Gunnar Thöle wrote:
Dave Arquati schrieb:

I found riding buses in London to be quite difficult because
information is not very complete. But the underground network is cool.

That's interesting. What don't you consider complete about the
information? In my (probably more limited) experience, London has the

Mainly its the onboard information i found missing. Travelling to
Crystal Palace on a bus i was constantly looking outside for some
building that might be a palace... Whereas i would have preferred to
drowse and just glimpse at some kind of in-bus display once in a while...
Also i would have liked a map with all bus lines on them (yes, this
would have to be very very huge). My Hamburg town map shows bus lines,
for example. Does an A-Z show bus lines?

A-Z's don't show bus lines (although some very old ones used to have a
map of important bus routes in the back).

I can understand the problem with on-board information. As Neil
suggested, LEDs with the next stop would be very useful. Ideally I'd
also like to see important real-time information displayed on these too
(like Tube, DLR & rail disruptions, and bus diversions). I'd imagine
this could be delivered relatively easily using GPRS.

A number of buses have screens fitted to them now (one on each deck)
which show CCTV images from around the bus - presumably to deter
vandals. However, this isn't necessarily very useful at busy times, and
they could be used to display the sort of information I am talking about.

most comprehensive bus information of anywhere I have ever been. For
example: the spider maps (although I know John dislikes them :-) ).

Yeah, its quite comprehensive, Hamburg surely isn't better than London
in this regard. But IMHO its not perfect. Problem: I don't know how
offboard information (at the stop) could be made much better.

What i found very good was the Countdown system. Hamburg is just now
starting to install something similar.

I would have said Countdown was the worst of the stop information!
Although I appreciate the idea (particularly when making a choice
between bus & tube at Piccadilly Circus for example) I don't think it
works well; many buses are not listed and the information tends to be
inaccurate. It may be better in some parts of London than others; at
Piccadilly Circus and South Kensington it certainly doesn't seem to be!

online information (www.journeyplanner.org). The WAP version of TfL's
site also extremely comprehensive and valuable information.

Yes, WAP is cool. I got a flat tariff for WAP now (5 Euro per month for
unlimited WAP) and this changed my journey habits very much. I use
http://mobile.bahn.de/ as my journey planner for everywhere now, it
knows all Hamburg transport systems, most of germany, and it will even
tell me London rail timetables. This is so useful.
And for getting to stations http://pda.mappy.com/ shows me the way
everywhere...

As well as the TfL site, I also regularly use the National Rail one
(live arrivals and departures info is very handy, as well as the journey
planner) and the BBC's road traffic information (not as good but
sometimes useful).

I'd say the next step for the TfL sites (normal web & WAP) is to
introduce Tube next-departure info like they have for the DLR (they're
trialling at the moment I think). Whilst they're at it, they could nick
National Rail's info too. After that, an option for "next departures
from nearest stop" would be great, where it gives that information based
on your location.

I'm sure on 3G networks something more sophisticated would be possible -
e.g. bringing up a map of your surrounding area, highlighting nearby
stops or stations with their live next-departure information.


--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London

(Richard) wrote in message . ..
On Fri, 03 Sep 2004 23:01:16 +0200, Gunnar Thöle
wrote:
[1] That said, bus stops in Germany are typically *much* further apart
than they typically are in the UK - certainly in Hamburg.
Yes, thats true, 500m and more. Also each and every bus stop has an own
name and there is a full timetable for every bus and train in Hamburg.
Just ask the journey planner at http://www.geofox.de/ which works very well.

Almost as good as London's www.journeyplanner.org :-)

Richard.

For real amusement value try http://www.transportdirect.info/TransportDirect/en

In article ,
(Neil Williams) wrote:

If the electric motors are of the three-phase type often employed on
recent[1] rail stock, the "gear change" is actually a change in the AC
frequency being applied to the motors as they speed up. It (put
simply) has broadly the same effect as a gear change, but no physical
"gear" is being "changed" as such.

[1] While all EMUs built since the 1990s have this technology, it's
not always audible for various reasons. The Class 323 EMUs used in
the Manchester area seem the most obvious.

ITYF that the noise is more pronounced on older three phase designs.
Current production uses a later three-phase technology which has a less
pronounced "gear change" effect.

--
Colin Rosenstiel

(Colin Rosenstiel) wrote in message ...
In article ,
(Neil Williams) wrote:

If the electric motors are of the three-phase type often employed on
recent[1] rail stock, the "gear change" is actually a change in the AC
frequency being applied to the motors as they speed up. It (put
simply) has broadly the same effect as a gear change, but no physical
"gear" is being "changed" as such.

[1] While all EMUs built since the 1990s have this technology, it's
not always audible for various reasons. The Class 323 EMUs used in
the Manchester area seem the most obvious.

ITYF that the noise is more pronounced on older three phase designs.
Current production uses a later three-phase technology which has a less
pronounced "gear change" effect.

The older AC drives used GTO thyristors which operated at a frequency the
human ear can hear and because they had a max operating frequency some
sort of electronic equivalent of gear changing had to occur to let them
drived the motors at the full range of speeds required (don't know the details
I'm not an electronic engineer). The newer drives use IGB transisters which
operate at a much higher frequency though if the new stock on the northern
line is anything to go by you can still hear a very high pitched whine.

B2003

"Boltar" wrote in message
om...

ITYF that the noise is more pronounced on older three phase designs.
Current production uses a later three-phase technology which has a less
pronounced "gear change" effect.

The older AC drives used GTO thyristors which operated at a frequency the
human ear can hear and because they had a max operating frequency some
sort of electronic equivalent of gear changing had to occur to let them
drived the motors at the full range of speeds required (don't know the
details
I'm not an electronic engineer). The newer drives use IGB transisters
which
operate at a much higher frequency though if the new stock on the northern
line is anything to go by you can still hear a very high pitched whine.

Yep, that's just about right.

The gear changing is required because it's easier and more desirable [1] to
keep a fixed ratio of device (i.e. GTO) switching frequency to modulation
frequency (the latter is roughly proportional to the motor speed), and you
have a maximum limit on the GTO switching frequency [2].

From start-up you clearly need a high frequency ratio as the motor speed -
hence modulation frequency - is very small. Since GTOs cannot switch at
high speeds (well they can but you need snubbers to slow them down to stop
them blowing up) you cannot maintain a high frequency ratio as the motor
speed increases beyond a certain point, so when the maximum switching speed
has been reached the ratio steps down to the next suitable value. The
modulation frequency remains the same, since the motor speed is the same,
but the switching frequency has been reduced. It is the switching frequency
which you can hear changing through the motor. This process happens many
times as the motor speed increases.

IGBTs can switch more quickly as they don't generally need snubbering, and
hence a higher switching frequency is used. It's just about audible (as
Boltar said, I think it may be the whine you hear on the Northern Line). As
the switching frequency is higher, the ratio of switching to modulation
frequency is greater and can be non-integer. The switching frequency is
therefore fixed, and so you don't hear the gear-changing.

[1] If this ratio is less than approx. 21 and not an odd integer then
subharmonics are a problem. Above approx. 21 it's less of a problem and
non-integer values can be used.

[2] Just to clarify, the devices - whether IGBTs or GTOs - switch to form a
high-frequency square wave. The duty ratio of this square wave is ratio of
the time it spends on to the total period, so if the duty ratio is 1/3, it
spends 1/3 of the period on and 2/3 off. The duty ratio is varied over many
switching cycles to follow a sinewave (in classic examples). However the
motor is inductive, and this has the effect of filtering out the switching
and producing a current proportional to the *average* of the square wave.
This average is proportional to the duty ratio. Hence if the duty ratio
varies as a sinewave, the current will also be approx. sinusoidal. In an
induction motor we need a variable-voltage, variable-frequency sinewave on
each phase. Varying the duty ratio amplitude and frequency (=modulation
frequency) has this effect. The advantage of using pulse-width modulation
(PWM) switching to achieve this is that the switching process is very (90%)
efficient, since the devices only pass high currents at high voltages (hence
burn lots of power) when switching. You could use a linear amplifier (i.e.
a scaled-up audio amplifier) but its efficiency is rarely above 50%, which
is clearly a no-brainer.

