72 votes

Why are two wires used in railway overhead equipment?

Overhead line worker here. It's about speed. To answer your question, the purpose of the catenary wire is to get the contact wire to lay flat, so it isn't catenary itself. In your second photo, there ...
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43 votes
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Transmitting power over long distances what is better AC or DC?

It is more efficient to transmit DC using about the same infrastructure. This is because of several effects: Skin effect experienced with AC. There is no skin effect with DC. Higher voltage ...
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  • 11.2k
41 votes

Transmitting power over long distances what is better AC or DC?

I actually worked on HVDC schemes, back in the mid-to-late 90s. Olin Lathrop's answer is partially right, but not quite. I'll try not to repeat too much of his answer, but I'll clear up a few things....
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  • 521
12 votes

Why are two wires used in railway overhead equipment?

It isn't to do with current-carrying capacity; it is to maintain good contact between the current-carrying wire and the pantograph pickup on the locomotive, as it allows the contact wire to be ...
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  • 341
7 votes

Transmitting power over long distances what is better AC or DC?

They're talking about complexity and costing (\$\$\$\$\$) The people saying "DC is less efficient" are using the word "efficiency" to talk about design factors like complexity of conversion hardware, ...
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6 votes

Why are two wires used in railway overhead equipment?

Why two wires: A wire hanged at two points sags (it forms a "catenary curve"). The pantograph can only handle a certain sag before losing contact and arcing. The acceptable sag depends on ...
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  • 231
5 votes

Wind turbines with down tower power units. Why aren't they more common?

The math doesn't make any engineering sense. A 5MW turbine typically rotates at about 10 RPM, near enough 1 radian per second. Assuming you had reasonably big sprockets on the chain drive, say 2 ...
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5 votes
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Why do trains use the same wheels for staying on track and propulsion?

Trains do sometimes use different means for propulsion: Rack railways use cogs, and Funiculars use ropes I think the reason these are uncommon is that the available traction of smooth tracks is more ...
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  • 136
5 votes

Why are both conductors in a High Voltage Direct Curent powerline isolated from ground?

There are a few possible reasons. Elimination of electrolysis problems with ground connections. Elimination of variations in ground resistance. Grounding one of the conductors on the HVDC line might ...
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  • 7,499
5 votes
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Why are both conductors in a High Voltage Direct Curent powerline isolated from ground?

Because they're both live Just because you see multiple wires doesn't mean they are carrying different things. They are frequently paralleled for more ampacity. It's perfectly common in HVDC lines to ...
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4 votes
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Why is it bad to run power through BNC (RG58) cables?

Because it is not a power cable (Q1) using power connectors (Q2). BNC cable has a solid conductor and a ground braid to electrically shield and mechanically protect the conductor. Electrical reason: ...
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4 votes
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Power systems unclear voltages

Note the problem specifies the load is "delta connected". There is no neutral connection to measure phase voltage ($V_{LN}$) against. Also note the supply frequency is 60 Hz. 208 V is a ...
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3 votes
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Why in the construction of power transmission towers , the rods are hinged oblique?

I think this question is about additional cross bracing. With a rectangular frame in a vertical plane the ability to carry compressive loads is excellent, but a comparatively small lateral force can ...
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3 votes

How does power generation (hydro, wind etc...) account for variable power consumption?

This is more of an addition to the previous answer by blacksmith37. I think it might be more appropriate as a comment, or perhaps an edit to the previous answer. With no ability to comment at this ...
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  • 156
3 votes
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Attaching Gear onto Motor

Here you go: https://uk.rs-online.com/web/p/spur-gears/8787907/ The trouble is that a 1MOD 12 Tooth gear has a pitch diameter of 12mm, i.e.the bottom of the teeth is less than 12mm, so once you drill ...
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3 votes
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Right angle gearbox, proper name or design

Your terminology is correct, but also sometimes called bevel gearboxes. A cheap off the shelf unit is a few hundred dollars. If that is too expensive you probably won't save any money designing and ...
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  • 2,402
3 votes

Right angle gearbox, proper name or design

these things are sold cheaply (less than $20) for bending the output of an electric drill through 90 degrees, so you can drill holes in cramped places. they can handle from 1/4 to 1/3 horsepower ...
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3 votes

How does my automatic car shift without complete temporary loss of acceleration

Multiple Clutches Many manual transmissions feature just a single clutch between the engine and the transmission. This requires that the clutch be disengaged before switching gears, during the switch,...
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3 votes
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Is transmitting windmills' mechanical power to ground level that complex?

TL;DR:IMHO, the driver for keeping the electrical generation closer to the hub is for primarily for eliminating -as much as possible- moving parts for safety concerns. The secondary benefit is the ...
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  • 22.6k
2 votes

Why in the construction of power transmission towers , the rods are hinged oblique?

If you imagine a square or rectangular shape made from rods joined with points at the corners. If those pins act as hinges then the whole shape can easily deform, effectively acting as a 4 bar link. ...
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2 votes

What is meant by "shock load" in gears?

a shock load on gearing is imposed when the gear train is forced to start or stop turning very suddenly, or when a heavy load is suddenly applied to a set of rotating gears. A good example of this is ...
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2 votes

Transmitting power over long distances what is better AC or DC?

All else being equal DC transmission is more efficient than AC transmission at the same nominal voltage due to the elimination of reactive losses. However all else is rarely equal. At a given voltage ...
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2 votes

What's the history of the 345 kV voltage level in power transmission?

With the high voltage AC power lines, there are trade offs between losses due to resistance in the wires, where the higher voltages are better and losses due to capacitance to the air, etc. where ...
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2 votes

Torque and RPM calc

The transmission ratio is related to the number of teeth on the worm gear, and the number of starts on the worm. In your case, $$i=\frac{z_{worm\ gear}}{z_{worm}}=\frac{25}{1}=25$$. This means that ...
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2 votes

Attaching Gear onto Motor

What are the respective tolerances on the “6mm”? Either it will be a press fit which will be sufficient to handle the torque and shock loading or it will not. If not, then you have to fit set screws ...
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  • 13.6k
2 votes

Attaching Gear onto Motor

Boston Gear or McMaster-Carr might have suitable off the shelf gears. You could also press the gear onto a hub that has a set screw. I would avoid pressing anything directly onto a motor shaft, you ...
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  • 2,402
2 votes
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How to connect a motor shaft to a plate

That might be overkill in your application (but I don't know). Figure 1. A random rigid flange coupling from an image search. A rigid flange coupling may be a more economic choice if it suits. From ...
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  • 7,499
2 votes
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Delivering RPM from a fixed wheel to a moving wheel

you can use a pantograph belt. They use them in large machines to transfer rotation to a moving drill to cut squares and what not. Basically they are several pullies assembled on a pantograph with ...
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  • 20.9k
2 votes
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How does my automatic car shift without complete temporary loss of acceleration

I don't know why the other answers are talking about CVTs. Maybe I'm missing something? But the basic way how automatic gearboxes achieve smooth switches is that they use multiple clutches, instead of ...
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  • 1,835
2 votes

Fiber optic Power transmission

Although probably not what you are after, there is Power-over-fiber, which is a technology analogous to "Power-over-Ethernet". To be honest, I haven't seen any devices that take advantage of ...
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  • 22.6k

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