On 15/8/22 15:30, Mark Skinner wrote:
> You'd wonder why such colossal current spikes are required on start up...and whether there's something simple to ameliorate it.

>

> Mark Skinner

>

> On Mon, 15 Aug 2022, 11:54 am TP, historyworks@...> wrote:

>

> The problem, as with many comparisons, is the lack of matching

> information about the things you're comparing. You can get certain

> stats about one and an overlapping set of other stats about the

> other, but not a common set for both. I would like to know what

> would be the current draw on acceleration of a Skoda 15T or a set

> of Tatra T3s. The only clue I ever got is when I asked once

> whether the fast acceleration of Prague trams resulted in higher

> operating costs and was told that the difference was so tiny they

> stopped measuring it years ago, so that suggests it's not a big

> issue for them and they often have multiple trams accelerating

> together with their stops holding two trams. Yet it's an issue in

> Melbourne?

>

May be differences in billing for electricity too - in Australia if you are large consumer (like railways, tramways, or even a factory with lots of large machines), you will get put on a 'demand' tariff that charges biased to maximum demand, not actual usage. The reasoning for this is the supplier has to supply infrastructure capable of supporting that maximum demand not the average, even if you only use that maximum 1% of the time. This means it's in the consumers interest to 'load level' their demand some how.

With a modern rail vehicle you can either program the motor controllers with a lower 'jerk rate' , thus starting current or you put some some of on board storage (batteries, capacitors) and use them to level out the starting demand peaks and keep your acceleration performance but not spike the supply network and attract that 'maximum demand' charge.

It's possible in Prague due the power generator historically being city owned along with the tramway that they don't get a penalty for high maximum demands, and the possibly the infrastructure was built (and paid off by the city) long ago to cope with that maximum demand from the city tram network. So naturally they don't care. And they probably don't want to draw attention to any spikes they generate in case the power supplier/generator gets in in their heads to switch the tramway to a demand tariff...