On 06/07/2019 20:55, Tim+ wrote:
Last year we rode a funicular railway with a single overhead wire and
a large bank of resistors on the roof that got very hot when it was
descending. I'm guessing that it was a DC motor/generator setup with
the resistors absorbing the generators output on the way down.

Today we rode a train with two overhead wires but no resistor banks.
This train apparently runs on a three phase supply. Presumably the
rails supplied the third "leg" of the supply but how safe is this
with AC? Wouldn't the rails be dangerously live relative to earth?

Why would they be? If the rails were earthed...

a three phase supply doesnt have to have each limb symmetrical with
respect to earth.

Consider a star or delta transformer with one phase earthed.



There were no warning signs and the track was unprotected so it must
be safe but I don't understand how. Can anyone explain? Also, how
did the braking work?

Feeding overvoltage back into a low impedance supply.


https://en.m.wikipedia.org/wiki/Petit_train_de_la_Rhune

Tim



--
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