Also see http://www.twoof.freeserve.co.uk/TRACTION3.htm for a good summary.

Cheers
Angus

On Sat, 4 Sep 2004 12:39:34 +0100, Annabel Smyth
wrote:
Neil Williams wrote to uk.transport.london on Sat, 4 Sep 2004:
[...]
As a minimum, all buses should have a large-font LED-style display
mounted at roof height at the front (one upstairs and one downstairs
on a decker) displaying the name of the next stop. Ideally, there
would also be an automatic announcer (though obviously with the number
of stops in London this would take longer to implement), and certainly
a public address system so the driver can speak to all passengers
(e.g. to advise that the bus is terminating early). None of this
would be exceptionally expensive to implement, and to someone using an
unfamiliar route would be very useful indeed.

I don't think the number of stops matters really. I've heard voice
synthesis used for bus announcements and it works well. A simple
means as mentioned below is to get the driver to do it. This is
standard in Zurich, though as it's in Swiss German it can be hard to
tell whether someone's announcing a stop or clearing their throat.

They do have PA on many buses. But I agree, I wish we had more on-board
information - couldn't it somehow be linked with Countdown, or with
whatever is due to replace Countdown in the near future?

I'd argue that the above is vastly more deserving of investment than
Countdown displays and their ilk.

I think these are all aspects of the same thing. The most important
thing for service regulation and quality-of-service reporting is
knowing where the buses are. I think that once you know that, the
Countdown displays are a useful way to show the information to the
passengers, but the operators still need to know anyway. Things like
bus lane enforcement cameras and traffic light priority could also be
done by the on-bus part of the system.

In Paris the bus displays occasionally show the journey time to the
next main place, which seems to be calculated in real time. That
might be useful here.

Richard.

"Angus Bryant" wrote in message ...
frequency) has this effect. The advantage of using pulse-width modulation
(PWM) switching to achieve this is that the switching process is very (90%)
efficient, since the devices only pass high currents at high voltages (hence
burn lots of power) when switching. You could use a linear amplifier (i.e.

How does that efficiency compare with the old DC systems where at full power
the motor was pretty much just connected directly to the power rail(s) as
opposed to the new systems where you still have the electronics driving the
motors?

B2003

In article ,
Boltar wrote:
"Angus Bryant" wrote in message ...
frequency) has this effect. The advantage of using pulse-width modulation
(PWM) switching to achieve this is that the switching process is very (90%)
efficient, since the devices only pass high currents at high voltages (hence
burn lots of power) when switching. You could use a linear amplifier (i.e.

How does that efficiency compare with the old DC systems where at full power
the motor was pretty much just connected directly to the powern rail(s) as
opposed to the new systems where you still have the electronicsn driving the
motors?

B2003

I don't have data to hand, but I imagine the efficiency is very high
for both the old DC systems, and the modern induction motor systems.
Unlike mechanical engineers, electrical engineers are quite good at
making their machines efficient. You'll be looking at 95%+.

The real advantages of the modern AC traction systems over the older
DC systems are the following:

1. DC motors have brushes, which cause mechanical noise and which wear
out and have to be replaced; AC induction motors do not.
2. You get more power per kg of motor with AC induction motors than you
do with DC motors.
3. The control of Ac induction motors is done entirely electronically - there
are no mechanical parts (eg, relays, tap-changers) like the old DC systems
have and, again, which wear out quickly.

Furhter to what other people have said, the 'gear change' sound
is found only in the systems manufactured in the mid-90's. Newer systems -
and here I am thinking of Northern Line tube trains and the Heathrow
Express - have no such 'gear change' sound.

The reason for this is that the AC systems made up to the mid-90s use
a power electronic switch called the gate turn-off thyristor (GTO)
which has a maximum switching speed of only a few kHz. Therefore,
as the train speeds up, the frequency of the PWM square wave keeps
on being taken down a notch so as not to exceed this maximum switching
frequency. More modern systems use insulated gate bipolar transistors
(IGBTs) which can switch up to 20kHz and don't have to have their
freuqency notched down as the train speeds up.

Hope that this makes sense!

David.

In article , D.M. Garner
writes
The real advantages of the modern AC traction systems over the older
DC systems are the following:

1. DC motors have brushes, which cause mechanical noise and which wear
out and have to be replaced; AC induction motors do not.
2. You get more power per kg of motor with AC induction motors than you
do with DC motors.
3. The control of Ac induction motors is done entirely electronically - there
are no mechanical parts (eg, relays, tap-changers) like the old DC systems
have and, again, which wear out quickly.

Plus, surely, no resistances in the circuit (and wasting power) at other
than full settings.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

Angus Bryant wrote:

"Boltar" wrote in message
om...

ITYF that the noise is more pronounced on older three phase designs.
Current production uses a later three-phase technology which has a less
pronounced "gear change" effect.

The older AC drives used GTO thyristors which operated at a frequency
the human ear can hear and because they had a max operating frequency
some sort of electronic equivalent of gear changing had to occur to let
them drived the motors at the full range of speeds required (don't know
the details I'm not an electronic engineer). The newer drives use IGB
transisters which operate at a much higher frequency though if the new
stock on the northern line is anything to go by you can still hear a
very high pitched whine.

I've noticed the sound produced by by the 3 phase drives of some GTO
powered trains can be heard on an AM radio. Perhaps someone here might
like to take a Walkman on one of these buses, to see if you get the same
effect.

Yep, that's just about right.

The gear changing is required because it's easier and more desirable [1] to
keep a fixed ratio of device (i.e. GTO) switching frequency to modulation
frequency (the latter is roughly proportional to the motor speed), and you
have a maximum limit on the GTO switching frequency [2].

From start-up you clearly need a high frequency ratio as the motor speed -
hence modulation frequency - is very small. Since GTOs cannot switch at
high speeds (well they can but you need snubbers to slow them down to stop
them blowing up) you cannot maintain a high frequency ratio as the motor
speed increases beyond a certain point, so when the maximum switching speed
has been reached the ratio steps down to the next suitable value. The
modulation frequency remains the same, since the motor speed is the same,
but the switching frequency has been reduced. It is the switching frequency
which you can hear changing through the motor. This process happens many
times as the motor speed increases.

What are snubbers?

IGBTs can switch more quickly as they don't generally need snubbering, and
hence a higher switching frequency is used. It's just about audible (as
Boltar said, I think it may be the whine you hear on the Northern Line). As
the switching frequency is higher, the ratio of switching to modulation
frequency is greater and can be non-integer. The switching frequency is
therefore fixed, and so you don't hear the gear-changing.

[1] If this ratio is less than approx. 21 and not an odd integer then
subharmonics are a problem. Above approx. 21 it's less of a problem and
non-integer values can be used.

[2] Just to clarify, the devices - whether IGBTs or GTOs - switch to form a
high-frequency square wave. The duty ratio of this square wave is ratio of
the time it spends on to the total period, so if the duty ratio is 1/3, it
spends 1/3 of the period on and 2/3 off. The duty ratio is varied over many
switching cycles to follow a sinewave (in classic examples). However the
motor is inductive, and this has the effect of filtering out the switching
and producing a current proportional to the *average* of the square wave.
This average is proportional to the duty ratio. Hence if the duty ratio
varies as a sinewave, the current will also be approx. sinusoidal. In an
induction motor we need a variable-voltage, variable-frequency sinewave on
each phase. Varying the duty ratio amplitude and frequency (=modulation
frequency) has this effect. The advantage of using pulse-width modulation
(PWM) switching to achieve this is that the switching process is very (90%)
efficient, since the devices only pass high currents at high voltages (hence
burn lots of power) when switching. You could use a linear amplifier (i.e.
a scaled-up audio amplifier) but its efficiency is rarely above 50%, which
is clearly a no-brainer.

Why do you need a sinewave - what's wrong with a VVVF squarewave?