[time-nuts] HP and other equipment failure

Brian Alsop alsopb at nc.rr.com
Mon Jun 17 14:34:02 UTC 2013


Something else has gotten much worse with switchers-  RFI.

While most of them are supposed to be "approved" in some way, about 80% 
of them generate unacceptable levels of RF interference.  So do the 
supplies for the under the counter LV lamps and LED drivers.

How was the 80% figure arrived at?  Bought 10 supplies and tested across 
the 1.8 -30 MHz range by looking at pan adapter output attached to my 
ham radio.

8/10 produced unacceptable noise levels.

Then there is the worst of all-- most plasma display TV's.
They can wipe out blocks with their noise.

Then there are the treadmills, high efficiency air conditoners  and now 
washing machines.  Anything with a variable speed DC motor...

Regards,
Brian




On 6/17/2013 13:56, Jim Lux wrote:
> On 6/17/13 5:33 AM, Peter Gottlieb wrote:
>> The current distortion from simple transformer-rectifier-capacitor power
>> supplies contains a lot of third harmonic content.  In a 3 phase system
>> (as are all distribution systems for commercial and industrial) the
>> third harmonic ADDS in the neutral, or creates circulating currents in a
>> delta configuration.  These currents, as you mention, can get very large
>> and were the cause of many transformer explosions in cities as these
>> power supplies became common.  The transformer designs had to be
>> improved, but the PFC supplies make a big difference.
>>
>> How many of you have looked at the power line waveform, especially in an
>> industrial or commercial area?  Doesn't look much like a sine wave, does
>> it?  So it's pretty funny to see audiophile outlets
>> (http://www.dedicatedaudio.com/power_outlets).
>>
>> Peter
>>
>
> The "PFC correction" stuff is, as you say, more about harmonic content
> reduction than actual power factor. The rules on the current waveform
> came in as part and parcel of the power factor rules, so maybe it was
> just a simpler way to explain it?
>
> It's all about looking more like a resistive load.
>
> The US National Electrical Code was updated about 15-20 years ago
> because of the neutral current problem.  In light industrial, office,
> running 208/120Y is very common, the old codes allowed the neutral to be
> smaller than the phase conductors (assuming that the loads would be
> resistive and all balance out)
>
>   but with all those capacitive input filters, the current in the
> neutral got pretty high and there were fears of fires and overheating (I
> don't know if there were actually any fires, but poor voltage stability
> and heating of distribution hardware is probably more likely).
>
> Certainly, the utilities weren't wild about the harmonic currents, so
> they almost certainly agitated for the change as well.  (Imagine you're
> a utility servicing a multitenant building, but the tenants all have
> single phase service, which the utility spreads around the three phases.
>   The utility has the problem of the distribution transformers and the
> triplex currents.
>
> And, in fact, this harmonic thing is hard to fix in distribution
> equipment anyway (some set of tuned traps?) so it does make sense to
> push it to the user.
>
> The issue also arises with fluorescent and other gas discharge lighting,
> particularly with "electronic" ballasts (e.g. switchers).  The old
> "magnetic" ballasts (basically just a big inductor) sort of inherently
> act as a low pass filter, and solve the harmonic problem by getting
> warm. And, they'd have a very lagging power factor, but a fairly fixed
> on that you could compensate with capacitor banks.
>
>   As folks transitioned to the newer ballasts, the non-sinusoidal
> current problem probably got worse.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2242 / Virus Database: 3199/5917 - Release Date: 06/16/13
>
>



-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2242 / Virus Database: 3199/5917 - Release Date: 06/16/13




More information about the Time-nuts_lists.febo.com mailing list