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K0CQ > INFO 24.07.02 00:01l 75 Lines 3453 Bytes #999 (0) @ WW
BID : 7253_W0AK
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Subj: CP K0CQ: CP K0CQ: 110 vs 230 v mains and frequencies
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Sent: 020720/0446Z @:W0AK.#CIA.IA.USA.NOAM #:7253 [Des Moines] $:7253_W0AK
From: K0CQ@W0AK.#CIA.IA.USA.NOAM
To : INFO@WW
Original to G8BFF@GB7COV.#29.GBR.EU
Original to G8BFF@GB7COV.#29.GBR.EU
There were few controls in the beginning and many frequencies in use.
In practice 16-2/3 and 25 Hz are preferred for traction motors (series motors
in trolleys and locomotives) because the commutation is better than at higher
frequencies and the construction is simpler because the laminations required
to minimize eddy current loss are thick and few per transformer, motor, or
alternator. Those low frequencies work poorly for lighting because of flicker
being visible to nearly all eyes, even with the thermal inertia of tungsten
filaments. The flicker argument is often used to justify 60 Hz over 50 Hz.
That and the 10% saving in iron and copper for 60 Hz. transformers and motors.
I know where 25 Hz is still being used in Keokuck Iowa for arc furnaces. Up
until the 50s, 50 Hz was used in southern California, its noticeable in early
sound movies as the ripple roared through the recording system.
As for voltage, in the US, 120 volts is never used with the center grounded to
give 55 or 60 volts to ground. Its always used with one leg grounded, and then
only at the service panel and distribution transformer. There's a separate
ground wire for safety.
110/220 volts with the midpoint grounded was first used by Thomas Edison in
his DC power plants. And since he made light bulbs which were easier to make
for 110 volts than 220 volts, AC systems continued with the same voltages and
grounded neutral. He probably used those voltages because of commutation
difficulties with higher voltages in his early generators.
In my experience, 120 volt arcs tend to be self extinguishing, e.g. they blow
enough material away to make a gap wide enough that the rate of voltage rise
going through zero is slower that the rate of ionization clearing so that arcs
can stop on their own. 220 and higher voltage arcs have just enough faster
rate of voltage rise that the arcs to ground won't clear until interrupted by
some other apparatus. In particular 480 volt circuits tend to self destruct as
the arc travels towards the power source, never drawing enough current to trip
an overload (fuse or circuit breakers) but dissipating enough power to turn
the panels into molten blobs.
Because of that tendency for arcing, GB engineers have produced some very fine
(and expensive) fast blow fuses for use on their higher voltage secondaries.
New to the latest National Electrical Code is a requirement for arcing fault
sensing circuit breakers in bedrooms in homes. Since such a breaker might seem
to depend on the RF characteristic of an arc, I fear it will be sensitive to
HF radio energy and prove to be unreliable around a ham station or MF
broadcast station. These being 120 volt circuits, the requirement seems to be
different from my experience of 120 volts arcs being self extinguishing.
Perhaps the concern is that before the 120 volt arc clears it can cause
ignition of bedding...
I used to have a book, a collection of articles by one early US electrical
engineer that had an article about the selection of voltages and frequencies,
that article dated about 1921. It should be available in good engineering
libraries.
73, Jerry, K0CQ @ W0AK.#CIA.IA.USA
[ Received via HF CLOVER at KB6LE ]
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