4 ms·

You just synchronize to wherever you are on the wave. Your offset will not be the same as your neighbors offset, but that's fine. Maybe imagine a line of buoys

by csours 3y ago

You just synchronize to wherever you are on the wave. Your offset will not be the same as your neighbors offset, but that's fine. Maybe imagine a line of buoys in the ocean as a wave passes.

shadowgovt 3y ago
But if I have power from two sources coming into my facility, they wouldn't be in phase with each other, right? How do I use both? (Perhaps the obvious answer is correct here: "Grids don't work that way; you'd never do that.")
- generalizations 3y ago
  I wonder if the solution is similar to routing traces on PCBs where there's high-frequency stuff going on - you add and subtract length from the line pairs until the phases match up. Sometimes the dumb solutions are the best ones? Weird how all the replies so far misunderstood your question.
  - marcosdumay 3y ago
    There's a lot of high-frequency stuff going on, but the line length is so much that most of it irradiates away. You don't go adding more line to compensate anything, but you do add filters at some places.
- londons_explore 3y ago
  The sum of two sine waves of differing phase is a sine wave with some phase between the two.
- ilyt 3y ago
  In most cases where you do have more than one source (say datacenter for redundancy) you don't just tie them together directly, in simplest config you'd just switchovered from one to another if one failed.
- asdfman123 3y ago
  Imagine you've got two cables coming into your factory. One is 500 meters longer than the other. That would mean that the sine waves are 0.01% out of sync. I'm pretty sure for home electronics the phase difference doesn't even matter that much. Everything sensitive seems to be converted to DC anyway. Maybe it matters in large industrial applications, I have no idea. But I also imagine in their situation it's probably pretty straightforward to clean up the power supply.
  - gooseyman 3y ago
    Would be fun to see this turn up as a case study for two identical assembly lines driven by motors. One on the “fast” frequency and the other on the slow. In my imagination, the specialists are brought in only to learn that the RPMs in one motor were juiced because someone didn’t practice cable management
    - asdfman123 3y ago
      The electrical phases would be the exact same frequency still, 60 hz.
- londons_explore 3y ago
  In reality, the phase difference is always small, and it ends up not mattering. But... If you had a worldwide electricity grid running at 60Hz, it would start to matter, and you would make sure to use local capacitors/inductors to make phase shifts to make sure that you didn't have big circulating currents in loops (they just are wasting energy)
  - csours 3y ago
    Napkin math: Speed of light is 300,000 kilometers/second. At 60 hz, the wavelength would be 5,000 km. 1% of that would be 50 km. Imagine a triangle with 2 generators 100km apart, and a factory almost due south of one generator: ga ......... gb __f I think the offset would be something like sin(gb.f) - sin(ga.f) But really this comment is bait for an EE to school me. Here's a video of old school mercury arc rectifiers as payment: https://www.youtube.com/watch?v=YhaQqgXrMMU https://www.youtube.com/watch?v=YhaQqgXrMMU
- sidewndr46 3y ago
  you would have to be in a location to straddle synchronous grid. There may be some places that allow that. Otherwise, the two sources are already in approximately in phase anyways. To put it simply though, you put some devices on one feed and some devices on another feed. So it is a non-issue. If you have local generation you want to combine with grid power you usually just sync your local generation to the grid. If you don't want to do that you can just use a DC intertie that is local. Basically you'd have two AC -> DC converters and a single DC -> AC converter.
- applied_heat 3y ago
  An airport or hospital might be fed from two different nearby substations. The substations are probably fed from the same transmission lines with parallel circuits. The substations will have transformers with the same winding configuration for a consistent phase shift from transmission to distribution level voltages. The airport or hospital will procure transformers that have the same winding configuration and impedance so the phase shift and voltage drop across them will also be the same. The low voltage windings of the transformers at the hospital can be paralleled so they both feed the load. Reverse power protection would be implemented so the hospital can’t back feed the distribution line. What phase difference do you expect in this case? What effect would it have?
michaelt 3y ago
So what happens if you've got three power plants in different states, connected in a triangle?

