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Potential catenary danger?

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Posted by Erik_Mag on Saturday, July 24, 2021 12:08 PM

Harding's 1915 ICS textbook Electric Railway Engineering has a section on "thermit" welding, indicating that it was well established at the tie the book was written.

Getting back to the original theme of this thread, the most likely scenario for shock or electrocution is a streetcar/LRV derailing on a hard surfaced street.

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Posted by Overmod on Saturday, July 24, 2021 12:37 PM

Erik_Mag
Harding's 1915 ICS textbook Electric Railway Engineering has a section on "thermit" welding, indicating that it was well established at the time the book was written.

But you may also find a section on autogenous fusion welding, something that was a black art then and for some time thereafter -- really, until the practical introduction of shielding-gas techniques.

Goldschmidt recognized the iron-oxide/aluminum reaction in 1895 and patented it in 1898 in Germany -- I think he was researching making pure iron without carbon from fuel contamination or graphite electrodes.  As I recall the uses for welding were quickly and well appreciated...

Getting back to the original theme of this thread, the most likely scenario for shock or electrocution is a streetcar/LRV derailing on a hard surfaced street.

Perhaps more specifically, a newly-wet hard-surfaced street where there hasn't been time for conductive surface contaminants to be washed off.

I was a strong proponent of the original 'intermittent dynamically-activated contact' scheme the first time I read about its details (I think in Brush, 1911).  There the entire 'hot' contact architecture is switched to be on only when the path through the controller and motors is 'correct', and is turned off in a variety of other failure concerns, one of which (I believe this was discussed) being the situation where a particular contact sticks 'live' and poses a contact-path issue... note that the very most likely return path would be to one of the adjacent rails and not something either 'buried' or outside the nominal gauge.  I note that most of the current 'center third rail' systems use a similar power approach, now in a continuous insulating support structure and with nominally much better control and switching integrity.

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Posted by daveklepper on Sunday, July 25, 2021 3:32 AM

Usually, a derailment means the pole leaves the wire.

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Posted by Overmod on Sunday, July 25, 2021 8:01 AM

daveklepper
Usually, a derailment means the pole leaves the wire.

Yes, but... the OP's original question specifically 'posited' that the current collector remain on the wire.

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Posted by Paul P on Sunday, July 25, 2021 5:42 PM

The pantograph is connected to the transformer primary via a breaker and insulated cable.
When the throttle is closed there is no connection between the pantograph and traction motors.

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Posted by Overmod on Monday, July 26, 2021 11:53 AM

Paul P
The pantograph is connected to the transformer primary via a breaker and insulated cable.

And is isolated from the carbody structure on insulators.  The concern is not the connection from the pan to the primary; it's the connection from the primary to return (which in one-wire catenary implies ground return through the (bonded) rails).

When the throttle is closed there is no connection between the pantograph and traction motors.

The 'throttle' on many electrics is a secondary tap-changing switch.  Whether or not one leg of the motor circuit goes to common for all the taps is interesting from certain accident standpoints in the original question, but interrupting the taps at the switch would de-energize any secondaries and hence any current through the motors.  But  unless the throttle were interlocked with the primary, which it surely could be, closing the throttle would not isolate the pantograph from the wheels, which is the stated accident concern.

On an Ignitron locomotive, control is off the DC side of the rectifiers, and I believe again that no voltage could be present at the motors or their cabling with the throttle closed.  But here too it's the primary return we're concerned with.

An issue here is that any short-circuit breaker in an individual locomotive has to be set to a current above (perhaps well above) the power director's breaker for that whole section.  That might result in considerable potential or arcing in the OP's original scenario.

Welcome to the forums, Paul.  Your first few posts are held up in moderation, and I saw they took 17 hours to get around to approving it... when you've made a few more, they'll take you out of mod status like nearly everyone else and you'll have no irritating lag in commenting.

 

 

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Posted by daveklepper on Tuesday, July 27, 2021 7:34 AM

A reminder:  As part of operator training, throwing the line-switch off is an immediae reaction to any derailment.  All cars except PCCs, where it is controlled by a toggle on the dashboard, that I ever operated, in service on the The Bronx Bailey Avenue line or at trolley museums, have the line switch in a black box overhead with a wood handle.  It is also the main circuit-breaker.  In double-end cars, there are, at least in the cars I ran, two in series, one on each end.

Of course, there are songle-end cars with simpler "hostler's controls" behind a panel on the rear end.  The ex-C&LE lightweight interurban cars on LVT were an example, and I don't recall a rear-end line-switch on them.   Was there?

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