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| Re: GM10B (Re: Early Conrail) (678200) | |||
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Re: GM10B (Re: Early Conrail) |
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Posted by Bill West on Mon Sep 8 06:10:50 2008, in response to Re: GM10B (Re: Early Conrail), posted by trainsarefun on Sun Sep 7 23:47:03 2008. Will, where do I start? You contribute much knowledge and thought to this board but it always seems to invite us to dig up more info. Here goes:1. The Railway-Technical link only speaks of modern induction motor drives. AC locos until the 50’s used AC series motors. 2. The RRnet link is rather light on knowledge of AC series motors. 3. The Doc Steve link spends half the page on the wrong kind of motor and then calculates the motor RPM without actually saying anything about how it works. There is another site as well that has incorrectly calculated GG-1s as if they had synchronous motors. 4. All the Class I RR interest in electrification in the early 70’s was driven by oil prices. No long term noble, save the earth goal, BN’s fuel bill was a million dollars a day. 5. Permanent magnet fields are for small servo motors and the like. Rarely would they reach 1 horsepower. 6. Ac motors are: -synchronous, usually DC slip rings to a rotating field. Runs at a synchronous speed, frequency per second times 60 seconds divided by pairs of poles gives speed in revs per minute. -single phase induction, mainly home use. Not over 10 hp, becomes more costly than 3 phase. -induction, no rings or commutator. Field is induced to the rotor. Runs with a 3-20% slip below synchronous speed. This is the most common industrial motor. It is also in modern AC drive locomotives/cars with a variable frequency inverter giving the speed control. Because it doesn’t need commutator space it gets about 20-30% more winding and core between the wheels and so can have a higher rating or more overload reserve. -wound rotor induction, same as induction but the rotor winding is brought out through 3 slip rings to speed control resistors. This is an older industrial practice. -universal motor, this is the same as a DC commutator motor but it is only suitable for fractional horsepower home use. -single phase series AC traction motors. At their most basic these look like DC series motors complete with a commutator and they do run on DC. But after that they are a very peculiar breed with much attention paid to commutation and starting torque. The transformer effect’s unintended coupling of power to the armature results in the brushes bridging and shorting turns, leading to very severe sparking unless the inventor really understands what he’s dealing with. It took GE’s Stienmetz many years to figure out even part of the theory. The shunting in the RRnet link was not just field weakening for higher speeds, it was to do with shifting the phase angle of the field to get adequate starting, commutation and power factor. There are several sub variations of the railway AC series motor. The use of twin motors was in part to help some of the problems. GE and WH’s numbering systems did not distinguish between AC and DC series motors as they were structurally so similar. 7. Then as you covered, for electronics era locomotives one has to be careful of the power supply and the final drive. In addition to using AC on AC motors and DC on DC motors one can use an AC source to power DC motors through a rectifier or chopper or a DC source to power AC motors through an inverter. If the power is coming from a diesel engine it could be driving a DC generator or an AC alternator giving DC through a rectifier. Lots of combinations. 8. ASEA’s toasters are indeed AC supply through thyristor(SCR) choppers to DC series motors. The design traces back to 1965 when SCRs were new and locomotive size inverters were unheard of. Many later received AC inverter/induction motor drives in rebuild. Your Tydall.nu link ties in the GM10B as having ASEA DC traction motors while the GM6C used EMD DC traction motors. 9. Try a library for reference books. “Standard Handbook for Electrical Engineers” has been published in various years from 1907 onwards with various editors, look in the railroad or transportation chapters. The writers of these chapters have included GE and Westinghouse’s head railway designers and in the 1949 edition the chapter is written by New Haven’s chief electrical engineer. Another is “Handbook for Electrical Engineers”, the 1922 edition is in the Internet Archive, unfortunately its chapters are not as conveniently divided. If your university library has AIEE Transactions, search the indexes about AC railway motors in the 1904 - 1940 era. The Internet Archive has also just added Westinghouse’s professional publication, The Electric Journal. It only covers 1904 -1921 but I’ve already printed about an inch of paper from it. Bill PS Trains, Penn Central would not have had a future need for 50kv but it would have been nothing for ASEA to adjust the little bit of high voltage switchgear and design the transformer input winding for 50kv if any other customer had a use for it. I suspect that if that Wikipedia entry is correct about 50kv, it should be 60hz not 25hz. |
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