You should also beware that the common garden tramway resistor has probably a short term rating, about 30 mins, as they are only for starting purposes. You will probably need a series / parallel combination for your running resistor section to achieve an acceptable time rating ( working temperature).
If you trace out the resistors on a scrubber you will find this configuration
Regards Kevin ----- Original Message ----- From: Richard YOUL To:TramsDownUnder@... Sent: Sunday, July 08, 2012 8:58 AM Subject: Re: [TramsDownUnder] Re: Heritage trams on the MLR
[Prepared before Matthew's posting, but covers extra ground]
Electrical voltages, both from the supply network and devices using it, are nominal. The 240v into our homes could be anywhere between 230v and 250 which would be quite normal and depends on who is using how much power in the area. Appliances can handle this range.
For traction motors, 3 factors come into play. One is the figure at which the electricity will jump through the insulation causing a short circuit to the metalwork. The tolerable voltage would probably drop with age. Another factor is the mechanical strength of the glues, varnishing and binding holding the coils of wire in place in the armature. Too much speed can cause mechanical failure, and extra voltage will help this critical speed to be reached. A further cause of trouble is arcing of brushes on the commutator which will increase with extra voltage and speed.
For a tram's traction motors, running in series on a high voltage would negate factors 2 and 3, but the motor(s) at the + end of the supply would have the possible problem of insulation breakdown as the potential difference between the windings and their frames (- or Earth) would be the full 750 or whatever volts.
As there is only one compressor, it would be best in series with its own fixed resistance. Otherwise the factors concerning the traction motors would apply to its motor as well, and the frantic movement up and down of the pistons could be a mechanical problem if run too fast.
As mentioned previously, the lights can be tamed with one or two 240v lamps substituted in the lighting circuit.
Nevertheless it is amazing just how little voltage a 600v traction motor will work with. Years ago when the late Graham Beller first got hold of the D scrubber (now under restoration at Loftus) which had been on 2' gauge at the Goulburn museum, its truck had to be moved across his yard to be run under the tram. I took along my electric welder and a chunky rectifier bridge thinking that applying power to one of the motors would make the truck, sitting on sleepers, easier to push. We were amazed when the truck slowly moved along unaided on around 35V DC.
Similarly I was involved in making the W2 owned by the ill-fated Newcastle tram museum mobile in an out of the shed at Wallsend. This was also done initially on my welder. Even the compressor built up to 70psi but it took quite a while. The Linebreaker would not operate, but was wedged shut with something. The electricity meter spun like fury, but the tram moved. Even more surprising was when one of their W2s was used to push another at the old Newcastle meatworks the next day, despite the power reaching the trams by means of a number of extension cords. This worked better on a 110v transformer owned by Russell Phemister who was a driving force at that museum. This was subsequently the power source at Wallsend.
I know that the Loftus museum also uses rather low voltages to test traction motors after overhaul but I do not know the voltages concerned, or whether this has been used to move any trams.
On 07/07/2012, at 7:39 PM, Noel Reed wrote:
A range of recommended traction voltages is given in this table from Wikipedia
Electrification system Lowest non-permanent voltage Lowest permanent voltage Nominal voltage Highest permanent voltage Highest non-permanent voltage 600 V DC 400 V 400 V 600 V 720 V 800 V 750 V DC 500 V 500 V 750 V 900 V 1 kV 1,500 V DC 1,000 V 1,000 V 1,500 V 1,800 V 1,950 V 3 kV DC 2 kV 2 kV 3 kV 3.6 kV 3.9 kV 15 kV AC, 16.7 Hz 11 kV 12 kV 15 kV 17.25 kV 18 kV 25 kV AC, 50 Hz 17.5 kV 19 kV 25 kV 27.5 kV 29 kV
To operate a heritage tram nominally operating on 600 V DC on a 750 V Dc light rail system, this table indicates the highest permanent voltage as 720 V.
In the possible use of a heritage tram on a tourist service or a 'cafe tram' operation, constant stopping and starting at every station would not be required.
