What pantographs should actually be raised. I've number of journeys in different countries this week. And trains either have the rear raised, the front raised or all raised. What should it be thanks.
I think different operators have different rules. Here on the ECML LNER use the rear panto on their Azuma's, unless it's a 5+5 car set where they'll use the front panto on the front unit, and the rear panto on the rear unit. Hull Trains meanwhile use the front when not operating two sets coupled together
In Germany, usually the rear pantograph is raised. This gives the driver more time to lower it should anything be wrong on the overhead wires. Exceptions: flammable goods behind the loco (tanker wagons) goods that could be damaged by debris (car transporters) etc. In the case of double headers, the two pantographs furthest apart should be used (i.e. front on the first and rear on the second loco), with the same exceptions (then both front).
There're way too many nuances regarding them which inhibits one from creating a generalized set of rules regarding their operations. As others have rightfully pointed above, it depends on the per country and per operator basis alongside the nature of operations. Some places would prevent you from raising the rear pantograph if the loco. is hauling flammable or sensitive cargo behind it. Others would prevent you from raising the front one in extreme cold conditions as the snow and ice dislodged from the overhead cables builds up on the roof. Locos. like BR Class 86 & 87 have a single pantograph so you don't even have a choice in that case. No, nothing fancy or dramatic I'm afraid. Both pantographs are connected to the same power supply carrying the same voltage everywhere. So unless something is VERY wrong with the loco; raising both pantographs isn't a problem. Locos. like E94 raise both their pantographs regularly. That helps in distributing the electric current being drawn from the overhead system by half per pantograph. That in turns reduce the loss of electrical energy to the environment in form of heat to a quarter (as per the Joule's law of heating)
Good question. I think two raised pantos in close proximity are to be avoided unless this is not possible (like double headers with multi-system locos with only one panto for each system coupled together. Also, in winter sometimes both pantos are raised, probably in order to remove ice from the underside of the overhead wires with the first one and ensuring proper electricity flow through the second one. But those are rare exceptions. I do not know the exact electrical reason. The first thing that comes to mind is avoiding an arc between the two, e.g. in damp and humid conditions. Apart from that, probably it is nothing serious, maybe only a reduction in efficiency or disturbance of the system. We have to take into account that Germany uses 25 kV which is a much higher voltage than some DC systems around the world.
For US trains, it's usually set that that < shape of the pantograph points towards the direction of travel.
I have a 3 kV DC line in my city. I regularly see electric locomotives carrying freight trains start moving with all pantographs raised to prevent the overhead wire from being burned out by the high currents.
Rear: By default - if something destroys it, the front pantograph is still operative and can move the loco away. If the front one collapsed, it could take the rear one with it. Front: If there is something sensitive behind the loco, because there is a lot of graphite, sparks and other debris falling from it. Flammable cargo like tree logs, tanker wagons, or something sensitive to physical damage and dirt, like new cars or another locomotive. Both: On locos with old single-contact pantographs (modern pantographs usually have multiple points of contact), also under DC voltage if the loco is standing on one spot for longer time or when heavy train starts moving out, again to have more points of contact to prevent melting the pantograph to the wire. Sometimes the ideal setting is not available though, some locos have only one pantograph, modern multisystem locos may have many pantographs, but only one suited for the currently required size and voltage. Pantographs have rather high pressure in upward direction, so it is preferred to have multiple raised pantographs as far apart as possible from each other to spread this pressure and keep the wire stable at higher speeds.
That's not a correct assumption though. Once you have two raised pantographs on one loco, they can be connected to two power supplies, and arc them together through the locomotive Usually the neutral sections are longer than expected loco length, but in some cases they don't have to be. I believe in Slovakia the tracks in stations are split in half and it is forbidden to change between odd and even track groups with a raised pantograph overall. There the neutral section can be just a few dozen centimeters. There can also be intentionally dead wire (usually at construction sites) that has power cut off. If your first panto connects to the dead wire while the second is still touching a live wire, you will arc the voltage into the dead one, which is not very healthy for the workers.
I’m wondering whether the 25kV picked up by one pantograph would ever be passed down the length of the train to a second one even if both were raised. Isn’t it more likely that the two would be isolated from one another and lower voltages used when necessary to connect front and rear power units? In which case problems such as bridging across neutral sections etc would not occur.
Yeah, all those cases are true. Neutral & dead sections bring their own operational complexity. I took the liberty to assume that the OP were expecting some show of fireworks & explosions so I simplified my response earlier to make it more accessible.
i always wondered if those older locos caused a voltage drop between the 2 pantos, like bulbs connected in series, I'm not an electrician i kinda understand the basics like fixing and tracing faults in wiring and the like.
