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Post by charleyfarley on Dec 4, 2012 17:43:13 GMT
I can't help noticing that when a 313 shuts its doors, it begins moving almost instantly whereas a 378 (its replacement) seems to sit there for a good 10-15 seconds before starting to move. So frustrating on a journey of 15-20 stops.
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Post by Deleted on Dec 4, 2012 18:57:33 GMT
If its conductor operated its because conductors have to work from inside the train. DOO operations are faster.
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Post by Deleted on Dec 4, 2012 22:08:29 GMT
I can't help noticing that when a 313 shuts its doors, it begins moving almost instantly whereas a 378 (its replacement) seems to sit there for a good 10-15 seconds before starting to move. So frustrating on a journey of 15-20 stops. Charley, are you in a position to estimate any difference in performance between the DC third rail and AC overhead line sections of the track? The older trains are driven by DC motors as opposed to AC in the 378. I am not familiar with the precise electrical block diagrams of the two trains but I can tell you that the electrical equipment on a modern AC motor unit when driven from DC is complex and I wonder if this creates delays (just listen to an S Stock coughing and spluttering as it gets going) but once under way the performance should improve. I wonder if the performance improves on the AC part of the line. As a comparison, are there any similar start up delays on the 2009 stock? |
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Post by charleyfarley on Dec 4, 2012 22:19:47 GMT
2009TS goes off like a rocket. Beautiful performance
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Post by Deleted on Dec 4, 2012 22:59:51 GMT
I can't help noticing that when a 313 shuts its doors, it begins moving almost instantly whereas a 378 (its replacement) seems to sit there for a good 10-15 seconds before starting to move. So frustrating on a journey of 15-20 stops. Charley, are you in a position to estimate any difference in performance between the DC third rail and AC overhead line sections of the track? The older trains are driven by DC motors as opposed to AC in the 378. I am not familiar with the precise electrical block diagrams of the two trains but I can tell you that the electrical equipment on a modern AC motor unit when driven from DC is complex and I wonder if this creates delays (just listen to an S Stock coughing and spluttering as it gets going) but once under way the performance should improve. I wonder if the performance improves on the AC part of the line. As a comparison, are there any similar start up delays on the 2009 stock? I can tell you that. There is no difference in the time taken to move whether on AC or DC power for 378s. However the 378s under AC power are a lot quicker to accelerate than on DC. S stock acceleration has been restricted as mentioned on other threads. On modern trains with AC motors, the DC is converted into 3 phase AC for the motors. Under AC I believe the current is converted to DC first then 3 phase AC for the motors. |
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Post by Deleted on Dec 4, 2012 23:41:05 GMT
Many thanks for this data; in fact the AC can only be single phase but the really interesting information you have given is the conversion of AC to DC; this is fascinating.
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Post by trt on Dec 5, 2012 9:48:32 GMT
The AC collected by the pantograph can only be one phase...
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Post by Deleted on Dec 5, 2012 12:03:59 GMT
Yes but it had to be converted to 3 phase for the motors : early example.
There are two types of AC motor, synchronous and asynchronous. The synchronous motor has its field coils mounted on the drive shaft and the armature coils in the housing, the inverse of normal practice. The synchronous motor has been used in electric traction - the most well-known application being by the French in their TGV Atlantique train. This used a 25 kV AC supply, rectified to DC and then inverted back to AC for supply to the motor. It was designed before the GTO thyristor had been sufficiently developed for railway use and it used simple thyristors. The advantage for the synchronous motor in this application is that the motor produces the reverse voltages needed to turn off the thyristors. It was a good solution is its day but it was quickly overtaken by the second type of AC motor - the asynchronous motor - when GTO thyristors became available.
The 378s use asynchronous motors and IGBTs.
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Post by Deleted on Dec 5, 2012 12:51:52 GMT
The 378s (and indeed most modern emus) when working off AC convert to DC and then back to AC for the motors
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Ben
fotopic... whats that?
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Post by Ben on Dec 5, 2012 13:07:38 GMT
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Post by caravelle on Dec 5, 2012 21:04:19 GMT
Correcting Ben's hyperlinks: [a href="http://www.class90electriclocogroup.co.uk/373_to_307_A_Very_Brief_AC_Traction_Introduction[1].pdf"]http://www.class90electriclocogroup.co.uk/373_to_307_A_Very_Brief_AC_Traction_Introduction[1].pdf[/a] buhrkall.dk/OHs Traction System Case Study.pdf This second link will work if you paste it in the address bar and hit enter (at least for IE9) |
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Ben
fotopic... whats that?
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Post by Ben on Dec 5, 2012 21:53:04 GMT
Thankyou! You should have seen what they looked like before I had a go at cutting them down to size!  |
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