[time-nuts] Low cost synchronization

[Dave Brown]

----- Original Message ----- 
From: "Magnus Danielson" cfmd at bredband.net

snip

>
> BTW, measuring the 53rd overtone frequency may not give a clear 
> picture of the
> frequency deviations at the base frequency. Overtone spectras 
> experience quite
> a different phase shift from the way it is produced by a number of 
> devices
> which vector-add to become the seen frequency and phase. Turn on or 
> off a
> strong producer of that frequency may shift that phase quite a bit 
> while the
> fundamental is barly shifted.


Quite true, the majority of loads that produce high order harmonics 
back into the grid are almost always varying considerably in the short 
term-thus they produce short term variations in the resultant harmonic 
spectra that renders the lines somewhat broader than you might think.
Ski lift motor drives are a good example of this. Such loads, without 
adequate filterimg at the point of supply for the load, produce high 
harmonic levels in the associated supply network, to the detriment of 
any telecom cable network that happens to run parallel for significant 
distances-as they always do in rural areas!

The old manual method that used to be used for power grid frequency 
checking involved a comparison of two clocks, one driven from a 
reference and the other from the grid itself-more usually the output 
of a local generator in the days prior to strong grid linkages. The 
comparison was typically done once or twice a day and appropriate 
adjustments to the generation plant made to correct the grid driven 
clock and keep its reading 'syncronised' to the reference clock.

 I have here the remains of an attempt in the early seventies to bring 
this type of system up to date - it comprised an HP 105 series quartz 
reference, a K20- HP 5280A up down counter and an HP 5321B clock.
The up down counter was driven from 100 Hz signals derived from both 
the 105B and the power grid. An HP 6933A D/A converter on the BCD 
output from the counter had its plus/minus 10 volt output interfaced 
to the generation plant.  The 5321B clock reading was initialised from 
the local time service(radio time pips) and then used to fine tune the 
control system (D/A conveter to generator coupling) so the up down 
counter stayed at or near zero reading and grid time ran in sync with 
national standard time.
I dont know how successful this system was but I think it was in 
service for several years.

 I have the up down counter and  the D/A converter almost fully 
operational again- but only have parts ratted circuit boards from the 
5321B clock and I never got the 105B.

 DaveB, NZ




-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.10.13/78 - Release Date: 19/08/2005