same feeder as a residential area. My guess is that things were rearranged after a while, removing the instability. But it is interesting that the tap changer system could be lead into instability. Just imagine what havoc could happen if it were on the internet and hackers got into it.

TJ McDermott
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Re: Cool Story
TJ McDermott   8/16/2013 11:10:03 AM
For that matter, was anything done to eliminate the problem? Different transformer?

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Load variation in feeder lines
Mydesign   8/16/2013 7:14:45 AM
1 saves
"There is usually a variable-tapped transformer in the substation that adjusts to smooth out fluctuations in voltage for downstream customers. What happened was that the transients matched the frequency with which the transformer adjusted the voltage, causing it to oscillate wildly."

Dwight, even I found that sometimes my lights at home are flickering, but so far I hadn't found any reason for that. Now I suspect it may be due the load variation in the feeder. Thanks for lightening such ideas and info's.

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Cool Story
tekochip   8/15/2013 2:50:48 PM
Did the operations center verify that extra load dampened the oscillations?

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