operation of point end

[Savitha]

hi,
what will be the advantages of sequential operation of point ends over parallel operation of point ends?.
if both the ends of points are operated simultaneously, the response time will be less. but sequential operation of point ends is preffered. why?

regards,
savitha

[dorothy.pipet]

I'm not all that clued up but ... avoids all point machines drawing maximum power load at once.

In UK mainline it is rare to provide sequential proving for A, B, ends of the same points. OTOH SSI style interlockings are generally configured to stager point calls to the different Sets of points very slightly.

There are probably other advantages.

[Peter]

While it is quite normal to start the operation of points likely to be called a the same time in order to stagger the inrush current at the start of the move, this is unlikely to extend to the individual A and B end of crossovers.

There will have been older interlocking practice that had "point to point" locking so a certain end does not become unlocked until a related end is detected in the relevant position. This is not related to the power demand.

We are only talking about a delay of less than a second and is normally achieved by careful selection of the TFM address so they are at different positions in the SSI cycle time so you would not expect to see a significant impact on the total operation time.

Peter

[PJW]

Unless there is a local points battery, then the power to move the points must be provided directly from the power feeder. If this is a long length then the series resistance can result in significant volt drop along it from the source of the supply. The power distribution design must ensure that the voltage does not drop below the specified lower limit and therefore the number of points thaty can move simultaneously (particularly at the end of a long feeder) is very significant factor and could lead to large cross sectional area cable being needed and hence reducing peak demand is advantageous to avoid this.

As others have said, in the UK we generally do not stagger very significantly, but yes the SSI TFM does deliberately introduce a short stagger between its outputs for separate points to avoid the very high peak (120V applied to an initially stationary motor with low dc resistance) initial current surge (once motor is turning it generates back emf and therefore takes less current). As Peter has said, the way that SSI operates iis that it addresses the separate TFMs on a cyclical basis so if the module numbers are chosen not to be adjacent then the amount of stagger between the points on the separate TFMs is increased a little.

While it is quite normal to start the operation of points likely to be called a the same time in order to stagger the inrush current at the start of the move, this is unlikely to extend to the individual A and B end of crossovers.

There will have been older interlocking practice that had "point to point" locking so a certain end does not become unlocked until a related end is detected in the relevant position. This is not related to the power demand.

We are only talking about a delay of less than a second and is normally achieved by careful selection of the TFM address so they are at different positions in the SSI cycle time so you would not expect to see a significant impact on the total operation time.

Peter