USAGE OF DC AND AC CURRENT ON THE RAILWAYS OF THE FORMER USSR

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От: Dima Zinoviev (dmitry@pavel.physics.sunysb.edu)
Дата: Tue Aug 26 1997 - 17:34:02 EDT


    USAGE OF DC AND AC CURRENT ON THE RAILWAYS OF THE FORMER USSR
                        QUESTIONS AND ANSWERS

Compiled from the messages of Yuri Danilov
(Yuri.Danilov@f605.n50.z2.fidonet.org), Dmitry Klimov (dmk@kosnet.ru),
Boris Paleev, Andrew Lomakin
(Andrew.Lomakin@f122.n5080.z2.fidonet.org) and Garry Tomkin posted to
fido7.ru.railways in July-August 1997, upon the request of Charlie
Mann (LNUSEMD1.ZZ1C5R@gmeds.com). Comments, additions, corrections, as
well as new questions and answers, are welcome!

----------------------------------------------------------------------
Q. Is it true that 3kV is used for passenger traffic, and 25kV for
freight traffic?

A. No.

Q. Is it true that 3kV is an obsolete technology?

A. Yes. Originally, all railways were fed by 3kV dc current, because
high-voltage dc-to-ac converters were too big to fit into electric
locomotives. Then, 25kV ac current was introduced. AC current can be
transformed, so it is easy to obtain high voltages. AC-fed locomotives
are more efficient, but less reliable (by 30-40%).

Q. Do they plan to upgrade all railways to ac current?

A. Probably yes.

Q. How does a loco pass the boundary between an ac and a dc region?

A. Very simple (e.g., at Uzunovo station): a segment of the contact
wire over the main track can be switched from ac to dc and back. An
ac loco is detached from the train and goes to the depot, then the
voltage is switched, and a new dc loco is attached to the train.

In Yaroslavl oblast there is Danilov station that serves as an ac/dc
gateway, too.

Q. Do dual-voltage locomotives exist?

A. Yes, they do -- VL82. It is a dc electric locomotive supplied with
a transformer and a ac-to-dc converter. The loco can make a guess in
which mode to operate.


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