Amps carried through air

[w0z]

The majority of the European railway network operates on 25kV. There are some notable exceptions but going into that will only muddy the water.

I have summarised to the main principles greatly so please do not pick faults as it is a complicated subject and I KNOW that some things are omitted but I have done this to make it easily readable.

Under the EU technical standards for interoperability (TSI) trains draw about 200 amps when accelerating, and the protection settings are set at 600 amps full maintained feeding within each principal section of the route.

The OHL operates at between 23.5kV and 29.5kV in normal service and the trains are designed to operate normally within that envelope.

The system is designed to withstand fault currents of up 12kA, and BR short circuit testing work some years ago identified voltage running up to 60kV before the breakers tripped.

Currently the system is based upon a nominal maximum of 60v running from the train into the track. This is the maximum voltage permitted in these circumstances on an electrified railway.

The protection settings are set for the breakers to trip at a maximum of 12kA , with a disconnect time of 3m/s (0.03 second). Traction return and equipotential earth bonding ensures that in most circumstances the railway infrastructure becomes a large Faraday cage, however the SCADA system is design for the protection of the trains and Equipment. Whilst in normal operational condition s a member of the public would not become exposed to the risk of electrical shock, that is only the case for someone acting in an appropriately responsible way. The system is NOT designed for intentional touching (or urination onto the Equipment - which does happen) and in such cases (IF you are lucky) you will die, if you are unlucky you will suffer very severe burns to the body surface, your clothes will be on fire, and the only treatment is to be anaesthetized and placed into a bath of oil whilst you die slowly and painfully or possibly recover to horrendous injuries.

It is interesting to note that I calculated a short circuit in a domestic premises could easily generate over 900 amps and I believe the rated Ampage protecting the DNO equipment is is something like 16kA.

Hope this helps ?

I have an unrelated question, save for the fact that it's about train electrics.
Some trains have 13A sockets for use of passengers. How is the voltage and waveform derived/regulated for these? I ask because someone I know recently had a laptop supply and it got VERY hot on one of these compared to how it usually runs at home. If I had a portable scope I'd be tempted to take it with me next time I'm on a train...

 

[FatAlan]

My ex BIL worked/works at a energy production plant in Gdansk and years ago a maintenance guy entered a generator for maintenance, to be honest I can't remember the full story but the power surge cooked his body from the inside and he died in pain a few days later.

No disrespect to the poor chap that died but is Pain a suburb of Gdańsk?

 

[Squid]

No disrespect to the poor chap that died but is Pain a suburb of Gdańsk?

My ex BIL saw the guy, can you imagine a large microwave cooking a man from the inside, it wasn't nice and you wouldn't be joking about it if you where there.

 

[johnduffell]

If I had a portable scope I'd be tempted to take it with me next time I'm on a train.

That would be a good way to pass the time, could bring a full testing setup and give it once over!

 

[bomjac]

Mostly from HV shock, the injured party will survive and die soon after due to internal injuries caused by the heating effect. The 500 ohms resistance is the accepted nominal for a person. 500 for each limb, and the same for the body trunk. So 1.5k ohms, and roughly 20 amps and 40 or 50 times as much is needed to kill you.

20 amps, 1.5k gives you about 600 kW of heat through your internal organs. Even for only 0.1 seconds that is going to cause some pretty severe damage internal. You can actually see the veins and arteries burned through someone's flesh who's had a HV shock.

Arc Flash is a very big focus atm in the NEC these days, and having been literally 12" away from a 480v UPS that arced across the incomers, it is pretty scary.

There was a guy in my present company received a 13.8kV shock (beore I joined), made it to the control room and called his wife to tell her he would not be home. He died a few hours later to internal injuries.