What is "Field Divert"

[cossie4i]

455s have a camshaft setup and they have Shunt, Series, Parallel and Weak Field

Same as the old 400 series stock.

I used to enjoy notching up

 

[Emblematic]

455s have a camshaft setup and they have Shunt, Series, Parallel and Weak Field

Rather confusingly the term 'shunt' has different and unrelated meanings in the electrical (= parallel wired) and railway (= move vehicles) industries, and the controller uses both sets of definitions! Unlike the other three, the Shunt setting doesn't refer to the electrical configuration, it's just a slow-speed setting.

 

[Nym]

So it has nothing to do with shunting the notching relay hold coil?

Shunt prevents the notching relay from notching the camshaft further, regardless of the camshaft position on GEC RPA controlled stock.

Seires and Parallel (and indeed weak field on 73TS and D78 Surface stock) sets the limit pf the camshaft and limits when the NR can notch the shaft.

 

[Emblematic]

On older London tube stock, e.g. 1931 stock, I recollect that the term "weak field" was used and also "shunt", which both (I think) had to do with what happened as the train went faster - or to enable it to go faster.

Some LU stocks controlled weak field by a separate flag switch, visible when operated from outside the cab. This was to help ensure that it was only activated in open sections, where the higher speed it enabled was permitted.
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So it has nothing to do with shunting the notching relay hold coil?

I doubt it - why choose that (even if correct, which isn't how I recall the setup) over shunting the stator windings for field divert? I suspect Shunt for the low speed setting may predate camshaft control. It seems too tenuous a link - what would a train driver normally interpret Shunt to mean?

Anyway, it's still ambiguous!

 

[edwin_m]

I've always understood, from an old book I think, that Shunt keeps all resistances in series with the motors and therefore prevents acceleration beyond a very slow speed. I don't know if this is by "shunting" the relay to prevent notching, or by some other method, but "shunting" the stator windings would appear to have the opposite effect.

 

[contrex]

I've always understood, from an old book I think, that Shunt keeps all resistances in series with the motors and therefore prevents acceleration beyond a very slow speed. I don't know if this is by "shunting" the relay to prevent notching, or by some other method, but "shunting" the stator windings would appear to have the opposite effect.

I always had the impression that in the context of naming controller notches, the word "shunt" was used to mean that the stock being driven would only operate at shunting speed (i.e. very slowly)

 

[455driver]

I used to enjoy notching up

As did I (on 455s), especially pulling out of Guildford heading towards London Road, I think it was normally 3 notches of parallel to keep to the 30 up the hill.

 

[cossie4i]

As did I (on 455s), especially pulling out of Guildford heading towards London Road, I think it was normally 3 notches of parallel to keep to the 30 up the hill.

I used to enjoy EPBs and CEPs best as you could hear what was going on as well.
Leaf fall was a fun time, just taking a notch at a time just so you didn't get uncontrollable wheel spin.

 

[HarleyDavidson]

The 442s were quite good for notching too.

In fact I find that with a deft hand you can do better slip control than what the electronics do, having got units going when the electronics designed to do it couldn't! :roll: