I am interested in locating a trolley substation/rectifier for a prospective system in Texas. Must be somewhat modern with current safety controls installed. Please contact me via PM.

Harry Nicholls

I'd be interested in seeing what commercial solutions are out there. Me I'd just get a isolation transformer of the correct size that puts out 480 vac and run it through a bridge. Tap it down a bit if needed, Maybe fuse the output. Voila, 600 VDC.

Locomotives should have big enoughf diodes also add a coil to smooth out the voltage.

Old school trolleys are very forgiving of "dirty" DC. 3 phase 480, a bunch of diodes and capacitors for a rectifier, and you're good to go. You can, of course, make it as complicated and costly as you want......... if you want to power multiple cars on a long bit of track, you will need something better, and perhaps more than one - DC doesn't travel like AC. The big UPS units we have in data centers take the AC from the grid, rectify it to DC (which is where the emergency batteries hook up - rooms full of them) then carefully convert it back to very controlled and clean AC. You won't need the second half of it.

How does 480 become 600 in the final output?

#1 the AC output won't be very dirty at all. That is the magic of rectifying 3 phase.

#2 When talking distance vs voltage drop, the most significant factor is the amperage carried vs the wire gauge. Watts=volts * amps, so the way to make the amps go DOWN is to make the voltage go up. Hence 120/240 volts in the home, Thousands of volts on the street (2000 to 20000 I think), tens or hundreds of thousands of volts on the big inter-city transmission lines. When talking massive distances, (100's of miles) I think DC actually does better, and some long distance lines DO use DC. However, AC wins out most places simply because you can use a cheap transformer to easily step up and down voltage as you wish, to nearly any voltage you like. To change AC to DC only requires diodes, which were common by the early part of the century and have gotten smaller, better, cheaper ever since. (before that was rotary converters.). To change DC to AC or to change DC voltage (on a utility size scale) requires MUCH more complex equipment, even today.

#3 DC voltage is just 'read', AC voltage is expressed in RMS (Root Mean Square) which is basically the average voltage (AC voltage is constantly changing). When rectifying AC to DC, your output voltage is the peak AC voltage, which is Peak=RMS * (square root 2). 480*1.41=677 volts. Tapping down on the transformer should get that voltage closer to 600, and it will sag somewhat under load anyway.

Transformer

Please read above. If you try to rectify 600 VAC to 600 VDC all you will get is a very expensive mistake.

Pa. Trolley Museum designed and built a first class substation, 'from scratch', I believe. Maybe someone from PTM can weigh in with the details.

Dave

Young'un, please let the guys that have worked with this stuff provide the right answers.

Harry- PM sent-

Depending on the size of the installation and if you aren't grandfathered, the utility may make you conform to IEEE standard 519. IEEE-519 sets minimum standards for harmonic distortion of the input current of an installation. It so happens that 519 uses a 6-pulse rectifier (in the form of a wye-delta transformer with full-wave bridge) as a case study of a non-compliant device. Here at TMNY (Kingston NY) our utility has told us that a 12 or higher pulse unit must be used.

That standard seems to be more about harmonic distortion related to VFDs, (which could in worst case scenarios be pretty terrible), but what about systems with a resistive DC load? In any case a 12 pulse system doesn't look too hard to implement.

When discussing this with the utility the best analogy may be large 3 phase industrial welders. If those have become a problem, then you may have to deal with the THD issue.

My point is that something 'shop-brew' would get the job done fine and be made with modern components, and done at a much cheaper cost. Calling in someone to provide a turnkey solution is going to cost a LOT. Of course what you go with is going to depend some on how big and where you plan to operate.

See this previous thread for some salient information:

viewtopic.php?t=33318

/s/ Larry
Lawrence G. Lovejoy, P.E.

Gentlemen,

I thank you all for your responses. But, I am not going to build a rectifier, I am interested in a good, used rectifier or substation that has some of the modern controls for stand alone operation. I have been involved with the creation of a self built unit from loco diodes, tramsformers, etc. and am not going that route on this project. Several years ago, I had a new rectifier bid and installed for McKinney Avenue Transit in Dallas while I was the Executive Director. I still have the bid specs and can use them as a guide to what I am now looking to buy, if there is such a unit available.

The proposed project will require spes for future possible LRT operations and will be a part of a municipal division. Therefore, some standard unit will be required and a home built item will not pass muster.

If anyone knows of a possible, available unit, please PM me.

Thank you.