Re: WMATA crash & track circuits

On Fri, 25 Sep 2009 13:07:44 -0700, Joerg <invalid@xxxxxxxxxxxxxxx>
wrote:


... which in essence says that they chose a frequency of 1/3rd of line
frequency and that has been kept in place until today, except that they
went from 16.666Hz to 16.7Hz.

With 50Hz they had too much motor damage when accelerating large trains
from zero (when stopped).

In old days various motors with commutators and adjustable field
windings were used for variable speed operation. These worked of
course well on DC and in trains often with the possibility to connect
in parallel or series for even large speed range. Such motors can
also be used on AC with voltage (phase) control e.g. in small hand
tools at 50/60 Hz.

However, large AC/DC motors suitable for train operation did not work
very well on 50/60 Hz and this appears to be the reason for using such
low line frequency as 16.67 Hz in trains in some countries. Compared
to DC feed, in the AC feed, the operating voltage could (instead of a
variable resistor) be varied by selecting a different tap from the on
board transformer.

While it would be impractical to change a railway line voltage or
frequency, building new trains with a variable frequency drive and
induction motors would be more practical these days, possibly even
replacing the heavy 16.67 Hz transformer with a rectifier+inverter and
a high frequency transformer on the 15 kV side.

Paul

.

Relevant Pages

  • Re: Voltage supply for CNC
    ... centertapped delta to save the cost of another transformer on the pole ... and has no main or "center" leg. ... Motors run better on the high end of the voltage rating since they draw ...
    (alt.machines.cnc)
  • Re: UK v USA phase converter for spark eroder
    ... >separate 3 phase motors, which are all powered from 1 rather complex ... >transformer, I am looking to build a 3 phase ... >converter to power the whole thing. ... >Does a rotary converter "idle" motor need to be of the dual voltage ...
    (uk.rec.models.engineering)
  • Re: Regenerative Braking
    ... On a DC system you can only regenerate power if there is another load ... Thus you only have a 110V headroom from the light load voltage to the ... When trying to export say 2000A under regen braking with only ... that of the braking trains is used. ...
    (uk.railway)
  • Re: 1920s set worth anything?
    ... Do be careful how and where you store these old trains. ... wrapping trains in newspaper - the inks will transfer and dirty the trains. ... If the original transformer doesnt ... These old standard gauge trains are heavy, ...
    (rec.models.railroad)
  • Re: DC Motors
    ... was a torque motor but not sure. ... for DC motors can I get away with changing the voltage to a lower ... If you already have speed control, ...
    (sci.electronics.basics)