Another notice for uploaded book: the compressor, which is described in, is British compressor from EU06. Polish built locos have Polish compressor, but the electric motor is the same.
In Poland 3 kV DC system, distances between substations are shorter than in 25 kV AC (15-28 km). Shorter, because quite low voltage need high current to send the same power. High current gives high voltage (and energy) losses in catenary resistant, and small distance between substantions limit this losses to acceptable level. Between two areas of supply is special insulated gap in supply (upper) and traction wire. The voltages in two sections can be different. For example, on one section is train which start and have high current - and in section is 2,8 kV, and in second section, for example empty, or with free riding or braking train - full 3,2 kV (voltage is slightly higher than nominal for fight with decreasing it under high current of accelerating trains, in stations can be 3,6 kV). And when train with high current ride by then insulated gap, this difference of voltages make sparks and electric arc on pantograph and catenary. The current "wants to go" by one way. It's
make high wear of wire and surface of pantograph. In some conditions, the arc can melt and burn the wire, with break it, which make big damage of catenary. This is a reason. Of course, if driver forget We8, in 99% only protection relays turn off the circuits on loco, but situation isn't good for equipment.
In Poland driver should turn off traction current, and, in winter turn off the electric heating - by main contactor in loco. In locos that have compressor on 3 kV (f.e. ET22, EP09, ET21) turning off compressor is recommended. EU07 have compressors supplied on 110V side. Traction motor fans may be turn on. I think that in 25 kV AC you should turn off all circuit and traction transformer, because if not, is possible an "phase mismatch" in circuit with bad consequences for transformer and substations.
Traction motor fans have in Polish locos 2 functions: driving the fan and convert 3 kV to 110V for control circuits, charging battery and lighting. In some locos is a 3kV motor and small 110V generator (f.e. In EP09 motor drive generator by belt), in some, that EU07 and ET22 motor and generator is in one machine with two collectors. In 07 110V generator supply in addition compressor. In this machine is special transformer. It not convert the voltage, but in special connection to machines windings protects the machine, when is boundary between substations, or when pantograph have bad contact with catenary (vibrations etc.). Without transformer, in this state, 3 kV motor can begin the work as a generator, and make fire on collector. For example, EN57 EMU has 2 machine inverters, one converts 3 kV to 110V (without fan, EN57 traction motors has natural cooling by fans on it's rotors.), and second, smaller, converts 110V to 220V/500 Hz to luminescent interior light. For last years, in some rolling stock machine inverters are changed for electronic, silent inverters. In EN57 it's simple, in 07 not. F.e. EP07-1049 has electronic inverter 3kV/110V, 400V AC 3-phase, and additional AC traction motor fans. With We8 machine inverters can be turned on, sometimes protection relays can operate. Electronic inverters don't like We8 places, and after it sometimes need reset.
Driving loco on 3 kV DC is quite normal. Driver should remember, that resistant positions are only for accelerating, not for long ride, because resistors can overheat, and it's not economic. On resistant positions light special yellow control lamp, which inform driver about it. On non-resistant and shunt positions we can go long time. On locos driver adjust position manually, on EMU's is specific control. In EN57, EN71, ED72 main controller has only few positions: 0, manoeuvre, series, series-parallel, shunt 1, 2, 3. Real connections is maked by pneumatic-driven camshaft in electric compartment under motor car. Manoeuvre= all resistors applied, only for station manoeuvre, low speed. When driver turn controller on higher position, camshaft automatically make run to selected non-resistant position, and current relay allow camshaft to turn on next position when current is lower than 370 A (or lower when driver select "low acceleration mode", when is wheel slip, in rainy days). Turning position down is impossible, because camshaft turn only in one direction. Driver should turn to 0, and select new position. Camshaft fast turn to 0, ant to new selected position.
Links for You (unfortunately Polish only, but with some clear pictures)
http://trakcja.rail.pl/readarticle.php?article_id=1
(3kV catenary)
http://trakcja.rail.pl/readarticle.php?article_id=7
("We8" question)
http://transportszynowy.pl
Great site for railfans, especially part "Kolej" - kolej
http://transportszynowy.pl/eu06-07.php
Description of EU07, with photos of some interior devices
Best regards!
