Northwood points southbound

[roverlei]

Hi. Does anyone know why S8 trains tend to surge of the points just south of the southbound platform when leaving Northwood? There's always, but obvs in wet weather, a real lack of traction there.

[goldenarrow]

If it’s what I think you are referring to, it’s a double gap in the conductor rails which briefly cuts power to the motors hence the jolts.

You will find the same occurring at Rail Section Gaps which isolate the different sections that are electrified that are just after station platforms such as Ickenham WB, Victoria (SSR-EB), Kings Cross (SSR) and Baker Street (MET-NB), the later of which has the double whammy of complex track work and a Section Gap.

[t697]

The DC Sectionalisation Gaps are near to Northwood Sub-Station which is much closer to Northwood Hills. I think the current rail gaps just south of Northwood are just associated with the crossover points and the points leading off into the siding.
OP describes "lack of traction" so may be they meant poor adhesion and wheelspin instead? If so, may be rail head contamination from grease at the points mechanisms?

[philthetube]

I think it is just down to rail gaps, there does not seem to be an issue there with adhesion, It actually feels to me like low juice rails.

[class411]

Jun 9, 2019 7:36:57 GMT philthetube said:

I think it is just down to rail gaps, there does not seem to be an issue there with adhesion, It actually feels to me like low juice rails.

That would explain the reference to a 'surge'.

Although I would expect the controlling electronics for modern motors to be able to handle low voltages.

Most modern systems will work normally until the voltage drops to a certain level and then refuse to operate at all.

[t697]

S stock does handle low voltages properly. But once the car is 'gapped' there's no energy to keep it motoring!
Also, once it's above about 20km/h there is a feature to stop each pair of cars motoring in turn at the appropriate position along the track after the first car detected a gap, thus reducing shoegear arcs on subsequent shoegear sets.

[class411]

Jun 9, 2019 12:02:01 GMT t697 said:

S stock does handle low voltages properly. But once the car is 'gapped' there's no energy to keep it motoring!

Well, obviously.

The point I was making was that in older stock, a low voltage supply might cause the rate of acceleration to slow, and the motors might appear to 'surge' when the train entered a section of track with the correct voltage.

I would not have thought that applied to S-Stock.

Also, once it's above about 20km/h there is a feature to stop each pair of cars motoring in turn at the appropriate position along the track after the first car detected a gap, thus reducing shoegear arcs on subsequent shoegear sets.

So, if it's going fast enough, it forces the whole train to coast over the gap?

Damn sneaky these S-Stock engineers.