Re: electrical power

[Brian Whatcott <inet@INTELLISYS.NET>]

A list member wrote me:

> ...some of the stuff you've presented--tap changers and phase
> indicators are too vague to give me a good idea of how they work.

...

I think the level of detail that interests you would indeed be better
addressed to an electrical engineer handbook - such as Knowlton. Still I'll
try for a quick vignette of the two topics you queried again.
A tap changer is much like a transformer equipped with various taps like
the  110, 115, 120V connections that you sometimes see on domestic
transformers. Generalize this for multiple phases and changing taps under
load, and you have the concept. Because the switched power is appreciable,
and interruptions are not desired, a means is employed to reduce the
shorting current as the mechanism places two  taps on load together - a
'bridging" reactor, or a low voltage autotransformer section which cuts
down the arc
by limiting the circulating current.

Generator phase synchronization is accomplished in several ways: smaller
units connect  the main breaker before energizing the field: larger units
match speed with a frequency meter and match phase with a synchronizing
lamp which is driven from  instrument transformers across two phases of the
line and source respectively, and wired so that synchonism leads to a dark
lamp or alternatively, to a steady bright lamp. Alternatively, a
synchroscope, which is effectively a two phase motor with an indicator on
its rotor is arranged to rotate while a phase difference is detected.

Brian W



Brian Whatcott
  Altus OK                      Eureka!