Prev: Durofix RL435
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From: Paul Hovnanian P.E. on 22 Mar 2010 16:38
Jan Panteltje wrote:

> On a sunny day (Wed, 17 Mar 2010 16:14:09 -0700) it happened "Paul
> Hovnanian P.E." <Paul(a)Hovnanian.com> wrote in
> <4BA16241.F0FF0278(a)Hovnanian.com>:
>
>>VWWall wrote:
>>>
>>> Paul Hovnanian P.E. wrote:
>>> > Kevin Lang wrote:
>>> >> What would be the simplest way to derive a simultaneous three phase
>>> >> output from a sine wave produced by a single function generator IC
>>> >> ... that does not change as the frequency is varied?
>>> >>
>>> >> Specifically, two additional sinewaves remaining 120 and 240 degrees
>>> >> out of phase with the original as the frequency is varied between
>>> >> 100Hz and 1KHz.
>>> >>
>>> >> Kevin Lang
>>> >
>>> > Google "Scott Tee Transformer" and then figure out how to generate a
>>> > sine wave in quadrature to the reference.
>>> >
>>> From my reply in the same thread,3/11/2010 03:03PM:
>>>
>>> "Once you've got two sine waves in quadrature, getting three phase is
>>> simple. Just use a Scott-T transformer. These were once used for power
>>> applications, but since two phase power is almost extinct, they are now
>>> used for connecting servos that use synchros to those with resolvers."
>>>
>>> http://en.wikipedia.org/wiki/Scott-T_transformer
>>>
>>> Glad to see another old time power guy! :-)
>>
>>Yeah. These electronic types loose me when they start talking about 61
>>Hz or higher.
>
> Yes, I remember we had a 50 Hz frequency meter in the lab,
> it consisted of some metal tongues resonating at 46, 47, 48, 49, 50, 51,
> etc.
> Each tongue had the frequnecy written above it.
> Big thing :-)
> The one that vibrated the most indicated the frequency.
>
>
> frequency
> 48 49 50 51 52
> = = = = =

That's how underfrequency/overfrequency relaying was implemented in power
systems. There are two contacts that can be adjusted laterally to sit under
the reed that corresponded to the desired trip frequency. When that reed
began to vibrate, it would touch the contact, initiating a protection trip.

I'm sure the utility I used to work for still uses this level of
technology.*

*Back before the millennium rolled over, a friend of mine asked me if any
Y2K bugs would leave us all in the dark. I told him that we made it
through the 1899 - 1900 change just fine and not much has changed since
then.

--
Paul Hovnanian paul(a)hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
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