Wheel slide protection: Difference between revisions

{{refimprovemore citations needed|date=September 2016}}

[[File:Pískování 971.JPG|thumb|right|Sanding equipmmentequipment on a ČD class 971 driving trailer.]]Sanding is one method of reducing wheel slip or slide. [[Locomotive]]s and [[Multiplemultiple units]] have [[Sandbox (locomotive)|sandboxes]] which can deliverplace dry [[sand]] toon the rails, in front of the wheels. This may be initiated automatically when the Wheel Slide Protection system senses loss of adhesion, or the driver can operate it manually. Sanding may be connected to a computer system that determines the train's direction of travel and where the sand should be applied: either forwardin or aftfront of or behind the [[bogie|trucks]]. In older locomotives there was a manual lever attached to a valve that had three positions: Off, Forward, and Aft.{{cncitation needed|date=August 2017}}

When a train is braking, the low adhesion manifests as wheel slip where the wheelset is rotating at a lower velocity (speed) than the forward speed of the train. The most extreme example of this is where the wheel stops rotating altogether (wheel slide) while the train is still moving and can result in a “wheel“[[Flat flat”spot|wheel flat]]” caused by the softer wheel steel wheel being abradedworn away by the harder rail steel rail.

However, the wheelset does not need to lock up completely in order for damage to be caused. If the slide is significant, heat can build up in the contact patch between the wheel and the rail, sufficiently to permanently modify the crystalline structure of the wheel's steel alloy. The steel becomes more brittle ([[martensitic|martensite]]) which leads to cavities forming in the wheel. Wheel flats on railway vehicles are very evident by theira characteristicdistinct “bang-bang” noise made in time with the speed of the train. It is normally necessary to use a wheel lathe to remove a layer of wheel tread caused by a severe flat spot or cavity, which reduces the operational service life of the wheel and is a major operating cost to the rail industry.

If wheelslip occurs whilst the power controller is open, WSP will shut off power to the affected traction motor(s). Despite this, most railwayrail transport companies advise their drivers to close the power controller<ref name="FCC WSP">{{cite book|title=Autumn Brief - Driving in Low Adhesion Conditions|publisher=First Capital Connect|location=London, UK|date=September 2011}}</ref> and allow the slipping wheels to stabilize before re-opening the controller on a low setting because control of the train can be achieved more quickly.

However, when wheelslide occurs and the WSP releases the brakes on affected axles, drivers are instructed to leave the brake handle alone<ref name="FCC WSP"/> and let the WSP control the train's braking. This is because the driver is sitting over the leading bogie of the train where wheelslide is usually most severe.<ref name="FCC WSP"/> This wheelslide will partially clean the railhead and so further down the train the wheels will achieve better adhesion, and thus braking effect.

Driving a train under low adhesion conditions takes experience. Failing to recognize and respond correctly to railhead contamination or environmental conditions which cause low adhesion can lead to safety incidents and accidents such as a [[Signalsignal passed at danger]], collision or station overrun.

Manufacturers of WSP equipment include [[Faiveley Transport]], [[Knorr-Bremse]], [[Wabtec]], DAKO, KES & Co GmbH, Mitsubishi, Siemens, Selectron Systems AG, ABB and ABBLCA Ballauri.

Simulation testing employs a computer representation of the train and the track conditions, and signals are provided to the WSP system that effectively deceive it into thinking it is fitted to an actual train. Most of the WSP manufacturers have some simulation capability and there are also facilities available from national bodies or independent testing facilities such as [[Deutsche Bahn]] (DB Germany), [[Ferrovie dello Stato]] (FS Italy), and [[DeltaRail Group]] (formally BR research) (UK and Ireland).