Idea for increased desil electric eficciancy

[rdrdrdrd]

I was bored I stasrted looking uop the intricate workings of a desil-electric engine, what I have concluded is that most of the elecricity is wasted as heat. This is beacuse it can;t be used at that time so it is run through a metal grid with high resistance and disipates into heat vented out the top, if the heat could be used to make steam, the steam could be stored in high pressure tanks until a boost of power is needed when in would be injected into a turbine to help turn the wheels with a direct drive system. If the steam tanks are full it could be placed in capacitors to be used later. when these storage devices are filled it could be disipated as heat as normal.
Any comments or sugestions to my idea?

[JamieLei]

The problem is that electricity is ridiculously difficult to store, almost to the extent that it isn't storable. The closest we have to being able to store electricity on a large scale is by moving water vertically upwards when there's low demand (and excess electricity), and then letting it flow downwards when there's high demand and harnessing the hydro-electricity produced as a result (although this is still quite inefficient).

Logically, capacitors and steam turbines if they were able to effectively store electricity, would be widely used in diesel engines for the good reasons you've just mentioned. But my guess would be (and I'm no mechanic) that capacitors are not able to dispel electricity at a "slow" constant rate for it to be effective, and that putting steam into high pressure tanks would require far more energy than you'd be able to back from them, and combined with the excess weight of carrying around tanks and turbines would make the entire thing more trouble than it's worth.

Slightly off-topic, but an anti-electrification website once touted to me that diesel engines are more effective than electric engines, with efficiency rates of 30% and 40% respectively. On the other hand, one also has to consider the extra power needed to transport fuel around, and also that electric engines and increase their efficiently substantially by returning power to the grid by regenerative breaking (as currently happens in Britian's Class 357, 375, 377 and 390s).

[hertogjan]

You should also keep in mind that the generators that feed electricity to the electric motors are more easily driven when no electric energy is used in the system. In other words, the diesel engine will consume less fuel than when the electric traction motors are powered. This is just the law of conservation of energy: It costs significantly more energy to turn a generator that is actually powering something (so that electric current is flowing) than to turn a generator that is hooked up to nothing. This is caused by the effect that the electric currents that flow through the wiring inside the generator will exert a force in the magnetic fields of the generator, opposite to the direction it is turning.

Probably the reason for dissipating electricity through resistors is caused by the construction of the electric system. I think that even if no energy is consumed by the traction motors, then the diesel engine still has to run on a certain rpm in order to keep the voltage in the electric system within a fixed range. Or it might also be the other way round: That the diesels have to run at a certain rpm, and that the resistors are used to keep the voltage at an acceptable level. (Does anyone know? I am curious to what the real reason is.)

I believe that in older direct current systems (also vehicles powered by overhead wires or third rail) the amount of electric power provided to the traction motors is controlled by switching on or off extra resistors. These resistors just produce heat, which is probably all wasted.
In alternating current systems this can be done by a transformer, which is quite an efficient method. In modern direct current systems advanced electronics are used which are more efficient than the resistor method.

[doktorhonig]

Slightly off-topic, but an anti-electrification website once touted to me that diesel engines are more effective than electric engines, with efficiency rates of 30% and 40% respectively. On the other hand, one also has to consider the extra power needed to transport fuel around, and also that electric engines and increase their efficiently substantially by returning power to the grid by regenerative breaking (as currently happens in Britian's Class 357, 375, 377 and 390s).

Elecric Engines can have much higher efficiency rates, look for "electric motors" here. 90% are possible without problems. Those 40% also include the generation of power. So if you have large amounts of electric energy from hydro power, it's stupid to run diesel trains through the country.

[JamieLei]

The figures came from here (sorry I should have checked before I wrote the above post)

The figures for electricity also took into account losses in the grid, which are actually very substantial (about 2/3s - hence why we don't heat homes with electricity) so the 35% efficiency quoted is probably about right.

Nonetheless I agree that Electric is probably far more efficient once factors such as transporting the diesel, heavier train and lack of regenerative power fed back into lines are taken into account. It's just that people lean towards diesel due to the initial start-up costs of having to lay centenary, wires and substations.

[hertogjan]

Grid losses are actually not that high, especially in high voltage (i.e. low current) transmission. The article you mention also quotes generation losses. Actually, this means just the efficiency of power plants, which I believe is somewhere around the figure of 30%-40%. The reason that one does not use electricity for heating, is that it would introduce another transmission of energy where energy is lost. If you can use the heat from (e.g.) natural gas directly, why first turn it into electricity and then turn that into heat?

For trains on low voltage (usually dc) systems, the currents are quite high, and hence the heat losses in transmission are higher. That is why for heavy (electric) trains higher voltage is preferred.

Another issue that one may play an important role is cost. While electric engines may be less efficient than diesels (although I doubt that it is true, and if it is whether it is really significant), the electric energy may be cheaper than diesel (per energy unit). Also diesels are probably more difficult (and hence more costly) to maintain.

[JamieLei]

Until about a few months ago, I would have said that the price of oil was increasingly making electricity a very attractive option. With new schemes such as the London Array in the UK to increase the electricity supply via green means, it's also more sustainable.

From what I understand, 25kV AC was adopted as the international standard since it was the highest you could go (and therefore reducing loss) without any risk of the power leaping to the ground and short-circuiting. I'm not sure if electric trains are heavier though - if anything I would have thought they're lighter (although I may be wrong - I'm not the train expert )

[michael blunck]

Modern Diesel engines have efficiencies in the 40% to 45% range. O/c, in the case of a locomotive, this isn´t the overall efficiency. E.g., in case of a diesel-electric we´ll have to consider the efficiency of the electric power transmission (generators and electric motors), which would give something like 35% for total efficiency:

Code: Select all

n_eff = n_diesel * n_electric -> 0.44 * 0.80 -> 35.2%

Modern electric AC locomotives have efficiencies between 80% and 90%, and, depending on the way electric current is produced, overall efficiencies may vary between 24% (nuclear power plant), 38% (coal power plant), and 77% (hydroelectric power plant). In addition, electric locomotives generally allow for recovery of braking energy. This o/c, depends on many varying parameters and would only be possible to calculate for a well-known scenario. (IIRC, I´ve seen something like this some time ago from the SBB).

regards
Michael

[LaSeandre]

Until about a few months ago, I would have said that the price of oil was increasingly making electricity a very attractive option. With new schemes such as the London Array in the UK to increase the electricity supply via green means, it's also more sustainable.

From what I understand, 25kV AC was adopted as the international standard since it was the highest you could go (and therefore reducing loss) without any risk of the power leaping to the ground and short-circuiting. I'm not sure if electric trains are heavier though - if anything I would have thought they're lighter (although I may be wrong - I'm not the train expert )

I'm sure they're the same weight - especially AC ones as they have transformers and stuff to change the electricity to DC for the motors.

[chevyrider]

I'm sure they're the same weight - especially AC ones as they have transformers and stuff to change the electricity to DC for the motors.

And the DC loc's have choppers (thyristors) to feed the a-synchronic motors.

[Brianetta]

Perhaps spinning up a flywheel (Parry-style) would be a better way to dissipate unused electricity than warming up a bank of resistors. Certainly better than heating water for steam; it's easier to make a wheel and bearing smooth enough not to lose kinetic energy to heat and air movement than to make a pressurised, insulated container to safely contain hot steam without losing heat to the environment.