Is there a delay between power application and power output?

[CP165]

I've always wondered if there is a delay between a driver setting the power in the cab and the engine/motor responding. I would imagine it's different for different types of rolling stock i.e EMUs, DMU, Loco-hauled, and from a DVT. If there is, surely drivers have to compensate for this?

Anyway, some light on this would good, cheers.

 

[driver9000]

It varies on the DMUs that I drive, some respond immediately to the handle others have a slight delay between me moving the handle back and the engine picking up. The 150 and 153 are the ones with the most noticeable delay in my experience. This only happens when initially taking power from idle with subsequent movements of the handle the engines respond immediately. To avoid a roll back I hold the brake in step 1 until the engines power.

 

[TGV]

TGVs respond pretty much immediately in traction or rheo.

 

[brillopad]

Can I add another related question......I know about wheel slip protection under braking but is there any traction control to avoid spin up when taking power ?

 

[slick]

Can I add another related question......I know about wheel slip protection under braking but is there any traction control to avoid spin up when taking power ?

Yes for the the EMU traction I drive (Class 315/317/379) When wheelspin is detected, traction power going to the traction motors will be automatically cut to Notch 1 until the wheel stops spinning and comes within an acceptable speed range, irrespective of what notch the power is in. Normal Traction power will then be regained on the 315s and 317s. This is dealt with by the WSP racks on the PMOS coach on 317s and the DMS coaches on 315s. 379s may differ slightly but the logic and outcome is the same.

 

[Old Timer]

Speaking on Irish Rail 071s, which have a high speed GM engine, there is a slight delay as the fuel racks run up, which can cause a problems when starting away on a rising gradient.

To overcome this the practice when stopping is to release the train brake, and hold the train on a light application of the loco straight air. The real masters can shuttle from one to the other as the train rolls to a stand with not even a jerk.

On getting the right away, the power controller is moved to position 1, the engine speed runs down slightly and then starts to run up as the fule racks run up into position, you then move the power controller to position 2 and as the loco takes the weight, you ease off the straight air. You can sense the correct time as the loco starts to lean forward just before she starts to drag the brakes. If you get the release wrong the loco will snatch the train but done properly you are bleeding off the straight air as the wheels are freed up to rotate.

Starting away on the level and a falling gradient is simply a question of opening the power controller up to position 1 then as the speed dips, opening it up to position 2 and then forward steadily to full power.

These clips illustrate.
http://www.youtube.com/watch?v=k5EVXqYDEWc&feature=related

http://www.youtube.com/watch?v=rIV4EobOvhA&feature=related
On this clip at 2:18 you can see him shuttle the train and stright air brakes, and at 2:40 you can hear the drop as the power controller is opened and at 2:59 you can hear as the Driver opens up into position 2, as the loco takes up the train.

http://www.youtube.com/watch?v=eROHKB2NjRM&feature=related
This is probably the best departure, with a straight transition through the power controller positions. You can imagine what it was like on the footplate when these beasts were opened up.

 

[scotsman]

I'm told there's a 4 second delay between the power cars in HSTs - the lead always takes the power first.

 

[Old Timer]

Can I add another related question......I know about wheel slip protection under braking but is there any traction control to avoid spin up when taking power ?

All US locos are now fitted with this equipment, the GM system as fitted to the 071s acted by reducing the power to the bogie, however when the traction current was reapplied you would get surging which jerked the train. This made driving in poor rail adhesion conditions quite demanding, especiallyas GM fitted wheelslip protection which shut down the loco into a failure state if there was too much.

I was once on an 071 which started to lose her feet at high speed on some poor jointed track and the automatic wheel slip protection kept on cutting in faster than we could take the power off to the extent that the protection circuit cut in and we rolled to a stand with a complete loss of power. This was eventually overcome by some adjustments to the circuits but if not properly handled, especially on the climb out through Glanmire Road Tunnel, or on the Curragh or Ballybrophy bank, you could still trip the protection circuit.

GE operates by a system called IDAC which reduces the currrent running to the faster axle.

GM subsequently developed a creep control system which makes a partial straight air application to the bogie to the point where the slipping wheel is held at the point of slipping, thus giving maximum adhesion.
--- old post above --- --- new post below ---

I'm told there's a 4 second delay between the power cars in HSTs - the lead always takes the power first.

That is to allow for the equalisation of the engine speeds and to stop the rear power car from bunching the train into the lead power car - as described above.

