Railway Traction Supply

What is your secondary output voltage to the railway.

Normally, if you are supplying to railways, you should be feeding to his grid.

They normally transpose the phases at certain distances to more or less even out the loading pattern.

However if that is not the case, then you have problem and you will need some converter (eg Scott - T transformers, check it, a lot of literature is available on this configuration in books as well on net) or some other type of configuration.

Solid state may not be worth it.

Also note the efficiency is an issue here (even with scott-T)

Thankyou for the reply.

How the transposition is posible. We are giving only 2 phases. The two pases fed through transformer and output 25kv is used for traction.

Rgds

BRN

Normal cases the Railways take in all the three phases. The Phase 1 is used for say 20 KMs then the Phase 2 for the next 20 Kms etc, Between the Phase 1 and Phase 2 they use a neutral line for one span (In railways it is called dead-zone if I remember, in this if the Engine stops then it is dead- no power, It is kept away from the signals, so no engines are usually stop here)

Take the matter up with railways, in any case they must be using this concept. Nobody will give him a single phase supply at this high power requirement.

Offer him to feed his grid. Are you stand alone supplier , ie the only supplier for the line?

In case others are there you can just get into contact and find what others are doing.

Except Scott-T, or similar transformers or solid state I don;t find a way and they will not be very efficient ways.

That scheme would work if you had at least one train per 20KM all accelerating and decelerating at the same time. In any other case, you still have the potential for peak load imbalance that could trip protections.

This is not an easy problem to solve anyway you look at it. A company we work with also makes various train track over voltage protections, rectifiers and braking energy dissipating resistor banks used by various electric trains. The impulsive nature of the large load can also be a problem for utilities as far as voltage regulation is concerned.

As you suggested, this needs to be discussed with the rail company and be compared with existing systems. You don't want the lights of the city to go down every time that a train starts. It only takes a few percent of voltage drop to make the variation visible. That can happen if the electric company's capacity is not hundreds of times larger than the train's peak load. The geographical location has also an effect.

We manufacture large electronic power converters that could be used to balance your load in this power range. We presently use them as large power supplies (MW range) for ozone generation and as active harmonics filters. We have hundreds of those in operation. In your case we would use a parallel approach similar to an active harmonics filter to evenly distribute the load current to the three phases. This means that a 3MVA converter would do it at 100% with some spare capacity. The losses would be around 90KW (~3% losses).

The converter size could be reduced if you have other way of balancing your network with other single phase loads. The problem with balancing with single phase loads is that when the trains are not pulling much power, that line will be the one heavily loaded.

The active converter will adapt to variable load instantaneously and the over capacity could be used to continuously inject vars from full leading to full lagging. This may save you a voltage compensation station. It can also be used to reduce harmonics on the network it you have this problem.

Queensland Rail have a massive overhead traction system for hauling coal trains. Each feeder station has two 50MVA transformers installed. The primary voltage is 132KV and the traction voltage is 50KV centre tapped which supplies Autotransformers every 10KM to induce the current from the Cat / Con into the outside wire. The Cat / Con system is 25KV to ground as is the supply wire with 50kv between them.

The missing phase and harmonics are a huge issue. QR have filters and phase balancing Capacitor / Inductor networks at installed at each feeder station.

The minerals traffic system is modelled on the system used in France and is designed for high power over long distances. The lower powered British system used for suburban rail is somewhat different while still utilising 25KV to ground at the Cat / Con it has compensating transformers installed to induce the ground current into the outside wire for safety and signals integrity.

Suggested suppliers to contact ABB and Alsthom. Both are suppliers to QR. While my hands on experience is with QR the rail network in Bombay will have expertise too as will British Rail and SCNF.