[time-nuts] HP and other equipment failure

[Peter Gottlieb]

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




On 6/15/2013 6:56 PM, stan, W1LE wrote:
> PFC to me is power factor correction, not only the classical power factor to 
> minimize (VAR) volt-amp reactive component,
>  but also to remove the harmonic load  current imposd on the electrical power 
> system.
> A '90's onward technique. in th 80's and 90's without the harmonic load 
> current reduction and having
>  a few 100 end items of equipment, each withtheir own  a switch mode power 
> supplly,
>  it was not uncommon to find hundreds of amps of the third harmonc on neutra,
>   in the electrical power distribution system.
>
> Could be a serious EMC problem if you were dealing with voice grade channels.
> And people safety issues.
>
> Stan, W1LE   Cape Cod
>
>
>
> On 15-Jun-13 5:52 PM, J. L. Trantham wrote:
>> Sorry for the interruption but what is 'PFC'?
>>
>> Thanks.
>>
>> Joe
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Poul-Henning Kamp
>> Sent: Saturday, June 15, 2013 4:09 PM
>> To: Robert Atkinson; Discussion of precise time and frequency measurement
>> Cc: Perry Sandeen
>> Subject: Re: [time-nuts] HP and other equipment failure
>>
>> In message <1371329221.83869.YahooMailNeo at web171902.mail.ir2.yahoo.com>,
>> Robert  Atkinson writes:
>>
>>> While I agree with everything else you say, you CAN have too much
>>> filter capacitance. At least where dc rectifier / filter (smoothing)
>>> circuits are concerned. Increasing C causes increased ripple current
>>> [...]
>> And ripple current can be a major source of power-line frequency noise in
>> all electronics.
>>
>> The main reason why switchmode power-supplies today (can) outperform linear
>> power supplies with respect to noise, is because the legally mandated PFC
>> correction eliminates the bridge-rectifier ripple harmonics.
>>
>> I would not hessitate to use a good quality switchmode to replace the linear
>> supply in a HP5370B.
>>
>> I did some experiments a couple of years ago, with an audio-amplifier:
>> I put a standard PFC corrector chip on the secondary side of the trafo.
>>
>> The overall result was not satisfactory, but the 50 Hz "sneer"
>> we all know and hate was absent, and the "Tzoing!!!!!" power-on mechanical
>> shock from the trafo was also eliminated, as was the consequent dimming of
>> the lights ;-)
>>
>> The main reason not to do this, is that you need some physically gargantuan
>> coils for a 10A+ PFC-switcher.
>>
>>
>
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