A little technical tidbit came up at the aforementioned Link tour which hadn't occurred to me.
We were looking over the trains, which by the way are quite handsome, and I was wondering about regenerative braking, such as is done with hybrid cars and buses and such. Specifically I asked the question, based in the context of hybrids, of "where are the batteries?"
The answer, obvious in retrospect, is that there are no batteries, no need for them. When you're tethered to the network of electrical lines, the power recovered on braking is simply fed out into the network.
This strikes me as a beautiful detail of these systems. That this power flows in and out of the movement of Link, the trolley buses, and back out into the system, to feed your alarm clock, your lights, your water heater. Meanwhile, it dispenses with the need for the complex chemicals associated with creating and disposing of batteries, and may raise the efficiency of the storage and retrieval, moving from the chemical process to the electrical.
Anyway, to dampen the moment of zen, and while we're on the subject, I have to wonder: why can't we design overhead lines for the trolley buses which reliably stay put? Any ideas? Do buses elsewhere get their ties knocked off occasionally, as here?
Friday, June 20, 2008
Overhead Lines: A step beyond hybrid
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16 comments:
Not only that, electric motors last much longer than internal combustion.
Are you talking about the poles getting knocked off? It happens all the time here in SF.
Do Link trains and trolley buses actually have regenerative brakes, or are you just thinking aloud?
I think the poles get knocked off so often because they have to be designed to switch overhead wires when turning, and such. But I'm not really sure...
I drove trolley buses for Metro on and off for nearly 9 years. And the majority of the time I dropped the poles off the wire, it was my own fault. I went through a switch too fast, forgot to activate a switch, or turned from one street to another too fast. Trolley buses need to slow down anywhere the wires cross. Otherwise, the shoes (the part of the pole that glides along the wire) can get jammed. But for the most part, if you follow the rules that are taught in training, you can drive a trolley bus at the same speed as the rest of the traffic around the bus. I do have to admit I do miss driving an eco-friendlier vehicle from time to time.
rizzuhjj, Link trains do indeed have regenerative brakes. I don't know if our new trolleys have them, but I know Link does. In fact, if you go check out the Seatrans flickr pool, there are pictures of the generators on the axles!
The hybrids and trolleys Metro has have regenerative brakes. If you sit in the back of a hybrid, you can hear it working when the bus is slowing down coming off the freeway. It sometimes sounds like a jake brake from a semi truck.
the old AMG trolleybuses in boston that ran on the 70-routes over near cambridge didn't dewire all that much - then again, the trolleybus overhead in that area was pretty simple and the running speeds were incredibly low due to traffic.
the new kiepe poles on the trolleybuses in seattle seem to be a lot better at sticking to the wires than the old brass poles on the MAN, Breda and AMG coaches. this is just a rider's take on it but it seems like the kiepe poles are a bit stickier though sometimes at some intersections, there's not much you can do.
i've also been on the #10 a couple times recently where the bus has dewired, apparently as a result of one of the charming folks hanging around the convention center stop - when the bus is about to go, someone has gone and yanked the rope attached to the poles, dewiring the bus and then run off....
Just call it a plug-in hybrid. Then it sounds cool, and it's not technically lying, because it really is always plugged in. Btw, those things on the axles of the train are not just generators, they are also motors. Another benefit of electric propulsion: the motors and equipment are much more compact.
As for trolleybuses and de-wiring, some of the time it's the fault of the driver, such as forgetting a switch or not driving under the wire properly or going too fast through a crossing, and sometimes it's the condition of the overhead or even something else. Just about all de-wirings happen at crossings or switches, they're the weak point of the whole system.
So how does a trolley bus driver set the switch, anyway?
I have seen dewirings at non-switch locations, including on Campus Parkway on the approach to the University Bridge.
One time I think it was because of leaves and branches hanging over the wires. Several other times it happened on the underpass under Roosevelt Way.
cdc, the operator uses the turn signals, I believe. These turn on a signal in the trolley arms (can't call it a pantograph, I guess) that is detected before the switch. There are these loops you can see on the overhead wires preceding each switch that detect the signal the bus sends.
There are also directional switches. When a trolley coach is turning, the ploes make contact with two contact points on the wire at the same time to activate the switch. If the trolley coach is going straight, only one pole hits the contact at a time, and the switch doesn't activate. They're common in the Atlantic Base yard, but you can see a few in the intersections of 15th & John/15th & Thomas for Rt 43.
jayson, I had no idea. That's pretty cool. :)
Using regenerative braking and feeding the electricity back into the grid has been a standard feature of electric railroads for about 100 years now. It has the advantage over battery type hybrid systems in that you don’t need to carry around the dead weight of a battery bank. It’s a great system and works very well.
I was under the impression that if the bus is drawing power through the switch then it will "switch" or not ... depending on the primary route
I don't think it has anything to do with the blinkers. but I may be wrong.
There are three kinds of trolley switch. The radio-controlled "Fahslabend" switch is controlled by turn signals and is mostly how Metro trolleys are controlled in service. There are a few switches that are controlled based on the angle that the two poles contact the wires before the switch - this is how the old Seattle trolleys were mostly controlled I think. Seattle doesn't use the third approach that Gordon mentioned, which controls the switch depending on whether power is applied or not approaching the switch.
Drivers can be at fault for going off-wire, but the design and maintenance of the overhead system can also play a part. Sometimes a wire takes a sharp turn that could be less sharp if more support wires are installed (many support wires making a smooth curve is called speed wire because drivers can make the curve at full speed). Sometimes switches are provided to allow buses to make emergency reroutes, but less switches would allow buses not to slow down and de-wire less frequently. Trolleys need to slow down to 10 mph as they pass through switches and other special work. And if they roll backwards on a hill into a switch, bad things can happen.
I remember about few years ago when I lived in Rainier Valley area. I saw a old M.A.N. articulated trolley bus that stalled near an intersection of Rainier Ave S and Graham St., Guess what I saw? One of the pole was ripped right OFF the bus and was dangling on the wire overhead. I don't know how it happened but I saw that it happened already, but didn't see the action of course.
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