 

[TGV]

Interesting regarding the 4 second delay on HSTs. When power is requested in a TGV, both power cars respond immediately. There are, however only 2 couplers in the formation unlike an HST and both of those have large shock absorbers so there is no "bunching".

 

[Passenger John]

Hope this is not off topic and not too ignorant but why does a class 365 starting off sound like it is changing gear.

 

[swt_passenger]

Hope this is not off topic and not too ignorant but why does a class 365 starting off sound like it is changing gear.

It's a feature of the particular design of inverter (GTO) which does the DC > AC conversion for the motors. The frequency of the electronic switching controlling the inverter changes as the overall speed increases.

 

[Hairy Bear]

I'm told there's a 4 second delay between the power cars in HSTs - the lead always takes the power first.

Totally not true.
The power is instant.If anything the rear one will produce more power quickly than the front due to it idling faster at the time.
But the overall time it takes for it to go from idle to max is all down to the load regulator/governer, and they all vary.

 

[colchesterken]

I have watched HST drivers at Paddington and Kings cross. they seem to pull the handle down several notches then as the revs pick up to go back
While we are on the subject can someone tell me if the power handle on a diesel electric controls the fuel to the engine or the electric power to the motors
if it is the diesel then there is no direct control on the motors they must just do their own thing ?

 

[Cruithne3753]

I suppose this relates to something I've wondered about: When you have formations of mismatched units (such as 158/143 which I presume have quite different performance profiles!), how does it avoid the wheels turning at different speeds for a given control setting?

 

[ChristopherJ]

Deleted.

 

[driver9000]

I suppose this relates to something I've wondered about: When you have formations of mismatched units (such as 158/143 which I presume have quite different performance profiles!), how does it avoid the wheels turning at different speeds for a given control setting?

Having driven varying combinations of Sprinter+Pacer I can confirm that this is not an issue. Despite the differing size of engine the notch settings are set the same (ie notch 4 is 54%).

 

[Spagnoletti]

I have watched HST drivers at Paddington and Kings cross. they seem to pull the handle down several notches then as the revs pick up to go back
While we are on the subject can someone tell me if the power handle on a diesel electric controls the fuel to the engine or the electric power to the motors
if it is the diesel then there is no direct control on the motors they must just do their own thing ?

On the preserved diesel electric traction I've worked on, neither. You're actually controlling the speed setting of the engine governor which in turn controls the fuel rack and so maintains the engine speed regardless of load.
Also connected to the governor is the load regulator - on 1950's designs a fiendishly complex bit of mechanical linkages which sets the generator field to the appropriate amount depending on engine speed. There are feedback mechanisms from the load reg back into the governor to ensure the engine & generator aren't over/underloaded and that field diverts occur as line speed increases. On newer kit most of this is done with electronics.

Oh and if the connection between power handle and governor is pneumatic it only takes a blocked strainer or something to slow down the rate at which the loco takes power. It's not uncommon for locos to be slightly sluggish especially at initial application because of this.

 

[TDK]

67's are intant however it does take a while for the amps to peak in each notch.

168's have a lul of about 2 seconds before the power and movement it noticable.

 

[Smudger105e]

if it is the diesel then there is no direct control on the motors they must just do their own thing ?

On basic diesel traction (the Shunter!) moving the power controller to notch 1 closes the motor contactors, notches 1 to 2 alters the generator field strength, and notches 2 to 3 mechanically increase engine revs by pulling on the governor linkage. Can't remember what happens going to notch 4! lol I might have to get out the schematics for an 08 to find out...

 

[Hydro]

Oh and if the connection between power handle and governor is pneumatic it only takes a blocked strainer or something to slow down the rate at which the loco takes power. It's not uncommon for locos to be slightly sluggish especially at initial application because of this.

I've got a pair of 37's on my train at the moment, and our chauffeur for the day has commented one is sluggish to take power and the other is sluggish to reduce power!

 

[12CSVT]

The class 37/9s were designed to have a time delay between power application and output.

When class 20s are working in multiple there always seems to be a delay of about a second between the leading loco and second loco taking power.

 

[Driver Bob]

I seem to recall in the dim mists of time in my memory that the Class 27's were slow on taking power. Open the power handle and have a cup of tea while waiting for the loco to start moving!

 

[RPM]

As TDK says, 168s have a delay when taking power, but 165s don't. If you are driving a mixed formation from the 168 end, when you take power you can feel the 165 trying to shove you before the 168 fires up.