600 v dc > " 27.5 v dc & 60 Amp" 'possible??

[semsemhits]

I am working in the field of electric railway
the overhead wire carrying 600 v dc
I want a circuit to convert

600 v dc > " 27.5 v dc & 60 Amp"


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please help
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by the way i am a mechanical engineer , mean i want some simple explanation

thanks,,
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[chuckey]

A very common type of power supply is called a Switched Mode Power Supply (SMPS). If you wanted a mains to 28V power supply from the 230V mains,the input circuit would rectify your incoming AC, this would give, 230 X 1.4 ~ 325V DC. A high frequency switching circuit would run of this voltage and apply 325V pulses to a transformer which would then reduce the voltage to 28 V AC, this would be rectified back to DC. Thee would be some sort of stabilising circuit to keep the DC voltage constant.
So you could take the high frequency circuit and modify it to cope with 600V instead off 325 VDC, this would mean rewinding the transformer to reduce the output voltage more (was 325 :28, now 600 :28).
A way that fascinates me would be to take two 230V 14V, 60A supplies and wire the mains inputs in series and also the outputs. There are dangers, there will be mains filtering capacitors connected to earth, but one power supply now has 300V on its neutral input and 600V on its live, so these would have to be re-engineered. There would be a general question of safety with this power supply because if the output is near earth potential, there will be printed circuit conductors close to them that are running at 600V. Buts its basically a simple idea.
Frank