FAST AND HEAVY RAILWAY SERVICE. 235
A.M. during which period six trains would be in service
on each half of the line. Of these the outgoing trains
would be nearly empty, but on the other hand all the in-
going trains would be crowded, and one or two of them
would carry an extra car. We must, therefore, allow for
extra load, and a fair assumption would be to consider all
the trains as three-car trains well loaded. 'This means not
far from 120 k. w. per train, about 1440 k. w. for the full
output of the station.
The working voltage should be as high as feasible.
Without any radical innovations it is quite practicable to
allow a normal voltage of 600 at the motors. ’T'his should
not be much exceeded, while the pressure may without
trouble be allowed to fall ten per cent below this at the
termini during heavy loads. Let us first examine the ter-
minal conditions. Two trains will ordinarily be handled
in that region, requiring by our assumption 240 k. w. To
allow for rapid acceleration of a heavy train, fully this
amount of power may be temporarily required, but two
trains will not have to start together. If, following Fig.119,
we allow 500 amperes available at the terminus we shall be
safe so far as this point is concerned.
As to drop, if we take ten per cent as average during
the busy hours we shall not go far wrong, allowing twenty
per cent at the termini during heavy loads. Even a little
more would be safe if occasion demanded, so that if the
dynamos gave about 600 volts overcompounded about ten
per cent, say, to 670, the minimum pressure could be safely
taken down 150 volts to 520. We must then have at the
termini enough feeder capacity to give 500 amperes with-
out dropping the voltage below 520.
Now for such a road as we are considering the track
should be first class, rails not less than eighty pounds per
yard, and most carefully bonded. Four lines of eighty
pound rails give an equivalent conductivity of about 5,120, -
ooo c. m. Assuming that the bonding lowers the con-
ductivity one-third, the track is equivalent to about
3,400,000 c. m. of copper. In spite of this the heavy