Friday, September 6, 2013

Spark Gap Lightning Arrester

As part of our earlier discussion of car lightning arresters, Dan Mulvihill has provided some new information.

This comes from an ARM reprint of a New Orleana Public Service equipment book. 

This is a nice, clear explanation of how a spark gap arrester works.  (Although there seems to be a misprint in Design Principles #1.  Should be   "Arrester must be inoperative on trolley voltage.")

I was struck by the reference to the "left hand three-finger" rule.  In physics we always use a right-hand rule, although there are various versions of it.

And I still don't understand the statements in the Westinghouse AMM manual about leaving the light circuits on during an electrical storm.  In any case, thanks, Dan!


Anonymous said...

I attended the 60th anniversary event last Monday and rode a two car electric train expertly operated by Mr. Hicks. In thinking about the comment regarding capacity loads I was wondering if there is any limit to the number of cars which can be operated in a train either at the museum or formerly in regular service. I almost always see one or two cars operated at the museum but I would assume that is based on required capacities.

Randall Hicks said...

That's an interesting question. In regular service, trains on the CRT/CTA were (and are) limited to eight cars by the length of the platforms. The CA&E would regularly operate eight car trains. The North Shore would sometimes operate six or seven car trains, I think, but I'm not sure on that. Experts will correct me soon. For the South Shore, I just don't know off hand.

At IRM, we're mostly limited by the substation capacity. We've run a five-car North Shore train, but I'm not sure if all cars were motoring.

The depot is laid out based on two-car trains, which are usually adequate for our needs. Anything longer is slightly inconvenient.

Joe S. said...

As Randy said, at IRM the length is usually 2 cars. The platform on station track 1 is set up with 3 berths that each fit 2 cars, so it works well. In past years, we used to run 3 car trains during Thomas, and other busy days to handle crowds. It is rare that we are busy enough to need more than 3 cars. We have run 5 NSL cars all motoring, and I think we have run 4, but maybe 5 6000s all motoring. We don't have any more operable cars at the moment to see what our substation might do, but we have two rectifiers and they both are of fairly large capacity.

In regular service, it depends what kind of limitation you want to look at. Most cars have an electrical limitation because of the control current required to pick up all the contactors on each car. North Shore cars are limited to 10, they have a 25 amp fuse and use about 2 amps or so per car. Then there is substation capacity, although most of the Chicago interurbans had plenty of power available. The last, is platform length and other length restrictions such as at the terminals. The North Shore terminal at Milwaukee could hold a 5 car train with part of it on the street, although they did run longer trains closer to Chicago.

Randall Hicks said...

This Saturday, we're planning to run a four-car CA&E train for Member's Day. Two of them are half-motors, so it's a total of 12 traction motors, or the equivalent of three motor cars. So I think odds are slightly better than even that I'll be able to make it back from the east end.