by csours 3y ago

You just synchronize to wherever you are on the wave. Your offset will not be the same as your neighbors offset, but that's fine. Maybe imagine a line of buoys in the ocean as a wave passes.

shadowgovt 3y ago

But if I have power from two sources coming into my facility, they wouldn't be in phase with each other, right? How do I use both? (Perhaps the obvious answer is correct here: "Grids don't work that way; you'd never do that.")

generalizations 3y ago
I wonder if the solution is similar to routing traces on PCBs where there's high-frequency stuff going on - you add and subtract length from the line pairs until the phases match up. Sometimes the dumb solutions are the best ones? Weird how all the replies so far misunderstood your question.
- marcosdumay 3y ago
  There's a lot of high-frequency stuff going on, but the line length is so much that most of it irradiates away. You don't go adding more line to compensate anything, but you do add filters at some places.
londons_explore 3y ago
The sum of two sine waves of differing phase is a sine wave with some phase between the two.
ilyt 3y ago
In most cases where you do have more than one source (say datacenter for redundancy) you don't just tie them together directly, in simplest config you'd just switchovered from one to another if one failed.
asdfman123 3y ago
Imagine you've got two cables coming into your factory. One is 500 meters longer than the other. That would mean that the sine waves are 0.01% out of sync. I'm pretty sure for home electronics the phase difference doesn't even matter that much. Everything sensitive seems to be converted to DC anyway. Maybe it matters in large industrial applications, I have no idea. But I also imagine in their situation it's probably pretty straightforward to clean up the power supply.
- gooseyman 3y ago
  Would be fun to see this turn up as a case study for two identical assembly lines driven by motors. One on the “fast” frequency and the other on the slow. In my imagination, the specialists are brought in only to learn that the RPMs in one motor were juiced because someone didn’t practice cable management
  - asdfman123 3y ago
    The electrical phases would be the exact same frequency still, 60 hz.
londons_explore 3y ago
In reality, the phase difference is always small, and it ends up not mattering. But... If you had a worldwide electricity grid running at 60Hz, it would start to matter, and you would make sure to use local capacitors/inductors to make phase shifts to make sure that you didn't have big circulating currents in loops (they just are wasting energy)
- csours 3y ago
  Napkin math: Speed of light is 300,000 kilometers/second. At 60 hz, the wavelength would be 5,000 km. 1% of that would be 50 km. Imagine a triangle with 2 generators 100km apart, and a factory almost due south of one generator: ga ......... gb __f I think the offset would be something like sin(gb.f) - sin(ga.f) But really this comment is bait for an EE to school me. Here's a video of old school mercury arc rectifiers as payment: https://www.youtube.com/watch?v=YhaQqgXrMMU https://www.youtube.com/watch?v=YhaQqgXrMMU
sidewndr46 3y ago
you would have to be in a location to straddle synchronous grid. There may be some places that allow that. Otherwise, the two sources are already in approximately in phase anyways. To put it simply though, you put some devices on one feed and some devices on another feed. So it is a non-issue. If you have local generation you want to combine with grid power you usually just sync your local generation to the grid. If you don't want to do that you can just use a DC intertie that is local. Basically you'd have two AC -> DC converters and a single DC -> AC converter.
applied_heat 3y ago
An airport or hospital might be fed from two different nearby substations. The substations are probably fed from the same transmission lines with parallel circuits. The substations will have transformers with the same winding configuration for a consistent phase shift from transmission to distribution level voltages. The airport or hospital will procure transformers that have the same winding configuration and impedance so the phase shift and voltage drop across them will also be the same. The low voltage windings of the transformers at the hospital can be paralleled so they both feed the load. Reverse power protection would be implemented so the hospital can’t back feed the distribution line. What phase difference do you expect in this case? What effect would it have?

michaelt 3y ago

So what happens if you've got three power plants in different states, connected in a triangle?