Re: Power supply mysteries
  Matthew Geier

On 11/8/22 01:17, TP wrote:
> Not being an electrical person, I have to find my way in the dark, so

> to speak (pardon the pun), but I'm curious about the power supply

> issue that's said to place limits on Melbourne's tram operation.


It's not traction load - the modern 3 phase drives are very efficient.
It's the air conditioning. At every stop, 5 large double doors open and
dump all the air conditioned air out into the street. The AC units then
go into overdrive to cool the saloon back down, and barely get the car
down to temp when the tram stops again and dumps all the conditioned air
in the street again.

If the trams are not fitted with 'industrial strength' High Volume Air
Conditioning, the passengers complain the cars are 'sweat boxes' in the

It's the same on the railways - a significant amount of electrical power
goes into air conditioning the station platforms :-)

At this time Prague only has a minority of it's fleet with air
conditioning, although I imagine most have heaters. And it's possible
Prague tram users understand what door open buttons are for unlike

The first time I rode an E class the driver was desperately trying to
'educate' passengers to press the door open buttons instead of standing
next a closed door looking confused. Many announcements were made 'press
the button to exit'. I suspect most drivers will have given up and just
use 'open on release' mode.