If such an operation was conducted on the MLR system, a tourist or cafe service could depart from the city or suburban terminus immediately following a regular light rail vehicle and operate non stop at a sedate pace , running for most of the time in the 'Series' driving position. This would not overstress the motors although brief periods of 'Parallel' operation could be permissible.
Any comments ?
From:TramsDownUnder@... [mailto:TramsDownUnder@yahoogroups..com] On Behalf Of Richard YOUL Sent: Saturday, 7 July 2012 7:40 AM To:TramsDownUnder@... Subject: Re: [TramsDownUnder] Re: Heritage trams on the MLR
At the time the D scrubber was to run on the SLR I believe that Bill Parkinson put an extra resistor/resistors in the traction circuit to limit current to the tram's motors and presumably something for the compressor circuit also. There is no need to add a globe to the wiring circuit. Just change one or two 100 volt globes for 240v globes of a suitable wattage. (Interstate members may not know that Sydney used light globes with standard domestic bayonet-cap bases, not the Edison Screw variety used in Melbourne, which I once heard was to deter employees from taking the globes home to use!)
While adding resistance to the traction circuit would reduce voltage to the motors under load, as the tram sped up (for example running in Parallel with the scrubbing blocks raised) the current through that circuit would drop and consequently the voltage would increase so that if running fast enough, the motors would get close to 750 volts anyway. That is a characteristic of resistors - as the load (amps) drops, the voltage increases. Matthew could explain that better than me.
I believe that Restaurant Tram 442 also had extra resistors permanently in the motor circuit, but believe me, you would never know it when powering down a decent hill!
Years ago I visited the Blonay-Chamby museum operation in Switzerland, and I am certain I was told that a particular little city 4 wheeler designed for 600 volts was running there on 900 volts DC and the chap shrugged his shoulders and said that the extra voltage 'didn't seem to matter'. The car had no air brakes.
On 07/07/2012, at 12:12 AM, trackless wrote:
G'day, Jeff, and all. Seeing that no-one has answered your question yet, I'll stick my neck out! Apart from the solution listed below, a modern option is to stick a piece of electrical "gadgetry" in the tram's wiring so that the tram's electrical circuitry doesn't receive the full "modern" line voltage, but only what is acceptable to the car's particular system (i.e. 500v. or 550v.). These days, such preventative devices are fairly common in the electrical world. Greetings from a very wet (and getting wetter) Britain. Rod McG.
--- InTramsDownUnder@..., jeffrey bounds <jebounds@...> wrote: > > Noel/Greg. > What has to be done to change the tram voltage from 660v to 750v.? > Jeff >
> > > A heritage tram HAS run on the SLR.
> > > The pantograph was off one of the Berlin cars I believe, 134s has it's > > > > > trolley pole back these days. It's still fitted with a 'City - Loftus' > > > > > selector switch - which I think only adds an extra light bulb to the > > > > > lighting circuit so the bulbs don't blow on 750v. > > > > > > > > > > > > > > > > > > > > > > > > > ------------------------------------ > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ------------------------------------ > > > > > > > > Yahoo! Groups Links > > > > > > > > http://groups.yahoo.com/group/TramsDownUnder/ > > > > > > > > Individual Email | Traditional > > > > > > > > http://groups.yahoo.com/group/TramsDownUnder/join > > > > (Yahoo! ID required) > > > > > > > >TramsDownUnder-digest@... > > > >TramsDownUnder-fullfeatured@... > > > > > > > >TramsDownUnder-unsubscribe@... > > > > > > > > http://docs.yahoo.com/info/terms/ > > > > > > > > ----- > > > > No virus found in this message. > > > > Checked by AVG - www.avg.com > > > > Version: 2012.0.2178 / Virus Database: 2437/5109 - Release Date: 07/03/12 > > > size=1 width="100%" noshade color="#aca899" align=center> > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.2178 / Virus Database: 2437/5109 - Release Date: 07/03/12 >
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