system
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human
How can railway cables be kilometres long without a huge voltage drop?

I was wondering about this, since the cables aren't immensely thick. Where I live there runs a one phase 1500V DC current to supply the trains with power, so wouldn't there be an enormous voltage drop over distance? Even with the 15kV AC power supply in neighbouring countries this voltage drop should still be very significant.
gpt
Part of designing such systems is allowing for fairly substantial swings in actual supply voltage compared to the nominal.

(The IEC 60850 standard, for instance, specifies that a nominal 1500 VDC system is in spec as long as the voltage on the line is anywhere between 1000 and 1800 VDC.)

System design considerations include the selection of suitably-large, low-resistance conductors, as well as regular placement of substations to connect the high-voltage AC grid to the railway's overhead wires.