Touring electric coach stranded at Eden Project after failing to find charging point in Cornwall

[Steve Walker]

London's underground trains are manoeuvred in maintenance depots by plugging long leads into sockets on the train.

[williamwright]

Like I said a few days ago!

Bill

[Dave Plowman (News]

Trams have the return through the rails.

Have you not noticed the difference between a tram pickup and trolley bus one?

[Dave Plowman (News]

If cost doesn't matter, true. But on most routes the bus does more hours than the driver.

[Paul]

I found an example today, of a bus that uses on-route charging at 500KW. The claim is, it doesn't need to "depot-charge". I think the idea of that one, is a "topping up" charge at the terminus, on each trip.

As well as a couple schemes for pantograph charging. A device rises from the bus, to make contact with a charger overhead. I guess that's so the driver doesn't get his hands dirty.

It's possible the "lesser buses" also being tested, are in the running because of the price. They use more conventional materials, suited to automotive construction.

The one that charges at 500KW, doesn't use laptop batteries. It's a different chemistry altogether.

If you see lithium iron phosphate buses winning on bids, it implies they'll be using overprovisioning, and the bus is considered "a battery pack on wheels, that happens to pick up a few passengers".

I also saw a reference in a product lineup, to a "self driving bus". If the drivers were getting comfortable driving the lekky bus, it won't be for long. "The robots will take over." Presumably The bus company is buying an off-the-shelf self driving kit, as the bus company would not be doing the development itself.

Paul

[Chris J Dixon]

Indeed they do, because it is unsafe to have power rails inside the depot. Having spent my working life designing rolling stock, I know about this, and have seen it done.

The supply is generally fed from a trolley running on power rails up above, so that it can move to follow the train out, without having unwieldy lengths of cable.

Once the shore supply is plugged into the train, all shoegear is live, which is why you really pay attention when the cry goes out "Juice coming on number <n> road!"

Chris

[Tim Streater]

Electric shoes, eh? Gosh, what will they think of next?

[newshound]

A very nice illustration of the size of a 2.1MWh battery. Driving back from Cornwall this morning, very few of the windmills were turning.

Google has a few pics of battery rooms at old telephone exchanges and at power stations, but I can't immediately spot any capacity figures. Until quite recently these were almost invariably lead-acid.

[charles]

They don't need to light enough to carry around and size doesn't matter, too much

[Paul]

You can't run a CO off battery any more.

Battery worked, back in the electromechanical switch and subscriber circuit powering days. The battery loading then, made it possible for the facility to survive for 24 or 48 hours.

Modern COs, can be using 3kW per 7 foot or 9 foot rack. The fans for cooling on the units are so loud, you have to wear hearing protection when standing near the equipment.

The CO also has aircon.

On a failure, the battery room only has to "hold up" the load, until the in-building diesel starts up.

During maintenance, a trailer mounted diesel parked outside the building, keeps the facility powered. For the main CO downtown (multiple floors of a skyscraper), they had a 40 foot trailer there one day. A "standard locomotive engine" was inside, or 2000HP*746W or 1.5MW. And that locomotive, based on exhaust volume, was flat out. And it was filling the "valley" in the street with diesel fumes. I started walking in the opposite direction to get away from it all. Disgusting. Maintenance should really be done on windy days.

When mains power goes off, the aircon is switched off in the room. They throw open the double doors on either end of the facility for cooling. Smart operators place box fans in the doorway, to move some air through it. The equipment has a max ambient of 50C. And the temperature limit is "real", because the lasers running the fiber optics in there, start to extinguish at 70C junction or so.

The CO design then, is thermally limited. How much shit can you stuff in the hall, before, on a power failure, it overheats and tips over. I could see an incentive for buying "bigger box fans". You'd better hope it's not a hot day outside (in much of the USA right now, I doubt they could handle a power failure to a CO, because of the ambient). In the news just a few days ago, some of the Starlink home phased-array antennas were shutting down on "high temp" :-)

And lots of digital comms equipment, has no power-saving features. They tend to run constant power. The embedded processing in the box can save power, when it's not doing call control. But lots of other garbage in the boxes is datapath.

Paul

[Andy Burns]

[newshound]

Sure, I realise that (even though I can't figure out what CO stands for). Interesting to read the detail, though.

However the requirement at a power station is still like it used to be in the old days. In a fossil fuel station there is enough battery capacity to do a "black start" from a cold station with no grid connection. As well as getting fuel and water to the boilers this means running the forced draft and induced draft fans at either side of the fire. Even in a nuclear station (which is not allowed to do a black start, at least in the UK) there is quite a complicated hierarchy of power supplies starting with DC from the batteries. These days the main "back-up" comes from gas turbines (diesels at older stations) but ultimately DC can start these up as well as supplying the most important instrumentation, emergency lighting, etc.

[Steve Walker]

You don't necessarily need any batteries for a black start.

Back in the '90s, I was involved in the supply of 2 off 24MW gas-turbine generator sets for an oil rig. They supplied the power for the whole rig.

In the case of a black start, there was a 1.2MW diesel generator, that provided power for the instrumentation, lubrication pumps, fuel pumps and ventilation fans and also provided hydraulic power for the starters on the RB-211s that were the gas generators for the turbines.

The black start diesel itself was started from retained pressure in nitrogen filled hydraulic accumulators. There were three of those, giving three attempts at starting. If the third attempt failed, someone would have to use the hand pump to pump hydraulic fluid into one or more of the accumulators to try again.

The only batteries on the system were for if both of the gas turbine sets shut down and the rig was in a black out state - enough batteries to run both 22kw emergency lubrication pumps for 8 hours! Without those pumps, residual heat would have melted the front bearings of the power turbines.

[Andy Burns]

North American CO = central office = UK telephone exchange

[newshound]

Interesting (but I was talking about a land-based power station).

The megawatt sized diesels at Magnox nuclear power stations had an interesting setup with several electrical devices on a common shaft (driven from the diesel by a centrifugal clutch, IIRC). These included a DC generator for charging the batteries, a DC motor driven by the batteries that could drive an AC generator to bring up other services, then an AC motor that would keep the batteries topped up either from the grid (if connected) or station output (if not). And the generators could also be driven by the diesel. Some stations had a separate steam turbine that would drive a variable frequency generator so that the speed of the reactor cooling fans could be varied. Power station designers were very keen on belt and braces!

[Steve Walker]

I know, but I was just pointing out that land based or not, it is perfectly possible to have a black start set up without any batteries. Even if it means starting a "small" unit to then start a larger one to enable starting the largest one.

[newshound]

Yes but my point was that, at least up to the end of the CEGB, all UK thermal power stations had one and often two rooms full of lead acid batteries. That may not be the case for CCGTs that came later.

[Chris J Dixon]

Indeed they did. Because of this much of the control equipment operated from the battery-backed dc supply.

My working life was spent involved with the design and production of railway rolling stock, and they were one of the only other fields routinely to use dc equipment, so a potential source of components was those variants made for use by the CEGB.

Chris