Pantograph Mechanism

Does the pantograph mechanism have its own compressor or is it a feed off the main compressor?

Is it just a servo that controls the pantograph? If it's just a servo could a ERTMS balises be developed that could interface with the controls for the servo to make possible the ability to remotely have the pantograph lower or raise?

Train pantographs are raised and lowered by the buttons in the cab, which I assume would work one or more valves to control the air supply that keeps it raised. So there is obviously some sort of electrical control and other systems could control it via relays if necessary. Incidentally trams don't usually have air supplies and I believe their pantographs have an over-centre spring that will keep it either raised or lowered, and an electric actuator to lift or lower it.

I can sort of see a reason for a balise to lower the pantograph at an OLE to third rail transition if the driver forgets to do so. However one to raise the pantograph going the other way could be a hazard, as the driver may wish to keep the pan down for some safety reason. The worst that can happen if it isn't raised when it should be is the train being stranded, probably able to raise it and carry on. However if it is not lowered when it should be then someone might be injured when it hits the first bridge.

The Thameslink Train Infrastructure Interface Spec already requires ETCS control of the changeover sequence, including the pantograph.

The Unit Specific Transmission Module (STM) shall send a command to the automatic AC/DC power
changeover system to initiate a power changeover on receipt of a Packet 44 power changeover
message from track mounted Eurobalise.
TIIS_1784

The Unit automatic changeover system shall initiate and control the power changeover sequence (i.e.
open the main circuit breaker(s)/contactor(s), deselect the pantograph/shoegear, reconfigure the
traction equipment for DC or AC as appropriate, select shoegear or deploy the pantograph as
appropriate, confirm the traction equipment is configured correctly for the appropriate system and that
line volts are present, and close the main contactor(s)/circuit breaker(s) as appropriate)).
TIIS_1484

Click to expand...

They've already thought of this, so the thread can probably stop now...

Most pantographs are air operated. There is an auxiliary compressor which runs off the batteries. When the train is dead the aux compressor runs to pressurise the pan system. Once it's up to pressure it shuts off ( I think about 3 bar). Then the driver can then raise the pan by the pan up button in the cab.

Sent from my SM-T535 using Tapatalk

Pantographs are operated from the main air reservoir and system, charged by the main compressor(s). The auxiliary compressor is a small battery powered unit designed to raise the pan when the rest of the train/loco is dead.

The raise command can be given by any input (usually driver in cab) but can also be from a track-side balise in ETCS conditions (think bi-mode operation...). The input signal, depending on the train will energise an electrovalve at 110v (or whatever the battery voltage on the train happens to be) which permits air into the "raise" cylinder or raise-side of the cylinder and the pan does the rest.

swt_passenger said:

The Thameslink Train Infrastructure Interface Spec already requires ETCS control of the changeover sequence, including the pantograph.



They've already thought of this, so the thread can probably stop now...

Click to expand...

Will that also cover situations like Retford with one at either end of a section where the train has to lower the pan and coast?

swt_passenger said:

The Thameslink Train Infrastructure Interface Spec already requires ETCS control of the changeover sequence, including the pantograph.



They've already thought of this, so the thread can probably stop now...

Click to expand...

And it's in use!

SpacePhoenix said:

Will that also cover situations like Retford with one at either end of a section where the train has to lower the pan and coast?

Click to expand...

Doubt it as that's an emergency situation, and the incoming IEPs/AT300s will have bi-mode capability or (Class 801) a single power pack for self-recovery.

The pan head has compressed air within the carbon strip. the pan relies on compressed air from the main air system to apply contact pressure to the OHLE. Its not highly pressurised as the pan needs to be able to rise and fall to keep contact with the contact wire. Should the pan head become damaged the air pressure is lost and therefore the pan retracts automatically. Theres an image on the Retford problems thread that shows a damaged carbon strip and the air line can be seen.

gimmea50anyday said:

The pan head has compressed air within the carbon strip.

Click to expand...

I was under the impression that the Carbon strip is just an insert that is put into the Pantograph's head as it is easier to replace than the entire pantograph.

Thats my understanding of it anyway. I could be completely wrong.

The carbon strip is a relatively easy job to replace. You wont need to change the entire pan unless you have left bits of it at Retford!

Domh245 said:

I was under the impression that the Carbon strip is just an insert that is put into the Pantograph's head as it is easier to replace than the entire pantograph.

Click to expand...

It is made of carbon (graphite) which rubs off onto the wire and reduces friction, so it will wear down over time and need replacing. Hence it is designed to be easy to replace, but it is also hollow so that excessive wear or damage will vent the compressed air from inside and drop the pan as described.