This is a brief explainer about how overhead (catenary) wires feed electricity from the grid into an electric train's motor; how that electricity is manipulated via transformers, rectifiers,...
Exemplary
This is a brief explainer about how overhead (catenary) wires feed electricity from the grid into an electric train's motor; how that electricity is manipulated via transformers, rectifiers, inverters, and other devices to physically power the vehicle; and how it's distributed throughout the train.
25 kV AC power delivery (at various frequencies) exists in the United States, but is not standardized; the video author is from India where this voltage is widespread. DC power is less common for mainlines for power loss reasons, but still exists. You can see a map of electrification standards worldwide with one of the overlays on OpenRailwayMap. Even in the US, there are multiple different voltages and frequencies: most of the Northeast Corridor (NEC) runs on 12 kV @ 25 Hz power, except near Boston where it's 25 kV @ 60 Hz; the New York area features additional standards, including third rail delivery (which is an alternative to catenary delivery). The newly electrified Caltrain line in San Francisco is running at 25 kV @ 60 Hz, which will also be the standard for California High-Speed Rail.
European voltages are also not standardized for historical reasons, though some Asian countries have managed it. In general, individual countries tend to have preferences for their own systems and there is little international cooperation on electrification standards. Different types of rail (such as main lines and subways) also sometimes have different standards from each other, often also for historical reasons. For example:
France's 25 kV @ 50 Hz for the TGV and apparently 1.5 kV DC for some other lines
Germany's 15 kV @ 16.7 Hz (not sure how they settled on that one)
Italy and Poland's 3 kV DC
The UK's 25 kV @ 50 Hz (except London's variously 750 V DC)
The Nordic countries' perplexing 15 kV @ 16.67 Hz. It's a real mess.
In China, all electrified railroads are standardized at 25 kV @ 50 Hz (remarkable for such a large country, but predictable given how new its infrastructure is)
India is likewise completely standardized at 25 kV @ 50 Hz
South Korea uses 25 kV @ 60 Hz
Japan is of course on a hundred different standards (including 20 kV @ 50 Hz, 20 kV @ 60 Hz, and 25 kv @ 60 Hz) but the dominant one is 1.5 kV DC
South Africa has the uniquely high-voltage 50 kV @ 50 Hz, plus more common standards
Catenary power is typically preferred over third rail for mainlines because it can run higher voltages, can generally support higher speeds, works better in a variety of climates (such as dealing with snow), and is much safer (no exposed electrified material where people can walk or debris can cause a short-circuit). There are specific engineering reasons why it can be impractical sometimes, such as low tunnels (even an adjustable pantograph requires a certain clearance, and some old tunnels have literally inches to spare) and in underground systems. Metros often use third rail for this reason, naturally with protections (such as shoe covers or, ideally, platform screen doors) to reduce passenger electrocution risk. Catenary wires have to be tensioned in a particular way for trains to run at high speeds, such as auto-tensioning or constant tension.
Battery-powered trains exist but are generally used in a hybrid locomotive to go through non-electrified tunnels on otherwise electrified lines. It is not practical to bring batteries on a high-speed train because they're very heavy (which slows down the vehicle) and simply can't provide that much power. Currently, they're more expensive to operate than any other standard and therefore have little utility except as stop-gaps. As battery technology improves, it's possible that hybrid overhead/battery trains will become more common, but I would be surprised if they usurped traditional electrification methods due to the physical limits of energy density.
The video doesn't discuss it, but if you need to run a train across tracks with different voltages or frequencies, you don't technically need to do a locomotive change. A converter can allow the train to run on either AC or DC, and you can configure a train to have both a catenary pantograph and a third rail shoe. As discussed, static or rotary converters (like inverters/rectifiers) can handle different frequencies and voltages. Supporting multiple standards is typically expensive and requires careful planning from the operators. Also, investing in specialized rolling stock tends to reinforce the status quo rather than necessarily offer a path toward standardization.
The video also glosses over why the engine might take three-phase AC power (as opposed to single-phase). The latter simply provides more power throughput, which is necessary to sustain high speeds with a train. Something like the Long Island Railroad (LIRR) in New York state uses single-phase third rail, but this system is pretty unusual for multiple reasons. Single-phase is generally only suitable for short-distance travel at low to moderate speeds, like a commuter rail service.
