Thanks Liam,

1500A on a 600V overhead, is not good in terms of voltage drop. Ive not
been to Melbourne for a while, is it still a single contact wire, or are
there dual contact wires and additional feeder wires like railway approach
to reduce voltage drop?

Peter

On Sunday, 14 August 2022 at 16:50:07 UTC+10 Mal Rowe wrote:

> Liam Davies has the following comment on tramway substations in Melbourne:

>

> ====

>

> I've just been lurking on TDU and noticed a discussion about

> substations. I think there is some confusion about overall electricity

> consumption over the course of the year and draw on the substations at

> any one point in time.

>

> When Yarra say a W draws 500 amps and an E draws 1500 amps, these are

> maximum figures, not continuous. Five hundred amps is around 300kW, but

> only as a spike, there is no way that a W consumes 300kWh per hour. I am

> not sure the actual number, but PTUA say a D consumes approx.1.5kWh per

> km ( https://www.ptua.org.au/myths/tram-emissions/ note that this is

> lower than a W because of regenerative braking), assuming average speed

> of 14km/h, that is about 21kWh per hour. (for reference, 82,000MW per

> year, with 25 million VKT works out to about 3.2kWh per km)

>

> This is exactly the same as a car. To accelerate takes large amounts of

> fuel, but once at speed fuel consumption decreases considerably.

> Additionally, In the case of trams, braking reverses the consumption, by

> recovering energy expended on acceleration and feeding it back into the

> grid. This means that for trams, the draw can be higher than overall

> consumption.

>

> The Es draw significantly more, around three times as much, which means

> that draw can spike closer to 1MW. So this means that three Es could

> draw close to 3MW if they all take off at once. If this is tripping the

> substation, it would indicate that the substation has an output capacity

> below 3MW. As an example, the new (refurbished?) substation on Brunswick

> Road is 1.97MW ( https://beon-es.com.au/beon2/case-studies/yarra-trams/

> ); around 3,300 amps (assuming 600 volts).

>

> Taking Tony's figures of 200MW and 41 substations, means the average

> (and, yes, I know this is crude) is around 4.8MW per station, or around

> 8,100 amps. It seems that Prague has fewer substations, which are more

> powerful, than Melbourne. Prague also has a legacy of operating coupled

> vehicles, which means their power supply system likely needed to have

> more capacity than Melbourne's.

>

> As far as I can tell this is why the F/G class trams will have

> batteries. Either the supply system can be upgraded to accomodate large

> amounts of draw, or the vehicles can be fitted with batteries to reduce

> their draw (but they will still consume the same amount of power, just

> over a larger period of time, thereby reducing strain on the system).

> Melbourne seems to have opted for vehicles with lower draw while also

> upgrading the supply network.

>

> Cheers,

> Liam.

>