The reasons passenger railroads would be inclined to run electrified service despite its additional upfront infrastructure and rolling stock costs are that electric trains are lighter, have dramatically higher maximum speeds, are more efficient and cheaper to operate, have fewer moving parts and are significantly less prone to maintenance problems, produce no greenhouse gas emissions, produce no toxic diesel particulate matter, and are quieter than diesel engines. Railroad electrification is a net benefit for society, we just have to make the initial investment.
It's possible to electrify freight trains, and could even provide various operational benefits, but the cost of electrification infrastructure is generally far too expensive for freight operators to consider. Speed and reliability (which electrification provides) do matter to freight companies, but not nearly as much as it matters to passenger railroads.
This is a brief explainer about how overhead (catenary) wires feed electricity from the grid into an electric train's motor; how that electricity is manipulated via transformers, rectifiers, inverters, and other devices to physically power the vehicle; and how it's distributed throughout the train.
25 kV AC power delivery (at various frequencies) exists in the United States, but is not standardized; the video author is from India where this voltage is widespread. DC power is less common for mainlines for power loss reasons, but still exists. You can see a map of electrification standards worldwide with one of the overlays on OpenRailwayMap. Even in the US, there are multiple different voltages and frequencies: most of the Northeast Corridor (NEC) runs on 12 kV @ 25 Hz power, except near Boston where it's 25 kV @ 60 Hz; the New York area features additional standards, including third rail delivery (which is an alternative to catenary delivery). The newly electrified Caltrain line in San Francisco is running at 25 kV @ 60 Hz, which will also be the standard for California High-Speed Rail.
European voltages are also not standardized for historical reasons, though some Asian countries have managed it. In general, individual countries tend to have preferences for their own systems and there is little international cooperation on electrification standards. Different types of rail (such as main lines and subways) also sometimes have different standards from each other, often also for historical reasons. For example:
Catenary power is typically preferred over third rail for mainlines because it can run higher voltages, can generally support higher speeds, works better in a variety of climates (such as dealing with snow), and is much safer (no exposed electrified material where people can walk or debris can cause a short-circuit). There are specific engineering reasons why it can be impractical sometimes, such as low tunnels (even an adjustable pantograph requires a certain clearance, and some old tunnels have literally inches to spare) and in underground systems. Metros often use third rail for this reason, naturally with protections (such as shoe covers or, ideally, platform screen doors) to reduce passenger electrocution risk. Catenary wires have to be tensioned in a particular way for trains to run at high speeds, such as auto-tensioning or constant tension.
Battery-powered trains exist but are generally used in a hybrid locomotive to go through non-electrified tunnels on otherwise electrified lines. It is not practical to bring batteries on a high-speed train because they're very heavy (which slows down the vehicle) and simply can't provide that much power. Currently, they're more expensive to operate than any other standard and therefore have little utility except as stop-gaps. As battery technology improves, it's possible that hybrid overhead/battery trains will become more common, but I would be surprised if they usurped traditional electrification methods due to the physical limits of energy density.
The video doesn't discuss it, but if you need to run a train across tracks with different voltages or frequencies, you don't technically need to do a locomotive change. A converter can allow the train to run on either AC or DC, and you can configure a train to have both a catenary pantograph and a third rail shoe. As discussed, static or rotary converters (like inverters/rectifiers) can handle different frequencies and voltages. Supporting multiple standards is typically expensive and requires careful planning from the operators. Also, investing in specialized rolling stock tends to reinforce the status quo rather than necessarily offer a path toward standardization.
The video also glosses over why the engine might take three-phase AC power (as opposed to single-phase). The latter simply provides more power throughput, which is necessary to sustain high speeds with a train. Something like the Long Island Railroad (LIRR) in New York state uses single-phase third rail, but this system is pretty unusual for multiple reasons. Single-phase is generally only suitable for short-distance travel at low to moderate speeds, like a commuter rail service.
The reasons passenger railroads would be inclined to run electrified service despite its additional upfront infrastructure and rolling stock costs are that electric trains are lighter, have dramatically higher maximum speeds, are more efficient and cheaper to operate, have fewer moving parts and are significantly less prone to maintenance problems, produce no greenhouse gas emissions, produce no toxic diesel particulate matter, and are quieter than diesel engines. Railroad electrification is a net benefit for society, we just have to make the initial investment.
It's possible to electrify freight trains, and could even provide various operational benefits, but the cost of electrification infrastructure is generally far too expensive for freight operators to consider. Speed and reliability (which electrification provides) do matter to freight companies, but not nearly as much as it matters to passenger railroads.